strange readings at the test panels of ni6254

[I_Pant]

Hello everyone
I face this problem: I got some unexpected readings from my ni6254 multifunction DAQ and run the test panels from MAX. With nothing connected on the card (no external input signal) i am getting a measurement of 10.6 volts despite the fact that the max amplitude level is 10 volts. Again without input signal i reduce the max amplitude level to 1 an i get a 1.6 volts reading!.

I tried the self calibrate and the reset device option from MAX but nothing happens..
Any ideas ?
thank you very much in advance...
Yiannis

[Elizabeth W]

Hello Yiannis,

When you have nothing connected to the input, there is no way to say what the "right" value is that you should be reading.  The reason you are seeing out-of-range values is because the instrumentation amplifer at the input is railing. 

It is common to see the values of unconnected inputs float between random values, and at times rail at the maximum output voltage of the instrumentation amplifier for a given input voltage range. This random voltage is due to the inputs floating in a high impedance state. Any bias current or other current that is moving through the floating input will appear as a high potential on those channels.

If you are concerned about this causing unwanted noise in your system, you should ground all unused channels on your DAQ device.  Let me know if you have any questions about this!

[I_Pant]

Hello Elizabeth and thank you for your answer...

After some experiments I came to this conclusion myself and now I read it in your message. I will ground all other channels and I guess it will be ok.

Thanx again

Yiannis

[chakko]

Hello Yiannis,

Have you solved this problem? I am currently having the same problem with my PCI 6221 and can not solve it. I always get -10.6V or +10.6 as analog input voltage whatever the input is. I need your feedback on this. Could you please tell me what you have done to solve the problem?

Thanks.

[chakko]

Hello Yiannis,

Have you solved this problem? I am currently having the same problem with my PCI 6221 and can not solve it. I always get -10.6V or +10.6 as analog input voltage whatever the input is. I need your feedback on this. Could you please tell me what you have done to solve the problem?

Thanks.

[Henrik_Volkers]

This thread is about 3 years old and the poster last visited the forum 2008 😉

However. providing a path for the bias currents will solve your problem. Take a look at the manual to see how to do it, usually a resistor to ground solve the problem.

[chakko]

Thank you Henrik,

I think you say that I should connect a resistor (1K?) between AI0 and AI GND if I try to measure the analog input #0, right?

[Henrik_Volkers]

more in the 10k to 1M region, depending on the impedances of your source and the DAQ input. (See manual)