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Local device and process diagnostics in a process control network having distributed control functions

  • US 6,026,352 A
  • Filed: 10/07/1998
  • Issued: 02/15/2000
  • Est. Priority Date: 10/04/1996
  • Status: Expired due to Term
First Claim
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1. A field device for use in a process control system including a plurality of field devices mutually coupled by a two-wire, digital, powered bus, the bus supplying a field device control signal to the field device, the field device comprising:

  • a pneumatically operated fluid control valve having an actuator connected to a pneumatic pressure line, wherein said actuator is adapted to cause the fluid control valve to move to a position ranging from an open position to a closed position;

    a position sensor coupled to the fluid control valve that senses the position of the fluid control valve;

    a pressure sensor coupled to the pneumatic pressure line that senses a pneumatic pressure within the pneumatic pressure line;

    an electrical to pneumatic transducer coupled to the actuator by the pneumatic pressure line adapted to control the pneumatic pressure in the pneumatic pressure line as a function of an electrical signal;

    an electronic controller communicatively coupled directly to the electrical to pneumatic transducer, the pressure sensor, and the position sensor other than through the bus, the electronic controller including a control logic that determines the electrical signal based on feedback signals indicative of a pressure sensed by the pressure sensor and a position sensed by the position sensor and based on the field device control signal; and

    a digital interface coupled to the two-wire, digital, powered bus and coupled to the electronic controller, the digital interface including;

    a power circuit adapted to be coupled to the bus that supplies power derived from the powered bus to the electronic controller and the electrical to pneumatic transducer, anda two-way communication circuit adapted to receive a field device control signal from the bus and to transmit signals indicative of a status of the field device to the bus.

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