Travel/Pressure Control; End Point Pressure Control; Characterization - Fisher FIELDBUE DVC6200 Instruction Manual

Instruction Manual
D103557X012

Travel/Pressure Control

Field Communicator Configure > Manual Setup > Travel/Pressure Control (2‐2-3)
End Point Pressure Control (EPPC)
D EPPC Enable—Select 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 maintained at a
certain value. This value is configured through the Upper Operating Pressure feature. 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
ensure there is an alert when an output pressure deviation occurs, setup the alert as described under Pressure
Deviation Alert.
D EPPC Set Point—Used in conjunction with End Point Pressure Control, End Point Pressure Control 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 EPPC Saturation Time—End Point Pressure Control Saturation Time is the time the digital valve controller stays in
hard cutoff before switching to pressure control. Default is 45 seconds.

Characterization

D Input Characterization
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 Characterization menu. You can select from
the three fixed input characteristics shown in figure 3‐1 or you can select a custom characteristic. Figure 3‐1 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.
D Custom Characterization
To define a custom input character, from the Characterization menu select Custom Characterization. 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 Characterization 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
Configuration
April 2016
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