How to calculate Repeatability of an Instrument?

A

Thread Starter

Anonymous

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
 
C

Curt Wuollet

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.
 
W
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.
 
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