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PRTs and Resistors

Standards and Reference Resistors

ASL provides a range of Standards Resistors for use when calibrating Platinum Resistance Thermometers. With this range is the world renowned Wilkins Standards Resistors and the ASL RR Series Reference Resistors.

RW Series - Wilkins Standards Resistors

The design of the Wilkins Standards Resistors is a result of several years of development. Based on an original design by F. J. Wilkins of the National Physical Laboratory, it has evolved over time as a result of many tests on stability and temperature coefficient using both a.c. and d.c. The design aim was to produce a four terminal Standards Resistor of the highest performance, suitable for both a.c. and d.c. work up to a frequency of 1592Hz.

The RW series are made from a specially selected alloy having a low temperature coefficient mounted in a strain free manner, on formers made from a material of low dielectric loss but of high mechanical stability. All connections are welded. Prolonged heat treatment of the elements ensures long term stability and low temperature coefficient of resistance. The elements are hermetically sealed in stainless steel containers which are first evacuated and then filled with dry oil (No.4 Kerosene). Provision is made for inserting a thermometer, but the resistors are intended to be used in a controlled temperature oil bath.

Maximum dissipation for the resistors is 1 watt, but the highest performance will be obtained with dissipation limited to 10 milliwatts, which is the ideal working condition. No damage will occur if the dissipation is increased to 1 watt, but self heating will affect the resistance value after a few minutes.

The "Wilkins" design has been adopted by National and major industrial laboratories as their primary standard since it's introduction. Long term use has shown that these resistors are stable to within 1 ppm over a period of 10 years.

Features
		High Accuracy, <20ppm
		Excellent long term stability
		Low temperature coefficient
		Rugged stainless steel construction
RW Series Brochure (PDF, approx 83KB)
For more information about this product contact ASL

RR Series Reference Resistors

ASL's RR series of 4 wire reference resistors offer high accuracy and stability at an economic cost. Designed specifically for use as a comparison standard for resistance thermometry on the ASL range of AC resistance bridges, the RR series may also be used in electrical standards laboratories.
In addition to standard fixed values, resistors can be supplied in any value between 1 and 1000 Ohms. Typical applications for the RR series are as transfer standards or reference source in temperature calibration or electrical standards laboratories.

Features
		High Accuracy, ± 0.01% or better
		Excellent long term stability
		Low temperature coefficient
		Rugged stainless steel construction
		4mm insulated terminals with optional BNC adaptors
RR Series Brochure (PDF, approx 134KB)
For more information about this product contact ASL