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CHAPTER SENSORS AND TRANSDUCERS 19.0 TABLE OF CONTENTS 19.1 INTRODUCTION 1 19.2 TYPES OF SENSORS 2 19.2.1 Thermal Sensors 3 19.2.2 Force Sensors 3 19.2.3 Positional Sensors 4 19.2.4 Fluid Sensors 5 19.2.5 Optical Sensors 6 19.2.6 Motion Sensors 6 19.2.7 Presence Sensors 7 19.2.8 Environmental Sensors 8 19.3 FAILURE MODES OF SENSORS 9 19.4 SENSOR FAILURE RATE MODEL DEVELOPMENT 12 19.5 REFERENCES 18 19.1 INTRODUCTION A sensor is a hardware device that measures a physical quantity and produces a signal which can be read by an observer or by an instrument. For example, a thermocouple converts temperature to an output voltage, which can be read by a voltmeter. For accuracy, all sensors are calibrated against known standards. A transducer is a device that is actuated by power from one system and supplies power usually in another form to a second system. For example, a loudspeaker is a transducer that transforms electrical signals into sound energy. A standard definition for a sensor or transducer does not exist and the words sensor and transducer are used synonymously, specific names being given depending on the application. Also, suffixed derivatives ending in -meter such as accelerometer, flowmeter and tachometer are used. For convenience, the basic sensor will be used in this chapter to describe these units. Analog sensors produce a continuous output signal or voltage, which is generally proportional to the quantity being measured. Physical quantities such as temperature, velocity, pressure and displacement are all analog quantities, as they tend to be continuous in nature. For example, the temperature of a liquid can be measured using a thermometer or thermocouple, which continuously responds to temperature changes as Sensors and Transducers 19-1 Revision B

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