IET Labs HARS-X Series, User And Service Manual

Page: 7 / 15

1
INTRODUCTION
HARS Series
Chapter 1
INTRODUCTION
The High-Accuracy Resistance Substituter ( HARS )
series of resistance decade substituters is a family of
instruments providing a very broad choice of high-
performance resistance sources. Any number of de-
cades from one to eleven is available in a choice of
accuracies.
The HARS substituter is a precision resistance source
with excellent characteristics of stability, temperature
coefficient, power coefficient, and frequency re-
sponse.
The HARS Series employs very-low-resistance
switches with silver alloy contacts. A special design
keeps zero resistance to less than 1 m
Ω
per decade.
Self cleaning keeps the silver contacts from becom-
ing tarnished when unused, or when only low cur-
rents are passed through them. This is most often the
case when only minute test currents are drawn by
digital multimeters or other test instruments. Contact
resistance is stable and remains low and repeatable.
High-quality gold-plated tellurium-copper binding posts
serve to minimize the thermal emf effects which would
artificially reflect a change in dc resistance measure-
ments. All other conductors within the instrument, as
well as the solder employed, contain no metals or junc-
tions that could contribute to thermal emf problems.
The standard models offer a choice of one through
eleven decades. The panels are clearly labeled show-
ing the step size and maximum voltage and current
limitations for each decade.
With a resolution as low as 1 m
Ω
and a maximum
available resistance of over 111 M
Ω
, the HARS se-
ries may be used for exacting precision measurement
applications requiring high accuracy, good stability,
and low zero-resistance. They can be used as com-
ponents of dc and ac bridges, for calibration, as trans-
fer standards, and as RTD simulators.
The HARS Series may be rack-mounted to serve as
components in measurement and control systems.
Figure 1.1. HARS-X Series High Accuracy Resistance
Substituter