We just purchased an NI-9219 universal bridge module to go with a cDAQ-9172 chassis we had 'lying around'. Most of the testing we do is load vs deflection in some form or another and a lot of the time this is done using a standard load cell and string potentiometer, such as the SP series string pots from Celesco, which we calibrate in-house in our metrology lab.
That being said, what I end up with is calibration documentation from metrology, and in the case of our string pots, this is usually in the form of a slope and intercept. Here's where I'm hung up... Our metrology lab calibrates everything using 10v of excitation so the slope is the full scale of the device across a 10v range. Normally this is not a problem because the majority of our DAQ hardware is SCXI and 1520 bridge modules which have 10v of internal excitation so the slope, when entered as a custom scale, works. I can also set my Signal Input Range to the full Min/Max of the transducer (0-25" in the case of this perticular string pot). Problem I'm having is these 9219 modules only output 2.5v of excitation so the slope no longer scales correctly.
Add to that, DAQmx forces me to use this "Use Excitation For Scaling" option which I've never had to use before.
So to give a bit more background, we use Signal Express exclusively. All the devices that require bridge conditioning I run through the 1520 bridge module in Full Bridge Differential mode. I create custom Linear scales for all the transducers since they usually come back from Metrology with slightly different sensitivities than before. So long as my Signal Input Range is within the limits of the custom scale the output signal is spot-on within the full range of the sensor.
So how do I scale a sensor that has a slope curve based on 10v excitation when the signal conditioning only supplies 2.5v? Currently if I plug this slope in as a linear custom scale and set my input range to 0/min 25/max I get an errror:
Error -200077 occurred at DAQ Assistant
Requested value is not a supported value for this property. The property value may be invalid because it conflicts with another property.
Property: AI.Max Requested Value: 25.000000 Value Must Be Greater Than: -166.200000e-3 Value Must Be Less Than: 166.200000e-3
Attached is an example of our cal sheet from metrology.