7102
User’s Guide
34
Stabilization and Accuracy
The stabilization time of the bath depends on the conditions and temperatures involved. Typically, the
test well will be stable to 0.1 °C within 10 minutes of reaching the set-point temperature. Ultimate
stability is achieved 30 minutes after the bath reaches the set temperature.
If you insert another cold probe into a well, this requires another period of stabilizing, depending on the
magnitude of the disturbance and the required accuracy. For example, if you insert a .25-in diameter
room temperature probe at 200 °C, it takes 5 minutes to be within 0.1 °C of its settled point and takes
10 minutes to achieve maximum stability.
To speed up the calibration process, know how soon to make the measurement. Make typical
measurements at the desired temperatures with the test probes under test to establish these times.
Calibration
Note
Consider this procedure a general guideline. Each laboratory must 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 equipment and environment of the laboratory.
You may want to calibrate the bath to improve the temperature set-point accuracy. To adjust
calibration, adjust the controller probe calibration constants R0, ALPHA, and DELTA 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. Use a good thermometer and this calibration procedure and the bath
can be calibrated to an accuracy of better than 0.5 °C up to 200 °C.
Calibration Points
When you calibrate the bath, adjust R0, ALPHA, and DELTA to minimize the set-point error at each of
three different bath temperatures. Any three reasonably separated temperatures can be used for the
calibration. Improved results can be obtained for shorter ranges when you use temperatures that are
just within the most useful operating range of the Product. 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. For instance, if you choose 50 °C to 150 °C as the calibration range, then the
calibrator may achieve an accuracy of say ±0.3 °C over the range 50 °C 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.
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