The comparative measurement is performed in stirred, temperature-controlled liquid baths.During calibration, the thermal coupling of the reference device and the device under test occurs by means of the corresponding liquid bath. The reference device measures the tempering temperature in the liquid bath and is compared to the temperature measured by the device under test.
The calibration is performed on the basis of 3 or 5 measurement points, alternatively 4 freely-chosen measurement points in the -20...150°C range (-20...200°C for A2LA calibrations), which are distributed over the temperature range. By default, the calibration is performed with factory settings using the analogue output (current) or, alternatively, visually using the display of the device or the analogue output (voltage).
The calibration is performed at the specified radiation temperatures in front of a black body radiator with a reference pyrometer used as the standard device, on the basis of the international temperature standards following the ITS-90.
ifm offers an alternative to the traditional calibration procedures: the TCC.
Thanks to the calibration check technology, the TCC permanently checks its own drift behaviour. The sensor compares the temperature value to the simultaneously measured reference value. If the deviation is outside the tolerance range, which can be set between 0.5 and 3 K, the TCC provides an optical signal and sends a message to the central controller via IO-Link and the diagnostic output. The same applies to cases of serious malfunctions.
To check the calibration status, operating history in hours, temperature and drift value, limit and status are also documented – thus facilitating compliance with the requirements of many standards.
The design of the TCC family of instruments includes two sensing elements that self-detect and send a warning if any signal drift is occurring.
The PTC (Positive Temperature Coefficient) element increases its resistance with increasing temperature. The NTC (Negative Temperature Coefficient) element decreases its resistance with increasing temperature. Because the PTC and NTC react to temperature change in opposite directions, the microprocessor is able to measure the differential between the two elements and alert the user to a potential decrease in accuracy.