10 Test Probe Calibration
Foroptimum accuracy and stability, allow the calibrator to warm up for 10
minutes after power-upand then allow adequate stabilization time after reach-
ing theset-point temperature. After completing calibration, allow the block to
cool before switchingthe power off.
Forinformation on automating your testing, contact Hart Scientific, Inc.
10.1 Comparison Methods
10.1.1 Direct Calibration
Directcalibration involves testing a probe directly against the dry-well’s tem-
perature display.The method provides the advantage of being quick and easy.
Insert the probe to be calibrated into the well of the dry-well calibrator. The
probe should fitsnugly into the calibrator probe sleeve yet should not be so
tightthat it cannot be easily removed. Avoid any dirt or grit that may cause the
probe to jaminto the sleeve. Best results are obtained with the probe inserted to
the full depth of the well. Once the probe is inserted into the well, allow ade-
quate stabilization time to allow the test probe temperature to settle as de-
scribed. Once the probe has settled to the temperature of the well, it may be
compared to thecalibrator display temperature. The display temperature should
be stable to within 0.1°C for best results.
Caution: Never introduce any foreign material into the probe hole of the
insert. Fluids, etc., can leak into the calibrator causing damage to the cal-
ibrator or binding and damage to your probe.
10.1.2 Comparison Calibration
Comparison calibration involvestesting a probe against a similar reference
probe. The advantageto this method is that better accuracy can be achieved
since errors due to dry-well inaccuracy,stem effect, and drift can be reduced.
After inserting the probes to be calibrated, allow sufficient time for the probes
to settle and the temperature of the dry-well to stabilize.
Both thereference probe and theprobe under testshould be the same size and
construction. Using probes with different lengths, diameters and materials will
havedifferent stem effects causing an unknown temperature difference. All
dry-wellshave horizontal and vertical gradients that change with temperature .
This isan unknown variable which can be factored out if probes are the same
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10Test Probe Calibration