1
INTRODUCTION
PRS Series
Chapter 1
INTRODUCTION
The PRS Series (Figure 1.1) is a broad line of high
precision manual and programmable decade substi-
tuters. They provide direct resistance substitution as
well as RTD (Resistance Temperature Detector)
simulation, in a wide selection of ranges, tolerances
and ratings.
The PRS substituter is a precision resistance source
with excellent characteristics of stability, temperature
coefficient, and power coefficient. High dynamic
ranges are available, starting as low as 1 mΩ, and
extending to as many as 10 decades. These features
combined with a low virtually constant “zero resis-
tance” make for very versatile instruments.
The PRS Series features two optional special set-
tings. An “open circuit” and a “short circuit”. These
modes are useful for obtaining reproducible transi-
tions between settings, i.e. break-before-make or to
short between settings. The “short circuit” setting
also provides a reduced zero resistance.
Operation is both local using convenient direct-read-
ingfront panel thumbwheel switches,and remote with
optional parallel BCD, RS-232, or IEEE-488 inter-
faces. Both can provide an optional extra “10” posi-
tion for each decade.
The PRS Series employs very low resistance, low
thermal emf relays with gold-clad silver-alloy con-
tacts. A special design keeps contact resistance to a
minimum. The gold plating keeps the silver contacts
from becoming tarnished when unused, or when only
low currents are passed through them. This is most
often the case when only minute test currents are
drawnbydigital multimetersandothertestinstruments.
Contact resistance remains low and repeatable.
High-quality gold-plated tellurium-copper five-way
binding posts serve to minimize the thermal emf ef-
fects, which would produce errors in dc resistance
measurements. All other conductors within the in-
strument, as well as the solder employed contain no
metals or junctions that could contribute to thermal
emf problems.
With a resolution as low as 1 mΩand a maximum
available resistance of over 100 MΩ, the PRS-202
Series may be used for exacting precision measure-
ment applications requiring high accuracy, good sta-
bility, and low zero resistance. They are suited for
automatic and manual calibration and testing, simu-
lationof RTD’S, programmable loads,and many other
laboratory and industrial applications.
The PRS Series may be rack mounted to serve as
components in measurement and control systems.
Figure 1.1: High Precision Manual or
ProgrammableDecadeResistance Substituter
