Problem with taking pressure transducer reading using Compact RIO and NI 9237

MajTal · ‎07-30-2014

I have a CRio 9024 controller installed on a CRio 9014 chassis. I also have a NI 9237 module to read the data from a couple of pressure transducers. At the beginning, I was trying to apply different pressures to the transducers to make sure the readings I get from the module is in a good agreement with calibration sheet. The excitation voltage is 10 volts. At low pressure values (about 30 to 40 psi) the readings increase as long as I increase the pressure but at some points (which is not fixed) the reading does not go up anymore. For example at 30 psi, the output voltage should be about 15 mv and therefore the y axis should show 0.015volts/10V=0.0015 that it is and at 40 and 75 psi the corresponding values should be 0.002 and 0.0035 but they are not.

I was struggling with this issue for a couple of days but I could not find any solution for it. The 9237 module can take up to 25 mv/V and the maximum value in my case (at 200 psi) should be about 10 mv/V with 10 v excitation voltage. I checked the voltage of the transducers using a multimeter and they agreed very well with calibration data. I have attached my program and the graphs for clarificaion. I hope someone can let me know what is wrong. The vertical axis shows the data in volts/V in these graphs. I also attached a typical calibration sheet for the transducers.