I am using a PXIe-4080 to do multiple DMM reads of multiple signals and I noticed that there is a noticeable difference in execution speed when programming the DMM to use 5 1/2 digits versus 6 1/2 digits. I put a basic VI together to try to benchmark the difference. With resolution set to 6 1/2 digits, 10 reads takes about 2.9s, whereas when setting to 5 1/2 digits, 10 reads only takes 46ms:
Is the 5 1/2 bit option actually working with 5 1/2 digit accuracy, or are other settings changing under the hood?
Why is there such a big difference in execution time between 6 1/2 digit and 5 1/2 digit options? The difference seems too big to attribute to the difference in required settling time.
Thanks in advance for the help!
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Part of getting more resolution is to average the reading over a longer period of time.
Yes, higher digits of resolution are always slow as it takes lots of averaging and calibration routines to get the additional digits of resolution.
This is documented in the Help file with the measurement default settings - https://zone.ni.com/reference/en-XX/help/370384V-01/dmm/408x_dmm_defaults/
Based on the range used, the settling times also vary,
Based on this information, it justifies the durations observed by you,
6 1/2 digits, 10 reads takes about 2.9s, whereas when setting to 5 1/2 digits, 10 reads only takes 46ms
You are free to adjust these settings to speed up measurement but the specifications of the instrument are based on this combination of settings, deviating from these settings will put you at an unknown accuracy spec.
Understood. Thanks for pointing me to that table in the documentation. That clarifies all the settings that are different between these two resolution settings.