Yokogawa YVP20S - Manual (Page 82)

9-5
IM 21B04C50-01E
<Toc> <Ind> <9. CONFIGURATION SERVICES>
9.2.2 Position Limit
The Position Limits frame provides parameters that allow you to limit the valve, to force the
valve to close tightly or open fully at specified positions, to set the trip points of the limit
switches (DI Block). You can also activate a warning when a deviation lasts longer than the
Time 1 or to force the valve to its failsafe position if the deviation lasts longer that time 2.
Since there is a dead zone of 1%, Tight Shut Off is disabled if the valve position setpoint is
1% more than this value.
WARNING
Position Limit parameters are powerful tools to alter the valve performance to be non-linear.
Use them with caution and only when the process requires special performance
● Tight Shutoff Below
If the valve target position is less than this value, the valve is forced to fully close. A value of
-10 removes this function from the normal travel range, unless the calibration of valve travel
has been adjusted. Set this between 1 and 3 to minimize seat leakage. There is a dead
band.
Since there is a dead zone of 1%, Full Open Above is disabled if the valve position setpoint
is 1% less than this value.
CAUTION
When Tight Shutoff below is configured to a positive value, small flows will not be control-
lable.
● Full Open Above
If the valve target position is more than this value, the valve is forced to fully open. A value
of 110 removes this function from the normal travel range.
WARNING
Use of Full Open Above at values less than 110 may result in rapid increase in flow rate if
input reaches this value. Use with extreme caution.
● Position Lower Limit
The valve target position may not be less than this value. This will prevent the valve from
closing. Use only when required by the control strategy. A value of -10 removes this
function from the normal travel range.
● Position Upper Limit
The valve target position may not exceed this value. This will prevent the valve from
closing. A value of 110 removes this function from the normal travel range.
● “Near Closed” Value
The threshold below which the valve is considered “near closed.” “Near Close” term is
useful for estimating when to change the valve trim. This value does not affect valve travel.
It is used only for reporting the time that valve is near the seat.