Problem with reading an analog input on PCI 6220

[geert256]

Hello,

I have a problem with reading two analog channels at the same time. I use Visual C++ (NIDAQmx driver) as software. I can read the two analog channels at the same time, but I get some noise on my readings. The noise that I read on the first signal, comes of the second signal. One signal is a pressure measurement, it is a slow varying signal the other signal is a time measurement, but this one is not a slow varying signal. The voltage of the pressure sensor lies between 0 and 10 V, but the one of the time measurement lies between -10 and 10 V. I use the following command (      DAQmxCreateAIVoltageChan(taskHandle2,"Dev1/ai0:2","",DAQmx_Val_NRSE,-10.0,10.0,DAQmx_Val_Volts,""); ) for the configuration and I read the channel with (       DAQmxReadAnalogF64(taskHandle2,20,10.0,DAQmx_Val_GroupByChannel,pressure,60,&read ,NULL); ) How can I read the two channels on the same time without the disturbance of the second channel?

 Thank you,

Geert

[geert256]

In attachment I have added the results (some plots) of the readings. You can see clearly that the time-measurement disturbs the pressure reading…

[eweltmer]

It may have something to do with the multiplexing the 6220 card does when using more than one channel.

I had the same problem. I reduced the voltage to three AI input through some 50 K ohm potentiometers. The 50K was too high & I saw some of the signal on the other channels presumable through the card AI multiplexing.

Reducing the potentiometer value to 10K solved my problem.

Earl