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The current and voltage across the thermistor depend on the particular circuit configuration. As a simple example, if the voltage across the thermistor is held fixed, then by Ohm's law we have = /, and the equilibrium equation can be solved for the ambient temperature as a function of the measured resistance of the thermistor:
The Steinhart–Hart equation is a model relating the varying electrical resistance of a semiconductor to its varying temperatures.The equation is = + + (), where is the temperature (in kelvins),
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For example, a PTC heating element with a sharp change in resistance at a particular temperature can be fitted with a constant voltage source and a variable-speed fan. With the fan at a low setting, the heating element draws only a small amount of current, resulting in a low heat output.
For example, if 120 V AC RMS is applied to a resistive heating element it would heat up by exactly the same amount as if 120 V DC were applied. This principle was exploited in early thermal converters. The AC signal would be applied to a small heating element that was matched with a thermistor, which could be used in a DC measuring circuit.
Such relationship may take the form of a graph, where numerical values of a circuit variable are plotted versus frequency or component value (the most common example would be a plot of the magnitude of a transfer function vs. frequency). Symbolic circuit analysis is concerned with obtaining those relationships in symbolic form, i.e., in the ...
For example, resistors, capacitors, and inductors are linear, while diodes and transistors are nonlinear. An I–V curve which is a straight line through the origin with positive slope represents a linear or ohmic resistor, the most common type of resistance encountered in circuits.
Another possibility to minimize the temperature dependence of a heat flux sensor, is to use a resistance network with an incorporated thermistor. The temperature dependence of the thermistor will balance the temperature dependence of the thermopile. Another factor that determines heat flux sensor behavior, is the construction of the sensor.