noise reduction

[fhkoeln]

I am reading PT-100 devices with a DAQCard 6024E, but I have a lot of noise. My current source is very stable but the voltage input reading is oscillating in the range of 100 to 250 mV. I tried already with a simple resistor and I got the same result. I use differential mode with bias resistors and the highest resolution (input limited between -0,05 and +0,05V). Testing my differential channel with a short-circuit between the inputs, I have readings of 200-250 mV. Is this offset value rigth for such DAQCard?

[Brent_R]

This offset is much higher than normal for the 6024E, even when the input range is set to +-10V. Try running the Online E Series Diagnostic Utility and see if this helps. This utility will test all of the major features of the card (AI, AO, counter, etc.) and perform a self calibration. You can also perform only the self calibration by calling the E Series Calibrate VI (LabVIEW users) or Calibrate_E_Series().

Regards,

Brent R.
Applications Engineer
National Instruments

[Filipe A.]

Hello;

One thing you can try is to short circuit both inputs of the analog channels and connect them to ground. If you still see the offset, you can try to use the external calibration Labview VIs, or NI-DAQ functions, to get rid of that offset. If that doesn't work, the best way to go about that is to send the DAQCard back to NI to perform an internal calibration.

If you don't see the offset when you connect the Analog Inputs to GND, you have a noise problem. I'm attaching an App Note talking about noise and ways to get around it. Furthermore, you can try to include a RC low pass filter at the input channels. That might help to attenuate the noise level.

Hope this helps.
Filipe A.
Applications Engineer
National Instruments