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A degaussing circuit using a PTC thermistor is simple, reliable (for its simplicity), and inexpensive. As heaters, in the automotive industry, to provide cabin heating (in addition to heating provided by a heat pump or the waste heat of an internal combustion engine), or to heat diesel fuel in cold conditions before engine injection.
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.
A big drawback is that it is low-impedance: that is, the power used to heat the thermistor comes from the circuit being measured. If the circuit being measured can support the heating current, then it is possible to make a post-measurement calculation to correct the effect, as the impedance of the heating element is known.
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 ...
The temperature coefficient of a PTC heating element generally is a function of temperature. The Steinhart–Hart equation is often used to approximate this function. In some applications where the heater is used only in a narrow temperature range, a simple linear equation may be adequate.
The suggested setting for the configuration shown, is with R1 = R2, and R3 around the middle of the range of the RTD. Looking at the Wheatstone bridge circuit shown, the voltage drop on the lower left hand side is V_rtd + V_lead, and on the lower righthand side is V_R3 + V_lead, therefore the bridge voltage (V_b) is the difference, V_rtd − V ...
“A thermistor is a type of resistor with resistance inversly proportional to its temperature.” A physical quantity y is said to be inversely proportional to a quantity x if the following equation holds:y=A/x where A is a quantity that does not depend on x. What you wanted to say is that the function R(T) is monotonically decreasing.
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.