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We purchased an instrument with specs of 0.3% repeatability and 1% accuracy. What is the correct way to determine/establish the repeatability of this instrument?

Thanks in advance

Present it with the same input multiple times and observe how consistent the reading is.

Regards

cww

Give the same input at least 5 times and record the output. The deviation between any two outputs should not be more than 0.3% of the range if your repeatability has been defined as 0.3% of the range.

Take 5 consecutive measurements with same input. The Repeatability percentage will be (max.reading-min.reading/min.reading)*100. This should be within specified limits.

The below statements are not quite correct as it is not just any five consecutive measurements. Please refer to the ANSI/ISA Standard 51.1, "Process Instrumentation Terminology," pg. 49, which defines repeatability and Figure 23 on pg. 50, which provides a graphical representation of repeatability based on instrument calibration curves.

William (Bill) L. Mostia, Jr. PE

My reply was based on NIST. I have no access to the ISA standard. As the measurements will normally be on the linear portion of scale/range, I guess the Repeatability figures will be about same in that measurement range.