Thermistors And Resistive Temperature Detectors In the circuit wherein an

# Thermistors and resistive temperature detectors in

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Thermistors And Resistive Temperature Detectors In the circuit wherein an ammeter is used : The thermistor has a negative temperature coefficient (Arrow is going down ). (Not universally accepted) As the temperature of the thermistor rises, its resistance decreases, and the current increases. If the characteristics of the thermistor are known, it is possible to relate the current measurement to the actual temperature. In the circuit wherein a voltmeter is used : The thermistor has a positive temperature coefficient (Arrow is going up ). (Not universally accepted) As the temperature of the thermistor rises, its resistance increases, and the voltage across the thermistor increases. If the characteristics of the thermistor are known, it is possible to relate the voltage measurement to the actual temperature.
Thermistors And Resistive Temperature Detectors In the circuit wherein a bridge is used : The thermistor has a negative temperature coefficient (Arrow is going down ). (Not universally accepted) Bridge circuits are inherently superior to other measurements because the meter which detects bridge imbalance can be made very sensitive . As the temperature of the thermistor rises , its resistance drops . – The bridge becomes imbalance . R3 is adjusted manually or automatically until the bridge is again balanced. – The position of the wiper of R3 represents the temperature. – The shaft of R3 is mechanically linked to the shaft of a temperature pointer . Since the thermistor response is nonlinear, the temperature scale is also nonlinear . Since thermistors are nonlinear, they are not suited for measuring temperature over wide ranges , but they are well suited for small temperature changes . The natural nonlinearity of thermistors can be partially corrected by connecting several matched thermistors together in a series-parallel combination called thermistor composite network.
Thermistors And Resistive Temperature Detectors As a general rule, thermistors are preferable when the expected temperature band is narrow , and RTDs are preferable when the expected temperature band is wide . Thermistors are manufactured for use somewhere between – 150 0 F and +800 0 F , although there are thermistors which can be used at extremely low temperatures. RTDs are available for use at temperatures from – 400 0 F to + 2000 0 F . To prevent the internally generated heat of thermistors from affecting measurements, the internally generated heat is kept as low as possible by making the current passing through it small . Thermistors can also be used in applications wherein the internally generated heat is used . Some of these applications are time delays , protecting delicate components from surge currents, and detecting the presence or absence of thermally conductive material.