Emerson Fisher FIELDVUE DVC2000 Instruction Manual page 78

DVC2000 Digital Valve Controller
INPUT SIGNAL
(4-20 mA, 9 VOLTS)
DVC2000 Operation
The DVC2000 digital valve controller uses a traditional
4-20 mA input signal and converts it into a pneumatic
output pressure that is delivered to the control valve
A
actuator. Accurate control of the position of the valve
is enabled by valve stem position feedback. The way
in which the DVC2000 accomplishes this is through a
two-stage positioner design. Refer to figure A-1 for a
block diagram of the positioner operation.
A traditional 4-20 mA signal provides the set point and
power to the instrument. At the same time, the HART
protocol provides instrument and process data through
digital communications. The instrument receives this
set point and positions the valve where it needs to be.
D The input signal provides electrical power and
the set point simultaneously. It is routed into the
terminal board through a twisted pair of wires. The
terminal board contains the termination points for the
loop signal (+11/−12). If the options board is installed,
an additional options board set includes additional
terminals for the transmitter output (+31/−32), switch
#1 output (+41/−42), and switch #2 output (+51/−52).
A-2
NON-CONTACT
POSITION FEEDBACK
MAIN BOARD
ASSEMBLY
TERMINATIONS
&
POSITION
SENSOR
BOARD
TRAVEL = 66.8%
14.6 MA 0.29 BAR
Figure A-1. FIELDVUE DVC2000 Digital Valve Controller Block Diagram
ACTUATOR
PRESSURE
SENSOR
MINOR LOOP SINGLE ACTING
FEEDBACK RELAY
(POWER
AMPLIFIER)
I/P
PRESSURE
SIGNAL
I/P
CONVERTER
(PRE-
DRIVE
AMPLIFIER
SIGNAL
D The input signal is then directed to the main
electronics board assembly where the microprocessor
runs a digital control algorithm resulting in a drive
signal to the I/P converter.
D The I/P converter assembly is connected to
supply pressure and converts the drive signal into a
pressure signal. The I/P converter is the pre-amplifier
stage in the two-stage positioner design. This
component enables high static gain for
responsiveness to small changes in the input signal.
D The I/P output is sent to the pneumatic relay
assembly. The relay is also connected to supply
pressure and amplifies the small pressure signal from
the I/P converter into a larger pneumatic output
signal used by the actuator. The pneumatic relay is
the power amplifier stage in the two-stage positioner
design. This component enables superior dynamic
performance with minimal steady-state air
consumption.
OUTPUT
AIR SUPPLY
July 2009