The NTC thermistor is a temperature dependent semiconductor resistor according to DIN 44070 or IEC 60593, whose resistance value decreases with increasing temperature. Negative Temperature Coefficient (NTC) is about -2 to -6% per Kelvin and thus about ten times larger than for metals. NTC thermistors are therefore well suited for temperature measurements.
Thermistors consist of oxides and doping supplements. These are processed into a powder mass and, after the addition of a binding agent, sintered at temperatures above 1000°C. Thereafter, the ceramic elements are contacted with metal and cured by means of a special heat treatment to enhance long term stability.
The change of resistance in operation can occur by temperature change in the environment (external heating) or by self-heating due to excessive measuring current. Therefore, it is very important to comply with the specified maximum performance of the thermistor. While monitoring of a specified temperature is firmly specified by Nominal Response Temperature NRT of PTC thermistors, the resistance of a NTC has to be measured as a non-linear characteristic at different temperatures.
Thermistors (NTC) are mainly used to monitor resistance changes over a wide temperature range. The characteristic of a thermistor is showing a non-linear behaviour compared to platinum sensors (as Pt100) due to the temperature dependency of the resistance.
For correct measurement one has to consider the tolerance in the base resistance value as well as the tolerance in the curve slope (so-called B-value).