A Division of VT TSS (UK) Limited
The information in this Manual is subject to
change without notice and does not represent
a commitment on the part of SG Brown
VT TSS (SG Brown Division) Ltd
1 Garnett Close
Greycaine Industrial Estate
Watford
Hertfordshire WD24 7JZ UK
Telephone +44 (0)1923 470800
Facsimile +44 (0)1923 470838
Meridian Gyrocompass
System Manual
Document P/N 060070
Issue 3.7
© SG Brown March 2004
Contents
DPN 060070 Issue 3.7 © SGBrown Page 1 of 6
CAUTIONARY NOTICESYour attention is drawn to the following cautionary notices that apply throughout this Manual.
WARNINGThe Meridian Gyrocompass weighs 15.5kg. To avoid personal injury, take proper pre-cautions if you lift or move the equipment.
CAUTIONThe Meridian Gyrocompass includes precision components and bearings. To avoid causing damage to any part of the System, handle all items with care.
Retain the original transit cases so that you can use them to transport the system when necessary. You will void the warranty if you use improper packing during transporta-tion.
CAUTIONSevere damage to the Meridian Gyrocompass can occur if you move the gyrocompass while the rotor is still spinning without the servo system in operation.
Note that the gyro rotor continues to spin for approximately five minutes after you power-off the system.
To avoid potential damage to the Meridian Gyrocompass, always allow a period of five minutes after power-off for the gyro rotor to come to rest before you attempt to move the gyrocompass.
CAUTIONDuring operation, the gyrocompass must remain level to within ±45°. If it experiences tilt greater than 45° in any direction, it will ‘topple’. Safety routines in the gyro software will then power-off the gyro rotor and show alarm conditions on the RCU. To restore normal operation, establish a level operating attitude and then power-on the gyrocom-pass normally.
Never apply a tilt of more than 45° with the gyro rotor spinning or during the gyrocom-pass initialisation procedure. Note that the gyro rotor continues to spin for approxi-mately five minutes after you power-off the System.
CAUTIONIf you install the gyrocompass in an enclosed space, make certain there is sufficient ventilation and circulation of free air to allow effective cooling.
CAUTIONDo not make any connections to the gyrocompass with power on the supply cable.
Meridian Gyrocompass
Page 2 of 6 © SGBrown Issue 3.7 DPN 060070
CAUTIONYou will void the warranty if you make any modifications to this equipment without prior permission from SG Brown.
DO NOT modify this equipment in any way without obtaining permission from SG Brown.
CAUTIONYou will void the warranty if you operate the gyrocompass outside the environmental conditions detailed in Chapter 4 and in BS EN 60945.
Contents
DPN 060070 Issue 3.7 © SGBrown Page 3 of 6
CONTENTS
1 INTRODUCTION 1–11.1 System Description 1–31.1.1 Gyrocompass 1–31.1.2 Remote Control Unit 1–41.1.3 Auxiliary Inputs 1–41.1.4 Heading Outputs 1–5
1.2 Principle of Operation 1–5
2 INSTALLATION 2–12.1 Unpacking and Inspection 2–22.2 Physical and Electrical Installation 2–32.2.1 Selecting a location 2–32.2.2 Gyrocompass installation 2–42.2.3 External Remote Control Unit 2–92.2.4 Set the Gyrocompass DIP Switches 2–10
2.3 Alignment 2–122.4 Final Gyrocompass Installation Tests 2–122.5 Installation Drawings 2–13
3 OPERATING INSTRUCTIONS 3–13.1 Control Features 3–23.2 Initial Power-on 3–33.3 Operating Procedure 3–43.3.1 Latitude correction 3–43.3.2 Speed correction 3–43.3.3 DG operating mode 3–5
3.4 Error Modes 3–53.4.1 Loss of GPS 3–53.4.2 Loss of speed log 3–63.4.3 Gyrocompass system warnings and failures 3–6
3.5 Operating Considerations 3–83.5.1 General Operating Considerations 3–83.5.2 Corrections for Speed and Latitude 3–83.5.3 Operating at Extremes of Latitudes 3–83.5.4 Operating Considerations for High Speed Craft 3–9
4 TECHNICAL DATA 4–14.1 Specifications 4–14.1.1 Power Requirements 4–14.1.2 Performance (definitions as in ISO 8728) 4–14.1.3 Compensation 4–14.1.4 Environment 4–14.1.5 Signal Inputs 4–24.1.6 Signal outputs 4–24.1.7 Dimensions and Weight 4–24.1.8 Listener load requirement 4–34.1.9 Talker drive capability 4–3
Meridian Gyrocompass
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4.1.10 Standards 4–34.2 Data Formats 4–44.2.1 IEC 61162 Serial Data Formats – General information 4–54.2.2 Inputs 4–64.2.2.1 IEC 61162 input signals 4–64.2.2.2 Pulsed input 4–10
4.2.3 Outputs 4–114.2.3.1 IEC 61162 output signals 4–11
4.2.4 IEC 61162 sentence with Checksum 4–154.2.5 Other Output Formats 4–154.2.5.1 Course Recorder Output 4–154.2.5.2 Synchro Output 4–164.2.5.3 Resolver Output 4–164.2.5.4 Stepper S-Code 4–164.2.5.5 Rate of Turn 4–16
5 MAINTENANCE 5–15.1 Built-in Test Equipment 5–25.1.1 Azimuth Drift Adjustment 5–35.1.2 Azimuth Bias Adjustment 5–3
5.2 Test Connector 5–45.3 Diagnostic Output Sentence 5–6
A OPERATING THEORY A–1A.1 North-seeking Gyroscope A–2A.2 Gyrocompass Corrections A–5A.2.1 Latitude Correction A–5A.2.2 Gyro Damping A–5A.2.3 Speed Error A–6
A.3 Summary A–7
B CERTIFICATION A–1
Contents
DPN 060070 Issue 3.7 © SGBrown Page 5 of 6
TABLE OF AMENDMENTS
Old Issue New Issue Date Details
- 2.0 11 May 2000 New release.
2.0 2.0A 12 Dec 2000 Corrected identification of Azimuth Bias potentiometer and other details. Include DIP switch default settings.
2.0A 2.0B 1 Mar 2001 Modify power connection details.
2.0B 2.0C 23 Apr 2001 Add notification to avoid product modifications.
2.0C 3.0 Aug 2002 Substantial amendments to reflect product enhancements
3.0 3.1 Sept 2002 completion of enhancement features including compliance with IEC 61162
3.1 3.2 Jan 2003 Minor amendments and description of Diagnostic Output Sen-tence.
3.2 3.3 Feb 2003 Modification to specifications and addition of Appendix B to demonstrate Certificate of Type Approval.
3.3 3.4 Mar 2003 Minor amendments to a display warning and a note referring to confirming software release.
3.4 3.5 July 2003 Note added regarding modification kit available for alternative orientations when attempting correct speed compensation.
3.5 3.6 August 2003 Minor amendments to specifications throughout
3.6 3.7 March 2004 Amendments to alarm warning / failure designation
Meridian Gyrocompass
Page 6 of 6 © SGBrown Issue 3.7 DPN 060070
1 – Introduction
DPN 060070 Issue 3.7 © SG Brown Chapter 1 Page 1 of 6
1 INTRODUCTIONThe Meridian Gyrocompass is a master heading reference instrument that applies the charac-teristics of a dynamically tuned gyroscope and the effects of gravity and earth rotation to pro-vide a true north reference.
The Meridian Gyrocompass specification makes the System ideal for installation and opera-tion on board vessels of almost any size and in a wide range of applications.
Among the standard features of the Meridian Gyrocompass are:
A short settling time
Operation from a 24V DC electrical supply
This Manual is an important part of the Meridian Gyrocompass. It describes the System and contains full installation and operating instructions. You should retain the Manual with the System for use by personnel who will install and operate it.
Installation and operation of the Meridian Gyrocompass are not complex tasks. However, you should spend time to familiarise yourself with the contents of this Manual before you start to install or use the System. Time spent in identifying the task sequence now will ensure your System is operational in the minimum of time.
WARNINGSWhere appropriate, this Manual includes important safety information highlighted as WARNING and CAUTION instructions. You must obey these instructions:
WARNING instructions alert you to a potential risk of death or injury to users of the System.
CAUTION instructions alert you to the potential risk of damage to the System.
For your convenience, the Table of Contents section includes copies of all the WARNING and CAUTION instructions included in this Manual.
Throughout this Manual all measurements conform to the SI standard of units unless other-wise indicated.
For your convenience, this Manual includes several sections, each of which describes specific features of the Meridian Gyrocompass:
You should read sections 1 and 2 before you attempt to install the System:
Section 1 contains introductory notes and describes those items supplied as standard.
Section 2 describes how to select a suitable location for the gyrocompass. This section includes full instructions to install the System and connect it to external equipment.
Meridian Gyrocompass
Chapter 1 Page 2 of 6 © SG Brown Issue 3.7 DPN 060070
You should read sections 3 and 4 before you use the System:
Section 3 describes how to operate the Meridian Gyrocompass.
Section 4 includes the System specifications and descriptions of the data formats.
You should read sections 5 if you suspect a fault on the System:
Section 5 describes how to use the internal 60-way test connector and explains how to con-duct simple adjustments with the gyrocompass housing removed.
This Manual also contains the following appendices:
Appendix A explains how a gyroscope can be made north seeking for use in a gyrocompass.
CAUTIONYou will void the warranty if you make any modifications to this equipment without prior permission from SG Brown.
DO NOT modify this equipment in any way without obtaining permission from SG Brown.
1 – Introduction
DPN 060070 Issue 3.7 © SG Brown Chapter 1 Page 3 of 6
1.1 SYSTEM DESCRIPTIONThe Meridian Gyrocompass comprises two sub-assemblies:
The gyrocompass housing
The Remote Control Unit (RCU)
Figure 1–1 shows the combined gyrocompass housing with the RCU included as an integral unit.
The Meridian Gyrocompass applies dynamic tuning to settle automatically to the meridian. Due to the physical principles of a north-seeking gyrocompass, achievable accuracy depends on the operating latitude and the vessel dynamics. To optimise its performance, the Meridian Gyrocompass uses information supplied by external equipment, for example a GPS receiver and a speed log, to apply latitude and speed corrections.
Refer to Appendix A for a simplified explanation of the gyrocompass theory of operation.
1.1.1 GyrocompassFigure 1–1: Gyrocompass housing with integral RCU
Figure 1–1 shows the gyrocompass housing, which contains the following items:
True north seeking dynamically tuned precision gyroscope and gimbal suspension assembly.
Power supply board.
Digital and analogue control boards.
RFI filter and distribution board.
It is a relatively simple operation to install the gyrocompass and you should be able to accomplish this quickly without the need for special-ised personnel or equipment. How-ever, note that the gyrocompass weighs 15.5kg and you must take due care when you lift and move it.
The care that you take when you align the gyrocompass housing with the surveyed fore-aft axis of the vessel will have a direct impact on the accuracy of heading measurements delivered by the System. Since the Meridian Gyrocompass is an ideal source of heading information for use by other systems on board, such as radars and satellite communication antennas, the accu-racy of its heading measurements will have a wide impact throughout the vessel. You should
Meridian Gyrocompass
Chapter 1 Page 4 of 6 © SG Brown Issue 3.7 DPN 060070
therefore take care when you install and align the gyrocompass. Refer to Section 2 for full instructions to install, connect and align the Meridian Gyrocompass.
The only component available for user servicing is a 3.15A line fuse inside the gyrocompass housing. In case of failure, refer to Section 5 for instructions to renew this fuse and check the PSU board supplies.
1.1.2 Remote Control UnitFigure 1–2: Remote Control Unit
The Remote Control Unit (RCU) provides all the functions and indicators necessary to control and operate the Meridian Gyrocompass.
The four-character LED can show a range of information:
Heading in Degrees. 000.0 to 359.9
Latitude. 80S to 80N
Latitude Source
Speed in Knots. 00 to 90
Speed Source
Alarms and Status information
Seperate LED indicators show Power On and Compass Ready conditions
Refer to Section 3 for instructions to operate the Meridian Gyrocompass.
1.1.3 Auxiliary InputsAuxiliary inputs may be used for the Meridian Gyrocompass to apply latitude and speed cor-rections.
1 – Introduction
DPN 060070 Issue 3.7 © SG Brown Chapter 1 Page 5 of 6
Ideally, the Meridian Gyrocompass should accept latitude and speed information from exter-nal sources such as a GPS receiver or a speed log. However, you may supply this information manually if external sources are not available. The advantage of using GPS or a speed log to provide correction signals is that they allow automatic corrections to be applied without oper-ator intervention.
Section 2 includes instructions to connect and configure the external sources of latitude and speed information.
Section 3 includes instructions to set the latitude and speed manually.
1.1.4 Heading OutputsThe Meridian Gyrocompass is a self-contained precision navigation instrument that is capable of supplying heading reference information simultaneously to a wide range of equipment on board the vessel. Throughout a typical vessel, applications that can use information supplied by the Meridian Gyrocompass include:
Autopilot
Radars
GPS
Radio direction finder
Course plotter and recorder
Satellite communication systems
Satellite television
To support this wide range of equipment types, the Meridian Gyrocompass can supply heading information simultaneously through multiple channels using any of the common transmission formats.
Refer to Section 3 for a description of the available output channels and their data formats.
1.2 PRINCIPLE OF OPERATIONIn the absence of external influences, a free-spinning gyroscope will try to maintain a fixed orientation in space. The Meridian Gyrocompass exploits this property and uses gravity con-trol and earth rotation to align the gyroscope spin axis with the meridian, i.e. the true north direction.
Refer to Appendix A for the general theory of gyrocompass operation.
Meridian Gyrocompass
Chapter 1 Page 6 of 6 © SG Brown Issue 3.7 DPN 060070
2 – Installation
DPN 060070 Issue 3.7 © SG Brown Chapter 2 Page 1 of 16
2 INSTALLATIONTo obtain the best performance from the Meridian Gyrocompass you must take care when you install and connect it. This section includes all the information and instructions you will need to complete these tasks.
You should read this section carefully and understand the important instructions that it con-tains before you begin to install or connect the equipment.
2.1 Unpacking and Inspection Page 2
Explains the inspection checks that you should perform as you unpack the Meridian Gyrocom-pass.
2.2 Physical and Electrical Installation Page 3
Choose a suitable location to install the Meridian Gyrocompass. Connect the system to an electrical supply and to external equipment.
2.3 Alignment Page 12
The care that you take as you align the Meridian Gyrocompass with the fore-aft datum on the vessel will have a direct influence upon its accuracy.
Meridian Gyrocompass
Chapter 2 Page 2 of 16 © SG Brown Issue 3.7 DPN 060070
2.1 UNPACKING AND INSPECTIONWARNING
The Meridian Gyrocompass weighs 15.5kg. To avoid personal injury, take proper pre-cautions if you lift or move the equipment.
CAUTIONThe Meridian Gyrocompass includes precision components and bearings. To avoid causing damage to any part of the System, handle all items with care.
Retain the original transit cases so that you can use them to transport the system when necessary. You will void the warranty if you use improper packing during transporta-tion.
CAUTIONSevere damage to the Meridian Gyrocompass can occur if you move the gyrocompass while the rotor is still spinning without the servo system in operation.
Note that the gyro rotor continues to spin for approximately five minutes after you power-off the system.
To avoid potential damage to the Meridian Gyrocompass, always allow a period of five minutes after power-off for the gyro rotor to come to rest before you attempt to move the gyrocompass.
The Meridian Gyrocompass undergoes a full series of electrical and mechanical tests during manufacture and before dispatch. The packing case has a special design to protect the contents against shock during transit so that the equipment should arrive without damage or defect.
As soon as possible after you have received the system, check all items against the shipping documents. Inspect all sub-assemblies carefully to check for any damage that may have occurred during transportation. If you see any damage file a claim with the carrier and imme-diately notify SG Brown.
To avoid loss or damage to any components of the system, store all sub-assemblies safely in the transit case until you need to install them. Obey the storage temperature limits listed in Section 4.
Notify SG Brown immediately if there are any components missing from the shipment.
The title page of this Manual lists the contact details for SG Brown.
2 – Installation
DPN 060070 Issue 3.7 © SG Brown Chapter 2 Page 3 of 16
2.2 PHYSICAL AND ELECTRICAL INSTALLATION2.2.1 Selecting a locationThere are certain guidelines that you should follow to install the Meridian Gyrocompass suc-cessfully:
CAUTIONDuring operation, the gyrocompass must remain level to within ±45°. If it experiences tilt greater than 45° in any direction, it will ‘topple’. Safety routines in the gyro software will then power-off the gyro rotor and show alarm conditions on the RCU. To restore normal operation, establish a level operating attitude and then power-on the gyrocom-pass normally.
Never apply a tilt of more than 45° with the gyro rotor spinning or during the gyrocom-pass initialisation procedure. Note that the gyro rotor continues to spin for approxi-mately five minutes after you power-off the System.
The gyrocompass weighs 15.5kg. Choose a mounting location that is level, flat and suffi-ciently strong to support the unit without flexing or experiencing extreme vibration. The mounting location can be open, as on a chart table, or enclosed within a cabinet.
CAUTIONIf you install the gyrocompass in an enclosed space, make certain there is sufficient ventilation and circulation of free air to allow effective cooling.
Choose a location that protects the Meridian Gyrocompass from damage.
Do not install or operate the Meridian Gyrocompass where the ambient temperature could fall below 0°C or rise above +45°C, or where rapid changes of temperature can occur.
Do not install the Meridian Gyrocompass close to strong mechanical or electrical noise sources, or in a location susceptible to vibration or shock.
Allow a minimum distance of 0.4m between the gyrocompass housing and any standard magnetic compasses.
Choose a location that allows convenient access to install, connect and service the Merid-ian Gyrocompass. Refer to Figure 2–6 for clearance dimensions.
Meridian Gyrocompass
Chapter 2 Page 4 of 16 © SG Brown Issue 3.7 DPN 060070
2.2.2 Gyrocompass installationYou must align the Meridian Gyrocompass so that its fore-aft axis is parallel to the fore-aft datum on the vessel. Any misalignment between the gyrocompass housing and the vessel will have a direct effect on the accuracy of heading measurements delivered by the system.
To install the Meridian Gyrocompass you will need the following tools:
Screwdriver 5.5mm × 150mm
Screwdriver 3mm × 75mm
Nut spinner 5.5mm
Combination spanner 10mm
Hexagon key 2mm
Adjustable spanner opening to at least 33mm
Suitable cables for the installation as indicated in Table 2–1.
There should be no need to remove the gyrocompass cover during installation. You may gain access to make power and signal connections by removing the gland plate assembly, compris-ing the Gland Plate and the Distribution Board. There is a removable panel on the top of the gyrocompass that allows access to the internal DIP switches and a 60-way test connector.
1. During installation you must align the Meridian Gyrocompass so that its fore-aft axis is parallel with the fore-aft datum on the vessel. It is not necessary for the gyrocompass to be on the vessel centre line. There are alignment marks on the base of the Meridian Gyrocom-pass to help you achieve the correct alignment.
2. Three elongated securing holes machined into the gyrocompass base allow you to make fine adjustments to alignment after installation. With the gyrocompass positioned accu-rately, mark the supporting surface with the centre positions for the three securing holes. Refer to Figures 2–5 and 2–6 for dimensions.
Table 2–1: Suitable cable types
Purpose Suitable cable
Power supply 7/0.5mm (1.5mm2) HOFR sheathed to BS6883
Synchro heading outputResolver heading outputStepper S-code output
7/0.4mm (1.0mm2) butyl or EP rubber insulated, CSP sheathed, wire braided and CSP oversheathed.
Serial data heading outputSerial data speed inputSerial data latitude input
1/0.85mm (0.6mm2) twisted pair, butyl or EP rubber insulated, CSP sheathed, wire braided and CSP oversheathed.
2 – Installation
DPN 060070 Issue 3.7 © SG Brown Chapter 2 Page 5 of 16
3. Remove the gyrocompass and drill three 8.5mm diameter holes, using the marks you have just made on the supporting surface as hole centres. Deburr the holes and remove any swarf.
4. Reposition the gyrocompass and align it to the fore-aft datum. Use three M8 bolts with washers and nuts to secure the gyrocompass in position.
5. Connect a 24V electrical supply (acceptable range 18V to 36V DC) to the Meridian Gyro-compass at J1, the three-pin power inlet on the Gland Plate. Figure 2–1 shows the Gland Plate.
Figure 2–1: Gyrocompass gland plate
CAUTIONDo not make any connections to the gyrocompass with power on the supply cable.
6. Connect the ship’s safety ground to the earthing stud adjacent to the power connector.
7. Make all necessary signal connections to the Meridian Gyrocompass at the Distribution Board. The Distribution Board accepts open tails for all connections. Pass cables through available glands in the Gland Plate. Glands A, D, E, F and J (identified in Figure 2–5)
Fuse
3.15AF
Compass Min. Safe Dist.
Build Standard No.
Serial No.
Mfg. Date
m
Watford, England.
CAUTION
Before removing the cover or the RCU
unit, remove the gland plate and
disconnect the RCU cable (TB1/17-22)
from the distribution board.
Gland plate release screws
Cover plate release screws
Meridian Gyrocompass
Chapter 2 Page 6 of 16 © SG Brown Issue 3.7 DPN 060070
accept cables up to 18mm diameter, while all other glands accept cables up to 14mm diam-eter. Refer to Figure 2–3, and Tables 2–3 and 2–4 for cable connection details.
8. To maintain EMC compliance, connect all the wire braiding on the cables to the grounding posts on the inside surface of the Gland Plate as shown in Figure 2–2.
Figure 2–2: Termination of wire braided cables
9. Refit the Gland Plate, making certain there are no trapped wires or cables.
Figure 2–3: Gyrocompass distribution board
2 – Installation
DPN 060070 Issue 3.7 © SG Brown Chapter 2 Page 7 of 16
Table 2–2: J1 – Power supply input pin details
Pin Description
1 Protective ground
2 +24V DC
3 0V
Table 2–3: Input signals
Signal description Signal type Distribution Board connector
DG TB1/1 TB1/2 (0V)
GPS input IEC 61162 RS232 TB1/3 TB1/4 (0V)
GPS input IEC 61162 RS422 TB1/5 (A) TB1/6 (B)
Log input IEC 61162 RS232 TB1/7 TB1/8 (0V)
Log input IEC 61162 RS422 TB1/9 (A) TB1/10 (B)
Log OK TB1/11 TB1/12 (0V)
Log TTL pulses TB1/13 (+) TB1/14 (0V)
Log relay Voltage free contact close TB1/15 (+) TB1/16 (0V)
RCU 24V in TB1/17 (+) TB1/18 (–)
RCU On/Off TB1/19 (N/C) TB1/20 (ON)
RCU Communications RS422 TB1/21 (S+) TB1/22 (S-)
Spare – TB1/23 TB1/24
Meridian Gyrocompass
Chapter 2 Page 8 of 16 © SG Brown Issue 3.7 DPN 060070
Table 2–4: Output signals
Signal description Signal type Distribution Board connector
Channel 2 IEC 61162 RS232 (all data) TB2/1 TB2/2 (0V)
Channel 1 IEC 61162 RS232 (all data) TB2/3 TB2/4 (0V
Channel 2 IEC 61162 RS422 (all data) TB2/5 (B) TB2/6 (A)
Channel 1 IEC 61162 RS422 (all data) TB2/7 (B) TB2/8 (A)
Heading TTL S-type TB2/9 (5V) TB2/10 (L1)TB2/11 (L2) TB2/12 (L3)TB2/13 (0V)
Heading Synchro/resolver TB2/14 (36V) resTB2/15 (26V) synTB2/16 (0V) syn/resTB2/17 (S1) synTB2/18 (S1) resTB2/19 (S2) syn/resTB2/20 (S3) syn/resTB2/21 (S4) res
Gyro fail Voltage free contact closure TB2/22 (CC)TB2/23 (normally closed, opens on failure)TB2/24 (normally open, closes on failure)
System Fail TTL TB2/25 TB2/26 (0V)
Gyro ready Voltage free contact closure TB2/27 (CC)TB2/28 (open when not ready, closes when ready)TB2/29 (closed when not ready, opens when ready)
Gyro ready TTL TB2/30 TB2/31 (0V)
Channel 2 IEC 61162 RS232 TB3/1 TB3/2 (0V)
Channel 2 IEC 61162 RS232 TB3/3 TB3/4 (0V)
Channel 2 IEC 61162 RS232 TB3/5 TB3/6 (0V)
Channel 2 IEC 61162 RS422 TB3/7 (B) TB3/8 (A)
Channel 2 IEC 61162 RS422 TB3/9 (B) TB3/10 (A)
Channel 2 IEC 61162 RS422 TB3/11 (B) TB3/12 (A)
Channel 2 IEC 61162 RS422 TB3/13 (B) TB3/14 (A)
Channel 2 IEC 61162 RS422 TB3/15 (B) TB3/16 (A)
Channel 2 IEC 61162 RS422 TB3/17 (B) TB3/18 (A)
Channel 2 IEC 61162 RS422 TB3/19 (B) TB3/20 (A)
Channel 2 IEC 61162 RS422 TB3/21 (B) TB3/22 (A)
Channel 2 IEC 61162 RS422 TB3/23 (B) TB3/24 (A)
Rate of turn Analogue ±10V TB3/25 TB3/26 (0V)
Course recorder IEC 61162 RS232 TB3/27 TB3/28 (0V)
2 – Installation
DPN 060070 Issue 3.7 © SG Brown Chapter 2 Page 9 of 16
2.2.3 External Remote Control UnitThe standard Meridian Gyrocompass has the Remote Control Unit (RCU) mounted integrally and available for immediate operation.
There may be applications where you prefer to install the RCU at some distance from the gyrocompass unit. A mounting kit, part number 929190, is available to use in these circum-stances. The kit includes the following items:
RCU housing
Mounting bracket
Blanking plate for the gyrocompass housing
There is no need to remove the gyrocompass cover to install the RCU externally:
1. Release and remove the four M3 screws at the corners of the RCU that secure it to the gyrocompass housing.
2. Remove the seven Gland Plate release screws marked in Figure 2–1. Remove the Gland Plate. Note the connection sequence of the RCU cable at TB1/17–22 so that you can restore the same connections through the extension cable.
3. Disconnect the RCU cable at TB1/17–22 .
4. Lift the RCU away from the gyrocompass and install it at the remote location.
The cable run between the RCU and the remote location must not exceed 100 metres.
5. Use the bracket with the mounting kit to fix the RCU to a desk or to a bulkhead. You may also flush mount the RCU in a panel. Choose a suitable location to mount the RCU:
The mounting surface can be vertical or horizontal according to requirements.
Avoid installing the RCU where it might experience severe shock or vibration.
Choose a location for the RCU that allows a clear view of the display in all conditions.
6. Use the two star knobs supplied to fit the RCU into the mounting bracket. Tilt the unit to a convenient viewing and operating angle and then lock it in place by tightening both star knobs.
7. Supply and fit a cable to connect the RCU to TB1/17–22 on the Distribution Board . The cable must have three screened twisted pairs and should not exceed 100 metres in length.Route the cable through a vacant cable gland on the Gland Plate and make the cor-rect connections to the TB1 terminals.
8. Refit the Gland Plate and secure it in place using the seven release screws.
9. Fit the blanking plate to fill the gap left in the cover by the RCU.
Meridian Gyrocompass
Chapter 2 Page 10 of 16 © SG Brown Issue 3.7 DPN 060070
2.2.4 Set the Gyrocompass DIP Switches1 There is a removable panel on top of the gyrocompass that allows access to the two inter-
nal DIP switches (shown in Figure 2–4) without the need to remove the main gyrocompass cover. Release and remove the three securing screws to lift off the panel.
2. Refer to Tables 2–5 and set the DIP switches carefully for the specific requirements of your installation. Do not adjust the settings of other preset controls inside the gyrocom-pass.
3. Refit the access panel to the top of the gyrocompass cover
Figure 2–4: Location of DIP switches.
2 – Installation
DPN 060070 Issue 3.7 © SG Brown Chapter 2 Page 11 of 16
Table 2–5: SW1 and SW2 DIP switch settingsFactory default settings appear in bold and are marked with an asterisk in this table.
The DIP switch settings described in this table are only applicable to gyrocompasses fitted with software versions BPR 0113 (Main) and BPR 0114 (RCU) or later. If neces-sary, you can view the software versions of the main and the control panel processors by pressing both the Up and the Down selection buttons simultaneously. The display will toggle between indications of the main processor software version (with prefix 'M') and the control panel software (with prefix 'R'). The display will continue to toggle for several seconds after you release the buttons and will then return to the heading indi-cation.
SW1 DIP Switches SW2 DIP Switches
Switch number
and settingFunction
Switch number
and settingFunction
1OnOffOnOff
2OnOnOffOff
Speed Log Input Type100 pulses per nautical mile200 pulses per nautical mile400 pulses per nautical mileLOG Serial Data*
1On
Off
Output Sentences typesAnalogue ROT Scaling +/- 60deg/minute = +/- 10VAnalogue ROT Scaling +/- 20deg/s = +/- 10V*
3OnOff
Channel 1 Baud rate96004800*
2OnOff
Channel 2 Heading decimal placesTwo decimal placesOne decimal place*
4OnOff
Channel 2 Baud rate96004800*
3OnOff
Channel 1 Checksum fieldChecksum transmittedNo Checksum transmitted*
5On
Off
Channel 1 update rate10 Hz (defaults to 1Hz if CH1 All Data is selected)1 Hz*
4OnOff
Channel 2 Checksum fieldChecksum transmittedNo Checksum transmitted*
6On
Off
Channel 2 update rate10 Hz (defaults to 1Hz if CH2 All Data is selected)1 Hz*
5 OnOffOnOff
6OnOnOffOff
Channel 1 Output SentencesAll Data (1Hz only)HDT + ROTROT onlyHDT only*
7OnOff
Channel 1 Heading Decimal placesTwo decimal placesOne decimal place*
7 OnOffOnOff
8OnOnOffOff
Channel 2 Output SentencesAll Data (1Hz only)HDT + ROTROT onlyHDT only*
8OnOff
Gyro controlFor special applications onlyFactory default setting*
Notes: 1. If you set All Data Output Sentence, the update rate will default to 1Hz.2. For full IEC 61162 compliance, a checksum must be transmitted.
Meridian Gyrocompass
Chapter 2 Page 12 of 16 © SG Brown Issue 3.7 DPN 060070
2.3 ALIGNMENTIt is important to align the gyrocompass to the vessel accurately. Any misalignment between the housing and the vessel will appear directly as a fixed error in heading measurements. Because measurements from the Meridian Gyrocompass are available for use by diverse sys-tems around the vessel, any misalignment between the gyrocompass and the fore-aft datum might have a significant impact in many other areas of application.
There are several methods you may use to align the gyrocompass to the vessel fore-aft datum:
Align the gyrocompass to the fore-aft datum using a known reference line, such as a sur-veyed bulkhead or frame member. The marks on the gyrocompass base plate are precision indicators of the gyrocompass alignment orientation.
To achieve correct speed compensation, the gyrocompass must be orientated so that the gland plate faces the forward end of the vessel. Note that modification kits are available for alternative gyrocompass orientations.
Use the services of a marine surveyor to align the gyrocompass precisely with the fore-aft datum.
Remove any residual misalignment by making minuscule adjustments to the gyrocompass mounting plate. When you have achieved perfect alignment, tighten the securing bolts fully to lock the gyrocompass in position.
2.4 FINAL GYROCOMPASS INSTALLATION TESTSAfter you have installed the gyrocompass and power supplies are available to it, perform the following installation tests:
1. Power-on the gyrocompass by following the instructions in sub-section 3.2. Wait for three hours before you perform the following tests.
2. Check the vessel heading against a known reference mark on a chart. Typically this could be the alongside position of the fitting-out dock. Alternatively, accurately survey an object at least five kilometres ahead of the vessel using the fore-aft line as a datum.
3. Check the displayed gyrocompass heading at intervals to make certain it is consistent with the surveyed vessel heading.
4. If there is an error larger than ±0.5°, re-check the vessel fore-aft datum to confirm that it is correct.
5. Check that all the repeaters are accurately aligned with the gyrocompass heading and make certain they maintain their alignment at all times while the gyrocompass is powered-on.
2 – Installation
DPN 060070 Issue 3.7 © SG Brown Chapter 2 Page 13 of 16
2.5 INSTALLATION DRAWINGSFigure 2–5: Gyrocompass installation – Sheet 1
30330 340
170
110
160
SE 130
140
120
150
7090
80100
E
NE 60
40
50
250
230
190 180200
S210
220
SW240
N
NW
320
270
260
W
280
300
290
310
20100350
Fuse
3.15AF
CompassMin.SafeDist.
BuildStandardNo.
SerialNo.
Mfg.Date
m
Watford,England.
CAUTION
BeforeremovingthecoverortheRCU
unit,removetheglandplateand
disconnecttheRCUcable(TB1/17-22)
fromthedistributionboard.
24VDC
Meridian Gyrocompass
Chapter 2 Page 14 of 16 © SG Brown Issue 3.7 DPN 060070
Figure 2–6: Gyrocompass installation – Sheet 2
S210
220
SW240
N
NW
320
270
260
W
280
300
290
310
20100350
Fuse
3.15AF
CompassMin.SafeDist.
BuildStandardNo.
SerialNo.
Mfg.Date
m
Watford,England.
CAUTION
BeforeremovingthecoverortheRCU
unit,removetheglandplateand
disconnecttheRCUcable(TB1/17-22)
fromthedistributionboard.
24VDC
30330 340
170
110
160
SE 130
140
120
150
7090
80100
E
NE 60
40
50
250
230
190 180200
2 – Installation
DPN 060070 Issue 3.7 © SG Brown Chapter 2 Page 15 of 16
Figure 2–7: RCU installation – Table mount
Meridian Gyrocompass
Chapter 2 Page 16 of 16 © SG Brown Issue 3.7 DPN 060070
Figure 2–8: RCU installation – Flush mount
3 – Operating Instructions
DPN 060070 Issue 3.7 © SG Brown Chapter 3 Page 1 of 10
3 OPERATING INSTRUCTIONSThis section explains how to power-on and configure the Meridian Gyrocompass after installa-tion. Refer to Section 4 for an explanation of the data formats relevant to the System.
3.1 Control Features Page 2
The RCU provides all the controls you will need to operate the Meridian Gyrocompass. It also includes a four-character display panel that shows the heading indication and any alarm mes-sages and error codes.
3.2 Initial Power-on Page 3
Explains how to power-on the Meridian Gyrocompass after installation and describes the ini-tialisation sequence.
3.3 Operating Procedure Page 4
Explains how to select the latitude and speed correction sources, and how to set the latitude and speed manually if necessary.
3.4 Error Modes Page 5
Identifies the system error modes. Use these indicators to identify a possible fault condition.
3.5 Operating Considerations Page 8
Includes general advice for operating the Meridian Gyrocompass on a vessel and on high speed craft.
Meridian Gyrocompass
Chapter 3 Page 2 of 10 © SG Brown Issue 3.7 DPN 060070
3.1 CONTROL FEATURESFigure 3–1: RCU front panel features
The RCU front panel includes all the operator controls for the Meridian Gyrocompass:
Table 3–1: RCU Control and Indicator functions
Control Function
Power switch. Recessed to prevent accidental operation.
Selection Up. Press to increase display brightness.
Selection Down. Press to decrease display brightness
Latitude selection button. Press to display current Latitude source and correction value. Use in conjunction with the Selection Up and Selection Down buttons to pre-set Latitude source and correction value.
Speed Selection. Press to display current Speed source and correction value. Use in conjunction with the Selection Up and Down buttons to pre-set Speed source and correction value.
Alarm. Press to silence the audible alarm.
012.3 Four digit alphanumeric display.Note: The display can show additional information by alternating the display contents at 0.5Hz. This is indicated throughtout the manual as, for example, L52N + SGPS
Power lamp (red) Indicates that the Meridian Gyrocompass is switched on when 24V DC nominal power is connected.
Ready lamp (green)
Indicates that the Meridian Gyrocompass has settled and a True Heading is available.
3 – Operating Instructions
DPN 060070 Issue 3.7 © SG Brown Chapter 3 Page 3 of 10
3.2 INITIAL POWER-ONThe Meridian Gyrocompass starting cycle is fully automatic after power is applied. For correct operation Latitude and Speed correction must be applied.
1. Check that there is a nominal 24V DC electrical supply available to the gyrocompass. The acceptable supply range is 18V to 36V DC.
To ensure continuous operation, the power supply for this unit should have a 200W power rating.
2. To start the Meridian Gyrocompass press the power switch on the RCU.
3. Check that the red ‘Power’ lamp on the RCU illuminates. This lamp indicates only that the Meridian Gyrocompass is receiving power and does NOT indicate a settled condition. Check that the instrument illumination is at maximum during the initialisation sequence. Even at its maximum setting, the instrument illumination may be difficult to see in bright ambient lighting.
4. The RCU will activate the audible alarm for about 1 second. The display will indicate T.E.S.T. and the ‘Ready’ lamp will be lit for about 10 seconds while the system performs a series of self-tests. After successful completion of the self-tests, the display will show the current Gyrocompass dial heading and the ‘Ready’ lamp will go off until the Gyrocompass has settled.
5. Set the source of latitude information by following the instructions in sub-section 3.3.1.
6. Set the source of speed information by following the instructions in sub-section 3.3.2.
Table 3–2: RCU display formats
Format Function
Heading0123.40123.4 + DG0123.4 + DG_L0123.4 + DG_X
Heading OnlyHeading with DG mode set at the RCUHeading with DG mode set by latitude greater than 80 degHeading with DG mode set by Distribution PCB connection
Speed (by pressing the Speed button)S_01 + S.MANS_01 + S.GPSS_01 + S.LOGS_01 + P.LOG
Speed value with Manual selected speed sourceSpeed value with GPS selected speed sourceSpeed value with LOG selected speed source (serial data input)Speed value with LOG selected speed source and Pulse Log DIP switch set (pulse input)
Latitude (by pressing the Latitude button)L.52N + S.MAN
L.52S + S.MAN
L.52N + S.GPS
Latitude value in the Northern Hemisphere with Manual selected Latitude sourceLatitude value in the Southern Hemisphere with Manual selected Latitude sourceLatitude value with GPS selected Latitude source
Meridian Gyrocompass
Chapter 3 Page 4 of 10 © SG Brown Issue 3.7 DPN 060070
7. Use the increase and decrease selection buttons to adjust the RCU illumination level to a comfortable setting.
8. Wait for the gyrocompass to settle. This will occur automatically and will take upwards of 24 minutes depending on initial heading offset and sea conditions. The Meridian Gyro-compass signifies its settled condition by illuminating the green ‘Ready’ lamp.
9. If necessary, you can view the software versions of the main and the control panel proces-sors by pressing both the Up and the Down selection buttons simultaneously. The display will toggle between indications of the main processor software version (with prefix ‘M’) and the control panel software (with prefix ‘R’). The display will continue to toggle for several seconds after you release the buttons and will then return to the heading indication.
3.3 OPERATING PROCEDUREThe Meridian Gyrocompass will settle automatically after power-on, to provide a true north reference. The system requires only latitude and speed correction, applied manually or from external sources, to perform to the specified accuracy.
Ideally, the Meridian Gyrocompass should accept latitude and speed information from exter-nal sources such as a GPS receiver or a speed log, which allow the System to apply corrections automatically.
3.3.1 Latitude correction1. Press and hold the Latitude selection button.
2. Use the up and down selection buttons to set the local latitude manually. The display will show the latitude in one-degree increments in the range 80°N to 80°S, for example L70N
To select automatic latitude compensation from a GPS receiver, use the up or down selec-tion buttons to scroll beyond 80°N or 80°S until the display shows LGPS.
If there is no valid input available from a GPS receiver, the display will indicate a LGPS alarm after 30 seconds.
3. Release both buttons to set the latitude to the displayed value or to set the gyrocompass to use GPS as the source of automatic latitude correction. The display will indicate the lati-tude setting and latitude source for several seconds and will then return to the normal head-ing display.
If you input the operating latitude manually, remember to change the setting when nec-essary. Note that, in medium latitudes, a 10° error in setting the operating latitude will result in a compass error of approximately 0.5°.
3.3.2 Speed correction1. Press and hold the Speed selection button.
2. Use the up and down selection buttons to set the speed manually in the range zero to 90 knots.
3 – Operating Instructions
DPN 060070 Issue 3.7 © SG Brown Chapter 3 Page 5 of 10
To select automatic speed compensation from a GPS receiver or a speed log, use the up selection button to scroll beyond 90 knots until the display shows SGPS or SLOG.
If there is no valid input available from a speed log or GPS receiver, the display will indicate a SLOG or SGPS alarm after 30 seconds.
3. Release both buttons to set the speed to the displayed value or to set the gyrocompass to use GPS or a speed log as the source of automatic speed correction. The display will indi-cate the speed setting and speed source for several seconds and will then return to the nor-mal heading display.
If you input the vessel speed manually, remember to set the average vessel speed and to change the setting when necessary. Return the setting to zero on completion of the voyage. For a vessel steaming in a northerly direction, a 5-knot error in speed setting will generate an error of approximately 0.5°.
3.3.3 DG operating modeFollow the instructions in sub-section 3.3.1 to set the latitude correction to the Directional Gyro (DG) mode. In this mode you can use the Meridian Gyrocompass as a direction indicat-ing instrument all the way up to the poles. If the gyrocompass has settled on north immediately prior to entering the DG mode, it will continue to provide a useful indication of the northerly direction for a period, but will not continue to seek north. The length of time that the direction indication remains valid depends entirely on the gyro drift characteristics.
Note: DG mode will be automatically enabled for latitudes set greater than 80 deg.
Note: that the gyrocompass will not north seek while operating in the DG mode.
3.4 ERROR MODESThe Meridian Gyrocompass has three possible Error modes:
1. Loss or corruption of GPS signal
2. Loss or corruption of speed log signal
3. Gyrocompass system warnings and failures
3.4.1 Loss of GPSThis failure mode can occur when you have selected GPS as the source of speed or latitude information and the signal corrupts or becomes lost for a period of 30 seconds. You can recog-nise this condition by the following indications:
The display shows S.GPS + FAIL for the loss of speed correction information.
The display shows L.GPS + FAIL for the loss of latitude correction information.
The audible alarm will sound.
Press the Alarm button to cancel the audible alarm.
1. The Gyrocompass will use the last valid speed and latitude values.
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Chapter 3 Page 6 of 10 © SG Brown Issue 3.7 DPN 060070
2. The RCU will continue to show the alarm message until a valid input signal is re-estab-lished or a different input source is selected.
3. If the valid input signal has not been established within a period of 30 minutes the audible alarm will be enabled.
3.4.2 Loss of speed logThis failure mode can occur when you have selected speed log as the source of speed informa-tion and the signal corrupts or becomes lost for a period of 30 seconds. You can recognise this condition by the following indications:
The display flashes SLOG + FAIL for the loss of selected serial data source information.
The display flashes pLOG + FAIL for the loss of pulsed selected source information.
The audible alarm will sound.
Press the Alarm button to cancel the alarm.
1. The Gyrocompass will use the last valid speed value.
2. The RCU will continue to show the alarm message until a valid input signal is restablished or a different input source is selected.
If a valid input signal has not been established within a period of 30 minutes the audible alarm will be enabled.
3.4.3 Gyrocompass system warnings and failuresThe Meridian Gyrocompass has a built-in system that monitors operation of the gyrocompass. The functions that this system checks are split into two categories.
Warning conditions
Failure conditions
A failure condition warning will result in the Gyroscope power supply being disabled. Refer to the maintenance section before activating the Power Supply.
Warning Conditions
If the gyrocompass detects a warning condition, it will use two methods to alert you:
The display shows <Message> + FAIL
The audible alarm will sound.
Press the Alarm button to cancel the audible alarm.
3 – Operating Instructions
DPN 060070 Issue 3.7 © SG Brown Chapter 3 Page 7 of 10
Table 3–3: Gyrocompass warning codes
The RCU will continue to show the alarm message until the fault condition has been removed. If the fault condition has not been removed within a period of 30 minutes the audible alarm will be enabled. Refer to sub-section 5.1 which outlines some simple checks that you can make to rectify these fault conditions. If necessary contact SG Brown or an approved local service agent for assistance.
Failure Conditions
If the Meridian Gyrocompass detects a failure condition, it will use six methods to alert you:
The display shows <Message> + FAIL
The audible alarm will sound.
The ‘Ready’ lamp will extinguish.
The Gyro Fail relay will activate.
Serial output will transmit empty sentences.
Stepper output will transmit an illegal code.
Press the Alarm button to cancel the audible alarm.
Table 3–4: Gyrocompass failure codes
These failures are considered to render, or be due to an unrecoverable fault condition, possibly due to a component failure.
To prevent damage to the Gyroscope the power supplies to it will be disabled.
The Gyrocompass will be disabled until it has been reset by the operator. Refer to the mainte-nance section before activating the Power Switch.
<Message>RCU Screen Definition of warning code
dc + fail Internal DC power supply is outside operating limits
ac + fail Internal AC power supply is outside operating limits
rdc + fail Loss of internal timing signals
Temp + fail Over or under operating temperature range
rMT + fail Loss of serial communication link with the RMT
<Message>RCU Screen Definition of failure code
rot + Fail Rate of Turn exceeds 300o/s
Meridian Gyrocompass
Chapter 3 Page 8 of 10 © SG Brown Issue 3.7 DPN 060070
3.5 OPERATING CONSIDERATIONS3.5.1 General Operating Considerations You should leave the Meridian Gyrocompass running continuously. Power-off the system
only during long periods of lay-up, for example during vessel dry-docking. To power-off the Meridian Gyrocompass, press the ‘Power’ button. The heading display will go blank and the front panel lamps will switch off. The gyro rotor will take approximately five min-utes to come to rest.
If you intend to leave the system powered-off for an extended period, you should arrange to run the gyrocompass for a period of at least thirty minutes at intervals of six months or less.
The Meridian Gyrocompass has full protection against interruption of its electrical supply. It will re-start and align itself automatically on restoration of electrical power. The heading indication will be accurate when the RCU ‘Ready’ lamp is on.
Monitor the Meridian Gyrocompass performance regularly. When functioning correctly, and provided the correct Speed and Latitude compensations are applied, the heading error in latitudes up to 60° and for speeds up to 25 knots will normally be less than 0.75° regard-less of the vessel manoeuvres.
Never move the gyrocompass with the gyro rotor spinning unless you leave the servos operational. Note that the gyro rotor continues to spin for a period of approximately five minutes after you power-off the gyrocompass.
3.5.2 Corrections for Speed and Latitude Gyrocompass operational accuracy depends, to a large extent, upon accurate corrections
for speed and latitude being applied.
Most users find that the facilities for the automatic application of speed and latitude cor-rections, via signal inputs from GPS and/or ships log, are a convenient method of applying corrections.
However, users should be aware that if the input signal contains the wrong information, then the wrong corrections will be applied. For instance, it has been noted that some GPS installations, under certain circumstances, will output a “valid” signal with the speed and latitude fields set to all zeros indicating that the vessel is stationary on the equator.
An incorrect input of speed and/or latitude will cause the gyrocompass to indicate an incorrect heading and in the case of extreme errors could cause, in certain circumstances, the gyrocompass to come out of the “Ready mode”.
3.5.3 Operating at Extremes of Latitudes As latitude increases (north or south) the magnitude of the horizontal component of the
Earth’s rotation rate reduces in proportion to the cosine of latitude. Consequently, the effectiveness of the gyrocompasses north seeking action reduces with increasing latitude.
At latitudes greater than 80o it is recommended that the gyrocompass be operated in the directional gyro mode.
3 – Operating Instructions
DPN 060070 Issue 3.7 © SG Brown Chapter 3 Page 9 of 10
If correction for the effect of latitude on the vertical component of Earth’s rotation is made manually via the RCU, then correction is available to 80o. Thereafter, the directional gyro mode should be manually selected. Errors in the indicated heading will increase with time and increasing latitude above 80o to a maximum of approximately 0.25o /hour. To re-align the gyrocompass, operating latitude must be reduced below 80o and the gyrocompass mode of operation re-selected.
If correction for the effect of latitude on the vertical component of Earth’s rotation is made automatically via a serial data input, then correction is available above 80o and directional gyro mode is automatically selected above this latitude. The compass will still be subject to small inherent drifts while operating in this mode. Reversion to the gyrocompass mode will be made automatically when the serial data latitude input falls below 80o.
3.5.4 Operating Considerations for High Speed Craft The gyrocompass gravity control gives rise to errors whenever the gyrocompass acceler-
ates or decelerates along the north-south line, that is whenever the northerly speed or course changes. These errors are caused by the inertia of the pendulous element of the gyro, which produces a torque about the horizontal axis and therefore a precession in azi-muth. This effect, called ballistic deflection, causes an increase in error during accelera-tion.
The precession in tilt that arises from the damping component of gravity control is called ballistic tilt. The combined effects of ballistic tilt and ballistic deflection cause the gyro-compass to tilt downwards. Because of the factors that guide the behaviour of a damped gyroscope, the gyro spin axis will return to the settled position by the normal anticlock-wise spiral after the acceleration has ceased.
In the Meridian Gyrocompass, gravity control comes from an accelerometer (pendulum), which generates an electrical signal related to the tilt of the gyro spin axis. This devices has two important design features; it is heavily damped and the range of output is restricted to a small angle.
The use of accelerometer damping by the Meridian Gyrocompass is of prime importance in the reduction of a particularly serious form of ballistic error called inter cardinal rolling error. This type of error occurs most noticeably when the vessel steams on an inter cardinal heading while rolling simultaneously through a significant angle.
If the gyrocompass is installed at some distance above the vessel centre of roll rotation, as is usually the case on commercial vessels, the resulting lateral acceleration components along the east-west and north-south axes of the gyrocompass combine to build an error in the northerly settle point.
If the effect persists for long enough, this error might become as large as several degrees. However, by damping the accelerometer using a time constant several times larger than the vessel rolling period, inter cardinal rolling errors are significantly reduced.
Another form of ballistic error arises from north-south accelerations generated by vessel manoeuvres. Such accelerations can arise from changes in speed and/or course. By limit-ing the angular output of the accelerometer, the Meridian Gyrocompass reduces the error potential typically to less than one degree.
Meridian Gyrocompass
Chapter 3 Page 10 of 10 © SG Brown Issue 3.7 DPN 060070
It is also possible to eliminate acceleration effects by temporarily operating the compass in the DG (Directional Gyro) mode. In this mode gravity control is used for tilt corrections only, so that ballistic effects would cause negligible heading error during short-term accel-eration periods. The DG mode can be selected manually from the control panel.
The Meridian Gyrocompass complies with all requirements of IMO Resolution A.821(19), Performance Standards for Gyrocompasses for High-Speed Craft.
4 – Technical Data
DPN 060070 Issue 3.7 © SG Brown Chapter 4 Page 1 of 16
4 TECHNICAL DATA4.1 SPECIFICATIONS4.1.1 Power RequirementsVoltage 24V DC (acceptable range 18V to 36V DC)
Power consumption 3A at power on, 1.2A continuous (The power sup-ply capacity should exceed 200W)
CAUTIONThe Meridian Gyrocompass should be supplied with power from an SELV source as defined in IEC/EN 60950. The power supply source should be switched and protected by a suitable circuit breaker.
To comply with the requirements of IMO Resolution A.821(19), Performance Standards for Gyrocompasses for High Speed Craft, power to the gyrocompass should be delivered by an uninterruptable power supply.
4.1.2 Performance (definitions as in ISO 8728)Settle point error 0.35° sec latitude
Static error 0.1° sec latitude RMS
Dynamic accuracy 0.3° sec latitude (Scorsby andIntercardinal motion tests)
Settle point repeatability 0.25° sec latitude
Follow up speed 200°/s
Time to settle within 0.7° Less than 45 minutes with a ±30° initial heading offset
4.1.3 CompensationLatitude compensation range 80°N to 80°S
Speed compensation range 0 to 90 knots
4.1.4 EnvironmentOperating environment EN 6095:1997 designated category ‘weather pro-
tected’
Operating temperature 0°C to +45°C (to ISO 8728)–15°C to +55°C (with reduced accuracy)
Storage temperature –25°C to +80°C
Meridian Gyrocompass
Chapter 4 Page 2 of 16 © SG Brown Issue 3.7 DPN 060070
4.1.5 Signal InputsLatitude IEC 61162 message string via RS232 or RS422
from GPS
Speed Pulse or contact closure at 100, 200 or 400 per nautical mile from speed log.
IEC 61162 message string at 4800 baud via RS232 or RS422 from GPS or speed log
4.1.6 Signal outputsS-type heading 1 × step-by-step, 6 steps per degree (TTL level)
update limited to 20o/s to prevent repeater mis-alignment
Synchro heading 1 × 26V 400Hz (11.8V maximum line-to-line),sector value 360°
Resolver heading 1 × 36V 400Hz (8V maximum per phase),sector value 360°
Analogue rate of turn 1 × rate of turn ±60°/min (±10V) or ±20°/s (±10V)
Serial data outputs 6 × RS23211 × RS422
Serial data formats IEC 61162 at 1Hz or 10Hz. Course recorder output (heading, date, time)
Status/alarm 5V TTL power/gyro failureVoltage free power/gyro failure contacts5V TTL system readyVoltage free system ready contacts
4.1.7 Dimensions and WeightDimensions 344mm (H) × 267mm (W) × 440mm (D)
Weight 15.5kg
RCU size (when mounted externally) 96mm (H) × 192mm (W) × 108mm (D)0
RCU weight 0.75 kg
4 – Technical Data
DPN 060070 Issue 3.7 © SG Brown Chapter 4 Page 3 of 16
4.1.8 Listener load requirementThe gyrocompass presents a listener load of 1.6mA typical at 2V or 3.5mA typical at 5V to all serial data input signals.
Figure 4–1: Listener input circuit
4.1.9 Talker drive capabilityThe gyrocompass has a talker drive capability of 150mA to ground.
Derived from 26C31 line drivers.
4.1.10 StandardsThe Meridian Gyrocompass is designed to meet the requirements of the following:
IMO Resolution A.424 (XI), Performance Standards for Gyrocompasses
IMO Resolution A.821 (19), Performance Standards for Gyrocompasses for High Speed Craft
BS EN 60945 (January 1997), General Requirements - Methods of testing and required test results
BS EN ISO 8728:1999, Shipbuilding – Marine Gyrocompasses
BS 6217:1981, Graphical Symbols for use on Electrical Equipment
CE marking
Electromagnetic Compatibility (EMC) Directive
The Marine Equipment Directive 96/98/EC
IEC 61162-1:2000(E) Maritime navigation and radio communication equipment and sys-tems - Digital interfaces. Note that IEC 61162-1:2000(E) is closely aligned with NMEA 0183 version 2.30.
Meridian Gyrocompass
Chapter 4 Page 4 of 16 © SG Brown Issue 3.7 DPN 060070
4.2 DATA FORMATSSet the DIP switches according to your specific input and output requirements. You will find the instructions to do this in sub-section 2.2.4.
Inputs – Refer to sub-section 4.2.2
Acceptable input formats: Latitude information using serial IEC 61162 GNS, RMC, GLL or GGA sentences. If more
than one of these formats is available, the Meridian Gyrocompass makes its selection in the stated preference order. Refer to Figures 4-3, 4-4, 4-5 and 4-6 respectively for a description of these formats.
Datum reference using IEC 61162 DTM sentence. The latitude offset is not used to correct the gyroscope latitude information, however the DTM sentence is re-transmitted.
Speed information using serial IEC 61162 VBW, RMC, VTG or VHW sentences. The sen-tences can contain speed information using knots and/or km/h. The Meridian Gyrocom-pass will use the speed in knots if available, in preference to speed in km/h. If more than one of these formats is available, the Meridian Gyrocompass makes its selection in the stated preference order. Refer to Figures 4-8, 4-4, 4-9 and 4-10 respectively for a descrip-tion of these formats.
If an RMC sentence is used it must contain both speed and latitude information.
TTL-compatible pulsed speed input with a TTL-level signal or contact closure.
Outputs – Refer to sub-section 4.2.3
Serial output formats:The Meridian Gyrocompass transmits selected information through RS232 and RS422 serial lines using the IEC 61162 format. The serial transmission rate can be either 4800 or 9600 baud, with updates occurring at 1Hz or 10Hz as defined by the setting of the DIP switches.
Other output formats:
Synchro Heading Output
Resolver Heading Output
Stepper S-code Heading Output
Rate of turn using a bipolar analogue voltage in the range ±10V
The following sub-sections describe each of the formats supported by the Meridian Gyrocom-pass .
4 – Technical Data
DPN 060070 Issue 3.7 © SG Brown Chapter 4 Page 5 of 16
4.2.1 IEC 61162 Serial Data Formats – General informationThe Meridian Gyrocompass accepts and transmits asynchronous serial data using 8 data bits, one stop bit and no parity through RS232 and RS422 transmit-only lines. The data bits occur in each packet with the least significant bit first. The most significant bit of the 8-bit character will always be zero.
Figure 4–2: Serial data format
All data is interpreted as ASCII characters that form IEC 61162 sentences split into individual fields. All fields, including null fields, are separated by commas.
The IEC 61162 format requires a checksum – if included, the checksum occurs as an addi-tional field immediately before the carriage return line-feed characters. It consists of an aster-isk (*) followed by a checksum derived by exclusive OR-ing the eight data bits of each valid character preceding the asterisk, but excluding the $ symbol, in the sentence. The absolute value of the checksum is transmitted in ASCII characters representing the value in HEX. For circumstances where the Meridian Gyrocompass retransmits serial data using the same IEC 61162 sentence format supplied by an external source, it will recalculate any checksum and insert the new value into the output sentence.
IEC 61162 sentences are usually transmitted once per second, however you can set a DIP switch to select a transmission rate of 10 per second. The outputs are grouped into two chan-nels that can be set independently to either 1Hz or 10Hz updates. The output option of head-ing, latitude, speed, datum, rate of turn and time sentences will always be transmitted at 1Hz.
Meridian Gyrocompass
Chapter 4 Page 6 of 16 © SG Brown Issue 3.7 DPN 060070
4.2.2 Inputs4.2.2.1 IEC 61162 input signalsThe Meridian Gyrocompass will accept sentences in both the IEC 61162-1:2000(E) and NMEA 0183 version 2.1 data formats.
In the following descriptions of input sentences, the Meridian Gyrocompass uses the data fields marked ‘XXX’ in the IEC 61162 sentence. The system does not use the fields marked ‘???’ and their descriptions are included here for completeness only. The gyrocompass will recognise the arriving sentence format and will extract the required data from it automatically.
GPS Interface (see Table 2-3 for connection details)
The Meridian Gyrocompass can accept speed, latitude, date and time inputs at the GPS inter-face in IEC 61162 format using GNS, RMC, GLL, GGA, VTG, VHW and ZDA sentences.
Figure 4–3: IEC 61162 GNS input sentence structure
Figure 4–4: IEC 61162 RMC input sentence structure
$??GNS,??????.??,XXXX.XX,X,?????.??,?,X--X,??,?.?,?.?, [CRLF]?.?,?.?,?.?*??
Talk
erid
entif
ier
(any
char
acte
rs)
Mne
mon
icfo
rG
NS
Sfix
data
UT
Cof
posi
tion
Nor
th/S
outh
Latit
ude
(ddm
m.m
m)
Long
titud
e
Car
riage
retu
rnLi
ne-f
eed
char
acte
rs
Sta
rtch
arac
ter
Eas
t/Wes
t
Diff
eren
tial r
efer
ence
stat
ion
ID
Che
cksu
mfie
ld
Age
ofdi
ffere
ntia
l dat
a
Geo
idal
sepe
ratio
n,m
Ant
enna
altit
ude,
m, r
e:m
ean-
sea-
leve
l (ge
oid)
HD
OP
Tota
l num
ber
ofsa
telli
tes
inus
e,0-
99
Mod
eIn
dica
tor
$??RMC,??????.??,X,XXXX.XX,X,?????.??,?,X.X,?.?,??????,?.?,?,X[CRLF]
Talk
erid
entif
ier
(any
char
acte
rs)
Mne
mon
icfo
rR
ecom
men
ded
Min
GP
Sda
ta
UT
Cof
posi
tion
(hhm
mss
.ss)
Latit
ude
(ddm
m.m
m
Mne
mon
icfo
rN
orth
orS
outh
Sta
tus,
A=
valid
, V=
Nav
. Rec
eive
rw
arni
ng
Long
itude
(ddd
mm
.mm
)
Mne
mon
icfo
rE
ast o
rW
est
Mag
netic
varia
tion
indi
cato
rea
stor
Wes
t
Gro
und
spee
din
knot
s
Mag
netic
varia
tion
inde
gree
s
Cou
rse
over
grou
ndin
degr
ees
Dat
eof
fix
Car
riage
retu
rnLi
ne-f
eed
char
acte
rs
Sta
rtch
arac
ter
Mod
eIn
dica
tor
4 – Technical Data
DPN 060070 Issue 3.7 © SG Brown Chapter 4 Page 7 of 16
Figure 4–5: IEC 61162 GLL input sentence structure
Figure 4–6: IEC 61162 GGA input sentence structure
Figure 4–7: IEC 61162 DTM input sentence structure
$??GLL,XXXX.XX,X,?????.??,?,??????.??,X,X[CRLF]
Talk
erid
entif
ier
(any
char
acte
rs)
Mne
mon
icfo
rge
ogra
phic
alLa
t and
Lon
Latit
ude
(ddm
m.m
m)
Long
itude
(ddd
mm
.mm
)
Mne
mon
icfo
rN
orth
orS
outh
Mne
mon
icfo
rE
ast o
rW
est
Car
riage
retu
rnLi
ne-f
eed
char
acte
rs
Sta
rtch
arac
ter
UT
Cof
posi
tion
(hhm
mss
.ss)
Sta
tus
Mod
eIn
dica
tor
$??GGA,??????.??,XXXX.XX,X,?????.??,?,X,??,?.?,?.?,?,?.?,?,?.?,????[CRLF]
Talk
erid
entif
ier
(any
char
acte
rs)
Mne
mon
icfo
rG
PS
fixda
ta
UT
Cof
posi
tion
(hhm
mss
.ss)
Latit
ude
(ddm
m.m
m
Mne
mon
icfo
rN
orth
orS
outh
Long
itude
(ddd
mm
.mm
)
Mne
mon
icfo
rE
ast o
rW
est
GP
Squ
ality
indi
cato
r
Num
ber
ofsa
telli
tes
inus
e(0
0-
12)
Hor
izon
tal d
ilutio
nof
prec
isio
n
Ant
enna
altit
ude
rela
tive
tom
ean
sea
leve
l
Mne
mon
icfo
rm
etre
s
Mne
mon
icfo
rm
etre
s
Geo
idal
sepa
ratio
n
Age
ofdi
ffere
ntia
l GP
Sda
ta
Diff
eren
tial r
efer
ence
stat
ion
(000
0-
1023
)
Car
riage
retu
rnLi
ne-f
eed
char
acte
rs
Sta
rtch
arac
ter
$??DTM,???,?,?.?,?,?.?,?,?.?,???*hh[CRLF]
Talk
erid
entif
ier
Mne
mon
icfo
rD
atum
refe
renc
e
Loca
l dat
umsu
bdiv
isio
nco
de
Latit
ude
offs
et
Loca
l dat
um
Ref
eren
ceda
tum
Nor
th/S
outh
Che
cksu
mfie
ld
Car
riage
retu
rnLi
ne-f
eed
char
acte
rs
Sta
rtch
arac
ter
Long
itude
offs
et
Eas
t/Wes
t
Alti
tude
offs
et, m
Meridian Gyrocompass
Chapter 4 Page 8 of 16 © SG Brown Issue 3.7 DPN 060070
Figure 4–8: IEC 61162 VBW input sentence structure
Figure 4–9: IEC 61162 VTG input sentence structure
Figure 4–10: IEC 61162 VHW input sentence structure
$??VBW,?.?,?.?,?,X.X,?.?,X,?.?,?,?.?,?*hh[CRLF]Ta
lker
iden
tifie
r(a
nych
arac
ters
)
Mne
mon
icfo
rD
ual g
roun
d/w
ater
spee
d
Long
itudi
nal w
ater
spee
d,kn
ots
Sta
tus:
wat
ersp
eed,
A=
valid
, V=
not v
alid
Tra
nsve
rse
wat
ersp
eed,
knot
s
Long
itudi
nal g
roun
dsp
eed,
knot
s
Car
riage
retu
rnLi
ne-f
eed
char
acte
rs
Sta
rtch
arac
ter
Tra
nsve
rse
grou
ndsp
eed,
knot
s
Sta
tus:
ster
ngr
ound
spee
d,A
=va
lid, V
=no
t val
id
Che
cksu
mfie
ld
Sta
tus:
grou
ndsp
eed,
A=
valid
, V=
not v
alid
Ste
rntr
ansv
erse
wat
ersp
eed,
knot
s
Sta
tus:
ster
nw
ater
spee
d,A
=va
lid, V
=no
t val
id
Ste
rntr
ansv
erse
grou
ndsp
eed,
knot
s
$??VTG,?.?,?,?.?,?,X.X,X,XX.X,X,X[CRLF]
Talk
erid
entif
ier
(any
char
acte
rs)
Mne
mon
icfo
rgr
ound
cour
sean
dsp
eed
Mne
mon
icfo
rT
rue
head
ing
Mne
mon
icfo
rM
agne
tiche
adin
g
Cou
rse
inde
gree
san
dte
nths
Mne
mon
icfo
rkn
ots
Spe
edin
knot
s
Spe
edin
km/h
Mne
mon
icfo
rkm
/h
Car
riage
retu
rnLi
ne-f
eed
char
acte
rs
Sta
rtch
arac
ter
Cou
rse
inde
gree
san
dte
nths
Mod
ein
dica
tor
4 – Technical Data
DPN 060070 Issue 3.7 © SG Brown Chapter 4 Page 9 of 16
Figure 4–11: IEC 61162 ZDA input sentence structure
Log Interface (see Table 2-3 for connection details)
The Meridian Gyrocompass can accept speed inputs at the Log interface in IEC 61162 format using VBW, VTG and VHW sentences only.
Figure 4–12: IEC 61162 VBW input sentence structure
Figure 4–13: IEC 61162 VTG input sentence structure
$??ZDA,XXXXXX.XX,XX,XX,XXXX,??,??[CRLF]Ta
lker
iden
tifie
r(a
nych
arac
ters
)
Mne
mon
icfo
rT
ime
and
Dat
e
Day
ofm
onth
(01
to31
)
Mon
thof
year
(01
to12
)
UT
C(h
hmm
ss.s
s)
Loca
l zon
eho
urs
(00
to±
13)
Yea
r
Loca
l zon
em
inut
es(0
0to
+59
)
Car
riage
retu
rnLi
ne-f
eed
char
acte
rs
Sta
rtch
arac
ter
$??VBW,?.?,?.?,?,X.X,?.?,X,?.?,?,?.?,?*hh[CRLF]
Talk
erid
entif
ier
(any
char
acte
rs)
Mne
mon
icfo
rD
ual g
roun
d/w
ater
spee
d
Long
itudi
nal w
ater
spee
d,kn
ots
Sta
tus:
wat
ersp
eed,
A=
valid
, V=
not v
alid
Tra
nsve
rse
wat
ersp
eed,
knot
s
Long
itudi
nal g
roun
dsp
eed,
knot
s
Car
riage
retu
rnLi
ne-f
eed
char
acte
rs
Sta
rtch
arac
ter
Tra
nsve
rse
grou
ndsp
eed,
knot
s
Sta
tus:
ster
ngr
ound
spee
d,A
=va
lid, V
=no
t val
id
Che
cksu
mfie
ld
Sta
tus:
grou
ndsp
eed,
A=
valid
, V=
not v
alid
Ste
rntr
ansv
erse
wat
ersp
eed,
knot
s
Sta
tus:
ster
nw
ater
spee
d,A
=va
lid, V
=no
t val
id
Ste
rntr
ansv
erse
grou
ndsp
eed,
knot
s
$??VTG,?.?,?,?.?,?,X.X,X,XX.X,X,X[CRLF]
Talk
erid
entif
ier
(any
char
acte
rs)
Mne
mon
icfo
rgr
ound
cour
sean
dsp
eed
Mne
mon
icfo
rT
rue
head
ing
Mne
mon
icfo
rM
agne
tiche
adin
g
Cou
rse
inde
gree
san
dte
nths
Mne
mon
icfo
rkn
ots
Spe
edin
knot
s
Spe
edin
km/h
Mne
mon
icfo
rkm
/h
Car
riage
retu
rnLi
ne-f
eed
char
acte
rs
Sta
rtch
arac
ter
Cou
rse
inde
gree
san
dte
nths
Mod
ein
dica
tor
Meridian Gyrocompass
Chapter 4 Page 10 of 16 © SG Brown Issue 3.7 DPN 060070
Figure 4–14: IEC 61162 VHW input sentence structure
4.2.2.2 Pulsed inputThe Meridian Gyrocompass can accept a speed input as a series of pulses or contact closures occurring at a frequency of 100, 200 or 400 per nautical mile as selected by a DIP switch. The gyrocompass determines the vessel speed by reference against the microprocessor timing cir-cuits. The speed pulses do not need to have a particular mark/space ratio, although they should be TTL-level. Contact closures should be of good quality and electrically floating.
4 – Technical Data
DPN 060070 Issue 3.7 © SG Brown Chapter 4 Page 11 of 16
4.2.3 Outputs4.2.3.1 IEC 61162 output signalsThe Meridian Gyrocompass can output serial data through RS232 and RS422 transmit-only serial lines using the IEC 61162-1:2000(E) format. The output of each channel can be set inde-pendently, using DIP switches, to contain either:
1. Heading - as described below, OR
2. Heading and Rate of turn - as described below, OR
3. Rate of turn only - as described below, OR
4. All data - all information described below, transmitted in the order stated
Heading information is transmitted using an HDT format sentence. The resolution of the heading information can be set to one or two decimal places at the DIP switches. Refer to Figures 4-15 for a description of this output format.
Rate of turn information is transmitted using a ROT format sentence. Refer to Figure 4–16 for a description of this output format.
Speed information is transmitted using a VTG format sentence if the gyrocompass is con-figured for manual or a pulsed speed log input. The VTG sentence also has provision for Heading and this is inserted at a resolution as set by the DIP switches. Refer to Figure 4-18 for a description of this output format. If the gyrocompass is configured for a GPS speed input and the speed information arrives at the gyrocompass in either VBW, RMC, VTG or VHW format, then the gyrocompass will retransmit the received format modifying the sen-tence to include the HE talker identifier. Refer to Figures 4-17, 4-20, and 4-18 for a description of these output formats.
Datum reference is retransmitted if the DTM sentence is received on the GPS input. The gyrocompass will re-transmit the received sentence modifying it to include the HE talker identifier. Refer to Figure 4-23 for a description of this output format.
Latitude information is transmitted using a GLL format sentence if the gyrocompass is configured for manual latitude input. Refer to Figure 4-14 for a description of this output format. If the gyrocompass is configured for a GPS latitude input and the latitude informa-tion arrives at the gyrocompass in either GNS, RMC, GLL, or GGA format, then the gyro-compass will retransmit the received sentence modifying the sentence to include the HE talker identifier. Refer to Figures 4-19, 4-20, 4-21 and 4-22 for a description of these out-put formats.
Date and time information is transmitted using a ZDA format sentence. The gyrocompass will transmit the ZDA sentence including the HE talker identifier. If this information is received from a GPS source, all fields will be retransmitted. If there is no valid date and time from an external source, the gyrocompass will transmit the ZDA sentence with empty data fields. Refer to Figure 4-24 for a description of this output format.
If “All Data” output format is selected at the DIP switches, the transmission update rate for that channel will be at 1Hz regardless of the setting of the channel update rate.
Meridian Gyrocompass
Chapter 4 Page 12 of 16 © SG Brown Issue 3.7 DPN 060070
In the following descriptions of output sentences, the gyrocompass sets the contents of fields marked XXX and leaves unchanged the fields marked ???
Figure 4–15: IEC 61162 HDT output sentence structure
Figure 4–16: IEC 61162 ROT output sentence structure
Figure 4–17: IEC 61162 VBW output sentence structure$HEVBW,?.?,?.?,?,?.?,?.?,?,?.?,?,?.?,?*hh[CRLF]
Talk
erid
entif
ier
(any
char
acte
rs)
Mne
mon
icfo
rD
ual g
roun
d/w
ater
spee
d
Long
itudi
nal w
ater
spee
d,kn
ots
Sta
tus:
wat
ersp
eed,
A=
valid
, V=
not v
alid
Tra
nsve
rse
wat
ersp
eed,
knot
s
Long
itudi
nal g
roun
dsp
eed,
knot
s
Car
riage
retu
rnLi
ne-f
eed
char
acte
rs
Sta
rtch
arac
ter
Tra
nsve
rse
grou
ndsp
eed,
knot
s
Sta
tus:
ster
ngr
ound
spee
d,A
=va
lid, V
=no
t val
id
Che
cksu
mfie
ld
Sta
tus:
grou
ndsp
eed,
A=
valid
, V=
not v
alid
Ste
rntr
ansv
erse
wat
ersp
eed,
knot
s
Sta
tus:
ster
nw
ater
spee
d,A
=va
lid, V
=no
t val
id
Ste
rntr
ansv
erse
grou
ndsp
eed,
knot
s
4 – Technical Data
DPN 060070 Issue 3.7 © SG Brown Chapter 4 Page 13 of 16
Figure 4–18: IEC 61162 VTG output sentence structure
Note In GPS mode only the talker identifier is changedIn manual mode, the magnetic course fields are empty.
Figure 4–19: IEC 61162 GNS output sentence structure
Figure 4–20: IEC 61162 RMC output sentence structure
$HEGNS,??????.??,????.??,?,?????.??,?,????,??,?.?,?.?, [CRLF]?.?,?.?,?.?*??
Talk
erid
entif
ier
(any
char
acte
rs)
Mne
mon
icfo
rG
NS
Sfix
data
UT
Cof
posi
tion
Nor
th/S
outh
Latit
ude
(ddm
m.m
m)
Long
titud
e
Car
riage
retu
rnLi
ne-f
eed
char
acte
rs
Sta
rtch
arac
ter
Eas
t/Wes
t
Diff
eren
tial r
efer
ence
stat
ion
ID
Che
cksu
mfie
ld
Age
ofdi
ffere
ntia
l dat
a
Geo
idal
sepe
ratio
n,m
Ant
enna
altit
ude,
m, r
e:m
ean-
sea-
leve
l (ge
oid)
HD
OP
Tota
l num
ber
ofsa
telli
tes
inus
e,0-
99
Mod
eIn
dica
tor
Meridian Gyrocompass
Chapter 4 Page 14 of 16 © SG Brown Issue 3.7 DPN 060070
Figure 4–21: IEC 61162 GLL output sentence structure
Note In GPS mode, only the talker identifier is changedIn manual mode, the longtitude and UTC fields are empty
Figure 4–22: IEC 61162 GGA output sentence structure
Figure 4–23: IEC 61162 DTM output sentence structure$HEDTM,???,?,?.?,?,?.?,?,?.?,???*hh[CRLF]
Talk
erid
entif
ier
Mne
mon
icfo
rD
atum
refe
renc
e
Loca
l dat
umsu
bdiv
isio
nco
de
Latit
ude
offs
et
Loca
l dat
um
Ref
eren
ceda
tum
Nor
th/S
outh
Che
cksu
mfie
ld
Car
riage
retu
rnLi
ne-f
eed
char
acte
rs
Sta
rtch
arac
ter
Long
itude
offs
et
Eas
t/Wes
t
Alti
tude
offs
et, m
4 – Technical Data
DPN 060070 Issue 3.7 © SG Brown Chapter 4 Page 15 of 16
Figure 4–24: IEC 61162 ZDA output sentence structure
4.2.4 IEC 61162 sentence with ChecksumWhen the checksum is to be sent with any of the above IEC 61162 sentences, it appears as an extra field inserted before the carriage return character as shown by example in Figure 4-24.
Figure 4–25: IEC 61162 sentence with optional checksum
The checksum consists of an asterisk followed by the checksum calculated by exclusive OR-ing the eight data bits of each valid character preceding the asterisk, but excluding the ‘$’ sym-bol, in the sentence. The Meridian Gyrocompass transmits the absolute value of the checksum in ASCII characters representing the value in HEX.
4.2.5 Other Output Formats4.2.5.1 Course Recorder OutputThe following ASCII data shall be transmitted on the Course Recorder Output every minute, in a suitable format to be output on an 80 column line printer.
359.99 True Lat 52 N Spd 10 Kts UTC 13:34:01 01/01/2001
Table 4–1: Course Recorder Output Sentences
Heading 999.99
Latitude 99
Hemisphere N or S
Speed Kts 99
Time hh:mm:ss
Date dd/mm/yy
$HEZDA,??????.??,??,??,????,??,??[CRLF]Ta
lker
iden
tifie
r
Mne
mon
icfo
rT
ime
and
Dat
e
Day
ofm
onth
(01
to31
)
Mon
thof
year
(01
to12
)
UT
C(h
hmm
ss.s
s)
Loca
l zon
eho
urs
(00
to±
13)
Yea
r
Loca
l zon
em
inut
es(0
0to
+59
)
Car
riage
retu
rnLi
ne-f
eed
char
acte
rs
Sta
rtch
arac
ter
Meridian Gyrocompass
Chapter 4 Page 16 of 16 © SG Brown Issue 3.7 DPN 060070
Date and time will only be output if a valid ZDA sentence is available on the GPS input.
4.2.5.2 Synchro OutputThe synchro heading output is available continuously at TB2 on the Distribution Board while the gyrocompass is powered-on – refer to Table 2-4 for connector details. The output is at 11.8V maximum line-to-line voltage derived electrically from a 1:1 resolver driven directly by the gyrocompass azimuth gimbal. The synchro reference voltage is a nominal 26V 400Hz sup-ply generated internally.
Electrical loading specification:
Not less than 5k between any two S lines.
Not less than 1k between the two R lines.
4.2.5.3 Resolver OutputThe resolver heading output is available continuously at TB2 on the Distribution Board while the gyrocompass is powered-on – refer to Table 2-4 for connection details. The output is at 8V maximum voltage per phase signal from a 1:1 resolver driven directly by the gyrocompass azi-muth gimbal. The resolver reference voltage can be set nominal 36V 400Hz or 10V 400Hz supply generated internally by jumper JP30 on PCB929066. The factory default setting is 10V 400Hz.
The resolver sine and cosine outputs must be electrically isolated from each other. Contact the SG Brown Service Department for technical advice if necessary.
Electrical loading specification:
Not less than 5k between any two S lines.
Not less than 1k between the two R lines.
4.2.5.4 Stepper S-CodeThe stepper S-code output is available continuously at TB2 on the Distribution Board while the gyrocompass is powered-on – refer to Table 2-4 for connection details.
The stepper output is a TTL compatible S-encoded signal with a 10mA sink capacity.
4.2.5.5 Rate of TurnThe ROT output is calculated by the internal processor updated at 10Hz and made available continuously at TB3 on the Distribution Board while the gyrocompass is powered-on – refer to Table 2-4 for connection details.
The ROT output is a bipolar analogue voltage in the range ±10V to represent rates of turn from –60° to +60° per minute or –20° to +20° per second. Positive rates of turn are to star-board.
5 – Maintenance
DPN 060070 Issue 3.7 © SG Brown Chapter 5 Page 1 of 12
5 MAINTENANCEWARNING
There is a danger of serious injury from voltages inside the Meridian Gyrocompass . Do not remove the gyrocompass cover unless you have the necessary skills and experi-ence to perform maintenance work on a system of this nature. Always power-off the system before you remove the cover for maintenance work.
Observe all local safety regulations as you work on the equipment. Reconnect the safety grounding straps and refit all safety covers to the equipment before you power-on the system.
CAUTIONPerform these simple maintenance instructions only if you have the skills and experi-ence required, and only when necessary. Inappropriate tampering with the internal controls and components of the gyrocompass can lead to damage or serious perform-ance degradation.
NEVER open the gyrocompass cover or make any adjustments inside the gyrocom-pass unless you are entirely confident in your actions.
There is very little need for user maintenance on the Meridian Gyrocompass and you should never need to remove the covers.
The following sub-sections explain some very basic procedures that you may attempt if you suspect the system has developed a fault. If you are in any doubt, contact SG Brown for advice and technical assistance before you begin any maintenance work on the system.
5.1 Built-in Test Equipment Page 2
The Meridian Gyrocompass performs a self-test routine during the initialisation sequence and monitors its status continually during normal operation. Any deviation from normal operation appears as an error message, with the cause declared as a message on the four-character dis-play panel. This sub-section explains some very basic tests and adjustments that you may per-form on the system.
5.2 Test Connector Page 4
There is a 60-way test connector that allows you to measure critical voltages and signals.
Perform the tests described in this section of the manual and have the results available when you contact SG Brown for technical assistance.
Meridian Gyrocompass
Chapter 5 Page 2 of 12 © SG Brown Issue 3.7 DPN 060070
5.1 BUILT-IN TEST EQUIPMENTIn Subsection 3.4.3 there are a list of two warning codes and five failure codes delivered by the built-in test equipment if it detects a fault in the gyrocompass. In these conditions, the four-character display will show <Message> + FAIL
If the built in test equipment detects a fault, use the following table to investigate the cause. You can measure the voltages and signals on the pins of the 60-way test connector (refer to Table 5–2 for details of the test connector).
Table 5–1: Test measurements
Failure Code Measure Expected value Signal source
dc+failFailure of DC power supply
DC supply42 (+ve) to 4344 (+ve) to 4317 (+ve) to 1850 (+ve) to 5152 (+ve) to 5145 (+ve) to 18
18V DC to 36V DC+24V DC ±0.5V DC–24V DC ±0.5V DC+5V DC ±0.1V DC+15V DC ±0.2V DC–15V DC ±0.2V DC+5V DC (+0.2V/–0.7V DC)
Ship’s mains/PSUDC/DC PSUDC/DC PSUDC/DC PSUControl Board analogueControl Board analogueControl Board analogue
ac+failFailure of AC power supply
19 to 4320 to 4321 to 4358 to 4357 (+ve) to 18
2.5V AC ±0.125V AC @ 19.2kHz14V AC ±1V @ 480Hz (18V AC ±1.5V at start (1-min))14V AC ±1V @ 480Hz (18V AC ±1.5V at start (1-min))12V AC ±0.2V @ 400Hz+5V DC ±0.2V DC
Control Board analogueControl Board analogueControl Board analogueControl Board analogueControl Board analogue
rdc+FailFailure of synchro-to-digital converter
58 to 4353 (+ve) to 5154 (+ve) to 51
12V AC ±0.2V @ 400Hz(5.4V DC ±0.5V DC) × sin heading(5.4V DC ±0.5V DC) × cos heading
Control Board analogueControl Board analogueControl Board analogue
rMT+failLoss of RMT communication
50 way IDC Cable (Part Number B929157)+ 5V DC Power Supply50 way Cable Loom (Part Number B929161)
ROT+failRate of turn exceed limit
>300o/s Check Gyro connection to the analogue PCB
Temp+failTemperature exceeds operat-ing range
<-20oC>+60oC
Check operating environment and ventilation
5 – Maintenance
DPN 060070 Issue 3.7 © SG Brown Chapter 5 Page 3 of 12
5.1.1 Azimuth Drift AdjustmentYou may use the following procedure to measure and, if necessary, adjust the azimuth drift:
1. Ensure that the gyrocompass is static and is operating in DG mode with the Speed input set manually to zero and the Latitude set to local latitude. Use the DIP switches to set DG mode – refer to Table 2–5. Refer to sub-sections 3.3.1 and 3.3.2 to set the latitude and speed.
2. Note the initial heading (H1) shown on the RCU display.
3. Wait for one hour and then note the heading (H2) shown on the RCU display.
4. Calculate the azimuth drift rate (H2 – H1) degrees per hour.
5. Use a digital meter set to measure DC volts and monitor the Tilt Bias between pins 30 and 51 of the 60-way test connector (with the positive test lead on pin 30).
6. Adjust the Tilt Bias potentiometer RV7 by 400mV × drift rate (°/hr). You must turn the potentiometer anticlockwise to compensate for azimuth drift towards higher readings. Fig-ure 2–4 shows the location of the Tilt Bias potentiometer.
7. Repeat steps 1 and 2 above to ensure that the calculated drift rate is less than 0.2°/hr.
5.1.2 Azimuth Bias AdjustmentYou may use the following procedure to eliminate small angles of heading error from the Meridian Gyrocompass . Measure and, if necessary, adjust for azimuth drift as described in sub-section 5.1.1 above before you adjust the azimuth bias.
Take care when you adjust azimuth bias – make only small adjustments each time and then allow the gyrocompass to settle for three hours before you make any further adjustments. Note the original position of the azimuth bias control before you start so that you can restore the starting condition if necessary.
1. Use a digital meter set to measure DC volts and monitor the Azimuth Bias between pins 29 and 51 of the 60-way test connector (with the positive test lead on pin 29).
2. Adjust the Azimuth Bias potentiometer RV9 to cause a change in the azimuth bias voltage that will produce the necessary change in compass heading. Figure 2–4 shows the location of the Azimuth Bias potentiometer.
3. Turn the Azimuth Bias potentiometer anticlockwise to cause the heading to change towards a lower reading. A 60mV DC change in Azimuth Bias will produce a 1-degree change in heading
Meridian Gyrocompass
Chapter 5 Page 4 of 12 © SG Brown Issue 3.7 DPN 060070
5.2 TEST CONNECTORThere is a sixty-way test connector accessible behind the removable panel on the top of the gyrocompass cover. Release and remove the securing screws and lift off the panel to see the two DIP switches and the test connector. A test box (SG Brown part number 929220) is avail-able to facilitate connection to the 60-way test connector.
Table 5–2: Sixty-way test connector
Pin Name Function
1 S1_SYNCHRO 11.8V RMS 400Hz synchro S1 phase
2 S2_SYNCHRO_RES 11.8V RMS 400Hz synchro S2 phase
3 S3_SYNCHRO_RES 11.8V RMS 400Hz synchro S3 phase
4 26V_SYNCHRO_R1 26V RMS 400Hz synchro R1 reference
5 0V_SYNCHRO_RES 26V RMS 400Hz synchro R1 reference
6 GA_MODE Directional gyro mode control (+5V logic)
7 GC_MODE Gyrocompass mode control (+5V logic)
8 AA_MODE Auto alignment mode control (+5V logic)
9 LAT_NS Latitude north selection control (+5V logic)
10 SERVO_EN Tilt and azimuth servo enable control (+5V logic)
11 WHEEL_BOOST Gyro wheel supply boost control (+5V logic)
12 LOG_OK Speed log OK flag (+5V logic)
13 GPS_OK GPS OK flag (+5V logic)
14 SYS_FAIL System fail flag (+5V logic)
15 GYRO_RDY Gyrocompass ready flag (+5V logic)
16 PREPARE Prepare mode (servo nulling) (+5V logic)
17 VCC 5V DC supply
18 GND 5V DC supply return
19 PICK_OFF_SUPPLY_1 Gyro pick off supply 2.5V RMS 19.2kHz sine wave
20 WHEEL_SUPPLY_1 Gyro wheel supply 0 phase 10V (18V) RMS 480Hz square wave
21 WHEEL_SUPPLY_2 Gyro wheel supply 90 phase 10V (18V) RMS 480Hz square wave
22 PWMO Compass card illumination PWM control 5V 85Hz square wave
23 ACC Gravity control signal ±150mV DC/min T=60s
24 10V 10V DC positive voltage reference
25 _10V 10V DC negative voltage reference
26 LAT_TORQ Latitude torquing input signal (–10 sin[latitude])V DC
27 SPEED_N_TORQ Speed N torque i/p signal (7.3e–3 × speed(kts) × cos[heading])
28 SPEED_E_TORQ Speed E torque i/p signal (–8.5e–3 × speed(kts) × sin[heading] × tan[latitude]V DC
5 – Maintenance
DPN 060070 Issue 3.7 © SG Brown Chapter 5 Page 5 of 12
29 AZ_BIAS Bias adj. to azimuth torquer ±2.2V DC (60mV/deg heading)
30 TILT_BIAS Bias adj. to tilt torquer ±2.2V DC (400mV/deg/hour heading)
31 TILT_TEMP Bias adj. to tilt torquer proportional to temperature (400mV/deg/hr heading)
32 AZ_TEMP Bias adj. to azimuth torquer proportional to temperature (60mV/deg/hr heading)
33 T Temperature ref (non-inverted) from gimbal thermistor (DC V proportional to temp)
34 T_ Temperature ref (inverted) from gimbal thermistor (DC V proportional to temp)
35 TILT_TORQUER_LO Tilt torquer signal 0.013V DC/mA (torquer scale factor 10°/hr/mA)
36 AZ_TORQUER_LO Azimuth torquer signal 0.006V DC/mA (torquer scale factor 10°/hr/mA)
37 TILT_PICK_OFF_DC Demodulated gyroscope tilt pick-off signal
38 AZ_PICK_OFF_DC Demodulated gyroscope azimuth pick-off signal
39 18V10V Gyro wheel positive supply
40 -18V10V Gyro wheel negative supply
41 UP_DOWN Accelerometer - Slave comparator
42 24V 24V DC positive supply
43 0V Supply return for ±24V DC
44 –24V 24V DC negative supply
45 PSU_LO PSU (+5V DC and ±15V DC) under voltage flag (+5V DC logic)
46 NOT USED
47 ACC_COS_LAT Latitude weighted gravity control signal (150/cos latitude)mV DC/min
48 SLAVE Slave accelerometer gravity control signal (10mV/bit)
49 ROT Analogue rate of turn output (0.5V DC/deg/s (10V DC max) CW +ve; ACW –ve
50 15V 15V DC positive supply
51 0Va Supply return for ±15V DC
52 –15V 15V DC negative supply
53 SIN_DC Analogue voltage proportional to sin(heading) (±0.1V DC/deg heading)
54 COS_DC Analogue voltage proportional to cos(heading) (±0.1V DC/deg heading)
55 RS232_RX_TEST RS232 receive port reserved for product testing
56 RS232_TX_TEST RS232 transmit port diagnostic output sentence
57 AC_OK AC supply (19kHz, 480Hz and 400Hz) OK flag (+5V DC logic)
58 400_REF_HI Reference supply 12V RMS 400Hz
59 AZ_MOTOR_HI Drive to azimuth follow-up DC servo motor
60 TILT_MOTOR_HI Drive to tilt follow-up DC servo motor
Table 5–2: Sixty-way test connector (Continued)
Pin Name Function
Meridian Gyrocompass
Chapter 5 Page 6 of 12 © SG Brown Issue 3.7 DPN 060070
5.3 DIAGNOSTIC OUTPUT SENTENCEAn ASCII character diagnostic sentence, delivered via RS232 line standard at 4800 baud, is available at test connector PL6/56-18(GND).
Note that this sentence information is only valid for gyrocompasses fitted with soft-ware of the following version or newer: BPR 113 (main) and BPR 114 (RCU).
This sentence may usefully be monitored when communicating with SG Brown for technical assist-ance. The sentence string may be read using "Microsoft Terminal" or similar ASCII reader.
Sentence Structure
Gyro Control 1 = slave accelerometer (new hardware)S = special applications only (new hardware)R = real accelerometer (original hardware)A = special applications only (original hardware)
Mode L = levelA = alignmentC = compassD = DG
Status F = failR = readyS = settle
Latitude (degrees) xx
Hemisphere N or S
Speed (knots) xx
Average Accelerometer (bits) Paxxx
ADC 1 (bits) rxxxADC 2 (bits) hxxxADC 3 (bits) txxxADC 4 (bits) axxxADC 5 (bits) Txxx
DAC 1a (bits) xxxDAC 1b (bits) xxxDAC 2a (bits) xxxDAC 2b (bits) xxxDAC 3a (bits) xxxDAC 3b (bits) xxx
Heading (degrees) $HEHDT,xxx.xx,T
Sentence Example
R CR 51N 06 Pa128r128h128 t128a128 T096 160 198 000 000 128 128 $HEHDT,000.00,T
During start-up, the Mode and Status characters will change in the following sequence:
1. LS for about 4 minutes2. AS for 25 - 60 minutes (dependent upon initial heading misalignment)3. CR in READY mode and functioning
Ensure that the Latitude and Speed values in the sentence correspond with the automatic or manually set values applied to the gyrocompass. Ensure that the Heading value in the sentence is correct.
SG Brown may use the remaining (bits) characters when diagnosing fault conditions.
5 – Maintenance
DPN 060070 Issue 3.7 © SG Brown Chapter 5 Page 7 of 12
Figure 5–1: System Block Diagram
GIM
BA
LA
SS
Y
DIS
PLA
YB
OA
RD
CO
NT
RO
LB
OA
RD
RE
MO
TE
DIS
TR
IBU
TIO
N
BO
AR
D
CO
NT
RO
LB
OA
RD
DIG
ITA
LA
NA
LO
GU
E
CO
NT
RO
LB
OA
RD
TE
ST
CO
NN
EC
TO
R
DC
/DC
PS
U
FIL
TE
RS
#1

24V
d.c
.
Tilt
Moto
r
Azim
uth
Moto
r
Tilt
Pic
koff
Azim
uth
Pic
koff
Tilt
Torq
uer
Azim
uth
Torq
uer
(vert
icalsensor)
(tem
psensor)
Resolv
er
Illu
min
atio
n24-0
-24V
d.c
.
5V
d.c
.
An
alo
gu
eC
on
tro
lS
ign
als
Azim
uth
To
rqu
er
Co
ntr
olS
ign
al
Tilt
Torq
uer
Contr
olS
ignal
Tem
pS
ensor
Sig
nal
Acce
lero
me
ter
Sig
na
l
Re
so
lve
rH
ea
din
gS
ign
al(s
in/c
os)
Tilt
Pic
koff
Sig
nal(a
.c.)
Azim
uth
Pic
koff
Sig
nal(a
.c.)
Tilt
Moto
rD
rive
Sig
nal
Azim
uth
Mo
tor
Drive
Sig
na
l
Illu
min
atio
nC
on
tro
l
Acce
lero
me
ter
Sig
na
l(h
igh
ga
in)
Tem
pS
ensor
Sig
nal
Re
so
lve
rH
ea
din
gS
ign
al(d
.c.)
Tilt
P.O
.S
ignal(d
.c.)
Azim
uth
P.O
.S
ignal(d
.c.)
Analo
gue
Headin
gS
ignals
SerialO
utp
ut
Sig
nals
Serial&
Dig
italIn
putS
ignals
Rem
ote
ON
/OF
FC
ontr
ol
Gyro
Sp
inM
oto
rS
up
ply
Gyro
Sp
inM
oto
r
Rem
ote
ON
/OF
F
Com
munic
ations
Display Driver Signals
Input
Sig
nals
Outp
ut
Sig
nals
5V
d.c
.
Com
munic
ations
929083
929074
929066
929033
929078
929049
929045
Pow
er
Pow
er
Switch I/Ps
Acce
lero
me
ter
Therm
isto
r
Meridian Gyrocompass
Chapter 5 Page 8 of 12 © SG Brown Issue 3.7 DPN 060070
Figure 5–2: Gimbal Assembly Functional DiagramZ
H
X
Y
N-S
H
Resolv
er
40
0H
zS
inH
Co
sH
Azim
uth
Torq
uer
Co
ntr
olS
ign
al
Sig
na
l(A
cc)
Acce
lero
me
ter
Co
ntr
olS
ign
al
Tilt
Torq
uer
Moto
r
Azim
uth
Dri
ve
Sig
na
l
Tilt
Moto
r
Dri
ve
Sig
na
l
Te
mp
era
ture
Se
nso
rS
ign
al
Azim
uth
Pic
koff
Sig
na
l
Tilt
Pic
ko
ff
Sig
na
l
1
2
8
5
9
67
3
4
10
1.D
am
pe
r
2.G
yro
sp
inm
oto
r
3.
Tilt
torq
uer
4.
Azim
uth
torq
ue
r
5.
Acce
lero
me
ter
6.
Azim
uth
pic
ko
ff
7.
Tilt
pic
koff
8.T
he
rmis
tor
9.
Tilt
moto
r
10
.A
zim
uth
mo
tor
5 – Maintenance
DPN 060070 Issue 3.7 © SG Brown Chapter 5 Page 9 of 12
Figure 5–3: Analogue Control Board Block Diagram
M
TILTTORQUERCOIL
PICKOFFCOILS
TILT
TILTMOTOR
Run
Align
TILT TEMPT+ T-
TILT BIAS+V Ref -V Ref
+/-
Hemisphere
+/-
Servo Enable
SCALING&
SHAPING
AMPLIFIER
FILTER&
AMPLIFIER
SCALING
SHAPING&
FILTER& PICKOFF
AZIMUTH
AZIMUTHMOTOR
COILS
M
COMPARATOR
COILTORQUERAZIMUTH
Align
DG
AZIMUTH TEMPT+ T-
AZIMUTH BIAS+V Ref -V Ref
Run
X10
AlignRun
Hemisphere (+/-)Servo Enable
DG
19.2 Khz Ref
Acc/Cosλ
ACCELEROMETER
THERMISTORAMPLIFIER
THERMISTORT+
T-
To Tilt & Azimuthtemperature pots
PRECISIONREFERENCE
Temperature
+V Ref
-V Ref
DIGITAL CONTROL BOARD ANALOGUE CONTROL BOARD GIMBAL ASSEMBLY
Hemisphere
36V26V
0V
R4R1
R2
ReferencePhase26V Synchro36V Resolver
400HzRESOLVERROTOR
STATORRESOLVER
S1
S311.8V Synchro8V Resolver
Heading Outputs
S2
S4
+/-
+/-
400Hz Ref
400Hz Ref
Wheel Boost
2.5V 19.2KhzPickoff Supply
Gyro Spin MotorSupply
MONO -STABLE
10V/18V 480Hz
V.Sin H.Tan λ R
Acc (High Gain)
Acc (Low Gain) τ = 60s
V.Cos HR
Rate of Turn RoT +/- 10V
10V/18V
10V/18V
∅1
2∅
PLD3.6Mhz
+24V
-24V
400Hz
19.2Khz
BANDPASSFILTER
400Hz Ref
400Hz Ref
BANDPASSFILTER
19.2Khz Ref
Sin H
Cos H
8V.Sin H
8V.Cos H
V = speed (knots x 6080 ft/hr)
λ = local latitude (deg) H = gyro heading (deg) τ = time constant Acc = accelerometer signal
Servo Enable
ω Sin λ
AC OK
+/-
+/-Azimuth Pickoff (d.c.)
Tilt Pickoff (d.c.)
REG+
REG-
480Hz ∅ 0
180∅ 480Hz 90∅ 480Hz
270∅ 480Hz
North seaking
Latitude correction
Easterly speed correction
Northerly speed correction
Damping
ω = earth rotation (15°/hr)
R = earth radius (20.9 x 106 ft)
(temp sensor)
(vertical sensor)
Meridian Gyrocompass
Chapter 5 Page 10 of 12© SG Brown Issue 3.7 DPN 060070
Figure 5–4: Digital Control Board/Remote Control Board Block Diagram
AlignRun
Hemisphere (+/-)Servo EnableDG
Acc/Cosλ
Temperature
ANALOGUE
Wheel Boost
V.Sin H.Tan
λ
R
Acc (High Gain)Acc (Low Gain)
V.Cos HR
Rate of Turn
400Hz Ref
Sin HCos H
V = speed (knots x 6080 ft/hr)
λ = local latitude (deg) H = gyro heading (deg) τ = time constant Acc = accelerometer signal
ω Sin λ
AC OK
Azimuth Pickoff (d.c.)Tilt Pickoff (d.c.)
ω = earth rotation (15°/hr)
R = earth radius (20.9 x 106 ft)
ANALOGUEMUX &10 BITADC
Tem
pera
ture
Azim
uth
Pick
off (
d.c.
)Ti
lt Pi
ckof
f (d.
c.)
Acc
(Low
Gai
n)Ac
c (H
igh
Gai
n)
RX TX
MAX487DRIVERRS422
P4
OPTO-COUPLER
PWMO
P2
P0
uCONTROLLER80C552
X1P4
XTAL
27C512EPROM
ADDR. BUS
DUARTSCN2681
CS
RS232/RS422 I/F
RS422DRIVERS
RS232DRIVERS
ADDR.DECODER CS
RAMHM62256
28C16AEPROM
AC OK
RESOLVERTO DIGITAL
CONVERTER
CS
LS373LATCH
AD7528DAC
CSAcc (Low Gain)
AD7528DAC
Cos H10V Ref
Sin H
AD7528DAC
10V Ref
CS
CS
CS
SCN2681DUART
CONTROL BOARDDISTRIBUTION BOARD
LS373LATCH
CS
SUPERVISORYPSU
MAX8213
DC PSU
System FailSystem Ready
Stepper O/P3 x RS232 IEC 611629 x RS422 IEC 61162RS422 Heading/ROT
GPS SerialNMEA 0183 All Data
Speed Log Serial
Speed Log Pulses
Remote Control
Course Recorder
Spare
DG Mode
RS422 I/FRS232/
CS
DAT
A BU
S
DIGITAL CONTROL BOARD
400Hz RefCos H
Sin H
REMOTE CONTROL BOARD
ADDR. BUS
Remote Control
P4
uCONTROLLER
RX
MAX487DRIVERRS422
MAX813LWATCHDOG
80C32X1 XTAL
PWMO
P2
P0
TX
CS
EPROM28C16A
HM62256RAM
ADDR.DECODER
EPROM27C512
DAT
A BU
S
WD1 PFO
RESET RESETCS
CS
CS
DISPLAYDRIVER
CS
LATCHLS373
CS
LS373LATCH
DISPLAY
READYSYSTEM
SOUNDERFAIL
KEYBOARD
5 – Maintenance
DPN 060070 Issue 3.7 © SG Brown Chapter 5 Page 11 of 12
Table 5–3: Spares list for Meridian Gyrocompass 929060
SG Brown P/N Description
929033 Gimbal assembly
929066 Control Board Analogue
929083 Control Board Digital
929049 Control Board Remote
929045 Display Board
929074 DC/DC Power Supply
856000 Filter #1
929160 Filter #2
346808 Fuse link 3.15A 250V
929164 Gland Plate assembly
929190 RCU Mounting Kit
929194 Transit case
929220 Test box
Meridian Gyrocompass
Chapter 5 Page 12 of 12© SG Brown Issue 3.7 DPN 060070
A – Operating Theory
DPN 060070 Issue 3.7 © SG Brown Appendix A Page 1 of 8
A OPERATING THEORYA gyrocompass is a navigational instrument that provides a true north indication without refer-ence to the earth’s magnetic field. For its operation, the gyrocompass depends upon the fol-lowing:
The inertial properties of a freely spinning gyroscope.
The rotation of the earth about its own axis.
Gravity.
Figure A–1 shows a free-spinning gyroscope mounted in a balanced gimbal suspension. The suspension allows unrestricted movement about the vertical and horizontal axes so that the gyro rotor can adopt any orientation.
Figure A–1: Free-spinning gyroscope
With the gyro rotor stationary, it is easy to turn the gimbal suspension about either axis and allow it to remain there in a balanced condition.
However, when it is spinning, the gyro rotor exhibits a property called gyroscopic inertia. This property causes the spin axis of the rotor to remain pointing in the same arbitrary direction in space and to resist any influence that tries to redirect that axis.
For simplicity, this explanation assumes the gyro rotor continues to spin perpetually at a con-stant speed. In a practical gyrocompass, the gyro rotor is the specially designed spindle of a motor that rotates at a constant speed.
To an observer on the surface of the earth, the free spinning gyroscope would appear to ‘tum-ble’ in its gimbal suspension once in every 24-hour period. This apparent deviation occurs because, although the spin axis actually remains fixed in space, the earth rotates relative to it.
Meridian Gyrocompass
Appendix A Page 2 of 8 © SG Brown Issue 3.7 DPN 060070
The apparent movement seen by the observer would depend on the location of the gyroscope and the initial direction of the spin axis.
To an observer at the equator:
With an initial spin axis alignment level and parallel to a meridian (so that it points in a true north-south direction), there would be no observable effect on the gyroscope during the 24-hour period.
With an initial spin axis alignment level and perpendicular to a meridian (so that it points in the east-west direction), the spin axis would appear to tumble about its horizontal axis with the eastern end of the spin axis rising. After 24 hours, the gyroscope would complete a single revolution in its gimbal suspension so that the spin axis would again point in the original direction relative to the observer.
With an initial spin axis alignment somewhere between these two extremes, the gyroscope would appear to tumble about its horizontal and its vertical axes to complete one single revolution in 24 hours.
To an observer at one of the geographic poles:
With an initial spin axis alignment vertical (so that it aligns with the axis of earth rotation), there would be no observable effect on the gyroscope during the 24-hour period.
With the initial spin axis level, the gyroscope would appear to turn clockwise (at the north pole) or anticlockwise (at the south pole) about its vertical axis once in 24 hours.
To an observer at some intermediate latitude with the gyroscope oriented in some arbi-trary initial direction:
The gyroscope would tumble about the north-south direction at and about the
east-west direction at , where Ω is the earth rotation rate (15° per hour) and λ is the latitude of the gyroscope.
A.1 NORTH-SEEKING GYROSCOPEGiven a constant spin rate and frictionless gimbals, the gyroscope described above will always maintain its initial alignment relative to free space. To an observer on the surface of the earth, the revolutions that such a gyroscope performs every 24 hours would make it difficult to use as an instrument of navigation.
The ideal situation is for the gyroscope to align perfectly with the spin axis of the earth so that it maintains a north-south orientation with no apparent tumbling during each 24-hour period.
To make the gyroscope north seeking, the gyrocompass uses gravity control and an effect called precession.
Ω λcos–
Ω λsin
A – Operating Theory
DPN 060070 Issue 3.7 © SG Brown Appendix A Page 3 of 8
Consider the example shown below where the gyroscope rotates about its spin axis in the direction shown.
When an externally applied torque acts on the gyroscope suspension in the direction shown, a point on the circumference of the rotor at 'O' will attempt to move in two directions simultane-ously:
It will accelerate in the direction OA under the influence of the applied torque.
It will continue to move in the direction OB as the rotor spins.
The net result of these two movements actually starts to move the point on the circumference of the rotor in the direction OC, which is the resultant of the two perpendicular influences.
Since every point on the circumference of the rotor experiences the same effect as it passes through point O, it follows that the rotor will rotate about an axis that lies at right angles to the axis of applied torque. This is the axis of precession. In this example, precession will act in the direction shown.
Eventually, the spin axis of the gyroscope will turn sufficiently so that its spin axis coincides with the axis of applied torque, at which point there will no further tendency for the gyroscope to rotate about the precession axis.
Summary:If a free spinning gyroscope comes under the influence of a torque whose axis is perpendicu-lar to the spin of the gyro rotor, a precession results that tends to align the spin axis with the axis of applied torque. The direction of this precession is such that, should alignment occur, the gyroscope spin direction will be the same as the direction of applied torque.
Precession
Meridian Gyrocompass
Appendix A Page 4 of 8 © SG Brown Issue 3.7 DPN 060070
Consider the example shown in Figure A–2(a), which shows a free spinning gyroscope aligned so that its spin axis is level with the horizon. In this example, the spin axis of the gyroscope aligns with the local meridian so that its north end points north. In the balanced condition shown, the weight suspended from the gyroscope bearings has no effect on operation and the gyroscope will maintain its alignment with the meridian.
Figure A–2: Gravity control of a gyroscope
It is more common for the initial alignment of the gyroscope to be at some angle away from true north. Two conditions are therefore possible:
1. Gyroscope initially level and aligned to the west of north.
With the spin axis of the gyroscope initially level but with the north end pointing to the west of true north, the arrangement would briefly be balanced as shown in Figure A–2(a).
However, over time the north end of the spin axis would begin to tilt downwards. This is because the earth rotates while the gyroscope maintains a fixed orientation in space. In this off-balanced condition, shown in Figure A–2(b), the weight would try to return to its central location and, in doing so, would apply an anticlockwise torque to the gyro suspension.
With the gyroscope spinning in the direction shown, precession arising from the anticlockwise torque would move the north end of the rotor eastwards. Therefore, because this condition arises from a westerly misalignment between the gyroscope and the meridian, the effect of the bottom weight is to drive the gyro rotor towards closer alignment with the meridian.
2. Gyroscope initially level and aligned to the east of north.
With the spin axis of the gyroscope initially level but with the north end pointing to the east of true north, the arrangement would briefly be balanced as shown in Figure A–2(a).
However, over time the north end of the spin axis would begin to tilt upwards with rotation of the earth. In this off-balanced condition, shown in A–2(c), the weight would apply a clockwise torque to the gyro suspension.
A – Operating Theory
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Precession arising from the clockwise torque would move the north end of the rotor further west and therefore into closer alignment with the meridian.
In practice, modern gyrocompasses, such as the Meridian Gyrocompass, exercise gravity con-trol by an indirect method. Tilt is detected by an electronic pendulum or accelerometer and the resultant electrical signals are used to produce torques that have the same effect as a suspended weight.
A.2 GYROCOMPASS CORRECTIONSA.2.1 Latitude CorrectionSub-section A.1 explains how the addition of gravity control to the gyroscope gives it the north-seeking characteristic necessary for use in a gyrocompass.
When operating at the equator, such a simple gravity control would be sufficient to maintain alignment with the meridian with no further need for corrections.
However, as the operating latitude increases towards either of the poles, there is a greater ten-dency for the gyroscope to experience azimuth drift with time.
The rate of change of azimuth due to the earth’s rotation is constant for a given latitude. There-fore, the gyrocompass must apply a controlling correction torque, perpendicular to the spin axis, to cancel the drift caused by the earth’s rotation. To generate this correction torque the gyrocompass needs to know the operating latitude.
A.2.2 Gyro DampingWhenever the gyroscope does not align perfectly with the meridian, precession caused by gravity control and the horizontal component of the earth’s rotation will cause the north end of the gyro rotor to trace out an anticlockwise elliptical path.
The application of latitude correction causes this elliptical path to be symmetrical about a point projected from the north end of the gyro rotor when horizontal and aligned with the meridian. For a given gyroscope, the ratio between the major and minor axes of this error ellipse is constant. The size of the ellipse depends on the initial displacement of the gyro axis away from the meridian and the horizontal plane.
By reducing the amplitude of ellipsoidal excursion in one plane, it follows that the amplitude of excursion in the other plane reduces proportionately to settle the gyro horizontally and in the meridian.
In the gravity controlled gyroscope, a tilt of the rotor spin axis produced a torque about the horizontal axis to drive the spin axis towards alignment with the meridian. However, to pro-duce a workable gyrocompass, there must be some form of damping.
One practical method for doing this is to include electrical feedback so that a tilt in the rotor spin axis also produces a torque about the vertical axis. The sense of this torque would be to cause a precession that would drive the spin axis towards the horizontal.
This would cause the vertical axis of the error ellipse to reduce progressively towards zero, reducing the horizontal axis simultaneously. This process results in the north end of the gyro
Meridian Gyrocompass
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rotor tracing a decreasing spiral path, eventually settling with the gyroscope horizontal and aligned with the meridian.
A.2.3 Speed ErrorFigure A–3 shows that the north end of a meridian-aligned free spinning gyro will appear to rise as it moves northwards from the equator. This upward tilt is independent of the earth’s rotation. If left uncorrected, this effect would interfere with the north-seeking properties of the gyrocompass because the compass would be unable to determine whether the tilt came from a misalignment or from the northward motion.
If left uncorrected therefore, the northward travel would cause an upward tilt that would cause the gyroscope to precess towards the west and then to go into a settling spiral. Eventually, given a constant speed of northward movement, the gyro would settle slightly to the west of true north.
Figure A–3: Gyrocompass speed error
Speed-related error is directly proportional to the north-south component of speed, and inversely proportional to the cosine latitude. This means that any error when the compass is on the equator would become twice as large at latitude 60°, three times as large at latitude 70°, and nearly six times as large at latitude 80°. At latitudes above 80° the gyrocompass becomes virtually unusable as a north seeking instrument.
The north-south component of speed is the product of actual speed and the cosine of the course made good. Speed related errors are therefore greatest when travelling in a northerly or a southerly direction.
To correct for these effects, the compass must know the direction and speed of travel. While it uses its own self-generated heading information to determine the direction of travel, speed information must come from an external source such as a speed log or a GPS receiver, or be applied manually.
A – Operating Theory
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A.3 SUMMARY A gyrocompass will indicate the true north direction after an appropriate settling period.
To maintain correct true north alignment, the gyrocompass must receive additional infor-mation concerning its operating latitude.
Also to maintain accuracy the gyrocompass needs to know its direction of travel, which it generates itself, and the speed of travel. Speed information must arrive from an external source, or be applied manually.
A gyrocompass becomes progressively less effective as a north seeking instrument at higher latitudes. Note that the Meridian Gyrocompass can be used successfully in high lat-itudes with the DG mode selected. In this mode, the gyrocompass acts as a directional gyro. A directional gyro does not north seek, but can maintain a reference heading for a short period. Follow the instructions in sub-section 3.3.3 to set the DG operating mode.
Meridian Gyrocompass
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B – Certification
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B CERTIFICATIONOn the following pages are the Certificates of Type Approval documentation obtained for the Meridian Gyrocompass.
Meridian Gyrocompass
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Figure B–1: Certificate of Type Approval
B – Certification
DPN 060070 Issue 3.7 © SG Brown Appendix B Page 3 of 4
Figure B–2: Certificate of Type Approval - Schedule 1
Meridian Gyrocompass
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Figure B–3: Conditions of Issue
Index
DPN 060070 © SG Brown Issue 3.7 Index Page 1 of 2
AAdjustments
Azimuth bias 5–3Azimuth drift 5–3Test connector 5–4
Alignment 2–4, 2–12Auxiliary inputs 1–4Azimuth bias adjustment 5–3Azimuth drift A–5Azimuth drift adjustment 5–3
CCable types 2–4Connections 2–7Continuous operation 3–8Control unit. See RCUControls 3–2Correction
Speed A–6Corrections 3–4
Latitude 3–4, A–5
DDIP switches 2–10Distribution Board connections 2–7
EError modes 3–5
GPS 3–5Gyro failure 3–6, 3–7Speed log 3–6
GGPS 1–4GPS failure 3–5Gravity control A–2Gyro damping A–5Gyro failure 3–6, 3–7Gyrocompass configuration 2–10Gyroscopic inertia A–1
IInstallation
Alignment 2–4, 2–12Cable types 2–4Choosing a location 2–3Connections to Distribution Board 2–7
LLatitude correction 1–4, A–5Latitude correction. See CorrectionsLoss of GPS 3–5Loss of speed signal 3–6
MMaintenance
Error modes 3–5Test connector 5–4
NNorth-seeking gyroscope A–2
OOperation
Continuous operation 3–8Lay-up 3–8Power failure 3–8Power-off 3–8Power-on 3–3
Operation during lay-up 3–8
PPower failure 3–8Power-off 3–8Power-on 3–3Precession A–2
RRCU
Controls and indicators 3–2External location 2–9
Remote Control Unit. See RCU
SSpeed correction 1–4, A–6Speed correction. See CorrectionsSpeed log failure 3–6
TTest connector 5–4Toppling 2–3
Meridian Gyrocompass
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