HP 34970A manual 417, Criteria

Chapter 9 Specifications

Interpreting Internal DMM Specifications

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Accuracy is a measure of the “exactness” to which the internal Vhh’s

measurement uncertainty can be determined to the calibration reference used. Absolute accuracy includes the internal Vhh’s relative accuracy specification plus the known error of the calibration reference relative to national standards (such as the U.S. National Institute of Standards and Technology). To be meaningful, the accuracy specifications must be accompanied with the conditions under which they are valid. These conditions should include temperature, humidity, and time.

There is no standard convention among instrument manufacturers for the confidence limits at which specifications are set. The table below

shows the probability of non-conformance forwith the given assumptions.

Specification	Probability
Criteria	of Failure
Mean ± 2 sigma	4.5%
Mean ± 3 sigma	0.3%

Variations in performance from reading to reading, and instrument to instrument, decrease for increasing number of sigma for a given specification. This means that you can achieve greater actual measurement precision for a specific accuracy specification number. The HP 34970A is designed and tested to meet performance better than mean ±3 sigma of the published accuracy specifications.

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