practical dnp3, 60870.5 & modern scada communication system
Post on 24-May-2015
410 Views
Preview:
DESCRIPTION
TRANSCRIPT
Technology Training that WorksTechnology Training that Workswww.idc-online.com/slideshare
Fundamentals of SCADA Communications
Technology Training that WorksTechnology Training that Workswww.idc-online.com/slideshare
Topics
• SCADA Systems
• Remote Terminal Units
• Communication Architectures
• Communication Philosophies
• RS-232 and RS 485
• MODBUS Protocol
Technology Training that WorksTechnology Training that Workswww.idc-online.com/slideshare
SCADA System
• Supervisory Control and Data Acquisition System
• Comprises a number of Remote Terminal Units (RTU’s) collecting field data connected back to a master station via a communications system
Technology Training that WorksTechnology Training that Workswww.idc-online.com/slideshare
Typical SCADA System
SCADAServer
RS-232
In InO ut
Analog D ig ita l
O utInstrum enta tion
& Contro l
HM I 1 HM I 2 Printer
RadioM odem
RadioM odem
PC PC
PC
I/OD atabase
Technology Training that WorksTechnology Training that Workswww.idc-online.com/slideshare
Remote Terminal Unit• RTU is a standalone data acquisition and control unit, generally
microprocessor based which monitors and controls equipment at some remote location from the central station.
O p tio na l
Sp a re RS-232 Po rt
O p e ra to r Sta tio n/Pro g ra m m ing Te rm ina l
O p tio na l
No nVo la tile
M e m o ry
Po we rSup p ly
a ndBa c kupBa tte ry
M o d e m
Ante nna
Ana lo gInp ut
M o d ule
Ana lo gO utp utM o d ule
Dig ita lInp ut
M o d ule AC M a ins
Po we r
Vo la tileM e m o ry
(RAM )
C e ntra lPro c e ssing
Unit
Dig ita lO utp utM o d ule
C e ntra l Bus
M a in RTU
Se ria l C o m m s Po rts(RS-232 / RS-422 / RS-485)
Pro g ra m m a b le Lo g ic C o ntro lle r
Ethe rne t
Technology Training that WorksTechnology Training that Workswww.idc-online.com/slideshare
Typical RTU Hardware• Control Processor• Analog I/O• Digital I/O• Counter Inputs• Communications Interface• Power Supply• RTU Rack and enclosure• Watchdog Timer• Real Time Clock
Technology Training that WorksTechnology Training that Workswww.idc-online.com/slideshare
Analog Input Module
Gain
A/D C o nv erte r
B uffe r/F IF O
S/H
Clo ck
S/H
S/ H
S/H
S/H
B u s Inte rfa ce Tim in g S yste m
C h a nnel-G ainA rra y Me m ory
Pro gra m m a bleG ain
A m pliferS a m ple &H old for
A/ D
S a m ple
E nd ofco n version
StartC o nv ersion
Step/N e xtC han n el
E xt. C lo ck
E xt. Trig ger
S a m pleIn p uts
R e a dC on versio n
P CD ATAB U S
D ataR e a dy
R e adD ata
P G A
+
-
In putC ha n nel
S a m ple &H old
Status &C o ntro lL in es
Channel
Inp
ut
Mu
ltip
lexer
Technology Training that WorksTechnology Training that Workswww.idc-online.com/slideshare
A/D Converters
• Integrating A/D– low sample rate– high accuracy
• Successive Approximation A/D– high sample rate– lower accuracy
Technology Training that WorksTechnology Training that Workswww.idc-online.com/slideshare
Digital Inputs (Optically isolated)
Technology Training that WorksTechnology Training that Workswww.idc-online.com/slideshare
Counter or Accumulator Inputs
Optical Isolation
Technology Training that WorksTechnology Training that Workswww.idc-online.com/slideshare
Polled (or Master-Slave)
• Advantages:– simple, predictable, no collisions– quickly detect link failure
• Disadvantages:– performance– all slaves must be polled (cannot spontaneously
report alarms)
Technology Training that WorksTechnology Training that Workswww.idc-online.com/slideshare
Prioritised Polling Technique
RTU 9
RTU 1
RTU 2
RTU 3
RTU 4
RTU 8
RTU 3
RTU 2
RTU 1
RTU 1
RTU 5
RTU 7
RTU 6
RTU 2
High Priority
RTU 1
RTU 2
RTU 3
Polling
Cycle
RTU 3
Technology Training that WorksTechnology Training that Workswww.idc-online.com/slideshare
Peer to Peer (CSMA/CD)
• Advantages:– Slaves can report alarms spontaneously– Can have many stations
• Disadvantages:– Need to control collisions (priorities)– Can lead to network collapse– Link failure detection slower
• Use Exception Reporting to cut down unnecessary traffic
Technology Training that WorksTechnology Training that Workswww.idc-online.com/slideshare
Connections between DTE & DCE
Technology Training that WorksTechnology Training that Workswww.idc-online.com/slideshare
Voltage Levels for EIA-232D a t a L i n e D r i v e r
C o n t r o l L i n e D r i v e r
0 ( S p a c e )
1 ( O n )
1 ( M a r k )
0 ( O f f )
D a t a L i n e s
D r i v e r R e c e i v e r
C o n t r o l L i n e s
D a t a R e c e i v e r
C o n t r o l R e c e i v e r
+ 2 5 V
+ 2 5 V
+ 2 5 V
+ 2 5 V
- 2 5 V
- 2 5 V
- 2 5 V
- 2 5 V
+ 5 V
+ 5 V
+ 3 V
+ 3 V
- 5 V
- 5 V
- 3 V
- 3 V
0 V
0 V
0 V
0 V
Technology Training that WorksTechnology Training that Workswww.idc-online.com/slideshare
EIA-232 Transmitters and Receivers
DCE DeviceDTE Device
TTL TTL
Data Transmit
Data Receive
Signal Common
Logic 1 : V = -V
Logic 0 : V = +Vt
t
Line DriverLine Receiver+V+V
+V+V
22
33
77OV
OV
-V-V
-V
Line ReceiverLine Driver
Vt
Note: TTL 0V = 0 +5V= 1
Technology Training that WorksTechnology Training that Workswww.idc-online.com/slideshare
RS 485
• RS-485 is the most common voltage standard in use today for multi-drop communication systems.
• Because:
• It is very resistant to noise
• It can send data at high speeds
• And can go long distances
Technology Training that WorksTechnology Training that Workswww.idc-online.com/slideshare
EIA-485 Interface Standard
• Distance: up to 1200m (4000 ft)
• Speed: up to 10 Mbps
• Up to 32 line drivers - balanced, tri-state
• Up to 32 balanced receivers
NOTE can only address 32 devices
Technology Training that WorksTechnology Training that Workswww.idc-online.com/slideshare
Installation of Bias Resistors to Minimize Noise
B A560 560120
120
Technology Training that WorksTechnology Training that Workswww.idc-online.com/slideshare
Modbus Protocol
• Developed by Modicon for use with Process Control Systems.
• Estimated by Control Engineering Magazine that over 40 % of industrial interfacing was done using this Protocol.
• Even the new Fieldbus state of the art standards appearing today have a Modbus Gateway.
Technology Training that WorksTechnology Training that Workswww.idc-online.com/slideshare
Open Protocol• While Modbus is not an actual system it is a
protocol used on many industrial systems
• Although it is an old standard (written in Fortran in the 1970s) it has become a highly successful Open protocol (defacto standard)
Technology Training that WorksTechnology Training that Workswww.idc-online.com/slideshare
MODBUS Protocol
• Originally intended to link Modicon PLC’s with intelligent terminals
• Half-duplex, Master/slave operation
• Connects 1 Master with up to 247 slaves
• Typically used with a multidrop bus
Technology Training that WorksTechnology Training that Workswww.idc-online.com/slideshare
A De-facto Standard
• Relatively Slow compared to other buses.
• Widespread acceptance.
• PLC jargon used in describing the standard....but used in instruments/gas chromatographs....etc
• Two versions:– Modbus RTU (Modbus-B sometimes)– Modbus ASCII– Very similar structure
Technology Training that WorksTechnology Training that Workswww.idc-online.com/slideshare
Physical Layer• No physical layer specified so Modbus can be used
with a variety of interface standards: – RS-232/RS-422 (point-to-point)– RS-485 (multidrop bus)– Bell 202 modem (switched and leased lines)– “Modbus modem” (baseband line driver on twisted pair
up to 5000m)– Asynchronous, byte-oriented frames
Technology Training that WorksTechnology Training that Workswww.idc-online.com/slideshare
Modbus Protocol Structure
Technology Training that WorksTechnology Training that Workswww.idc-online.com/slideshare
Memory Structure
Technology Training that WorksTechnology Training that Workswww.idc-online.com/slideshare
Application Layer• Two types of messages:
– Query/response - specific slave addressed– Broadcast - address 00, no response required
• Function codes specify:– what the slave is to do– what section of the memory map to find or deposit the
data• e.g. Coil Status, Input Status, Input Register, Holding Register
Technology Training that WorksTechnology Training that Workswww.idc-online.com/slideshare
Exception responses
• Are returned if error conditions occurred during communications
• the most significant bit of the function code is set in the returning message
• the error code is returned in the data field
Technology Training that WorksTechnology Training that Workswww.idc-online.com/slideshare
Validating Changes
• Can you trust the response that comes back when you are changing a critical parameter on the device?
• Methods to check:– Do a subsequent read request of that parameter.– Check some other associated parameter..e.g. start
a pump, check flow rate...
Technology Training that WorksTechnology Training that Workswww.idc-online.com/slideshare
DO YOU WANT TO KNOW MORE?
If you are interested in further training or information, please visit:
http://idc-online.com/slideshare
top related