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Keysight Technologies
Evaluation of the Performance of a
State of the Art Digital Multimeter
White Paper
Author
Bill Bruce, Hewlett Packard Company
Abstract
The introduction of a state of the art digital multimeter presents a real challenge
to the standards lab to provide external verification of its performance. The
advent of internal standards and automatic internal calibration of all the DMM's
functions from those standards pits the calibration expert, his methods and
equipment against an effective machine capable of extreme levels of accuracy.
Conventional metrology methods if used very carefully are capable of verifying
the DMM's performance but there is very little room for error. The mindset of
the metrologist must change because sources of error which may have been
negligible in the past are now significant.
The main purpose of this paper is to describe some methods which have been
found adequate to verify the performance of a very accurate automatically
calibrated DMM, the HP 3458A. The verification processes have been automated
as much as is practical. With well characterized processes in place it is possible
to develop history on the DMM's performance. Data have been obtained on a
number of HP 3458A's which indicate that the autocalibration processes work
extremely well and that the instrument definitely has the capability to perform
standards lab measurements at very high levels of accuracy. Also included is a
description of use of a 10 volt Josephson junction array to measure linearity of
the A/D converter of the 3458A, and some results of these measurements.
Verification of A/D converter linearity is imperative, since the A/D in the 3458A
is used to provide all the ratios needed for the internal autocalibration processes.
Introduction
The HP 3458A DMM represents