ties. Sensors and transducers can operate at Рlocations remote from the observer and in environments unsuitable or impractical for humans. Р Some devices act as both sensor and transducer. A thermocouple has two junctions of wires of Рdifferent metals, these generate a small electric voltage that depends on the temperature difference Рbetween the two junctions. A thermistor is a special resistor, the resistance of which varies with Рtemperature. A variable resistor can convert mechanical movement into an electrical signal. РSpecially designed capacitors are used to measure distance, and photocells are used to detect light. РOther devices are used to measure velocity, acceleration, or fluid flow. In most instances, the Рelectric signal is weak and must be amplified by an electronic circuit.
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