In many industrial control systems, it is required to activate an output function whenever any one of

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In many industrial control systems, it is required to activate an output function whenever any one of several inputs is activated. For example, in a chemical process it may be desired that an alarm be activated whenever the process temperature exceeds a maximum value or whenever the pressure goes above a certain limit. Figure 3-4 is a block diagram of this situation. The temperature transducer circuit produces an output voltage proportional to the process temperature. This voltage, VT, is compared with a temperature reference voltage, VTR, in a voltage comparator circuit. The comparator output, TH, is normally a low voltage (logic 0), but it switches to a high voltage (logic 1) when VT exceeds VTR, indicating that the process temperature is too high. A similar arrangement is used for the pressure measurement, so that its associated comparator output, PH, goes from LOW to HIGH when the pressure is too high. What is the purpose of the OR gate?


Figure 3-4

Temperature transducer Pressure transducer i Chemical process VTR VPR Comparator Comparator TH PH Alarm

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Digital Systems Principles And Application

ISBN: 9780134220130

12th Edition

Authors: Ronald Tocci, Neal Widmer, Gregory Moss

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