Fluke 9107 - Manual (Page 56)

type, length, diameter, and material. Probes should be inserted to the same
depth in the well.
The following procedure can be used to calibrate a probe against a reference
while eliminating error due to temperature gradients between wells.
1. Place the reference probe in one well.
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 measure-
ments in this way eliminates error due to temperature gradients be-
tween 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.
10.1.3 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.
10.2 Dry-Well Characteristics
Understanding the thermal characteristics of the dry-well calibrator can help
you achieve the best accuracy and efficiency possible.
52 Hart Scientific
10 Test Probe Calibration