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An NTC is commonly used as a temperature sensor, or in series with a circuit as an inrush current limiter. With PTC thermistors, resistance increases as temperature rises; usually because of increased thermal lattice agitations, particularly those of impurities and imperfections. PTC thermistors are commonly installed in series with a circuit ...
An NTC thermistor's resistance is low at high temperatures. When the circuit is closed, the thermistor's resistance limits the initial current. After some time, current flow heats the thermistor, and its resistance changes to a lower value, allowing current to flow uninterrupted. It is inherently impossible for 100% of supply voltage to appear ...
This characteristic made it useful for stabilizing circuits against fluctuations in power-supply voltages. [1] This device is often called a "barretter" because of its similarity to the barretter used for detection of radio signals. A modern successor to the iron–hydrogen resistor is the semiconductor PTC thermistor.
Sometimes, special circuits are built for the purpose of sensing and controlling the temperature or voltage status. Devices such as thermistors, voltage-dependent resistors, thermostats and sensors such as infrared thermometers are used to modify the current upon different conditions such as circuit-temperature and input voltage.
The equation model converts the resistance actually measured in a thermistor to its theoretical bulk temperature, with a closer approximation to actual temperature than simpler models, and valid over the entire working temperature range of the sensor.
In some applications, this self-regulating characteristic allows PTC heaters to be used without thermostats or overtemperature protection circuits. [1] One very important use of self-regulating heating elements is to assure the heating element will not become so hot as to damage itself or other parts of the heater.
A circuit that forces I C1 and I C2 to have a fixed N:1 ratio, [2] gives the relationship: = An electronic circuit, such as the Brokaw bandgap reference, that measures ΔV BE can therefore be used to calculate the temperature of the diode. The result remains valid up to about 200 °C to 250 °C, when leakage currents become large enough to ...
Another type of thermal switch is a PTC (Positive Temperature Coefficient) thermistor; these thermistors have a "cutting off" temperature at which the resistance suddenly rises rapidly, limiting the current through the circuit. When used in conjunction with a thermistor relay, the PTC will switch off an electrical system at a desired temperature.
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