Technical data

40 34980A Service Guide
2 Specifications
Accuracy Accuracy is a measure of the “exactness” to which the internal
DMM’s measurement uncertainty can be determined relative to the
calibration reference used. Absolute accuracy includes the Internal DMM’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 for each specification with the given
assumptions.
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 internal DDMM is designed and tested to meet performance better
than mean ±3 sigma of the published accuracy specifications.
24-Hour Accuracy The 24- hour accuracy specification indicates the
internal DMM’s relative accuracy over its full measurement range for short
time intervals and within a stable environment. Short- term accuracy is
usually specified for a 24- hour period and for a ±1°C temperature range.
90-Day and 1-Year Accuracy These long- term accuracy specifications are
valid for a 23°C ± 5°C temperature range. These specifications include the
initial calibration errors plus the internal DMM’s long- term drift errors.
Temperature Coefficients Accuracy is usually specified for a 23°C ± 5°C
temperature range. This is a common temperature range for many
operating environments. You must add additional temperature coefficient
errors to the accuracy specification if you are operating the instrument
outside a 23°C ± 5°C temperature range (the specification is per °C).
Specification Criteria Probability of Failure
Mean ± 2 sigma 
Mean ± 3 sigma
4.5%
0.3%