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Power supply for field mounted transmitter

  • US 5,535,243 A
  • Filed: 07/13/1994
  • Issued: 07/09/1996
  • Est. Priority Date: 07/13/1994
  • Status: Expired due to Term
First Claim
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1. A transmitter for use in a two-wire process control loop, comprising:

  • a sensor which senses a process variable and provides an output signal representative of the process variable;

    measurement circuitry coupled to the sensor to receive the output signal, the measurement circuitry transmitting a signal over the two-wire process control loop indicative of a value of the process variable;

    power supply circuitry coupled to the measurement circuitry, the power supply circuitry receiving a loop current from the two-wire process control loop and providing an energizing current to the measurement circuitry, the power supply circuitry comprising;

    an inductive element coupled to the measurement circuitry; and

    a switch selectively electrically connecting the inductive element to the two-wire process control loop to receive current from the two-wire process control loop;

    a capacitor for storing charge;

    modulation circuitry coupled to the measurement circuitry and the two-wire process control loop which responsively controls current through the two-wire process control loop; and

    startup circuitry coupled to the modulation circuitry which controls the modulation circuitry to cause an increase in control loop current during a startup condition whereby the capacitor in the power supply circuit is charged.

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