reading two analog inputs using NI USB-6212

[jannus]

Hi,

I am trying to read two devices as two analog inputs on NI USB-6212 (screw terminals pinout). I used one DAQ Assistant. When I set only 1 analog input (channel a1), for an acoustic sensor and then a current transformer, the output waveforms will vary (the output of both devices are voltage). The setting of terminal configuration is RSE (pin connection is 17-28); the mode is continuous sample; the rate is 100KS/s.

But when I connect the two analog inputs as channel a1 (17-28) and channel a2 (19-28), the shape of the two waves is almost the same. When there is an interference given on channel a1 (acoustic sensor), it will also affect the output display of channel a2.

While NRSE and Differential configuration cannot be used because it cannot detect the sensor or current transformer used.

I hope my NI DAQ can read both analog inputs and display different results according to the original shape of the wave.

Can anyone help me to solve the problem?

[Bob_Schor]

I suspect that your problem is an EE problem, probably associated with Grounding and Shielding.  I'm unfamiliar with Current Transformer, but think of them as designed to measure current, or maybe a voltage drop across a resistor.  In any case, when measuring voltages, it is almost always best to record differentially, connect Analog Ground (pin 28) to "Instrument ground" on the equipment being measured, and to have the input connections to your USB-6212 shielded, with the shield only connected at the Instrument Ground side (to Instrument Ground, of course).  But consult with a good Electrical Engineer (I'm not an Engineer of any stripe).

Bob Schor