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Field-mounted control unit

  • US 5,825,664 A
  • Filed: 06/07/1995
  • Issued: 10/20/1998
  • Est. Priority Date: 10/02/1989
  • Status: Expired due to Term
First Claim
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1. A smart field-mounted control unit for coupling to a two wire DC current process control circuit which carries a loop current, the two wire circuit electrically connected in series with a power source, a remote device and the control unit, the control unit comprising:

  • a housing;

    input circuitry in the housing adapted to be operably coupled to the two wire circuit, the input circuitry adapted to receive power from the power source through the two wire circuit which wholly powers the control unit and adapted to receive a process signal from the two wire circuit;

    a process variable sensor which provides a sensed process variable; and

    control circuitry in the housing operably coupled to the input circuitry, the process variable sensor, and the two wire circuit whereby the control unit is adapted to be electrically connected in series with the two wire circuit and the control circuitry provides a command output for the two wire circuit as a function of the sensed process variable and a previous value of the command output.

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