can strain gauges be calibrated in labview automatically?

[aa2105]

Hi

For an experiment I have 2 full wheatstone bridges from which I need to get data on the displacment. Of course, firstly I need to determine the calibration factor to convert a voltage to a strain. This can be done experimentally but I was wondering if LabView can do it?

Is there a built-in (or available) VI to collect data from a wheatstone formation of strain gauges? Thank you

Adnan

[MattBradley]

Do a search on wheatstone (at the NI site).  Lots of articles etc. come up.  Look through those first and see if one helps.

[BruceAmmons]

Adrian,

LabVIEW can read strain gages fairly easily.  There are a variety of signal conditioning options for reading a strain gage.  Look for strain gage modules on the NI web site and you will find a few options.

I don't know of a way to automatically calibrate a strain gage.  You need to provide a minimum of two points of data experimentally to do the calibration.  The only exception would be if you purchased a pre-calibrated device that uses strain gages, such as a load cell.  In this case, they would provide calibration data that you could use.

Some signal conditioning modules do have a shunt calibration available.  I don't think this would help you, though, because you wouldn't know what the shunt value was equal to.

Bruce

[Coq_Rouge]

Strain gauges/ weight cells are very often specified to be linear but with some offset error. This is why your electronic bathroom weight has to go through the calibration procedure before you can use it. If you step on your electronic bathroom weight to early, it will fail the calibration procedure and lock it selves.  If you are going to make an automatic calibration procedure you have to do two things

1) measure over some time to get a good indication of the error

2) During this time check for drift, and stable readings. For this you may use linear interpolation, and standard deviation measurement 

[hecmar.arreola]

Well, "calibration" of the strain gage will have to be done manually by the user entering in the GF (gage factor) for each strain gage.  You might be able to write a program that uses a known strain gage and calibrates an unknown strain gage...however, this doesn't seem very useful because once a strain gage is bonded it isn't going anywhere.  There is also the issue of making sure the two strain gages see the exact same strain.  Many factors can affect this even if your configuration is semetrical.

Some NI strage gage bridge completion hardware has offset and compensating functions that work pretty well.  I can't remember the details because it has been awhile since i've used strain gages.