Appendix A Principle Of Operation; Digital Valve Controller Operation - Fisher FIELDVUE DVC6200p Instruction Manual

Instruction Manual
D103563X012
Appendix A

Digital Valve Controller Operation

The DVC6200p digital valve controller has a single module base that may be easily replaced in the field without
disconnecting field wiring or tubing. The master module contains the following submodules: current‐to‐pneumatic
(I/P) converter, printed wiring board assembly, and pneumatic relay. The relay position is detected by sensing the
magnet on the relay beam via a detector on the printed wiring board. This sensor is used for the minor loop feedback
(MLFB) reading. The master module can be rebuilt by replacing the submodules. See figures A‐1 and A‐2.
Figure A‐1. FIELDVUE DVC6200p Digital Valve Controller Block Diagram
DIGITAL
SETPOINT
9–32 VOLT
FIELDBUS
AUXILIARY
TERMINALS
TERMINAL BOX
VENT
E1376
The DVC6200p digital valve controller is a bus‐powered instrument that provides a control valve position in response
to a digital setpoint from the control room. The following describes a direct acting DVC6200p digital valve controller
mounted on a sliding-stem piston actuator, where the valve is closed with zero power to the instrument.
The setpoint is routed into the terminal box through a single pair of wires and then to the printed wiring board
assembly submodule where it is read by the microprocessor, processed by a digital algorithm, and converted into an
analog I/P drive signal.
As the setpoint increases, the drive signal to the I/P converter increases, increasing the I/P output pressure. The I/P
output pressure is routed to the pneumatic relay submodule. The relay is also connected to supply pressure and
amplifies the small pneumatic signal from the I/P converter. The relay accepts the amplified pneumatic signal and
provides two output pressures. With relay A, an increasing setpoint will produce increasing pressure at output A and
decreasing pressure at output B. With relay B an increasing setpoint will produce decreasing pressure at output B
Principle of
PRINTED
WIRING BOARD
DRIVE
SIGNAL
I/P
CONVERTER
PNEUMATIC
RELAY
OperationA‐
OUTPUT A
SUPPLY
PRESSURE
OUTPUT B
Principle of Operation
A‐
VALVE TRAVEL FEEDBACK
VALVE AND ACTUATOR
June 2017
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