Instruction Manual

Detailed Setup
September 2013
4-11
Table 4-7. Guidelines for Manually Setting Pressure Set Point
Actuator Type Relay Type Zero Power Condition Partial Stroke Start Point Pressure Set Point
Single-Acting
A or C
Closed
Open Psupply − 2 psig
Closed 2 psig
Open
Open 2 psig
Closed Psupply − 2 psig
B
Closed
Open 2 psig
Closed Psupply − 2 psig
Open
Open Psupply − 2 psig
Closed 2 psig
Double-Acting A
Closed
Open Psupply − 5 psig
Closed 5 psig − Psupply
Open
Open 5 psig − Psupply
Closed Psupply − 5 psig
End Point Pressure Control (1-2-2-2-2)
 End Pt Control Enab— Yes or No. End Point
Pressure Control allows the digital valve controller to
pull back from saturation of the pneumatic output after
reaching the travel extreme. Rather than having the
instrument provide full supply pressure (saturation)
continuously at the travel extreme, the digital valve
controller switches to an End Point Pressure Control
where the output pressure (pressure controller set
point) to the actuator is controlled at a certain value.
This value is configured through Pressure Set Point.
Because the digital valve controller is constantly in
control and not allowed to reach a dormant or
saturated state, it is constantly testing its own
pneumatic system. If there is an output pressure
deviation, for example, the instrument will issue an
alert. To assure there is an alert when an output
pressure deviation occurs, set up the alert as
described under Pressure Deviation Alert.
 PST Start Pt—Defines the travel stop the valve
needs to be at before a partial stroke test can be
initiated. Also defines the travel stop for end point
pressure control. Setting this value to Not Configured
will disable partial stroke tests and end point pressure
control.
 EPPC Set Point— As part of End Point Pressure
Control, Pressure Set Point is the target pressure the
positioner controls to when the valve is at the travel
stop defined by PST Start Point. Default values for
Pressure Set Point are summarized in table 4-7. When
controlling pressure in the open position, Pressure Set
Point must be set at a value that ensures the valve will
remain open. When controlling pressure in the closed
position, Pressure Set Point must be set at a value
that ensures the valve will remain closed and has
enough force to maintain its rated shutoff
classification. For double-acting spring return
actuators, this is the differential pressure required to
either maintain the fully open or fully closed position,
depending on the valve and actuator configuration. For
a double-acting actuator without springs with a
fail-close valve, this is 95% of the supply pressure. If
the valve is fail-open, the upper operating pressure for
all actuator is set to the supply pressure.
Note
End Point Pressure Control will be set
automatically during the Setup Wizard
or during the Auto Calibration Travel
procedure.
Refer to table 4-7 for guidelines for manually setting
Pressure Set Point.
 EPPC Saturation Time—The amount of time
the digital valve controller stays in hard cutoff before
switching to pressure control. Default is 45 seconds.
Input Characterization (1-2-2-3)
Input Characterization defines the relationship
between the travel target and ranged set point.
Ranged set point is the input to the characterization
function. If the zero power condition equals closed,
then a set point of 0% corresponds to a ranged input
of 0%. If the zero power condition equals open, a set
point of 0% corresponds to a ranged input of 100%.
Travel target is the output from the characterization
function.
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