2017.06.19 FwdMan2.8.17.docx 13-111
13.3 Surface Temperature Sensor Calibration
Before delivery of a non-contact Dynatest IR (Infra-Red) Surface Temperature Sensor, the
best-fit calibration line for this sensor has been established from linear regression on a set of 9
values obtained from a reference calibration procedure performed by means of a high-
accuracy, certified, dry-block calibrator (with a special adapter giving the desired emissivity
of 0.95) traceable to international standards. The 9 reference temperatures are 5 to 45 C in
steps of 5 C. A sensor is only approved if it performs to linearity specifications.
The Temperature Applet needs two calibration “numbers” (V1 and V2, i.e. sensor output
values (in mV)) to calculate and display the air temperature. These values are the sensor
outputs at 0 C and 100 C calculated from the above-mentioned, linear regression line (and
therefore not necessarily the values which the sensor would actually output at these
temperatures). This procedure ensures maximum possible accuracy in the most important
range of 0 C to 50 C.
The Temperature Applet provides an automated procedure for periodic verification,
establishing the calibration numbers of the Surface Temperature Sensor in TWO points,
which is in most cases adequate, as the linearity of a sensor has been checked at the initial
calibration and normally does not change significantly with time, and two points therefore
will suffice to determine the (linear) calibration line.
Calibration of an IR sensor is NOT a simple task, so we recommend users NOT to perform
this procedure themselves unless absolutely necessary. For maximum accuracy, Dynatest
render a 9-point re-calibration service.
If a user decides to perform the two-point calibration verification procedure anyway, one or
two stirred water bath(s) can be used. To monitor the (reference) temperature of the water, we
recommend a digital reference thermometer with a traceable accuracy of 0.4 C or better (in
the 0 C to 50 C range) and a resolution of 0.1 C or less.
The temperature of the stirred water bath(s) must be adjustable to “low” and “high”, stable
reference temperatures. The low temperature should be in the range of 0 C to 10 C, and the
high temperature should be in the range of 40 C to 50 C. The Surface Temperature Sensor
and the liquid bath with the reference temperature sensor should be enclosed, so evaporation
from the water will not decrease its surface temperature, and also to prevent condensing
moisture on the lens of the Surface Temperature Sensor, which should be placed vertically,
preferably with a distance of some 300 mm between the lens of the sensor and the surface of
the water, with no objects between the lens and the water surface.
Calibration instructions are provided on the screen. The operator need only follow these
instructions to successfully perform a calibration. “Low” and “high” temperature
measurements are obtained as explained above. When each of the temperature readings has
stabilized, the buttons near the right edge of the screen can be used to enter the voltage values.
This reduces the possibility of typed input errors.
When the calibration is complete, the Temperature Applet will automatically calculate new
calibration voltages and display them in the fields labelled New V1 and New V2. The
operator may then click the Apply button to store and use the new calibration figures.
Alternatively, if the operator is not satisfied with the calibration results, he may click Cancel
to discard the new figures and keep the old ones.
If the operator wishes to enter calibration values without performing the calibration, he may
do so by clicking on the Calibration figure V1 and Calibration figure V2 fields and
manually overtyping the existing values. In this case, the operator would then click the OK
button to store the new values.
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