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6-1
Chapter 6
Operation
6.1 General
For best results, be familiar with the operation of the heat source and the read-
out instrument. Be sure to follow the manufacturer’s instructions for the read-out
instrument and the heat source.
6.2 Comparison Calibration of Other Instruments
The uniformity and stability of the heat source and the degree of accuracy
required determine the number of temperature measurements necessary.
However, to follow “good” practice procedures, always measure the triple point of
water (R
tp
) after each temperature measurement. The following equation
provides the most accurate measurement of the ratio:
tp
t
t
R
R
W =
All PRTs experience errors caused by self-heating of the element.
Self-heating is a combination of two factors, heat dissipation and heat sink.
Self-heating error can be reduced to have a negligible effect if the PRT is used
with the same excitation current and medium in which it was calibrated.
6.3 Immersion Requirements
Stem effect can cause measurement errors for any thermometer not immersed in
the fluid at least 152 mm (6 inches). This error is due to heat lost or gained by the
sensing element through the thermometer stem. In addition, heat losses occur
due to radiation losses from the sensing element to the housing.
1.888.610.7664 sales@GlobalTestSupply.com
Fluke-Direct.com
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