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2 Introduction
2.1 General
The Hart Platinum Resistance Thermometers (PRT) models 5608 and 5609,
are designed to be a secondary standard interpolating instrument convert-
ing temperature to resistance. The PRTs are used with a readout device to
detect temperature changes or actual temperature.
2.2 Application
Hart 5608 and 5609 thermometers are classified as secondary standards. A
secondary standard is used to transfer the ITS-90 from a standards labora-
tory to a customer’s laboratory. Secondary standards are calibrated using a
primary standard that has been calibrated in a primary calibration labora-
tory through a process called realizing the ITS-90.
2.3 Calibration
In order for any instrument to be used as a standard it must be calibrated.
These instruments are sold uncalibrated unless calibration is requested at
time of purchase. They are satisfactory as secondary standards and may be
calibrated by comparison to primary standards.
2.4 Recalibration
The recalibration of the 5608/5609 Secondary PRT should be scheduled ac-
cordingtotheuser'scompanyQualityAssurancerequirements.Normally,a
PRT is recalibrated annually. Unless the PRT is used only over a limited
range, calibration over the full range of the PRT is recommended. For infor-
mation on calibration services for the 5608/5609, contact an Authorized
Service Center for an RMA number and current pricing (see Section 1,
Before You Start)
Depending on the user’s Quality Assurance requirements, the PRT drift
should be checked periodically at the Triple Point of Water (TPW). Section 8,
Troubleshooting, provides information on drift with respect to mechanical
shock and oxidation. If the R
tp
cannot be restored after annealing to within
calibration tolerances, a full recalibration should be scheduled.
2
Introduction
5
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