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CONTROL OF A PROCESS VARIABLE BY A COMPUTER AND A CONTROLLER WHICH REPLACES THE COMPUTER

  • US 3,665,172 A
  • Filed: 06/25/1969
  • Issued: 05/23/1972
  • Est. Priority Date: 06/25/1969
  • Status: Expired due to Term
First Claim
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1. A system for controlling a process variable of a process, comprising:

  • a meter for measuring said process variable, said meter being operatively connected to said process and adapted to generate an output signal proportional to the measured value of said process variable;

    a digital computer operatively connected to said meter so as to receive the output signal thereof, said computer being adapted to produce an intermittent output signal proportional to changes that must be made in said process;

    a signal generator adapted to generate a signal proportional to the set value of said process variable;

    circuit means having input means connected to the output of said computer, to the output of said signal generator, and to the output of said meter, said circuit means including 1. an operational amplifier having an input and an output;

    2. a plurality of impedances;

    3. switching means, said switching means being connected between said impedances and the input of said operational amplifier and adapted to operate such that when said switching means are in one position the operational amplifier receives an output signal from the computer and said process is controlled by said computer but when said switches are in another position, said process is controlled by said operational amplifier in combination with a portion of said impedances such that said set value signal and said measured value signal are supplied to the input of said operational amplifier with opposite polarities;

    4. separate feedback impedance means included in the plurality of impedances and connecting the output of the operation amplifier to its input when the switching means is in said one position or said other position; and

    a correcting unit connected between the output of said circuit means and said process, said process, said correcting unit being adapted to control said process variable in accordance with the output signal of said operational amplifier.

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