DAQ analog measurement problem

[crossroad]

Hi guys,

I'm currently using a NI USB-6215 DAQ. Currently, when I measure voltage across a resistor and try displaying it on to the VI, I realsised that the voltage obtained always fluctuate around 20-150mv. I have verified the voltage reading with a multimeter and it doesn't fluctuate and stays constant. I require a more stable reading as I'm passing the voltage obtained into a formula. I have calibrated my DAQ with the proper measurements. I was wondering if the number of samples or the sampling rate will affect this. I've tried playing around with this but it still doesn't solve my problem. The most impt thing is for me to capture the readings similar to a multimeter that doesn't give me the fluctuations.

Really appreciate your advice and thanks in advance

Andy

[KateB]

Try suggestions in https://www.ni.com/en/shop/data-acquisition/measurement-fundamentals/field-wiring-and-noise-consider...

[crossroad]

Hi Kate,

Thanks for you reply

I looked through the methods provided on proper grounding. I ammeasuring the voltage across a resistance temperature sensor and have properly grounded the circuit.

The similar fluctuation occurs even if i measure the voltage directly from a DC power supply. The readings in which i obtained fluctates between 20-150mv.For this, my VI is very simple, just an ouput from the DAQ channel.

As such, i was wondering if the problem could be some settings with my DAQ, is it such that the DAQ is that sensitive or could it be from the power supply.

The channel which i measure voltage(mv) from a pyranometer stays pretty constant and the readings are pretty accurate.

Andy

[KateB]

Try changing voltage range as close as possible to real signal.

It's probably impedance problem.

Try using buffer circuit, or changing resistance probably help.

Use shield cable also worths a try.

[VeeJay]

I am having a similar problem. The voltage offset in my case and not fluctuation. It is not what is intended.

http://forums.ni.com/ni/board/message?board.id=250&thread.id=56204

VJ

[JÞB]

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VeeJay wrote:

I am having a similar problem. The voltage offset in my case and not fluctuation. It is not what is intended.

http://forums.ni.com/ni/board/message?board.id=250&thread.id=56204

VJ

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Stick to one thread VJ,  Its been solved twice for you there