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4.3.9.2 Pressure Units
Select the display units for the optional actuator pressure sensor
.
The available choices
are PSI, BAR or KPA.
The choice applies to both the local LCD display and to the displays with SVI3 DTM or the
SVI3 DD with HART Communicator
.
1. Press * to move from PSI to BAR to KPA.
2. Press + to continue to scroll through the configuration menu.
4.3.9.3 Tight Shutoff
Tight Shutoff is an optional performance feature that prevents leakage at the closed
position. Without this feature, at the closed position with an input signal of 0%, the valve
may not be forced tight against the seat with maximum available actuator force or it may
be only touching the seat with minimum force. In either case, it is under control, however
unwanted leakage or premature trim wear can occur.
To prevent leakage that can occur in the second case
,
configure TS ON and set a value of
position setpoint below which the actuator applies maximum seating force. As the position
signal drops toward the TS value, SVI3 moves the valve to the TS position value. When the
position reaches the TS value SVI3 applies maximum actuator force.
The TS function has 0.5% deadband to prevent chatter
.
If TS is set ON at 1%, for example,
then the valve begins to open when the setpoint reaches 1.5%.
4.3.9.4 Configuring TS ON
1. Press * to turn TS ON.
2. Press + to increase TS.
3. Press
-
to decrease TS.
4. Press * when finished to return to the CONFIG menu.
The CONFIG menu displays TS ON.
Rotary or Reciprocating valve with EQUAL
PERCENTAGE TRIM
Linear
Not recommended
Rotary or Reciprocating valve with EQUAL
PERCENTAGE TRIM
Equal Percentage
LINEAR
Table 8: Guidelines for Characteristic Choice
Valve Type and Built In Characteristic
Desired Installed Valve
Position Characteristic
Standard Positioner
Characteristic Selection
