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Acquiring voltage using NI 9219

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I am using an LVDT sensor (DS1000SUH) connected to an AC LVDT Conditioner Module (5M30), to measure displacements. I am trying to read the output voltages using an NI 9219 inside of a cDAQ-9171. However the voltage measurements I am getting are extremely small (on the order of uV). When I use the same setup connected to an oscilloscope, I get proper voltage readings (between -3.5V and +3.5V). Does anyone know why this is? I am using SignalExpress to acquire the voltage readings. I have the positive input signal (HI) connected to pin 4 and the negative input signal (LO) connected to pin 5 as indicated in the user manual. Any help is appreciated.




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Hi Duncan,


Are you able to read the data using a test panel in MAX? As well, have you set the input range according to the signal you're expecting?



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Accepted by topic author dpawson

Hi Justin,


When I use MAX I get the same output. I have set the input range to the signal I am expecting.


I tried switching the channels I was using and I actually get a proper signal when using channels ai2 and ai3, however not for channels ai0 and ai1. So, I suspect it is a malfunction in the hardware. The strange thing is, that I used channel ai0 not long ago for pressure measurements in the full bridge setup and it worked fine. Also, although I am not receiving the signal I expect on channel ai1, I do receive a signal that corresponds to displacement of my LVDT sensor, it is just several magnitudes off and not properly calibrated. The signal I receive on channel ai0 doesn’t correspond to displacement of my LVDT sensor at all. I am going to try another NI 9219 module and see if I get similar results.




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