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JOSEPHSON-VOLTAGE STANDARD IN A WORKING CALIBRATION
LABORATORY
Karl-Peter Lallmann
Fluke Deutschland GmbH
Heinrich-Hertz-Strasse 11
34123 Kassel / Germany
Phone:++49 561 9594 651
Fax: ++49 561 9594 609
E-mail: [email protected]
Abstract
One might ask if it is really necessary to use a Josephson Voltage Standard in an accredited calibration
laboratory. Yes, there are circumstances that make the use of such a standard necessary. With the
evolvement of dc reference standards and calibrators towards very small specifications on Direct Voltage it
becomes a good tool to bring measurement uncertainties to a level with which these instruments can be
checked to be within specifications. This papers describes the use of a Josephson Voltage Standard in an
accredited calibration laboratory operated by Fluke Germany
Introduction
Josephson-Voltage Standards are widely used in National Institutes for their work in metrology and scientific research.
However, there are several companies and other institutes in the United States of America that have established such
systems, but none of them are used in a Customer Support environment or accredited laboratory. We saw the
requirement of a Josephson-Voltage Standard coming with the evolvement of calibrators and dc reference standards
designed and produced by Fluke Corporation Everett/USA. The requirement to service and calibrate these instruments
for Fluke in Europe, made it necessary to develop and find new ways for low measurement uncertainties required to
calibrate and verify the specifications of these instruments. The only way this could be accomplished was with the use
of a Josephson Voltage Standard. However, there are some aspects that need to be defined before such an
investment may be done. Cost of purchase and operating costs were the most significant, but after looking at them
very closely it became obvious that it will be paid back in the long term.
The Josephson Voltage Standard
The Josephson effect is a super conducting physical phenomenon that relates voltage to frequency through the ratio
of fundamental constants. A Josephson array, using an integrated circuit containing a number of Josephson junctions,
i
is an intrinsic, independently reproducible standard that is used to represent rather than realize the SI volt.
The output of a single Josephson junction is defined as:
h
V J = 2e