NTC and PTC thermistors, thermostats and thermal cut-outs, thermal
fuses and PTC fuses, platinum sensors and circuit protection devices are
all available from the UK market leaders.
ATC Semitec Products
What is a thermistor? Thermistors are thermal resistors whose resistance changes with temperature. There are two main types; NTC (Negative Temperature Coefficient) whose resistance drops with temperature increase and PTC (Positive Temperature Coefficient) whose resistance rises with temperature increase.
NTC Thermistors - These are generally used for temperature measurement as their RT (Resistance vs. Temperature) characteristic is well defined and can be readily programmed into a microprocessor. Some larger disc thermistor variants are used for current inrush limiting as they offer a neat cost-effective solution to surge currents arising from switching on certain electronic and electrical products, e.g. S.M.P.S.s (Switch Mode Power Supplies) or halogen lamps.
PTC Thermistors - These are generally used as solid-state fuses or thermal switches because near their transition point (curie point), the resistance increases rapidly by several orders of magnitude over a small change in temperature. This allows them to be easily incorporated into electronic circuitry and in the case of motor protection thermistors, allows several to be used in series to protect each phase of a 3-phase motor.
What is a thermostat? Thermostats can be either pre-set or adjustable but their prime function is to closely control temperature with a minimum temperature differential (the difference in temperature between the thermostat switching on and switching off).
Pre-set thermostats are calibrated with a specific set-point (determined by mechanical design and their material limits), accuracy (the set-point tolerance) and differential (see above) to suit the intended application. Pre-set thermostats are available in several formats; probe, disc or surface.
Adjustable thermostats have a temperature range e.g. 5~35°C and they can be set by the user to give a suitable comfort level. Adjustable thermostats are generally air-sensing or surface-sensing.
A thermal cut-out is designed to safely control an over-temperature condition. It tends to have a wide differential (to stop a fault condition from rapidly cycling) and is a protection device that can have several reset modes: automatic, manual or self-hold.
The type of reset required depends on the demands of the application or safety standard that the product has to meet.
They can also be supplied in a probe style or a disc format.
What is a thermal fuse? A thermal fuse (or thermal cut-off, or t.c.o.) is a one-shot safety device designed to operate at a pre-set temperature. Thermal fuses cannot be reset or repaired, they have to be replaced.
Thus they offer ultimate safety in appliance protection and other electronic circuits. There are several types available based on different sensing element technologies; organic, solder or bimetal.