Accuracy voltage measurement, NI Elvis

[Terka]

HI,

I want to measure voltage in range of few mV (by NI Elvis II), but measure by my DAQ assistant looks very inaccuracy, voltage is changing in hundred of microV. I need accuracy like default NI Elvis oscilloscope, which is changing in tens of microV. I tried ti use RMS value, but this didnt work so much. Do you have some idea how can I do it?

Thanks for Your help.

[billko · Accepted solution]

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@Terka wrote:

HI,

I want to measure voltage in range of few mV (by NI Elvis II), but measure by my DAQ assistant looks very inaccuracy, voltage is changing in hundred of microV. I need accuracy like default NI Elvis oscilloscope, which is changing in tens of microV. I tried ti use RMS value, but this didnt work so much. Do you have some idea how can I do it?

Thanks for Your help.

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I'm thinking that this is a variation on a theme that occurs with regularity with people unused to taking measurements automatically.  That is, displayed values are usually formatted or otherwise coerced for human consumption, but measurements obtained automatically are often raw.  You might have to process it with your code to get it to align with your observed results (but I don't believe RMS is the way to go - that's something entirely different than what you are attempting to do).

[jozef.liptak]

Dear Terka,

what is the voltage source that you are measuring? How is it connected to ELVIS and to what Analog input is it connected (some schematic would be nice)? There is possibility, that also wrong grounding can affect your measurement, or maybe also the voltage source is like so (if you measured it with ELVIS scope and it variate just in range of 10uV then most probably this is not the case, but still)... What is set up in the express VI DAQ assistant2 (maybe you can also post your VI here, for simplicity) ?

B/R