Calibration Procedure; Calibration Points; Compute Delta - Fluke 9102S User Manual

9

Calibration Procedure

Note: This procedure is to be considered a general guideline. Each laboratory
should write their own procedure based on their equipment and their quality
program. Each procedure should be accompanied by an uncertainty analysis
also based on the laboratory's equipment and environment.
Sometimes the user may want to calibrate the dry-well to improve the temperature
set-point accuracy. Calibration is done by adjusting the controller probe calibra-
tion constants R0 , ALPHA, and DELTA so that the temperature of the dry-well as
measured with a standard thermometer agrees more closely with the set-point. The
thermometer used must be able to measure the well temperature with higher accuracy
than the desired accuracy of the dry-well. By using a good thermometer and following
this procedure the dry-well can be calibrated to an accuracy of better than 0.25°C over
its full range.
9.1

Calibration Points

In calibrating the dry-well, R0, ALPHA, and DELTA are adjusted to minimize the
set-point error at each of three different dry-well temperatures. Any three reasonably
separated temperatures may be used for the calibration. Improved results can be ob-
tained for shorter ranges when using temperatures that are just within the most useful
operating range of the dry-well. The farther apart the calibration temperatures, the
greater the calibrated temperature range. However, the calibration error is also greater
over the range. For instance, if 10°C to 100°C is chosen as the calibration range, the
calibrator may achieve an accuracy of ±0.25°C over the range 10°C to 100°C. Choos-
ing a range of 50°C to 100°C may allow the calibrator to have a better accuracy of
maybe ±0.2°C over the range 75°C to 105°C but outside that range the accuracy may
be only ±0.25°C.
9.2 Calibration Procedure
1. Choose three set-points to use in the calibration of the R0, ALPHA, and DELTA
parameters. These set points are generally 2°C, 50°C, and 100°C but other set
points may be used if desired or necessary.
2. Set the dry-well to the lowest set-point. When the dry-well reaches the set-point
and the display is stable, wait 15 minutes or so and then take a reading from
the thermometer. Sample the set-point resistance by holding down "SET" and
pressing the d. Write these values down as T
3. Repeat step 2 for the other two set-points recording them as T
and R
3
4. Using the recorded data, calculate new values for the R0, ALPHA, and DELTA.
9.2.1

Compute DELTA

A T = − T
3 2
respectively.
Calibration Procedure
Calibration Procedure
and R respectively.
1 1
and R
2
and T
2 3
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