Structure and performance of NTC thermistors

　　Materials commonly involved in making NTC resistors are oxides of platinum, nickel, cobalt, iron and silicon, used as pure elements or as ceramics and polymers. Depending on the production process used, NTC thermistors can be divided into three groups.

　　1. Bead thermistor

　　These NTC thermistors are made of platinum alloy leads sintered directly into the ceramic body. They generally offer fast response times, better stability and allow operation at higher temperatures than Disk and Chip NTC sensors, but they are more fragile. They are usually sealed in glass to protect them from mechanical damage during assembly and to improve their measurement stability. Typical sizes range from 0.075 to 5mm in diameter.

　　2. Chip thermistor

　　These NTC thermistors have metallized surface contacts. They are larger and therefore have slower response times than bead-type NTC resistors. However, due to their size, they have a higher dissipation constant (the power required to raise the temperature by 1°C), and since the thermistor dissipates power proportional to the square of the current, they can be more efficient than beads. Handle higher current type thermistors well. Disc thermistors are made by pressing a mixture of oxide powders into circular molds, which are then sintered at high temperatures. Chips are typically fabricated by a tape casting process, in which a material paste is spread out as a thick film, dried and cut to shape. Typical sizes range from 0.25-25mm in diameter.

　　3. Glass Encapsulated NTC Thermistor

　　typical application

　　NTC thermistors are used in a wide range 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 liquids, as current limiting devices in power circuits, temperature monitoring in automotive applications, and more. NTC sensors can be divided into three groups, depending on the electrical characteristics used in the application.

　　1. Resistance-Temperature Characteristics

　　Applications based on resistance-time characterization include temperature measurement, control, and compensation. These also include the use of NTC thermistors, making the temperature of the NTC temperature sensor related to some other physical phenomenon. This group of applications requires the thermistor to operate at zero power, which means that the current through it is kept as low as possible to avoid heating the probe.

　　2. Current time characteristics

　　Applications based on current-time characteristics include: time delays, inrush current limiting, surge suppression, and more. These characteristics are related to the thermal capacity and dissipation constant of the NTC thermistor used. Circuits often rely on heating from an NTC thermistor due to the flow of current. At some point, it will trigger some kind of change in the circuit, depending on the application that uses it.

　　3. Voltage-Current Characteristics

　　Applications of thermistor-based voltage-current characteristics often involve changes in environmental conditions or circuit changes, which result in changes in the operating point on a given curve in the circuit. Depending on the application, it can be used for current limiting, temperature compensation or temperature measurement.

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