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11 Calibration Procedure
11.1 Calibration Procedure
Calibration of this instrument should be performed at regularly scheduled inter
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vals by qualified authorized personnel in accordance with your company’s pol
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icy. Following is the recommended procedure for calibrating this instrument.
11.1.1 Calibration Equipment
Calibration requires a standard thermometer that is adequately accurate and fits
properly into one of the reference holes in the block. Recommended equipment
includes a laboratory grade PRT with a length of 30 to 300 mm (9 to 12 inches)
and a diameter of 4.76 or 6.35 mm (3/16 or 1/4 inches). The combined accu
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racy of the PRT and the readout which used to display the temperature should
be 0.025°C or better.
11.1.2 Calibration
The accuracy of the instrument over the full range is determined by the values
of the calibration parameters R0, ALPHA, DELTA, and BETA. The calibration
procedure involves measuring the error between the instrument and the refer-
ence thermometer at several temperature throughout the range and adjusting the
calibration parameters as necessary to reduce the errors to within acceptable
limits. The stated accuracy of the instrument can be found in the specification
table in Section 3.1. Because of the way the calibration parameters affect the
temperature the simplest way to proceed is to measure the errors at 0°C, 100°C,
50°C, and –70°C and adjust R0, ALPHA, DELTA, and BETA at each point re
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spectively. Be aware that you must use the appropriate fluid at each tempera
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ture. Follow these steps:
•
Set the set-point to 0°C and allow adequate time for the bath to reach this
temperature and stabilize. Adjust the R0 calibration parameter (see Sec
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tion 9.11.2) to make the bath temperature as measured with the standard
thermometer match the set-point. The approximate ratio between a
change in R0 and a change in temperature at 0°C is about 0.4 to 1. For ex
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ample, if the bath temperature is high by 0.1°C at 0°C then decrease R0
by 0.04.
•
Set the set-point to 100°C and allow adequate time for the bath to reach
this temperature and stabilize. Adjust the ALPHA calibration parameter
(see Section 9.11.3) to make the bath temperature as measured with the
standard thermometer match the set-point. The approximate ratio between
a change in ALPHA and a change in temperature at 100°C is about
0.00004 to 1. For example, if the bath temperature is high by 0.1°C at
100°C then decrease ALPHA by 0.000004.
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11 Calibration Procedure