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2 Introduction
2.1 General
The Hart Platinum Resistance Thermometers (PRT) models 5626 and 5628,
are designed to be the best secondary standard interpolating instrument
converting temperature to resistance. The PRTs are used with a readout de
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vice to detect temperature changes or actual temperature. The PRTs cover
the International Temperature Scale of 1990 (ITS-90) range from –200°C to
661°C. Two standard resistance values are available. The 5626 is 100Ω and
the 5628 is 25.5Ω. Standard lengths are 12, 15, and 20 inches. Custom
lengths are available on request.
The two PRTs are hand constructed at Hart Scientific by experts with years
of PRT manufacturing experience. Each PRT is carefully annealed at the ap
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propriate temperatures and precisely tested for stability. The sensing ele
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ment is fabricated using high purity platinum wire wound in a strain free
design on a specially designed support. The 1/4 inch O.D. Inconel 600
sheaths are sealed with a specially mixed gas and fit with a terminal box
handle and strain relieved connection to the four-wire cable. Gold plated
spade lugs terminate the wires.
2.2 Application
Hart 5626 and 5628 thermometers are classified as secondary standards. A
secondary standard is defined in terms of transfer of the ITS-90 from a
standards laboratory to a customer’s laboratory. Secondary standards are
2
Introduction
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Figure 1 Hart Model 5626 and 5628 Platinum Resistance Thermometers