Dry-well Calibrator
Calibration and Adjustment Procedure
25
Calibration and Adjustment Procedure
Note
This procedure is 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.
Use the instructions in this section to calibrate and adjust the Product. Calibration is done by
measuring the Product temperature with a calibrated reference thermometer fully inserted with a snug
fit in the Product measurement well. Adjustment is done by adjusting the controller calibration
constants R0, ALPHA, and DELTA so that the temperature of the Product, as measured with the
reference thermometer, agrees more closely with the set-point. The reference thermometer used must
be able to measure the Product temperature with higher accuracy than the accuracy of the Product.
Calibration Points
Fluke Calibration recommends calibrating the Product over the entire operating range at enough
temperature points to evaluate Product accuracy and to be able to adjust the Product, if needed. At
least three reasonably-separated temperature points are required to adjust the Product. Improved
results can be obtained for shorter ranges when using temperatures that are just within the most useful
operating range of the Product. The farther apart the calibration temperatures, the greater the
calibrated temperature range. However, the calibration error is also greater over the range. For
example, if 10 °C to 100 °C is the calibration range, the Product may achieve an accuracy of ±0.25 °C
over the range 10 °C to 100 °C. Choosing a range of 50 °C to 100 °C may allow the Product 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.
Calibration Procedure
1. Choose the desired calibration points. At a minimum, three points are needed to calculate new
calibration parameters R0, ALPHA, and DELTA. Typically, adjustment is based on measurements
at 2 °C, 50 °C, and 100 °C but other temperature points can also be used.
2. Set the Product to the lowest calibration point. When the Product reaches the calibration point and
the display is stable, wait at least 15 minutes and then take a reading from the reference
thermometer (T
1
). View and then record the Product control sensor resistance by holding down
SET
and pressing
d
(R
1
). Calculate the difference between the reference thermometer reading
and the Product displayed set-point to evaluate Product error.
3. Repeat step 2 for the remaining calibration points measuring in order of increasing temperature.
When the other two adjustment points are measured, record T
2
and R
2
and T
3
and R
3
respectively.
4. If adjustment is needed, use the recorded results to calculate new values for the R0, ALPHA, and
DELTA.
