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6212 USB voltage not reading correctly

A little overview, we are trying to measure torque on the output shaft of a motor using a USB6212 DAQ.

 

To do this, we are using the voltage feedback between channels ai1 and aiGND. Basically the readings I get when I measure with a multimeter do not match the output I am getting in Max.

 

Am i measuring the wrong terminals? Doesn't RSE on ai1 use aiGND as it's ground?

 

Additional Info:

  1. If I power up the servo board, motor, etc. I can turn the input shaft on the motor. I can see in MAX the voltage changing and going up and down like it should on ai1.
  2. If I hook a meter up to ai1 and a1GND those value match what I see in Max.
  3. I open the exe to run the motor, motor operates just fine.
  4. While running in the program, I get almost no output from ai1 with occasional spikes to 3-5 volts. If try to turn the input shaft, I get no correlation in voltage. However, if I put my meter on ai1 and aiGND I get what I would expect (even though I can’t turn the input shaft because it is being told not to move, I can see my voltage readings on the meter fluctuate correctly with torque input.)
  5. The exe program readings match what I am reading in max when it is not working. However what confuses me is my meter is reading correctly between those two terminal points. Which tells me it must be something with the 6212 board.
  6. If I turn off the 12-40V power supply to the motor and servo board. My readings then match meter.

 I also have a spare 6212 board which displayed the same problem.

 

I don’t believe the executable uses any custom scaling because it matches exactly what I see in max when I plot ai1 in RSE mode.  

 

Thanks,

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Hi sozdemir,

 

I have a few questions for you regarding your application:

 

What do you observe if you try hooking up your voltage input as differential?  Remember when you do this to change the input configuration to differential in MAX as well as changing the pins on your device.

 

Is your exe just running the motor, or are you using DAQmx tasks to acquire voltage with your USB 6212 as well?

 

Are you measuring any other analog inputs on your device, or just the torque?

 

Have a great weekend!

Andrew T.
National Instruments
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Thank you for the response. We believe we had the wrong wiring hook up and it's similar to what you are saying in your response. We had something hooked up to ground that should not have been.

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