Calibration Bath
Calibration Procedure
47
Calibration Procedure
Note
Consider this procedure a general guideline. Each laboratory should write their own
procedure based on their equipment and their quality program. Each procedure should
have an uncertainty analysis based on the laboratory equipment and environment.
In some instances, you may want to calibrate the Bath to improve the temperature set-point
accuracy. To calibrate, adjust the controller probe calibration constants R
0
and ALPHA so that the
temperature of the Bath (measured with a standard thermometer) agrees more closely with the
Bath set-point. The thermometer used must be able to measure the bath fluid temperature with
higher accuracy than the desired accuracy of the Bath. Use a good thermometer and carefully
follow procedures to calibrate the Bath to an accuracy of better than 0.02 °C over a range of
100 degrees.
Calibration Points
When you calibrate the Bath, adjust R
0
and ALPHA to minimize the set-point error at each of two
different bath temperatures. Use any two reasonably-separated bath temperatures for the
calibration. However, best results are obtained when you use bath temperatures that are just
within the most useful operating range of the Bath.
Note
The farther apart the calibration temperatures, the greater the calibrated temperature
range, and the calibration error.
If, for example, 0 °C and 100 °C are chosen as the calibration temperatures, the Bath can
achieve an accuracy of ±0.3 °C over the range –10 °C to 110 °C. Choosing 30 °C and 70 °C
allows the Bath to possibly have a better accuracy of ±0.1 °C over the range 25 °C to 75 °C, but
outside of that range, the accuracy may be only ±0.5°C.
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