US 5,684,451 A · Communication system and method

Abstract

The present invention relates to a circuit which is connected by two conductors to a control system for a variable analog DC input and that also enables bidirectional digital communication along the two conductors for diagnostic operations of an instrument. The novel circuit includes a switch circuit that has a first position that provided the ability to accept both the variable DC analog signals and the bidirectional digital communication signals by presenting a first impedance for the DC signals and a second switch position for providing a second substantially higher impedance while using the same two conductor system. The novel invention also includes an auxiliary analog input signal to the circuit which allows further control as a current feedback to a control algorithm in a microcontroller. An auxiliary process transmitter can sense pressure, temperature, flow or some other process related variable and couple it to the circuit for control of the instrument. Finally, the novel invention includes a novel voltage regulator and a capacitive voltage supply for utilizing the voltage on the two conductors from the controller to also power the device.

Claims18

Dependent claims

An instrument remotely coupled to a control system and powered by a single pair of wires for providing a control pressure to a valve actuator mechanically coupled to a valve, comprising:

a power circuit for providing DC power to said instrument from said single pair of wires;
means for receiving communications representative of a desired valve position over said single pair of wires;
means for sensing the valve position where the sensed valve position is a state variable representing the state of the instrument,
means for providing a command output as a function of the desired valve position and the sensed position;
transducer means receiving a supply of air, for providing a control pressure as a function of the command output;
diagnostic means forming part of said instrument for storing an attribute of the valve and providing a diagnostic output as a function of the stored valve attribute and a selected function of the stored valve attribute and a selected one of the state variables;
and
means for transmitting the diagnostic output in the form of digitally encoded communication signals over said single pair of wires.

5 more elements

A system for communicating between a control system and a remote instrument, the system comprising:

a single pair of first and second conductors coupled between the control system and the remote instrument for carrying DC power to the remote instrument to enable the remote instrument to perform selective tasks;
a process transmitter for generating a variable analog DC signal on a second single pair of third and fourth conductors coupled to the remote instrument;
and
a communication circuit forming part of the remote instrument having first and second input terminals coupled to the single pair of first and second conductors and having an output coupled to an operating device for controlling said operating device as a function of the variable analog DC signal from the process transmitter and simultaneously enabling bidirectional digitally encoded communication signals concerning supplemental data to be transmitted between the first and second input terminals and the control system over said single pair of first and second conductors.

1 more element

Dependencies are inferred from the claim text.

Communication system and method

Life of this patent

Communication system and method

Life of this patent

Abstract

Claims18