IET Labs HARS-LX, User And Service Manual, Page: 7 / 22

1
HARS-LX Series
1 Introduction
Chapter 1
INTRODUCTION
1.1 Introduction
The HARS-LX Series Laboratory Standard Decade
Resistance Substituter provides a very broad-range
high-performance resistance source.
The HARS-LX Series substituter is a precision re-
sistance source with excellent characteristics of ac-
curacy, stability, temperature coefficient, and power
coefficient. All these features serve to make it a labo -
ratory resistance standard, exceeded in performance
only by stand-alone standard resistors. The special
design of the HARS-LX requires no zero resistance
subtraction from settings.
Hermetically sealed wirewound resistors are used
for 1 Ω steps and over. These resistors are carefully
conditioned under power and temperature in order
to develop the best stability characteristics. Actual
experience has shown them to exhibit a storage sta-
bility of better than 5 ppm/year, improving as they
age. The low-resistance resistors are constructed with
resistance wire with a minimum of copper resistance
in series to limit temperature coefficient effects.
The HARS-LX Series employs completely enclosed
dust-tight very low contact resistance switches. They
feature solid silver alloy contacts and quadruple-leaf
silver alloy wipers which keep switch contact resis-
tance to under 1 m Ω per decade, and more impor-
tantly, keep switch contact resistance reproducible,
insuring repeatable instrument performance.
High-quality gold-plated tellurium-copper binding
posts 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
junctions that contribute to thermal emf problems.
The HARS-LX is designed to allow very convenient
maintenance of calibration over time. Most decades
are adjustable without changing components or sol-
dering resistors. The decades for the 100 Ω through
1 M Ω steps are adjusted with convenient trimmers.
Trimming of the lower decades is also possible.
With a resolution as low as 1 m Ω and a maximum
available resistance of over 12.2 M Ω , the HARS-LX
Series may be employed for exacting precision mea-
surement applications requiring high accuracy and
stability. They can be used as components of dc and
low frequency ac bridges, for calibration, as transfer
standards, and as RTD simulators.
Figure 1-1: HARS-LX Laboratory Standard
Decade Resistance Substituter 11 Dials with
Rack Mount
Figure 1-2: HARS-LX Laboratory Standard
Decade Resistance Substituter 2 Dials