IVI DMM Measurement Resolution Digits Out of Range

Updated Mar 10, 2018

Reported In

Driver

  • IVI Compliance Package
  • NI-DMM

Issue Details

I am trying to do a measurement with my National Instruments Digital Multimeter, but I can't figure out how to set the Digits of Resolution. For example, IN LabVIEW, the IviDmm Configure Measurement VI has an absolute resolution input, but can I somehow use Digits instead?
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Solution

The IviDmm Class Driver only accepts resolution in absolute units. This means you need to specify the resolution values in terms of the input range and type of measurement you are performing. For example, if you are using an NI DMM to take a resistance measurement with an input range of 10 MΩ and you want a resolution of 5.5 digits, you would need to use an absolute unit of 31.6227766 Ω (see example in the Additional Information section).

You have two options:

1. Converting from Resolution Digits to Absolute Units:

According to the Resolution topic from the NI Digital Multimeters Help:
 
Digits of resolution = log10(total span/absolute unit of resolution)

Where, total span is the complete input range. For example, if your input range is 10 V, it can in fact measure +/- 10 V for a total span of 20 V, but if you are performing a resistance measurement in the 10 MΩ range, you cannot perform negative measurements, so the total span in 10M.

You can integrate the calculation into the code to programmatically get the absolute resolution while specifying digits. For a calculation example, refer to the Additional Information section.


2. Using NI-DMM instead of IVI Class Drivers:

If you use NI-DIMM, you will have access to features that may not be available through IVI. For example, using the NI-DMM VIs in LabVIEW, you can configure the niDMM Config Measurement polymorphic VI to use Digits or Absolute Units very quickly by selecting the instance in its drop down menu.
 

Additional Information

As an example, if you want to measure resistance in the 10M input range with 5.5 digits of resolution, you have:
 
5.5 = log10(10M/absolute unit of resolution)

Solving for absolute unit of resolution:
 
absolute unit of resolution = total span/(10^Digits of resolution)

absolute unit of resolution = 10M/(10^5.5)

absolute unit of resolution = 31.6227766 Ω

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