NI 9222 Amplification

[dariley]

I have the NI-9222 module connected to a cDAQ-9174 chasis. Connected to the module is a piezoelectric sensor, which produces a voltage signal. Oscilloscopes and multimeters read the output voltage of the sensor for our specific application to be roughly 150mV. When using the NI hardware, LabVIEW (and NI Max test panels) are reading values of roughly 5V. The sensor cannot realistically output such a high voltage, so I am led to believe that the hardware is amplifying the signal. I have looked though the settings, but have not been able to find any way to remove this amplification. How can I go about doing this?

[Dennis_Knutson]

It sounds like you have not connected the signals correctly. You only have differential connections so please provide information on your physical connections.

[dariley]

Wires have been soldered to both of the piezoelectric sensor's terminals. One is marked positive, and the other is negative. The wires are shielded, and then clamped into the NI-9222 module. I understand that I only have differential connections to work with, but I do not exactly know what that means. Could you lend me a brief explanation?

[Dennis_Knutson]

http://www.ni.com/white-paper/7113/en/

Clamped to what? What pin numbers/names?

[dariley]

Not necessarily clamped, but fastened into ai0. There are times when two sensors are used, so channels ai0 and ai1 are used, and the same amplification occurs. 

[Dennis_Knutson]

A differential measurement is two wires so do you mean ai0+ and ai0-? Do you have the bnc or or screw clamp type.

[dariley]

Yes, the two wires are connected to ai0+ and ai0-. My chassis uses the screw-to-tighten metal clamps.

[Dennis_Knutson]

I would recommend a simple test with a small battery. If that reads correctly, perhaps you have a loose wire or terminal. If it still reads incorrectly, you should contact NI about an RMA.

[BoKnows]

Is it safe to assume you're working with the +/- 5V range for your measurement?  If so, we would expect a 5V reading if the channel isn't seeing any input.  That would match the loose connection suggestion Dennis had.  

[dariley]

Jeff, I will try to answer your post, but I am not sure I follow. My module is set to a measuring range of +/- 10V. When there is no input voltage, my module does not read any voltage. Should it be outputting a signal of 10V in this case?