Thermal Chip

Bead thermistors
Bead form these thermal chip are made from platinum alloy lead wires directly sintered into the ceramic body. They generally offer fast response times, better stability and allow operation at higher temperatures than Disk and Chip NTC sensors, however they are more fragile. It is common to seal them in glass, to protect them from mechanical damage during assembly and to improve their measurement stability. The typical sizes range from 0.075 – 5 mm in diameter.

Disk and chip thermistors
Disk thermistor these thermal chip have metalized surface contacts. They are larger and, as a result, have slower reaction times than bead type NTC resistors. However, because of their size, they have a higher dissipation constant (power required to raise their temperature by 1 °C). Since the power dissipated by the thermistor is proportional to the square of the current, they can handle higher currents much better than bead type thermistors. Disk type thermistors are made by pressing a blend of oxide powders into a round die and then sintering at high temperatures. Chips are usually fabricated by a tape-casting process where a slurry of material is spread out as a thick film, dried and cut into shape. The typical sizes range from 0.25 to 25 mm in diameter.

Glass encapsulated thermal chip
These are NTC temperature sensors sealed in an airtight glass bubble. They are designed for use with temperatures above 150 °C, or for printed circuit board mounting, where ruggedness is a must. Encapsulating a thermistor in glass improves the stability of the sensor and protects the sensor from the environment. They are made by hermetically sealing bead type NTC resistors into a glass container. The typical sizes range from 0.4 to 10 mm in diameter.

Typical Applications
Thermal chip are used in a broad spectrum of applications. They are used to measure temperature, control temperature, and compensate for temperature. They can also be used to detect the absence or presence of a liquid, as current limiting devices in power supply circuits, for temperature monitoring in automotive applications, and in many more applications. NTC sensors can be divided into three groups, depending on the electrical characteristic exploited in an application.

Resistance-temperature characteristic
Applications based on the resistance-temperature characteristic include temperature measurement, control, and compensation. These also include situations in which an NTC thermistor is used so that the temperature of the NTC temp sensor is related to some other physical phenomena. This group of applications requires that the thermistor operates in a zero-power condition, meaning that the current through it is kept as low as possible, to avoid heating the probe.

Current-time characteristic
Applications based on current-time characteristic are: time delay, inrush-current limiting, surge suppression, and many more. These characteristics are related to the heat capacity and dissipation constant of the NTC thermistor used. The circuit usually relies on the NTC thermistor heating up due to the current passing through it. At one point it will trigger some sort of change in the circuit, depending on the application in which it is used.

Voltage-current characteristic
Applications based on the voltage-current characteristic of a thermistor generally involve changes in the environmental conditions or circuit variations which result in changes in the operating point on a given curve in the circuit. Depending on the application, this can be used for current limiting, temperature compensation or temperature measurements.