Instruction Manual

Instruction Manual
D103409X012
Detailed Setup
December 2013
58
D Press Set Point—Used in conjunction with End Point Pressure Control, Pressure Set Point allows the user to select a
pressure to be delivered by the instrument at the travel extreme. For a fail‐closed valve, this pressure must be
sufficient to maintain the fully open position. For a fail‐open valve, this pressure (which is automatically set to
supply pressure) must be sufficient to fully close the valve and 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.
D Press Sat Time— Pressure Saturation Time is the time the digital valve controller stays in hard cutoff before switching
to pressure control. Default is 45 seconds.
Input Characterization
Field Communicator Configure > Detailed Setup > Response Control > 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.
To select an input characterization, select Input Characterization from the Response Control menu. You can select from
the three fixed input characteristics shown in figure 4‐1 or you can select a custom characteristic. Figure 4‐1 shows the
relationship between the travel target and ranged set point for the fixed input characteristics, assuming the Zero
Power Condition is configured as closed.
You can specify 21 points on a custom characteristic curve. Each point defines a travel target, in % of ranged travel, for
a corresponding set point, in % of ranged set point. Set point values range from -6.25% to 106.25%. Before
modification, the custom characteristic is linear.
Custom Characterization Table
Field Communicator Configure > Detailed Setup > Response Control > Custom Characterization Table (1‐2‐2‐4)
To define a custom input character select Custom Characterization Table from the Response Control menu. Select the
point you wish to define (1 to 21), then enter the desired set point value. Press Enter then enter the desired travel
target for the corresponding set point. When finished, select point 0 to return to the Response Control menu.
With input characterization you can modify the overall characteristic of the valve and instrument combination.
Selecting an equal percentage, quick opening, or custom (other than the default of linear) input characteristic
modifies the overall valve and instrument characteristic. However, if you select the linear input characteristic, the
overall valve and instrument characteristic is the characteristic of the valve, which is determined by the valve trim (i.e.,
the plug or cage).