THERMOELECTRIC TRANSDUCERS

Prepared by: JONI ROSE T. MAGKALAS

Temperature transducers

Thermoelectric sensor/transducer is a device which can convert the temperature change to the electricity change.

Temperature transducers can be divided into three main categories:

1. Resistance Temperature Detectors (RTD)2. Thermocouples3. Thermistor

Resistance Temperature Detector(RTD)

-Predict change in electrical resistance of some materials with changing temperature.

-Detectors of wire resistance temperature common employ platinum, nickel or resistance wire elements, whose resistance variation with temperature has high intrinsic accuracy. They are available in many configurations and size and as shielded or open units for both immersion and surface applications.

Thermocouple

- An electrical device that responds to a difference in temperature by producing an electric current. Thermocouples are used as measuring instruments and as control devices. Thermocouples are simple and rugged, can be used over a wide range of temperatures (from -200° C. to 1,600° C.), and permit great precision. For these reasons thermocouples are used to measure temperatures inside furnaces and jet engines and in laboratory experiments.

The thermocouple is based on the Seebeck effect, named after its discoverer, Thomas J. Seebeck. Thermocouple consists of two wires of dissimilar metals or alloys joined at their ends, with a potentiometer (or a voltmeter) connected in one side of the circuit. The other end of wires produces a voltage between the wires.

ThermistorA type of resistor whose resistance varies significantly with temperature. Semi-conductor thermistors have a Negative Temperature Coefficient (NTC). i.e. as temperature increases, the resistance decreases.The word is a contraction of thermal and resistor. Thermistors are widely used as inrush current limiters, temperature sensors, self-resetting over current protectors, and self-regulating heating elements.

Resistance

Tem perature

Note!The resistance decreases as their temperature rises-NTC

Types of Thermistor

TYPE RESISTANCE

DISC 1 to 1MΩ

WASHER 1 to 50kΩ

ROD high resistan

ce

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