63865-Ch06 - Components-3e-S Chapter 6 HARDWARE COMPONENTS...

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Unformatted text preview: Components-3e-S 06/04/07 Chapter 6 HARDWARE COMPONENTS FOR AUTOMATION AND INDUSTRIAL CONTROL REVIEW QUESTIONS 6.1 What is a sensor? Answer : As defined in the text, a sensor is a device that converts a physical stimulus or variable of interest (such as temperature, force, pressure, or displacement) into a more convenient form (usually an electrical quantity such as voltage) for the purpose of measuring the stimulus. 6.2 What is the difference between an analog sensor and a discrete sensor? Answer : An analog measuring device produces a continuous analog signal such as electrical voltage, whose value varies in an analogous manner with the variable being measured. A discrete measuring device produces an output that can have only certain values. Discrete sensor devices divide into two categories: (1) binary, in which the measuring device produces an on/off signal, and (2) digital, in which the measuring device produces either a set of parallel status bits or a series of pulses that can be counted. 6.3 What is the difference between an active sensor and a passive sensor? Answer : An active sensor is one that responds to a stimulus without the need for any external power. A passive sensor is one that requires an external source of power in order to operate. 6.4 What is the transfer function of a sensor? Answer : A transfer function is the relationship between the value of the physical stimulus and the value of the signal produced by the sensor in response to the stimulus. It is the input/output relationship of the sensor. 6.5 What is an actuator? Answer : An actuator is a hardware device that converts a controller command signal into a change in a physical parameter. An actuator is a transducer, because it changes one type of physical quantity, such as electric current, into another type of physical quantity, such as rotational speed of an electric motor. 6.6 Nearly all actuators can be classified into one of three categories, according to type of drive power. Name the three categories. Answer : The three categories are (1) electrical, (2) hydraulic, and (3) pneumatic. 6.7 Name the two main components of an electric motor. Answer : The two components are the stator, which is the stationary component, and the rotor, which rotates inside the stator. 6.8 In a DC motor, what is a commutator? Answer : called A commutator is a rotary switching device that rotates with the rotor and picks up current from a set of carbon brushes that are components of the stator assembly. Its function is to continually change the relative polarity between the rotor and the stator, so that the magnetic field produces a torque to continuously turn the rotor. 6.9 What are the two important disadvantages of DC electric motors that make the AC motor relatively attractive?...
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This note was uploaded on 09/15/2009 for the course INDUSTRIAL 0906533 taught by Professor Khaldountahboub during the Three '09 term at ADFA.

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63865-Ch06 - Components-3e-S Chapter 6 HARDWARE COMPONENTS...

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