voltmeter vi

[labview1958]

I have made a voltmeter.vi in LV 6.0. I am using it to measure a 5V dc signal. I am using a NI-6025E DAQ card. However my dc signal varies between 4 and 6 volts. My analog voltmeter reads 5V. However the readings on the digital scale on my front panel changes wildly between 4 and 6 volts. How do I get the digital scale to read like my analog voltmeter? I suppose I must take 100 readings and divide by 100. How do I do that? The vi is attached.

[Dennis_Knutson]

All that you have to do is wire the waveform output from the acquisition into the Mean function (Analyze>Mathematics>Statistics palette). You should already know that you're taking 1000 samples and how to change that to a lower or bigger number.

[Dynamik]

Hi labview1958,

      You're probably way past this now. but if not...

It might be good to understand the difference between the DMM and the values seen on your VI's FP.  I'd double-check that wiring and AI signal-reference settings (differential, RSE, NRSE) agree, and certainly look at the signal with a real (not virtual) oscilloscope - if one's available.

       I take it you were reading single voltage values(?) If so, look to the LabVIEW Examples for "multi-point" (AKA "waveform") acquisitions.  Dennis Knutson's directions will get you home.

Cheers.

[LV_Pro]

As Dynamik mentions, if you can put an oscilloscope on the signal, or even look at the waveform in Meas & Automation (MAX) it would be a good idea. It sounds like you have a lot of noise or ripple on your signal. 2 V p-p is a fairly large amount. Most DMM's in DC mode, automatically average the readings (which can cause other problems when it would be good to know that the signal/voltage is varying relatively rapidly) so that what you are reading with this kind of "signal" is the mean of the ripple + the DC component. Performing the avaraging (connecting to the MEAN function vi) will help, but I would still want to know what I am actually reading, which is why I too suggest the scope/MAX view.

P.M.