How Do I Calculate the Resistance Accuracy of NI DMM for Different Resolution Modes?

Updated Aug 16, 2018

Reported In

Hardware

  • PXIe-4081

Issue Details

The specification sheet talks about the NI DMM resistance mode accuracy values for 2 wire and 4 wire resistance measurements when the DMM is set to default resolution modes or when the aperture is set to ≥100 ms (7½-Digit). How can I get the the resistance mode accuracy for 2 wire and 4 wire resistance measurements at 5.5 and 6.5 digits resolution modes?

Solution

To calculate the reduced accuracy by using modes other than 7 ½ refer to the Calculating Accuracy for DMMs tutorial. Make sure you use the graphs in the respective specification document of the NI DMM instead of the noise graphs in this accuracy tutorial.

Additional Information

The accuracy and resolution are related, but two 6.5 digit DMMs could have very different accuracy specifications. In addition, the 4081 will perform four averages with the 7 ½ digit mode. Which has a 100 ms aperture time by default. This averaging is done in hardware and returned to the user as a single measurement.

There will be very slight decrease in accuracy. We would expect the accuracy to take hit of about 0.0003 Ohms when moving from 7.5 to 6.5 digits. The accuracy can be further increased if you do a custom measurement configuration.

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