Thermistors: An Overview
This article will discuss NTC thermistors.
Unlike PTC thermistors whose resistance increases with an increase in temperature, the resistance of NTC thermistors goes down as the temperature increases.
The Steinhart-Hart Equation
This equation is mentioned frequently when thermistors are discussed, especially when a thermistor’s resistance in relation to its temperature is measured.
Two things to remember about thermistors:
Commercial and Military Grade NTC Thermistors
Commercial grade NTC thermistors come in two models: surface mount and leaded.
Surface mount thermistors are used when temperature sensing functions are carried out. The thermal time constant and dissipation constant will vary depending on the type of mounting. There are also surface mount thermistors that can measure temperature in a defined and closed area, an example of which is the area containing crystals in oscillator circuits.
Surface mount thermistors are designed to accommodate soldering process and tape and reel packaging.
Commercial grade leaded NTC thermistors, on the other hand, come in a variety of types: you have the interchangeable NTC thermistor, which simply means that they have extremely tight tolerances that can trace a resistance-temperature curve. Most of these come with insulated leads. Another type – the bare-leaded thermistors- are suitable for low cost temperature measuring at -55°C and +150°C.
Military grade NTC thermistors are used for critical applications in the fields of temperature measurement, temperature and power control, interfacing of micro-processors and stabilization of amplifiers. They are particularly useful when hybrid circuitry involves bonding functions. Resistance and curve combinations are available for customization purposes.