Calibration Procedure; Calibration Points; Compute Delta - Fluke 7103 User Manual

12

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 bath to improve the temperature
set-point accuracy. Calibration is done by adjusting the controller probe calibra tion
constants R0, ALPHA, DELTA, and BETA so that the temperature of the bath 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 bath. By using a good thermometer and following this
procedure the bath can be calibrated to an ac curacy of better than 0.5°C up to 125°C.
12.1

Calibration Points

In calibrating the bath, R0, ALPHA, DELTA, and BETA are adjusted to mini-
mize the set-point error at each of three different bath temperatures. Any three
reasonably separated temperatures may be used for the calibration. Improved results
can be obtained for shorter ranges when using temperatures that are just within the
most useful operating range of the Micro-Bath. The farther apart the calibration
temperatures, the larger will be the calibrated temperature range but the calibration
error will also be greater over the range. If for instance 50°C to 150°C is chosen as the
calibration range then the calibrator may achieve an ac curacy of say ±0.3°C over the
range 50 to 150°C. Choosing a range of 50°C to 90°C may allow the calibrator to have
a better accuracy of maybe ±0.2°C over that range but outside that range the accuracy
may be only ±1.5°C.
12.2

Calibration Procedure

1.
2.
3.
4.
12.2.1

Compute DELTA

A T
B T
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Choose three set-points to use in the calibration of the R0, ALPHA, DELTA,
and BETA parameters. These set-points are generally –25°C, 0°C, 65°C, and
125°C but other set-points may be used if desired or necessary.
Set the bath to the low set-point. When the bath reaches the set-point and the
display is stable, wait 15 minutes or so and then take a reading from the ther-
mometer. Sample the set-point resistance by holding down the "SET" key and
pressing the "DOWN" key. Write these values down as T1 and R1 respectively.
Repeat step 2 for the other two set-points recording them as T
and R respectively.
4
Using the recorded data, calculate new values for R0, ALPHA, DELTA, and
BETA parameters using the equations given below:
T
4 3
T
3 2
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Calibration Procedure
Calibration Points
, R , T , R
2 2 3
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, T ,
3 4
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