chap2 - Automation & Engineering Services (ENG3618)...

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Automation & Engineering Services (ENG3618) Chapter 2 Page 1 Chapter 2 Sensors and Transducers Types and Characteristics A sensor is an element in a mechatronic or measurement system that acquires a physical parameter and converts it into a signal for display or other uses. The active element of a sensor is called the transducer. The main use of a sensor is to monitor and control dynamical systems. Very often the output of sensors are fed back to compare to a reference signal. The resulting error will be fed into a control unit to generate the control action. Therefore, how well a control system functions relies heavily on the accuracy of sensors. The type of transmission of information in a sensor can be classified into the following energy domains : Radiant Mechanical Thermal Electrical Magnetic Chemical In terms of the utilization of energy, sensors can be further classified as passive and active . A passive sensor requires no energy source other than the input signal. All the energy required at the output is provided from the physical input. An example is a thermocouple where an emf is generated proportional to the temperature difference between the two ends. Even without external power, this emf can be measured. These sensors often require amplification because of low energy. An active sensor on the other hand requires energy input to function. An example is a strain gauge. Mechanical strain merely causes a change in the resistance of the strain gauge; however, to see the output, we need to connect it to a Wheatstone bridge with external power supply before we can measure the voltage across the
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This note was uploaded on 11/09/2009 for the course ENG 91301 taught by Professor Lui during the Spring '08 term at Hong Kong Institute of Vocational Education.

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chap2 - Automation & Engineering Services (ENG3618)...

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