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Strain gage calibration--large percent error

Hi there,

 

I am having issues calibrating my strain gages using the LabVEW software, NI 9219, and CompactDAQ. When I attempt to calibrate my gages under the "device" tab within the DAQ Assist in LabVIEW, I receive a very large percent error value (around 30000%) which does not change or reduce regardless of the amount of calibrations I complete (by pressing the "calibrate button"). 

 

These strain gages are already installed beneath concrete, so should it be expected that the percent error would be high considering the gages are likely not experiencing exactly zero strain? How significant is this percent error value? Does it indicate inaccuracy within results?

 

Additionally, all the strain gages installed produce the exact same strain values after calibration--from past experience this seems incorrect, as typically the values slightly fluctuate, rather than all being the exact same number.

 

Finally, do the strain gages have to be calibrated each time a measurement is taken? I am looking to record readings once every day, and do not have enough ports to 'assign' each strain gage its own, so should a calibration be completed each day prior to taking strain measurements? 

 

Any insight is greatly appreciated!

 

 

 

 

 

Any insight to this is greatly appreciated!

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Kara,

I would start with the basics, as wiring and configuration are the most common stumbling points with strain gages. Additionally, the NI 9219 is a 'universal' module - so how you configured it, then wired it matters.

 

Setup the 'Task' in MAX - once you do-  it has a feature to show you the proper wiring, as you configured the task.

Also you can 'Test' the task - run the configuration in MAX - before you wire any labVIEW code - if it works there - then there is a super-cool way to have the Task generate your LabVIEW code!.

 

 

IDAQMx connection diagram.png

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Did you ever find a solution? I am having the same issue, and I can’t seem to trace the answer down.

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