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9 Calibration Procedure
9.1 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. The following is provided as a basis for developing your own procedure for
calibrating this instrument.
9.1.1 Calibration Equipment
Calibration requires a standard thermometer that is adequately accurate and fits
properly into one of the reference holes in each of the blocks. Recommended
equipment includes a laboratory grade PRT with a length of 230 to 300 mm (9
to 12 inches) and a diameter of 4.76 or 6.35 mm (3/16 or 1/4 inches). The com
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bined accuracy of the PRT and the readout which is used to display the temper
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ature should be 0.025°C or better.
9.1.2 Calibration
The accuracy of the instrument over the full range is determined by the values
of the calibration parameters R0, ALPHA, DELTA, and BETA (cold side). The
calibration procedure involves measuring the error between the instrument and
the reference thermometer at several temperature throughout the range and ad-
justing the calibration parameters as necessary to reduce the errors to within ac-
ceptable limits. The stated accuracy of the instrument can be found in the
specification table in Section 2.1. Because of the way the calibration parame-
ters affect the temperature the simplest way to proceed is to measure the errors
at 0°C, 100°C, 140°C, and –25°C and adjust R0, ALPHA, DELTA, and BETA
(cold side) at each point respectively. Follow these steps:
1. If “as found” data is required, first measure the error at various tempera
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tures throughout the range such as –25, 0, 25, 50, 75, 100, and 140°C.
The errors are measured by setting the controller to the desired tempera
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ture, allowing the block to reach the temperature and stabilize, and read
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ing the actual temperature of the block with the standard thermometer. If
the measured errors are all within acceptable limits, no further action is
required and the remainder of this procedure is not necessary. If the ac
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curacy needs to be improved, continue with Step 2.
2. Set the set-point to 0°C and allow adequate time for the block to reach
this temperature and stabilize. Adjust the R0 calibration parameter (see
Section 6.14.2) to make the block temperature as measured with the stan
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dard 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
example, if the block temperature is high by 0.1°C at 0°C, decrease R0
by 0.04.
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9 Calibration Procedure
Calibration Procedure