IGBT Modules - Technologies, Driver and Application (Second Edition) - page 460

Fig. 12.31
Characteristics of aPt100 sensor
Class A is defined for the temperature range from -200°C to 650°C for three- and four-
wire circuits. ClassBapplies generally for the range from -200°C to 850°C.
T 005 .0K30.0
T 002 .0K15.0
B Class
A Class
Eq. 12.25
In order to achieve themost precise measurements possible, the following points must
be borne inmind in addition to the inherent tolerance of the sensors:
Parasitical thermoelectric voltage
If the sensor wires are extended with copper wire, for example, a
thermoelectric voltage may occur at the joints when there are different
temperatures; this can distort themeasured values.
Self-heating depends on the rated resistance selected for the sensor and the
measuring current. At a constant measuring current (the values are usually
around 1mA), the internal losses of a Pt1000 sensor will be 10 times greater
than those of a Pt100. The Pt1000 resistance therefore heats up to a much
greater extent.
Heat transfer
When applying the sensor, the heat transfer to the object to bemeasured (e.g.
heatsink) or medium (e.g. coolant) must be effective. When it is built into the
heatsink, therefore, thermal compound is required in order to prevent air voids.
When measuring liquids, on the other hand, the flow velocity needs to be fast
enough todissipate the self-heatingproperly.
Cable error
Depending on the length of the sensor cable, different resistances are formed
that overlap the resistance of the sensor and cause distortion of the
measurement signal.
KTY sensors are semiconductor temperature sensors and are an affordable alternative
to metal-based temperature sensors. The design of this type of sensor is illustrated in
Essentially, it comprises a silicon portion that has two contacts. The Si
parent material is subjected to a neutron beam in a reactor, during which process, as
described in chapter
Si portion is converted to phosphorus at a defined ratio
1...,450,451,452,453,454,455,456,457,458,459 461,462,463,464,465,466,467,468,469,470,...548
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