Resistance thermometers general guide

RESISTANCE SENSORS
This is when some device that varies in resistance with changes in temperature is mounted in an assembly. This device is referred to as the 'DETECTOR or ELEMENT' while the assembly is called the 'SENSOR or PROBE'.
The operating range of resistance sensors is -200°C to 650°C with the limiting factor within this range being the method of sensor construction.

PLATINUM RESISTANCE DETECTORS
This is probably the most common resistance sensor in industry today, particularly popular in the brewing and food industries. It is constructed by winding a Platinum conductor around a ceramic former.
PT 100's have a resistance of 100Ω at 0°C ( the most common)
PT 130's have a resistance of 130Ω at 0°C
PT 1000's have a resistance of 1000Ω at 0°C

The characteristics of PT100's are documented in DIN 43760:1980 and BS 1904:1984 and are standard throughout the world.

DEPOSITED FILM DETECTORS
These detectors are manufactured in much the same way as circuit boards, where the platinum track is etched onto a small piece of circuit board. They also conform to BS1904 but are generally not as accurate as wire wound detectors.

THERMISTOR DETECTORS
Thermistors are semi-conductor devices that vary in resistance with changes in temperature, this relationship is not linear. If their resistance increases with temperature they are said to have a positive temperature coefficient (PTC). If the reverse is true they are called NTC (negative temperature coefficient.) They are particularly popular in the refrigeration industry.
Thermistors must be matched to the instrument. This is usually performed by adjusting the trimmer pot on the instrument. This is necessary because of wide manufacturing tolerances. Once the sensor is matched to an instrument, reasonable accuracy can be produced.
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