A sensor is often defined as a “device that receives and responds to a signal or stimulus.” This definition is broad. In fact, it is so broad that it covers almost everything from a human eye to a trigger in a pistol. Consider the level-control system shown in Fig. 1.1 . The operator adjusts the level of fluid in the tank by manipulating its valve. Variations in the inlet flow rate, temperature changes (these would alter the fluid’s viscosity and consequently the flow rate through the valve), and similar disturbances must be compensated for by the operator. Without control, the tank is likely to flood, or run dry.
KeywordsAdaptive Cruise Control Direct Sensor Inlet Flow Rate Passive Sensor Customary System
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