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Why voltage is so noisy through DAQ device although the value from multimeter is very stable?

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As title said, this is my serious concern.

I'm using NI PCI X-Series connecting to BNC 2120, and I want to acquire stable voltage with this. The value through device is differ from that of multimeter(Keithely 2000).

Why is this happening even I'm using shielded cable? Don't tell me about environment, since multimeter is in same condition too and there's no noisy source around this.

The noise at device is about 10mV, and from multimeter, it's 1mV or less.

 

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Main reason: The low pass filter in the Keithley 🙂

How does the signal from your X-Daq look like if you sample with 1kSPS for one or more periodes of your line frequency (or 1s) and look at the mean value?

 

The Keithley is a 6.5 digit device, what does the spec of your DAQ tells about noise and  accuracy?

 

Greetings from Germany
Henrik

LV since v3.1

“ground” is a convenient fantasy

'˙˙˙˙uıɐƃɐ lɐıp puɐ °06 ǝuoɥd ɹnoʎ uɹnʇ ǝsɐǝld 'ʎɹɐuıƃɐɯı sı pǝlɐıp ǝʌɐɥ noʎ ɹǝqɯnu ǝɥʇ'


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Thx for the reply.

So if the reason is "physical' low pass filter, what should I do for the terminal block(bnc 2120)?

I mean, before signal is connected to terminal, everything is fine, and the noisy something is happening in the terminal block, right?

Then does it mean I have no solution unless I open the block?

 

I can't upload the signal right now, but one thing is clear that it can't be use since I need relatively precise result...

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The Keithley 2000 is a 6.5 digit DMM with integrating ADC ..

Your DAQ (btw. what type?) has another type of ADC, so you will need to some signal processing (filter , wether in hard or software) to get similar results. Don't expect the same accuracy!

So: the joy of engineering is to do what you need with the stuff you can get.

What do you have?

What do you need?

(You want to meaure a voltage... how fast is it changing?  What is the source? ...)

Finally: You can use the Keithley to read the voltage 😉 

Greetings from Germany
Henrik

LV since v3.1

“ground” is a convenient fantasy

'˙˙˙˙uıɐƃɐ lɐıp puɐ °06 ǝuoɥd ɹnoʎ uɹnʇ ǝsɐǝld 'ʎɹɐuıƃɐɯı sı pǝlɐıp ǝʌɐɥ noʎ ɹǝqɯnu ǝɥʇ'


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