Calibration Of Multiple Probes; Dry-Well Characteristics; Vertical Gradient; Heating And Cooling Rates - Fluke 9140 User Manual

9140 Dry-well Calibrator
User's Guide
9.1.3
9.2
9.2.1
9.2.2
40
2. Place the probe to be calibrated, the unit under test (UUT), in another
well.
3. With the reference inserted into one well and the probe under test in-
serted into a second well, make measurements of each.
4. Swap the locations of the reference probe and probe under test. Allow
plenty of time for thermal settling.
5. Make another set of measurements of the reference probe and the probe
under test.
6. Average the two measurements of the reference probe. Average the two
measurements of the probe under test. Averaging the two measurements
in this way eliminates error due to temperature gradients between the
two wells.
7. You may now compare the averaged measurement of the probe under
test with the averaged measurement of the reference probe.
For best results repeat the test several times at the same temperature and at dif-
ferent temperatures.
This method can be used with different types of probes but the user must deter-
mine the uncertainty of the measurement.

Calibration of Multiple Probes

Fully loading the calibrator with probes increases the time required for the tem-
perature to stabilize after inserting the probes. Be sure that the temperature has
stabilized before starting the calibration.
Multiple probes may be calibrated simultaneously using either the direct or
comparison calibration method. Stem effect will cause less error in the compar-
ison calibration method than with the direct calibration method.

Dry-well Characteristics

Vertical Gradient

There is a temperature gradient vertically in the test well. The heater has been
applied to the block in such a way as to compensate for nominal heat losses out
of the top of the dry-well and minimize vertical temperature gradients. How-
ever, actual heat losses will vary depending on the number and types of probes
inserted into the calibrator and the block temperature. For best results, insert
probes the full depth of well.

Heating and Cooling Rates

Figures 7 and 8 show typical heating cooling rates of the 9140 dry-well
calibrator.