Flowserve 1400 Valtek Logix - Manual (Page 4)

46-4 Flowserve Corporation, Valtek Control Products, Tel. USA 801 489 8611
Figure 1: Logix 1000 Digital Positioner Schematic
Detailed Sequence of Positioner Operations
The positioner operates on a pressure equilibrium prin-
ciple with a spool valve apportioning supply to the
actuator. An increase in the command signal causes the
modulator pressure to increase, pushing the spool as-
sembly upward from its equilibrium position. This opens
the spool valve ports, supplying air to output 1 and
exhausting air from output 2. This causes the actuator
piston to move upward.
The upward motion of the piston is transmitted back to
the positioner through the stem-position feedback link-
age. The piston continues to stroke upward until the
stem-position signal of the sensor increases sufficiently
to counter the command signal being sent to the control
algorithm. At this point, the spool is at its equilibrium
position as the pressures in the cylinder stabilize and the
air flow to the actuator decreases. The computer will then
make small adjustments to fine-tune the desired position
and compensate for changes in dynamic loading.
A decrease in the command signal reverses the
described actions, causing a proportional downward
movement of the actuator piston and stem.
Tubing Positioner to Actuator
Proper tubing orientation is critical for the positioner to
function correctly and have the proper failure mode.
Referring to Figure 1 note that for air-to-open valves, the
output 1 port of the positioner manifold is tubed to the
bottom side of the actuator. The output 2 port of the
O O
Hall Effect Sensor
Electromagnetic Coil
Nozzle
Flapper
Digital Position
Algorithm
Spool Valve
Flame Arrestors
Collector Board
Pressure Sensor
Air Supply
LED
Dis-
play
Orifice
Exhaust
OUTPUT 1
OUTPUT 2
Exhaust
Flame
Arrestor
Stem Position Sensor
Air-to-Open
Configuration
Main PCB Tray
Ribbon Cable
Flame Arrestor
Filter
Regulator
positioner manifold is tubed to the top side of the
actuator. For air-to-close valves the above configuration
is reversed.
Wiring and Grounding Guidelines
Input Cable Shielding (Figure 2)
The fieldbus signal to the Logix 1400 digital positioner
should be in shielded cable. Shields must be tied to a
ground at only one end of the cable to provide a place for
environmental electrical noise to be removed from the
cable. In general, shield wire should be connected at the
source.
Cable Requirements
The Logix 1400 digital positioner utilizes the fieldbus
communication protocol. Refer to Fieldbus Foundation
document AG-140, Wiring and Installation 31.25 kbit/s,
Voltage Mode, Wire Medium Application Guide for full
information on wiring and building fieldbus networks.
Grounding Screw
The green grounding screw, located inside the termina-
tion cap, should be used to provide the unit with an
adequate and reliable earth ground reference.
This ground should be tied to the same ground as the
electrical conduit. Additionally, the electrical conduit
should be earth grounded at both ends of its run. The
green grounding screw must not be used to terminate
signal shield wires.