7.4.4 Calibrate Probe
The probe calibration (CAL PROBE) sub-menu contains functions for calibrat
-
ing probes with the triple point of water, calibrating ITS-90 coefficients, mea
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suring self-heating error, and testing the temperature conversion. These are
CAL TPW, CAL ITS-90, 1.414 x CURRENT, 0.707 x CURRENT, and CONV
TEST.
7.4.4.1 Calibrate TPW
The CAL TPW calibration function allows you to easily calibrate a probe at the
triple point of water. It adjusts the ITS-90 R(TPW) value. The calibration will
be performed on the probe being measured. The input channel must be set on
one channel (not alternating or scanning). The probe must be using the ITS-90
conversion.
Obtaining a precise measurement is very important when calibrating the probe.
It is recommended that you use filtering with a time constant of 20 to 60 sec
-
onds. Be sure the filter threshold is high enough.
To begin the calibration, place the probe in the triple point of water cell and al-
low the temperature to equilibrate. Press the CAL TPW soft-key. A window ap-
pears asking for the immersion depth in millimeters, of the probe in the triple
point of water cell. If you enter the value for the depth, the thermometer will
compensate for the error in temperature caused by the hydrostatic pressure of
the water. This error amounts to approximately 0.0002°C at a depth of 250 mm.
If you do not care to correct for this small error, enter 0.
The Super-Thermometer will begin to measure the resistance of the probe. You
may graph the measurements by pressing the GRAPH soft-key. When you are
1575/1590 Thermometer Readout
User’s Guide
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