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Low Voltage and Current Measurements Are Noisy when Using NI ELVIS

Primary Software: Driver Software>>NI ELVIS Driver VIs
Primary Software Version: 1.0
Primary Software Fixed Version: N/A
Secondary Software: N/A

Problem: I am using the DMM within NI ELVIS to take voltage and current measurements. I have noticed that when taking very small voltage and current measurements, the readings fluctuate and seem noisy. Is this noise inherent to NI ELVIS or is there something I can change in software to decrease the fluctuations in readings?

Solution: When using the DMM to take voltage and current measurements, the DMM is only acquiring 100 points to average by default. The number of samples needs to be increased to account for noise in the measurement. The current measurement is greatly affected by the low number of samples being taken and the AC voltage is affected when performing measurements on a signal with a frequency below 100 Hz.

Since NI ELVIS gives the user access to the source code, you can modify the DMM source code to increase the sample size when performing voltage and current measurements. The steps for increasing the sample size are listed below.

  1. Open the ELVIS - Digital Multimeter VI located in the ...\Program Files\National Instruments\NI ELVIS 1.0\Source Code\Digital Multimeter folder
  2. Go to the block diagram and make sure you are in the "Meas Volts/Amps" case of the large case structure
  3. Double-click on the NI ELVIS DMM - Read VI to open its front panel
  4. Go to the block diagram of the NI ELVIS DMM - Read VI and locate the ELVIS DMM - Acquire Waveforms VI within the inner-most case structure and located in the "Volts DC".."Current AC" case.
  5. Create a constant for the number of scans to acquire input and increase this to above 100 to increase the sample size.


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Report Date: 06/24/2003
Last Updated: 09/22/2004
Document ID: 2YN9ST0T

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