11 Calibration Procedure
11.1 Calibration Procedure
Calibrationof this instrument should be performed at regularly scheduled inter-
valsby qualified authorized personnel in accordance with your company’s pol-
icy.Following is the recommended procedure for calibrating this instrument.
11.1.1 Calibration Equipment
Calibration requires a standard thermometer thatis adequately accurate and fits
properly intoone of the reference holesin the block. Recommended equipment
includesa laboratory grade PRT with a length of 230 to 300 mm (9 to 12
inches) and ad iameterof 4.76 or 6.35 mm (3/16 or 1/4 inches). The combined
accuracyof the PRT and the readout which used to display the temperature
should be 0.025°C or better.
11.1.2 Calibration
The accuracyof the instrument over the full range is determined by the values
of the calibration parameters R0, ALPHA, DELTA,and BETA.The calibration
procedure involvesmeasuring the error between the instrument and the refer-
ence thermometerat several temperature throughout the range and adjusting the
calibration parameters as necessary to reduce the errors to within acceptable
limits. The stated accuracyof 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 wayto proceed is to measure the errors at 0°C, 100°C,
140°C, and –25°C and adjustR0, A LPHA, DELTA,and BETAat each point re-
spectively.Follow these steps:
1. If “as found” data is required then first measure the error at various
temperatures 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
temperature, allowing the block to reach the temperature and stabilize,
and reading the actual temperature of the block with the standard ther-
mometer. If the measured errors are all within acceptable limits then no
further action is required and following the remainder of this procedure
is not necessary. If the accuracy 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 8.11.1.1) to make the block temperature as measured with the
standard thermometer match the set-point. The approximate ratio be-
tween a change in R0 and a change in temperature at 0°C is about 0.4
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11Calibration Procedure