The IET (esi) RS925D is a four-terminal continuously variable decade resistor for
the most exacting calibration and test applications.
For a wider range or
more cost effective decade resistor with similar performance consider our
HARS-LX Series
The RS925D is the world's highest accuracy continuously variable
resistance decade for the most exacting calibration and test applications.
The RS925D resistance decade box is a precision resistance source with excellent characteristics of accuracy, stability, temperature coefficient, and power coefficient. All these features serve to make it a laboratory resistance standard, exceeded in performance only
by stand-alone standard resistors.
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 stability
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 resistance substituter has a fixed minimum resistance of 10 mΩ. This is implemented by mechanically limiting the 10 mΩ decade from going below the “1” position. In
this manner, no zero resistance subtractions have to be made, and the accuracy given is for the absolute reading.
The RS925D Resistance Decade 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 resistance to under 1 mΩ per decade, and more importantly, 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 measurements. All other conductors within the instrument, as well as the solder employed, contain no metals or junctions that contribute to thermal emf problems.
The RS925D Resistance Decade is designed to allow very convenient
maintenance of calibration over time. Most decades can be calibrated without
changing components or soldering resistors. The decades for the 100 Ω through
100 kΩ steps are calibrated with convenient trimmers. Trimming of the lower
decades is also possible.
With a resolution as low as 1 mΩ and a maximum
available resistance of over 12.2 MΩ, the RS925D Resistance Decade may be employed for
exacting precision measurement 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
