Patent ID: 6026352
Filing Date: 2000-02-15
Classification: G05B,Y02P

Abstract:
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; anda 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.