13.2 Air Temperature Sensor Calibration
Before delivery of a Dynatest Air 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 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 of the
calibration numbers of the Air 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.
For maximum accuracy, Dynatest render a 9-point re-calibration service.
For a user to perform the two-point calibration verification procedure, one or two stirred
liquid bath(s) will be required. To monitor the (reference) temperature of the liquid, 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 liquid 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 measuring tips of the Air
Temperature Sensor and the reference temperature sensor should be in as close contact as
possible at all times during the calibration.
Calibration instructions are provided on the screen. The operator need only follow these
instructions to successfully perform a calibration. When each of the temperature readings
stabilizes, 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 calculates 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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