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Transducers/Sensors: Sample Device Thermistor

Transducers/Sensors: Sample Device Thermistor. A thermistor is a temperature-sensing element composed of semiconductor material (typically a mix of metal oxides) that exhibits a large change in resistance in response to a small change in temperature

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Transducers/Sensors: Sample Device Thermistor

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  1. Transducers/Sensors: Sample DeviceThermistor • A thermistor is a temperature-sensing element composed of semiconductor material (typically a mix of metal oxides) that exhibits a large change in resistance in response to a small change in temperature • Thermistors usually have negative temperature coefficients, the resistance of the thermistor decreases as the temperature increases (Positive temperature coefficient thermistors also exist, they make good current limiting devices)

  2. Transducers/Sensors: Sample DeviceThermistor • Accuracy: Thermistors are one of the most accurate types of temperature sensors. Typical accuracy of ±0.2°C. • Range: Thermistors are fairly limited in their temperature range, working only over a nominal range of 0°C to 100°C . • Stability: Thermistors are chemically stable and not significantly affected by aging.

  3. Transducers/Sensors: Sample DeviceThermistor

  4. Transducers/Sensors: Sample DeviceThermistor • Linearity: Thermistors are highly non-linear, following a law called the Steinhart-Hart equation A, B and C are constants found experimentally by measuring R at three different temps and substituting back in the equation Graphs or tables of RvsT are usually used

  5. Transducers/Sensors: Sample DeviceThermistor Typical Thermistors

  6. Transducers/Sensors: Sample DeviceThermistor • Using a Thermistor to sense/measure temperature 1: If the thermistor is part of a potential divider then the output signal will vary with temperature. This simple circuit lacks precision, it’s often used in a set-point switch

  7. Transducers/Sensors: Sample DeviceThermistor Using a Thermistor to sense/measure temperature 2: The thermistor is one of the resistors in a Wheatstone Bridge – say R4. The output voltage is now related to temperature and will vary as the temperature varies. Calibration will enable temperature to be measured.

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