acpd - limos

8/20/2019 ACPD - Limos

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__________________________________________

LIMOS USER MANUAL

Software Version 1.x

__________________________________________

Martin C. Lugg

Technical Software Consultants Ltd.6 Mill Square, Featherstone Road,

Wolverton Mill, Milton Keynes, MK12 5RBUNITED KINGDOM

Document: TSC/MCL/1773Date: 8

th January 2008

Revision: 1.0 (1)Issue: 1

© 2008. Technical Software Consultants Ltd.


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Document Revision Approval Sheet

TECHNICAL SOFTWARE CONSULTANTS

LIMITED

6 Mill Square, Featherstone Road, Wolverton Mill,Milton Keynes, MK12 5RB

KEYWORDS:

Controlled Copy: Yes No

TITLE:

LIMOS USER MANUAL

Software Version 1.x

Document: TSC/MCL/1773

1.0 ( 1 )MCL Draft issue 08/01/2008

Issue(Rev) Initiated by Checked by Approved by Date

Issued Document Revisions


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TABLE OF CONTENTS

1. INTRODUCTION ................................................................................................... 1

2. HARDWARE REQUIREMENTS............................................................................2

3. INSTALLATION PROCEDURE ............................................................................. 3

4. OVERVIEW OF LIMOS.......................................................................................... 4

4.1. Glossary of Terms......................................................................................... 4

4.2. Start-Up Screen ............................................................................................5

4.3. Pull-Down Menus .......................................................................................... 6

4.3.1. File Menu............................................................................................. 6

4.3.2. Test Menu............................................................................................ 6

4.3.3. Collect Menu........................................................................................ 7

4.3.4. Data Menu...........................................................................................7

4.3.5. Help Menu ...........................................................................................9

4.4. Control Buttons ............................................................................................. 9

4.5. Display Area................................................................................................ 10

4.6. Data File Page Bar...................................................................................... 14

5. MULTIPLE FIXED PROBE ACPD ........................................................................17

5.1. Start Up and Instrument Settings ................................................................ 17

5.2. Setting Up A Test ........................................................................................ 20

5.2.1. New Test Settings................................ ................................ .............. 20

5.2.2. Channel Definition ............................................................................. 21

5.2.3. Site Definition .................................................................................... 22

5.2.4. Save Test Set-Up .............................................................................. 29

5.3. Running a Test............................................................................................ 29

5.3.1. Open Setup File................................................................................. 29

5.3.2. Collecting Data ..................................................................................30

6. Fixed Single Probe ACPD ...................................................................................34


6.2. Setting Up A Test ........................................................................................ 34



6.2.3. Site Definition .................................................................................... 37

6.2.4. Save Test Set-Up .............................................................................. 43

6.3. Running a Test............................................................................................ 43

6.3.1. Open Setup File................................................................................. 43


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6.3.2. Collecting Data ..................................................................................44

7. Moveable Single Probe ACPD................................................................ ............. 47


7.2. Setting Up A Test ........................................................................................ 48



7.2.3. Site Definition .................................................................................... 50

7.2.4. Save Test Set-Up .............................................................................. 55

7.3. Running a Test............................................................................................ 55

7.3.1. Open Setup File................................................................................. 55

7.3.2. Collecting Data ..................................................................................56


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LIMOS Vn 1.0 User Manual

New ACPD manual.doc Page 1

1. INTRODUCTION

This document describes version 1.x of the general purpose ACPDinspection/monitoring program LIMOS (Long-term Inspection and Monitoring Of

Structures). LIMOS was written for use with Technical Software Consultants' (TSC's)U20 Laboratory model ACPD Crack Microgauge to provide automated instrumentcontrol, data storage facilities and dedicated graphical output. LIMOS runs under theWindows 2000, XP or Vista environments, allowing easy data transfer to otherWindows programs such as spreadsheets and word processors.

LIMOS is used to control crack growth monitoring with the ACPD technique usingfixed probes. It also supports the deployment of single moveable voltage probes forcrack detection and sizing. Users unfamiliar with the ACPD technique should refer toTSC's introductory literature.

LIMOS operates in one of three modes:

a) Multiple fixed probe (e.g. large-scale monitoring test in laboratory)

b) Single fixed probe (e.g. single-site monitoring in the field, or laboratory CTsample)

c) Single moveable probe (e.g. obtaining depth profile in the field)

In fixed probe ACPD operation, LIMOS obtains a set of voltage measurements fromthe probes attached to the Crack Microgauge. The probes are arranged in pairs

(cross crack and reference) and the voltages from each pair are used to calculate acrack depth using the simple formula:

d1 =∆r 2

Vc

Vr -

∆c∆r

where ∆ is the probe spacing, and the suffices c and r designate cross-crack andreference respectively. (N.B. This formula applies to high aspect ratio cracks inferritic steel - other formulae or correction factors apply in other cases). LIMOS thenplots the array of depths as a crack profile. Scans of the probes can be made atuser-defined time intervals and LIMOS will then plot crack growth curves for any

given location.

Alarm levels can be set so that when defect depth exceeds a user -defined value, adigital output pulse is produced by the computer which can be used to stop a fatiguemachine, for example.

In moveable probe ACPD operation, LIMOS collects voltage measurement pairs ondemand to calculate depths. The cross crack and reference voltages can beobtained from successive readings from a single probe, or from two simultaneousreadings from a twin output probe. These depths can be assigned to positions todisplay a crack profile as with fixed probe ACPD.


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2. HARDWARE REQUIREMENTS

The software has been developed to run under the Windows environment (2000, XPor Vista).

The PC must also have a serial port (or USB to serial converter) for communicationswith the U20 instrument, and methods for installing the software (usually a CD drive)and for backing up data (e.g. CD writer or USB port).

The program is designed to control TSC's Model U20 ACPD Crack Microgauge. Thisinstrument was produced primarily for use in the laboratory and supportsmultichannel input as well as single probes. The top panel of the instrument isshown below:

The picture shows an instrument with one 16-channel module fitted. Up to four suchmodules can be fitted if required. Also, the number of field outputs fitted can beeither one or four.


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3. INSTALLATION PROCEDURE

This section describes how to install and start up the LIMOS software.

Note that Administrator rights are generally required to install the program onto aPC. The software packages are usually supplied on a CD-ROM.

Insert the CD-ROM into the drive on the PC.

Using Explorer or My Computer, select the CD-ROM drive.

Double click on the ReadMe file.

Follow the onscreen instructions to install the software.


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4. OVERVIEW OF LIMOS

This section describes the contents of the main menus and start-up screen ofLIMOS without going into any details. The following sections are intended to

introduce the user to the most commonly used features of LIMOS by followingtypical procedures for the three modes of operation listed in Section 1.

4.1. Glossary of Terms

The following list explains the terms used in the software.

Input A pair of wires carrying a voltage from the sample into the U20. Thereare two inputs available for manually deployed probes, while inputsfrom fixed probes are in groups of 16.

Module A group of 16 inputs. The standard U20 instrument supports up to 4modules (i.e. 64 inputs in total).

Field A current output from the U20 to the sample. The U20 instrument cansupport up to 4 fields.

Channel An input into the U20 (designated by module number and inputnumber within that module – e.g. Module M2 Input 10). A channel iseither a Crack Channel (meaning the input wires are across the crack)or a Reference Channel (meaning the input wires are adjacent to thecrack).

Point A pair of channels (one Crack and one Reference) used to calculate acrack depth measurement. Each point is linked to a field.

Site A group of points that are plotted on the same graph (usually coveringa complete crack). May include points from more than one field (e.g.for long cracks). LIMOS supports the use of multiple Sites, plotted ondifferent graphs.


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4.2. Start-Up Screen

The first screen seen on start up is the main screen:

The screen display is split into a four different regions top to bottom.

The first line under the title contains pull-down menus where all commands can beaccessed (including some which are also available elsewhere on the screen).

The next section down contains buttons to select which graphs are displayed (whendata is available), and to start and stop data collection, with windows on either sidedisplaying information on the test status.

The main central section is where the graphs are displayed.

The bottom section contains arrow keys to control which part of the data (Site, Timeand Location) is displayed.

The regions and their functions are described in more detail below.


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4.3. Pull-Down Menus

The top line contains the various pull-down menus:

The menus are accessed by clicking with a mouse, or by typing ALT to bring up a

highlight followed by the initial letter (e.g. F for File).

The various pull-down menus available are briefly described below:

4.3.1. File Menu

Typing ALT, F brings down the following menu:

The options available here allow the creation of new data files, the opening of oldfiles, saving and closing the program. Short-cut keys (if available) are shown next tothe menu option.

4.3.2. Test Menu

Typing ALT, T brings down the following menu:

The “Options” option brings up the following dialog:


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Set the Comms Port to that being used by the PC serial port. This will usually beCom1 or Com2 for a 9-pin serial port, but a higher number if a USB to serial adapteris used. The Baud Rate should be set to 19200 for use with the U20 instrument.

The other options contained here allow control over the experimental set-ups (e.g.

number of channels, sampling rate, graph scalings etc.). The Test Panel optionallows full control over the instrument settings.

4.3.3. Collect Menu

Typing ALT, C brings down the following menu:

The options contained here are used to start or stop scheduled data collection, ortake single sets of readings. These duplicate the functions of buttons in the secondsection of the display.

4.3.4. Data Menu

Typing ALT, D brings down the following menu:

These options are used to control the format and display of ACPD data in variousforms. The first option “Data Sets” brings up the following window listing the data

collected for the currently selected site:


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The next three options select which of the display types are shown in the main partof the screen (duplicating the functions of buttons in the second section of thedisplay).

The next two options apply (and remove) normalisation of the data. Normalisation isusually done at the start of a fatigue test and it adjusts the depth values to thosespecified as “Start Depths” in the test set-up. Typically, there is a known crack depthat the start of a test (usually zero), but small variations between nominal probe gapand actual gap give rise to small non-zero values of crack depth. Applyingnormalisation makes adjustments to the stored probe gap values to bring the initialdepths to the known values.

The “Export this site” option allows all data from the current site to be exported to aWindows Excel spreadsheet file for further manipulation if required.

Finally the last option allows individual data sets to be deleted.


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4.3.5. Help Menu

Typing ALT, H brings up the Help menu. This has one option – “About”, givingdetails of the version number of the software:

4.4. Control Buttons

The next line in the display contains the control buttons used to control the runningof the program and the display areas showing test progress:

The functions of all these buttons are duplicated in the Collect and Data menusdescribed above.

“Start” starts a scheduled test and “Stop” stops it. “Take” is used to collect dataimmediately as a one-off scan on the active Site, or to start taking single readingsfrom a moveable probe. “Normalise” adjusts the stored values of probe gaps to forcecalculated crack depths to match those specified as the “Start Depth” values.

The three icons above the buttons are used to toggle on and off the three differentgraphs displayed (Crack Depth Profile, Crack Growth Curves and Voltage readings).


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A tick appears over the icon when this graph is displayed. The box underneathdisplays graph values (time, depth, channel number, voltage etc.) when the cursor isplaced over any point on the graphs.

The window on the left shows the time of the next scan due during scheduled data

collection, and the most recent voltage readings. The window on the right shows theunacknowledged Events (including alarms triggered, error messages etc.). Pressingthe “Details” button brings up a more detailed list of all events, which may be filteredusing the tick boxes at the top, and acknowledged using the buttons at the bottom:

4.5. Display Area

The main central part of the screen is taken up with a number of displays of data.The actual displays used can be selected using the Graph buttons described abovefrom the types described in the following sections.


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4.5.1. Crack Growth Graph

The crack profile graph above is a plot of crack depth versus position. Crack depth isplotted downwards from the top so that the plot gives the appearance of a slice

through the specimen. The user can choose the vertical scaling (depth representedby each band, and the number of bands). This is done during the “Site Definition”task.

If a maximum crack depth is set up in Alarms, this value appears as a horizontal redline.

The window above the graph controls the horizontal scaling. Either all the points in asite are plotted, or all the points in the current data set, or a part of the current set(the start position of this set can be controlled using the slider bar). Note that thiswindow is duplicated above the Chart Recorder graph, so that changing settings in

either window affects both graphs.


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4.5.2. Crack Growth Graph

The crack growth graph above plots crack depth versus time (or cycles) for a seriesof measurements at one given point on the sample. This point can be changed usingthe Next/Previous buttons under the table. The vertical scale matches that chosen

for the Crack Profile plot.

If a maximum crack depth is set up in Alarms, this value appears as a horizontal redline.

The window above the graph controls the horizontal scaling. Either all the points in atest are plotted, or a subset (controlled using the From-To option or the slider). Thesubset can be forced to be the latest scans in a test by ticking the “Last” button(useful in test where crack initiation is a large fraction of the total test).


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4.5.3. Chart Recorder Graph

The chart recorder graph shows voltage readings plotted against position. Twovoltage traces are plotted, namely Vc (or Cross crack voltage) in red, and Vr(Reference voltage) in green. The user can choose the vertical scaling (difference in

voltage between top and bottom of graph) during the “Site Definition” task.

If maximum and minimum voltages are set up in Alarms, these values appears ashorizontal red lines.

The window above the graph controls the horizontal scaling. Either all the points in asite are plotted, or all the points in the current data set, or a part of the current set(the start position of this set can be controlled using the slider bar). Note that thiswindow is duplicated above the Crack Profile graph, so that changing settings ineither window affects both graphs.


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4.6. Data File Page Bar

The area immediately under the display area contains buttons to control the databeing displayed. They become active (i.e. ungreyed) when data has been collected.The active Site is selected in the left hand window. This is used to control which site

is being displayed (if more than one is defined). It also defines which site will benormalised when the “Normalise” option is selected.

The displayed Data Set (for Crack Profile and Voltage plots) is selected in themiddle window. The displayed Point (for Crack Growth plot) is selected in the righthand window. First, Previous, Next and Last Site, Data Set or Point can be selectedby the arrow buttons under each window.

Pressing “Details” under each window brings up the related dialog boxes showingmore details of the results. The data displayed on the graphs can also be controlledusing any of these dialog boxes.

Site Details brings up the “Site Definition” dialog:


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Data Set Details brings up the “Data Sets” dialog:

Selecting a data set here changes the data plotted in the Crack Profile and Chartrecorder graphs.

Pressing the “Edit/View Points” button here brings up the “Data Set Points” dialogwhere voltages and depth values can be seen.


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Finally, Measure Point Details brings up the “Measure Points Definition” dialog:

Selecting a Measure Point here changes the data plotted in the Crack Growth graph.


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5. MULTIPLE FIXED PROBE ACPD

This section describes a typical procedure for crack growth monitoring using fixedmulti-site ACPD. For more information about the theory and practice of the ACPD

technique see TSC's introductory literature.

5.1. Test Set-Up and Wiring

Connect the voltage inputs from the sample (e.g. spot-welded pins) to the 37 way D-connector(s) on the top panel of the U20 instrument. It is recommended thatseparate twisted pairs are used for each voltage input, as used in TSC’s multi-waycable, shown below:

The pin-out for the 37-way D connector is:


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The wiring of the TSC cable is as follows:

Pin No Colour Pin No Colour Pair / Input No

1 Brown 20 Black Brown/Black 1

2 Red 21 Black Red/Black 2

3 Orange 22 Black Orange/Black 3

4 Yellow 23 Black Yellow/Black 4

5 Green 24 Black Green/Black 5

6 Blue 25 Black Blue/Black 6

7 Brown 26 Green Brown/Green 7

8 Red 27 Green Red/Green 8

9 Orange 28 Green Orange/Green 9

10 Yellow 29 Green Yellow/Green 10

11 Blue 30 Green Blue/Green 11

12 Brown 31 Red Brown/Red 12

13 Orange 32 Red Orange/Red 13

14 Yellow 33 Red Yellow/Red 14

15 Blue 34 Red Blue/Red 15

16 Green 35 White Green/White 16

17 Black 36 White Black/Whitecommon mode

18 N/C 37 N/C

19 Screen

If a non-TSC cable is used, the wiring must follow the same scheme (i.e. eachtwisted pair is wired to pins 1 and 20, 2 and 21 etc).

The wires connected to pins 17 and 36 are used to remove any common-modevoltage. These wires should be fixed to the sample near to the centre of the test

area.


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The 16 pairs of wires for the voltage inputs should be soldered onto the pins with thelower pin number on the same side of the gap, otherwise some voltages will be ofopposite polarity. For example, if inputs 1 and 3 are cross-crack channels, and 2 and4 are reference channels, the wires should be connected as shown:

Connect the current input lead(s) from the sample to the connectors on the toppanel bulge on the U20. Connect the serial line between the U20 and the computer'sserial output port.

Start up LIMOS to obtain the following screen:


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5.2. Setting Up A Test

If the test settings have been set up before and stored under a Setup File name, thiscan be opened to restore those settings (see Section 5.3). If a new test is beingdesigned, follow the set up procedure described below.

5.2.1. New Test Settings

Select the button “New” on the screen to bring up the following dialog:

If a previously stored test with similar settings to those required for the new test isavailable, these stored settings can be opened and modified as required. Selecting“Yes” brings up the following dialog:

Select the required test file name and select “Open”, then select “Channels” from theTest pull-down menu to proceed with the test set-up.

If no suitable previously stored test settings are available, press “No” to proceeddirectly to the Channel definition set-up.


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5.2.2. Channel Definition

Selecting “Channels” from the Test menu (or pressing “No” after “New”) brings upthe following display (note that data will be present in the window if a previouslystored test has been opened):

In this dialog, all the individual inputs from the sample are defined in terms ofposition and probe spacing (gap between the contacts).

The channels will be a mixture of Cross crack and Reference inputs, and can be

connected in any order to the U20. However, it is usual to have Cross Crack andReference inputs in pairs at the same distance from the datum. In this case, it iseasiest to keep adjacent Cross crack and Reference input pairs as consecutiveInput numbers, and to connect up the pairs (Points) in order of distance from thedatum with a constant increment in distance between Points. To assist the dataentry in this situation, enter this constant increment distance in the “Auto IncrementDistance…” box, and tick the adjacent select box.

Start from the datum point of the sample (usually the first voltage reading from left toright on the sample). First select which module (between 1 and 4) this input isconnected to from the Module drop down list. Then select which Input of this module

the input is connected to from the Input drop down list.

Then type in the spacing in mm on the sample between the contacts in the “ChanSeparation” box, and the distance along the sample from the datum in mm in the“Location” box. Press “Save” to store this data – it will appear in the window on theright.

Then, enter all the Cross crack inputs in alternative Inputs (e.g. Module 1, Inputs 1,3, 5 etc). When all the Cross crack inputs are entered for a given Site, reset the“Location” to the start value (usually zero), and enter all the Reference inputs (e.g.Module 1, Inputs 2, 4, 6 etc).


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The window on the right displays all the entered data in the first 4 columns. The finalcolumn shows how many Points each input is assigned to. This will be determinedafter the Site Definition procedure in the next section.

If any inputs are later found to be wired up the wrong way round by mistake (i.e. anegative voltage reading is obtained), this can be corrected here by selecting the“Invert” box for that input.

Once the details of all the inputs have been entered and saved, press “Close” toclose this dialog box and proceed to the sites definition dialog by pressing the ”S ites”

button.

5.2.3. Site Definition

Selecting “Sites” from the main screen (or following “Close” in Channel Definitionwhen setting up a new test), brings up the following dialog box:


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First select the “Site ID” number. Most fatigue tests will have only one Site, but testson large specimens where more than one part is expected to crack, or testsinvolving more than one sample, will have more than one Site.

Then enter a short description of the Site in the “Description” box. More notesdescribing the test site can be entered in the “Site Notes” box if desired. Press the“Save” button at the bottom of the window.

Press the “Close” button (or press the “Measure Points” button if editing an old test)to bring up the “Measure Point Definition” dialog:

Use this dialog to pair up the Crack and Reference channels to form Points at whichcrack depth values will be calculated.

Assuming the channels have been set up previously, these will be available fromdrop down lists in the Crack and Reference channel boxes:


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Typically, these will be adjacent Inputs at the same distance from datum (e.g. Mod 1/ 1 above may be a Crack Channel, with Mod 1 / 2 being the associated ReferenceChannel). In some cases, however, the same Reference Channel may be used withmore than one Crack Channel.

For each Measure Point, a Start Depth value can be entered if the test is beingcarried out on a known pre-existing crack. This allows the software to remove any

small variations in calculated depth due to errors in measurement of ChannelSeparation gap etc.

Also, each Point must be assigned to the appropriate Field output, if more than oneis being used.

Following definition of each Point, press “Save” to store the data. The stored valuesappear in the window on the right:

Once all the Points have been set up, press Close to return to the Site Definitionscreen.

Now the schedule and other test settings can be set up. On the “General” tab underthe Site Notes, a Test Frequency can be assigned if required. If the fatigue test isrunning at a fixed frequency, tick the “Track Test Cycles” box and enter thisfrequency in the “Cycle Test Frequency” box. Crack growth curves can then beplotted against number of cycles instead of time.


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Now select the “Schedule” tab and define the schedule for data collection. Threeparameters can be defined – the test start, the test finish, and the interval betweenscans.

The scan interval is selected from the “Interval” drop-down list (with the shortestinterval being 5 seconds and the longest being 30 days). The first scan is defined inthe “Start” box to be either as soon as the scheduled test is started, or at a certain

time of day after the test is started.

The last scan is defined as being either after a set number of scans, or at a certaintime of day. Note that the test can also be stopped manually from the front screen,or when an Alarm is triggered, so for an indefinite test length, set the number ofcollections to a high number and stop the test manually when required, orautomatically through an alarm.

To set an alarm, select the “Alarm” tab:


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Alarm thresholds can be set on a maximum depth value, or on minimum ormaximum input readings (the latter being useful to check for faulty or broken wiring,or voltage saturation).

When an alarm threshold is broken, the software can be programmed to carry outany combination of the tickable actions in the “Action” box. “Log Event” simplyrecords the alarm in the log of events on the front screen; “Audible Alarm” producesa beep on the PC; “Stop Test” stops data collection; “Flag on USB port” (not yetimplemented) will output a pulse on the specified port number (which can be used tostop a fatigue test machine, for example).

Note that if “Enable Alarms” is selected, values must be entered for both “Maxdepth” and “Min” and “Max” voltage readings.

The “Instrument” tab is used to set up the instrument settings for the particular site.

In order to assist in setting the Gain, the “Test Panel” button can be used to checkthe voltages received by the instrument. This brings up the following panel:


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The black boxes in the bottom right indicate which channels have been configuredfor use (matched to the input numbers shown top right).

Before proceeding, the U20 ACPD instrument must be connected and turned on.

Select which Site is being set-up (if more than one is defined) using the control at

bottom left of screen. Select which Field is being used (if more than one is fitted).Then, after pressing the “Check Now” button, the software obtains a reading fromeach configured channel and displays them as shown:


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The “Gain” value, and/or field input positions on the sample, should be adjusted togive reasonably uniform values across all the channels, with values of betweenabout 200 and 500, depending on the maximum depth value expected during thetest.

For example, if the initial cross crack and reference voltages are both 200, andprobe spacings are 10mm, the maximum cross crack voltage reading obtainablebefore saturation (2040) will occur at a crack depth of 46mm. If the maximum depthwill only be 10mm, the initial voltage should be set higher (e.g. 700) to give optimumsensitivity.

The “Phase Angle” at which the instrument’s phase-sensitive rectifier is set can beadjusted to improve performance on different materials.

The “Settle” time is a delay to allow the voltage to reach a steady value after eachchannel select. This should be set to 100 for the U20 instrument.

“Filter Length” is the number of times a channel is read, with the displayed voltagebeing an average of these readings.

“Average” is the number of A-to-D samples taken for each reading.

Press “Check Now” several times and compare successive readings on onechannel. If these vary by more than one digit, try increasing “Filter Length” and/or“Average” to obtain more stable readings. If the readings are already stable, tryreducing “Filter Length” and/or “Average” to obtain faster data collection, whilemaintaining adequate stability.

Once satisfactory readings are obtained across the whole site, press the appropriate“Save” button, and proceed to the next Site (if more than one is defined).


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Finally, the “Scales” tab is used to set up graph scalings.

The “Depth Scale Step” sets the size of the gap between lines on the Crack Profileand Crack Growth plots. This should be set to a small value if only small crackdepths are expected during the test.

The “Number of Stripes” sets the number of lines on the graph. This can be chosen,for example, such that Depth Scale Step x Number of Stripes = sample thickness (ormaximum crack depth expected during the test.

The “Default Chart Recorder Range” sets the full-range scale on the VoltageReading graph (difference between maximum and minimum).

5.2.4. Save Test Set-Up

Once all the test settings have been completed, save the set up using the “Save As”(if creating a new test) or “Save” (if modifying an existing test) option in the “File”menu.

The set-up procedure is now complete and a test can be run.

5.3. Running a Test

5.3.1. Open Test File

If the test set-up has previously been stored, the set-up can be restored by openingthe LIMOS Test file as described below. If no set-up has been saved previously, theset-up procedure described in Section 5.2 must be followed before running a test.


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To open a stored Test file, enter ALT, F, O to bring up the following OPEN menu:

Select the required test file name and press “Open”.

It is recommended that the test settings are checked before starting data collection(as in section 5.2).

5.3.2. Collecting Data

To enable LIMOS to set up the instrument, ensure that the ACPD Crack Microgaugeis connected to the computer via the RS232 port and switched on. If LIMOS tries tocollect data without the instrument being connected and turned on, the followingmessage appears:

Before starting a scheduled test, it is possible to normalise all data collected, suchthat initial depth values will match those selected in the “Start Depth” box in the“Measure Point Definition” dialog (section 5.2.3.). If this is required, press the “Take”button to collect a one-off set of data from the required site. Then, if the depth

results are close to those expected, press the “Normalise” button. Repeat this forany other Sites defined.


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Note that, if any calculated depth differs from the defined Start Depth value by morethan 1mm, the following warning message will appear:

Check the values obtained and check for broken wires etc. before proceeding.

Once a satisfactory Normalisation has been carried out (if required), the data setscollected can be deleted, or stored in a separate file.

Note that it is possible to Normalise at any stage during a test, but this should bedone only if crack depths are still close to the defined “Start depth” values.

Now press the Start button to start the scheduled data collection. The first scan willbe taken either immediately (if option “At beginning of Test” was selected in theSchedule), or at the set time selected.

If data has already been stored in the file (e.g. during set-up and normalisation), thefollowing message appears:

Press “Yes” to remove and store this data in a new file, with the name .PreTest.pdt, or press “No” to keep the data in the current file. Note thatold data will be plotted against time of collection on the Crack Growth Graph (oragainst zero if using cycle counting).

If a site has not been normalised, the following warning appears:


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Press “Yes” to continue without normalising, or “No” to go back and carry out anormalisation.

If an extra scan is required at any time, pressing the “Take” button will immediately

initiate a scan of all probes.

Once data is available, the three graph buttons become operational (Crack Profile,Crack Growth, and Voltage Plot, as described in Section 4). Click on the icons totoggle each display on and off. When displayed, the icon shows an overlayed tick.Displays are tiled horizontally across the screen.

In the crack profile plot, the crack depths are plotted against location. The plot isdrawn as if looking face-on to the crack growing into the specimen, so that depth is


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plotted downwards from the top. The site and data set displayed can be changedusing the arrow keys under the display. The chart recorder plot shows the crosscrack and reference voltages associated with the crack profile.

The test progress display in the top left window is updated to show the time of the

last scan on each field and the time of the next scan.

As the test progresses, the crack growth plot is also updated. In this display, thedepth calculated at one particular point on one field is plotted against time (ornumber of cycles, if a test frequency was set). In this case, depth is plottedconventionally upwards, so that as the crack grows, this results in a line or curvesloping upwards from left to right. The point at which the depth is plotted can bechanged by using the arrow keys under the display.

Once started, the test will continue taking scans of the probes at the requestedintervals until the test is stopped by pressing the “Stop” button, or until the requested

number of scans (or end of test time) is reached.

Data is automatically saved in the test file, along with the set-up information.


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6. Fixed Single Probe ACPD

Data collection using a fixed single probe is set up in a similar manner to multipleprobe ACPD, but using just the Manual inputs. The main difference is that each scan

results in just a single depth measurement at a fixed point. This is obtained fromsuccessive readings of cross-crack and reference voltages from a 3 or 4 pin probeconnected to inputs Manual Probe1 and Manual Probe2.

6.1. Start Up and Instrument Settings

Connect the Cross-Crack channel to Manual Probe1 and the Reference channel toManual Probe2. Connect the current input lead from the sample to the Fieldconnector on the top panel bulge on the U20. Connect the serial line between theU20 and the computer's serial output port.



If the test settings have been set up before and stored under a Test File name, thiscan be opened to restore those settings (see Section 6.3). If a new test is beingdesigned, follow the set up procedure described below.


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Select the required test file name and select “Open”, then press “Channels” on themain display to proceed with the test set-up.

If no suitable previously stored test settings are available, press “No” to proceed tothe Channel definition set-up.


Selecting “Channels” from the main screen (or pressing “No” after “New”) brings upthe following display (but note that data will be present in the window if a previouslystored test has been opened):


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First select “Manual” in the “Module” drop-down list. Then select “Probe 1” in the“Input” drop-down list. Enter the cross crack probe spacing in the “Chan Separation”box. Press “Save” to store these settings. Then, select “Probe 2” in the “Input” drop-down list, enter the reference probe spacing and press “Save”:


Once the details of the inputs have been entered press “Close” to close this dialogbox and proceed to the sites definition dialog automatically (or select ”Sites” from theTest menu).


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Selecting “Sites” from the test menu (or following “Close” in Channel Definition whensetting up a new test), brings up the following dialog box:

Enter a short description of the Site in the “Description” box. More notes describingthe test site can be entered in the “Site Notes” box if desired. Press the “Save”button at the bottom of the window.

Press the “Close” button (or press the “Measure Points” button if editing an old test)to bring up the “Measure Point Definition” dialog:


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Use this dialog to assign the Crack and Reference channels to form a Point at whichcrack depth values will be calculated.

Assuming the channels have been set up previously, these will be available fromdrop down lists in the Crack and Reference channel boxes.

Select “Manual Probe 1” for the “Crack Channel” and “Manual Probe 2” for the“Reference Channel”.

A Start Depth value can be entered if the test is being carried out on a known pre -existing crack. This allows the software to remove any small variations in calculated

depth due to errors in measurement of Channel Separation gap etc.

Press “Save” to store the data. The stored values appear in the window on the right:

Press Close to return to the Site Definition screen.

Now the schedule and other test settings can be set up. On the “General” tab underthe Site Notes, a Test Frequency can be assigned if required. If the fatigue test is


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running at a fixed frequency, tick the “Track Test Cycles” box and enter thisfrequency in the “Cycle Test Frequency” box. Crack growth curves can then beplotted against number of cycles instead of time.

Now select the “Schedule” tab and define the schedule for data collection. Threeparameters can be defined – the test start, the test finish, and the interval betweenscans.

The scan interval is selected from the “Interval” drop-down list. The first scan isdefined in the “Start” box to be either as soon as the test is started, or at a certaintime of day after the test is started.

The last scan is defined as being either after a set number of scans, or at a certaintime of day. Note that the test can also be stopped manually from the front screen,or when an Alarm is triggered, so for an indefinite test length, set the number ofcollections to a high number and stop the test manually when required, orautomatically through an alarm.

To set an alarm, select the “Alarm” tab:


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Alarm thresholds can be set on a maximum depth value, or on minimum ormaximum input readings (the latter being useful to check for faulty or broken wiring).

When an alarm threshold is broken, the software can be programmed to carry outany combination of the tickable actions in the “Action” box. “Log Event” simplyrecords the alarm in the log of events on the front screen; “Audible Alarm” producesa beep on the PC; “Stop Test” stops data collection; “Flag on USB port” (notimplemented yet) will output a pulse on the specified port number (which can beused to stop a fatigue test machine, for example).


The “Instrument” tab is used to set up the instrument settings for the particular site.

In order to assist in setting the Gain, the “Test Panel” button can be used to checkthe voltages received by the instrument. This brings up the following panel:


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The black boxes in the bottom right indicate which channels have been configuredfor use


The instrument settings can then be adjusted in the top left panel. Then, after

pressing the “Check Now” button, the software obtains a one-off reading from eachconfigured channel and displays them. Alternatively, pressing the “Start Continuous”button displays continuous updates of the readings (press “Stop Continuous” t o stopdata collection):


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The “Gain” value, and/or field input connection positions on the sample, should beadjusted to give reasonably uniform values across all the channels, with values ofbetween about 200 and 500, depending on the maximum depth value expectedduring the test.

For example, if the initial cross crack and reference voltages are both 200, andprobe spacings are 10mm, the maximum cross crack voltage reading obtainablebefore saturation (2040) will occur at a crack depth of 46mm. If the maximum depthwill only be 10mm, the initial voltage can and should be set higher (e.g. 700) to giveoptimum sensitivity.





Press “Check Now” several times and compare successive readings on onechannel. If these vary by more than one digit, try increasing “Filter Length” and/or“Average” to obtain more stable readings. If the readings are already stable, tryreducing “Filter Length” and/or “Average” to obtain faster data collection, whilemaintaining adequate stability.

Once satisfactory readings are obtained, press the appropriate “Save” but ton.


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The “Depth Scale Step” sets the size of the gap between lines on the Crack Profileand Crack Growth plots. This should be set to a small value if only small crackdepths are expected during the test.


The “Default Chart Recorder Range” sets the full-range scale on the VoltageReading graph.




6.3. Running a Test

6.3.1. Open Test File

If the test set-up has previously been stored, the set-up can be restored by openingthe LIMOS Test file as described below. If no set-up has been saved previously, theset-up procedure described in Section 6.2 must be followed before running a test.


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To open a stored Test file, enter ALT, F, O to bring up the following OPEN menu:




To enable LIMOS to set up the instrument, ensure that the ACPD Crack Microgaugeis connected to the computer via the RS232 port and switched on. If LIMOS tries tocollect data without the instrument being connected and turned on, the followingmessage appears:

Before starting a scheduled test, it is possible to normalise all data collected, suchthat the initial depth value will match that selected in the “Start Depth” box in the“Measure Point Definition” dialog (section 6.2.3.). If this is required, press the “Take”button to collect a one-off set of data. Then, if the depth result is close to that

expected, press the “Normalise” button.


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Note that, if the calculated depth differs from the defined Start Depth value by morethan 1mm, the following warning message will appear:

Check the values obtained and check for broken wires etc. before proceeding.

Once a satisfactory Normalisation has been carried out (if required), the data setscollected can be deleted.

Note that it is possible to Normalise at any stage during a test, but this should bedone only if crack depth is still close to the defined “Start depth” value.

Now press the Start button to start the scheduled data collection. The first scan willbe taken either immediately (if option “At beginning of Test” was selected in theSchedule), or at the set time selected.

If an extra scan is required at any time, pressing the “Take” button will immediatelyinitiate a scan of all probes.

Once data is available, the three graph buttons become operational (Crack Profile,Crack Growth, and Voltage Plot, as described in Section 4).

In the crack profile plot, the crack depth is plotted as a single point, with increasing

depth plotted downwards from the top. The scan displayed can be changed usingthe arrow keys under the display.

The test progress display is updated to show the time of the last scan and the nextscan.

As the test progresses, the crack growth plot is also updated. In this display, thedepth calculated is plotted against time (or number of cycles, if a test frequency wasset). In this case, depth is plotted conventionally upwards, so that as the crackgrows, this results in a line or curve sloping upwards from left to right.


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Once started, the test will continue taking scans of the probes at the requestedintervals until the test is stopped by pressing the “Stop” button, or until the requestednumber of scans (or end of test time) is reached.

Data is automatically saved in the test file, along with the set-up information.


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7. Moveable Single Probe ACPD

Data collection using a single probe, is set up in a similar manner to fixed singleprobe ACPD. The main differences are that depths can be measured at several

locations along a crack, but that all data collection has to manually triggered. Data isobtained from successive placements of either a two-pin probe connected to inputManual Probe1 (which has to be moved between taking cross-crack and referencevoltages), or from readings from a 3 or 4 pin probe connected to both inputs ManualProbe1 and Manual Probe2 (which is not moved between cross-crack and referencevoltage readings).

7.1. Start Up and Instrument Settings

If using a 2-pin probe, connect this to the Manual Probe1 connector on the top panelof the U20 instrument. If using a 3 or 4-pin probe, connect the Cross-Crack channel

to Manual Probe1 and the Reference channel to Manual Probe2. Connect thecurrent input lead from the sample to the Field connector on the top panel bulge onthe U20. Connect the serial line between the U20 and the computer's serial outputport.



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If the test settings have been set up before and stored under a Test File name, thiscan be opened to restore those settings (see Section 7.3). If a new test is beingdesigned, follow the set up procedure described below.




Select the required test file name and select “Open”, then press “Channels” on themain display to proceed with the test set-up.

If no suitable previously stored test settings are available, press “No” to proceed tothe Channel definition set-up.


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Selecting “Channels” from the main screen (or pressing “No” after “New”) brings upthe following display (but note that data will be present in the window if a previouslystored test has been opened):

First select “Manual” in the “Module” drop-down list. Then select “Probe 1” in the“Input” drop-down list. Enter the probe spacing in the “Chan Separation” box.

Press “Save” to store these settings as shown:

If using a twin output (3 or 4 pin) probe, select “Probe 2” in the “Input” drop-down list.Enter the reference probe spacing, and press “Save”:


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Once the details of all the inputs have been entered and saved, press “Close” toclose this dialog box and proceed to the sites definition dialog by pressing the ”Sites”button.


Selecting “Sites” from the main screen (or following “Close” in Channel Definitionwhen setting up a new test), brings up the following dialog box:


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Enter a short description of the Site in the “Description” box. More notes describingthe test site can be entered in the “Site Notes” box if desired. Press “Save” to storethis information and “Close” to proceed to the “Measure Point Definition” dialog(Press the “Measure Points” button if editing a previous test):

Use this dialog to pair up the Crack and Reference channels to form a Point at whichcrack depth values will be calculated.

If the channels have not all been set up previously, select the “Channels Define/Edit”button to do this now.

Assuming the channels have been set up previously, these will be available fromdrop down lists in the Crack and Reference channel boxes.

If using a 2-pin probe, select “Manual Probe 1” for both Crack and ReferenceChannels. If using a 3 or 4-pin probe, select “Manual Probe 1” for the “CrackChannel” and “Manual Probe 2” for the “Reference Channel”.

If using the same manual probe input for both channels (i.e. a 2-pin probe), the“Moveable Deployment” box will be ticked automatically and greyed out. If usingboth manual probe inputs (i.e. a 3 or 4-pin probe) enter a tick in this box formoveable deployment.

Press “Save” to store the data. The stored values appear in the window on the right:


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Press Close to return to the Site Definition screen.

Note that the “Schedule” tab will now be greyed out.

To set an alarm (if required), select the “Alarm” tab:

Alarm thresholds can be set on a maximum depth value, or on minimum or

maximum input readings (the latter being useful to check for faulty or broken wiring).

When an alarm threshold is broken, the software can be programmed to carry outany combination of the tickable actions in the “Action” box. “Log Event” simplyrecords the alarm in the log of events on the front screen; “Audible Alarm” producesa beep on the PC; “Stop Test” stops data collection; “Flag on USB port” (not yetimplemented) will output a pulse on the specified port number (which can be used tostop a fatigue test machine, for example).


Select the “Instrument” tab to set up the instrument settings.


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In order to assist in setting the Gain, the “Test Panel” button can be used to checkthe voltages received by the instrument. This brings up the following panel (for a 2-pin probe):

The black box in the bottom right indicate which channel(s) has been configured foruse.


The instrument settings can then be adjusted in the top left panel. Then, afterpressing the “Check Now” button, the software obtains a one-off reading from theconfigured channel(s) and displays them as shown. Alternatively, pressing the “StartContinuous” button displays continuous updates of the reading (press “Stop

Continuous” to stop data collection):


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The “Gain” value, and/or field input connection positions on the sample, should beadjusted to give reasonably large values across the crack without saturation.

Place the probe over the deepest part of the crack (move the probe along the crackto find this). Adjust the gain to give the highest reading possible without saturation(i.e. less than 2000).





Press “Check Now” several times and compare successive readings. If these vary bymore than one digit, try increasing “Filter Length” and/or “Average” to obtain morestable readings. If the readings are already stable, try reducing “Filter Length”and/or “Average” to obtain faster data collection, while maintaining adequatestability.

Once satisfactory readings are obtained, press the appropriate “Save” button.



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The “Depth Scale Step” sets the size of the gap between lines on the Crack Profileand Crack Growth plots. This should be set to a small value if only small crack

depths are expected during the test.


The “Default Chart Recorder Range” sets the full-range scale on the VoltageReading graph.




7.3. Running a Test

7.3.1. Open Setup File

If the test set-up has previously been stored, the set-up can be restored by openingthe LIMOS Setup file as described below. If no Setup file has been saved previously,the set-up procedure described in Section 5.2 must be followed before running atest.


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To open a stored Setup file, enter ALT, F, O to bring up the following OPEN menu:




To enable LIMOS to set up the instrument, ensure that the ACPD Crack Microgaugeis connected to the computer via the RS232 port and switched on. If LIMOS tries tocollect data without the instrument being connected and turned on, a warningmessage “Com1!” appears in place of the voltage values:


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Once set up, data is collected by pressing the “Take Reading” button to bring up thefollowing live display:

If you are going to take a series of readings along a crack, enter the location of thefirst reading in the “Distance from datum” box, then press “Save”. A short note canbe entered at the same time, if desired.

If it is planned to take readings at regular intervals along the crack, enter this intervalin the “Auto Increment Distance by” box, and tick the adjacent tick box.


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Place the probe on the crack such that the Cross Crack pins straddle the crack.Watch the reading in the “Crack” window. When this reaches a stable value, pressthe “Take Reading” button, or type ALT-T to capture the Cross Crack value. Nowwatch the reading in the “Reference” window. When this reaches a stable value,press the “Take a Reading” button, or type ALT-T to capture the Reference value. A

crack depth value will now be calculated and displayed in the window on the left.

Continue taking readings as required along the crack.

If the field connection is not in good contact with the sample, the warning text “Field!”appears in the data window. In this case, check the field connections and retake thedata.

If a probe is not in good contact with the sample, the voltage value will appear in red.In this case, it is recommended that the data point is discarded and retaken.

Once data is available, the three graph buttons become operational (Crack Profile,Crack Growth, and Voltage Plot, as described in Section 4).

In the crack profile plot, the crack depth is plotted against location, with increasingdepth plotted downwards from the top. The scan displayed can be changed usingthe arrow keys under the display.


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If the cross-crack and reference readings are taken in the wrong order by mistake,such that a significant negative depth is obtained (< -0.5mm), the software

automatically switches the voltages in the depth calculation to give a positive depth.In this case, the depth value is highlighted in colour in the table of data:


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If scans are added at a later time, the crack growth plot can be used. In this display,the maximum depth calculated anywhere during each scan is plotted against time. Inthis case, depth is plotted conventionally upwards, so that as the crack grows, thisresults in a line or curve sloping upwards from left to right.

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