IGBT Modules - Technologies, Driver and Application (Second Edition) - page 459

Fig. 12.30
Measuring the temperature usingan infrared camera
Further types of sensors for temperaturemeasurement of heatsinks and similar include
Pt sensors andKTY sensors.
Pt sensors are temperature sensors based on the temperature-dependent change in
resistance of platinum (Pt). They are available in different rated resistances based on a
temperature of 0°C. The usual values are Pt100, Pt200, Pt500 und Pt1000. The
numerical value represents the rated resistance value R
in ohms. They are usually
constructed as a thin-film sensor, to which a layer of platinum is applied on an
aluminium oxide pad. The platinum layer is shaped into a spiral by laser trimming and
aligned with the relevant resistance value. For packaging, the design is then covered
with a layer of glass. Other designs create the sensor as awire-wound ceramic resistor.
The platinum wire is fed into a ceramic tube and filled with aluminium oxide. The
ceramic tube is then closedwith a glass plug. Inwire-wound glass resistors, by contrast,
the platinum wire is wound onto a glass rod and fitted into a glass tube. The two are
then fused together.
The measuring range of Pt sensors extends from -200°C to 850°C and behaves like a
PTC resistor. The range relevant to power electronics from approximately -50°C to -
200°C shows
for a Pt100 sensor. This is where the dependence of the
resistance on the temperature, and the resistance and temperature deviations of the
sensor, are shown at the correspondingmeasuring point. For deviations, two curves are
always shown; these represent tolerance classes A and B of the sensors. In addition to
these two tolerance classes, there are other classes, sometime agreed upon by the
manufacturer and the user.
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