How to measure strain gauges with Simcenter Testlab?

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Measuring Strain Gauges with Simcenter Testlab


Want to use Simcenter Testlab (formerly LMS Test.Lab) to measure with strain gauges?  Here is how to do it:


Supported Scenarios


Strain gauges can be hooked up directly to the Simcenter SCADAS frontend.  The SCADAS will provide all the needed signal conditioning.


Supported scenarios include:

  • Direct connection between gauge and SCADAS
  • Connection thru a slip ring to a strain gauge installed on a rotating part


VB8-II and VB8-III Cards


First, you will need a VB8-II or VB8-III (referred to as VB8 for remainder of article) card in your SCADAS Mobile or SCADAS Lab. The VB8 card has strain gauge conditioning capabilities: supply voltages, completion resistors, shunt resistors, sense line support, etc. 


A VB8 card also support other types of transducers in addition to strain gauges: potentiometers, ICP/IEPE devices, as well as voltage inputs. 


The cards have 8 channels with software selectable signal conditioning, which can be set independently per channel.  Users can select from: ICP, Voltage, Bridges (Quarter, Half, Full), Potentiometer, and Active Sensors. 


SCADAS_VB8_card.pngPicture 1: VB8-II card and with Open Wire (other end is LEMO) cable and BNC wire (other end is LEMO) cableThe card can be installed in any SCADAS Mobile or SCADAS Lab frame.  The card can be mixed with other signal condition cards (like V-24, V8-E, etc).




The VB8-II and VB8-III card has 7 pin LEMO-FGB.08.307 connections to accommodate power supplies, signal wires, ICP/IEPE and sense lines.  The card comes with two sets of cables to accommodate BNC and any other types of connectors: a LEMO to BNC pigtail cables, and a LEMO to open wire.


There are 16 cables total delivered with each card, 8 cables of each type: 7-pin LEMO to BNC cable (for ICP/IEPE and Voltage inputs) and 7-pin LEMO to Open Wire (for strain gauges, bridges, active sensors, etc.).


lemo_diagram.pngPicture 2: LEMO-FGB.08.307 Pinout for VB8-II card

It is necessary to wire the strain gauge to the open wire provided with the VB8 card.  The most common connections to make are:


vb8wiring.pngPicture 3: Common strain gauge wiring connections for VB8-II card

Quarter, half and full bridges are all supported.  Generally, when using strain gauges, the more wires, the better the quality of the signal.  In a full gauge, the signal is carried on two wires (a differential input), allowing common mode rejection to be employed to reject noise and Electro-Magnetic Field (EMF) interference. 


On quarter and half bridges, the signal is only carried on single wire (a single-ended input) which makes common mode rejection not possible, creating more susceptibility to EMF. Strain gauges, with their long wires and low voltage levels are particularly susceptible to EMF.


Software: Channel Setup


In Simcenter Testlab Signature Channel Setup worksheet, set the following to use the strain gauge (Note: If some fields are not showing, make them visible under “Tools -> Channel Setup Visibility”):


  • Input Mode: Select Quarter, Half, or Full Bridge as desired. Note that AC or DC coupling is also part of this selection. If in doubt, select DC.


pulldown.pngPicture 4: Simcenter Testlab pulldown menu choices for input mode

  •  Measure Quantity: Strain or Force as desired.
  • Bridge supply: Set the voltage supply level. Lower voltages make the signal levels low and susceptible to EMF interference, while high voltage supplies may cause thermal drift. Note that the voltage level is set to zero by default to avoid unintended damage to the gauges. Use the strain gauge excitation guide if uncertain.
  • Bridge gage resistance: This is a completion resistor used for quarter bridges, usually either 350 or 120 ohms. It can be set independently per channel. Check your gauge calibration sheet for the correct value.
  • Bridge strain gage factor: Usually a value around “2”. Check your gauge calibration sheet for the correct value.
  • Offset zeroing: Possible values are Always/Never/Once, default is 'Always'. Channels marked as 'Always' will be have an offset applied to make the signal read zero when performing a Zeroing operation.  Zeroing of the channel is done in the Calibration or Measure worksheet, and is covered in-depth later in this article. If a channel should not be zeroed, then set to 'Never' (for example, a non-gauge transducer).  The mode 'Once' is not often used - Zeroing can only be done in the Acquisition Setup screen by switching from Autorange mode to Zeroing at the bottom of the screen.  The 'Once' mode was intended to be used if a gauge had to be initially set to zero white setting up the test, before the measurement campaign started.  It prevents the gauge from accidentally be zeroed again in the Measurement worksheet.

channel_setup.pngPicture 5: Simcenter Testlab Channel Setup settings

  • Actual Sensitivity: The mV/EU (Engineering Unit) value. This value can be calculated during calibration or can be entered directly from the specification sheet if it is known.
  • Simulated Value: If using a strain gauge to measure a value other than strain (for example, could be load/force for strain gauge based load cell), this is where the expected value can be set for a 100 kOhm shunt resistor in units other than strain.
  • Range: To avoid quantization errors the range should be set to 0.1 V for strain gauges.  The default for strain gauges is 0.1 V, not 10 V.  This is because strain gauge signals are very low voltage levels compared to other transducers.


Virtual Channels


Math channels can be calculated from the strain measurements.  Channels can be filtered and integrated.  Rosette calculations can be performed live.  See the 'Rosette Strain Gauge' Knowledge base article for more information.


Software: Calibration


This section can be skipped if the all the needed strain gauge calibration information is already provided.  Go to the section titled “Software: Calibration Verification” to validate the supplied information is correct.


Otherwise, proceed with this section to perform a strain gauge calibration directly in Simcenter Testlab.


The sensitivity value of the gauge can be calculated in the Simcenter Testlab software via the “Calibration” worksheet.


calibration.pngPicture 6: Calibration Worksheet

Click on the “Calibration” worksheet.  Once the worksheet is opened, click in the upper right corner, and select “Bridge Settings” (default is AC Calibration).


bridge_calibration.pngPicture 7: Select "Bridge Settings" in the upper right hand corner of the Calibration worksheet

After selecting the channels to be calibrated, do the following:

  • Press the “Perform Bridge Nulling” button
  • Select “Perform Calibration” button
  • Press “Accept” when calibration finishes.


The system calibrates the gauge with two data points: a zero and at a shunt value.  The “Perform Bridge Nulling” zeros the gauge. 


calibration_error.pngPicture 8: If the gauge is improperly wired or not connected, an error occurs during calibration.

If there are problems with the gauge (for example, excessive drift due to temperature, or an improper wiring installation) usually the nulling or calibration will fail. A big red message “Error during Calibration” will appear at the bottom of the screen.


The cause of failure can be in the ShuntCalibrationStatus field. For example, if the gauge is installed improperly and is electronically drifting, the message “Unstable Offset” may be displayed.


unstable_offset.pngPicture 9: The type of error encountered during calibration is indicated in the ShuntCalibrationStatus field.

After correcting the problem with the gauge or gauge setup, the calibration should proceed without error. In the lower right corner of the Calibration worksheet, the "Advanced..." button has the criteria used to determine if the gauge has a stable signal.  The default settings check if the signal has low variation for at least 3 seconds to determine if the gauge is working properly and in a stable manner.


calibration_successful.pngPicture 10: The status bar at the bottom of the screen turns green when the calibration is successful.

One should get a big green message at the bottom of the screen saying “Done – Press ‘Accept’ to save the results.  After press the “Accept” button in the lower right corner, one can proceed to the “Measure” worksheet.


Software: Calibration Verification


To check that the strain gauges are working properly at any time, a “Shunt Check” can be performed.  In a Shunt Check, a known resistance is applied across the gauge and compared to the expected value. 


Simcenter SCADAS VB8 cards contain internal shunt resistors that can be applied to the gauges to perform a shunt check.  The default shunt resistor is a 100 kOhm shunt.


To apply the shunt resistor, go to the Measure worksheet:

  • Press “F3 Ranges” tab
  • Press the “F12 Shunt” tab
  • Press “Start”. Everything should come back Green.
  • Press “Stop” when finished.

shunt.pngPicture 11: Success shunt check will have a green status on all channels

If one of the gauges is not working properly, or the structure undergoing test was damaged significantly, the shunt check on that channel may fail.


bad_shunt.pngPicture 12: Channel value will be red if there is a problem during shunt

The channel will be colored red indicating a problem with the gauge setup, the gauge itself, or excessive damage to the part undergoing test.




To Zero the gauges before measuring, go to the Measure worksheet:

  • Press “F3 Ranges” tab
  • Press the “F11 Zero” tab
  • Press “Start Zero”. Everything should come back Green.
  • Press “Stop Zero” and “Set Offsets” when finished.



zero.pngPicture 13: Zeroing menu

It is possible to set which channels are zeroed, and which channels are NOT to be zeroed.  Use the “Offset Zeroing” field in “Channel Setup” worksheet and select Always, Once or Never as desired.




Go to the “Measure” worksheet (or press F8 if already in the worksheet) to acquire strain gauge data by pressing the Arm button and then the Start button (with Arrow symbol). 


measure.pngPicture 14: Measurement in progress

A useful feature is the “Shunt Measure Sequence”. This will automatically acquire separate 3 second measurements of zero values and shunt value before and after each measurement.


Under the “More…” button on the middle right side of the “Measure” worksheet, turn on the “Automatically Accept Measurement” and “Shunt measure sequence”. Then press the “Close” button.


shunt_sequence.pngPicture 15: Options under "More..." button for setting up Shunt measurement sequence

Now when measuring, a blue status “Zeroing” and “Shunting” will appear immediately before and after each measurement. Each time this occurs, a separate three second recording is made.


shunt_measure.pngPicture 16: Shunt measurement sequence automatically takes zero and shunt measurements (default 3 seconds each) before and after acquisition. Status is indicated by blue message.

These separate recordings can be referenced to discover when and if a part yielded in the middle of a measurement campaign.   This can be done by comparing before and after shunt and zero values.


shunt_measurements.pngPicture 17: Time histories of before and after measurements are stored automatically and separately

Hope these instructions are helpful.  


Questions? Email or download the Simcenter SCADAS brochure.


More Fatigue and Durability links: 

More Simcenter SCADAS Acquisition Tips:


Hello JohnHiatt

could you tell me why I have done Zero the gauges before measuring, but value of strain is not zero (~100 uE) ? please picture!hoi_destop.PNG


Here are some thoughts:


1.  Check your sensitivity.  For example, if you have a 3 wire quarter bridge with a 5V excitation, it should be about 0.0005 mv/V/muE.  If your sensitivity value is higher, like 0.5, it could make the signal appear to be large (100 muE to -50 muE) like you are showing.


2.  Check your wiring.  It looks like you have a 50 Hz electrical interference (5 cycles over 0.1 seconds).  Perhaps the gauge is wired wrong, or near an electrical line.


If you could share more information, that might help diagnose the issue.


Hello JohnHiatt

can you explaine thermal output effect and Self temprature consanpation (S-T-C) mismatchin strain gage with a one example?


Good Night friends.


Really interesting and amazing knows about all features that the Test.Lab offers.


I'd like to know about analyze data obtained by other device, e.g., work offline in Test.Lab with my data acquired from my strain gauges.


Please help with my doubt.


Siemens Phenom Siemens Phenom
Siemens Phenom

Hi Alvaro,


What file format are data acquire by other device? Testlab can import National Instrument diadem, Somat SIE, nCode, Nastran...etc  Once you import the file to Test.Lab then you can select Signature Throughput Processing to post process your data.  Can you provide more specific example?  Maybe screen shots?