초록 ▼

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 circui

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.

대표청구항 ▼

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 com

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.