Emerson Fisher FIELDVUE DVC2000, Instruction Manual

Page: 48 / 106

DVC2000 Digital Valve Controller
July 2009 4-8
the input to the characterization function. If the zero
control signal equals closed, then a set point of 0%
corresponds to a ranged input of 0%. If the zero
control signal 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, choose Select
Input Char from the Input Char menu. You can select
from the three fixed input characteristics shown in
figure 4-2 or you can select a custom characteristic.
Figure 4-2 shows the relationship between the travel
target and ranged set point for the fixed input
characteristics, assuming the Zero Control Signal 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.
To define a custom input characteristic, from the Input
Char menu select Define Custom Char. 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 Input
Char 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).
Set Point Filter Time—Time constant for the set
point filter, in seconds. The set point filter slows the
response of the digital valve controller and is typically
used with noisy or fast processes. The filter provides
improved closed loop process control. To disable the
filter, set the time constant to 0 seconds.
Min Opening Time—Minimum Opening Time is
configured in seconds and defines the minimum time
for the travel to increase the entire ranged travel. This
rate is applied to any travel increases. A value of 0.0
seconds deactivates this feature and allows the valve
to stroke open as fast as possible.
Min Closing Time—Minimum Closing Time is
configured in seconds and defines the minimum time
for the travel to decrease the entire ranged travel. This
rate is applied to any travel decreases. A value of 0.0
T
ravel T
arget,
%
Ranged Set Point, %
−
25 0 125 100
−
25 0 125 100
−
25 0 125 100
Input Characteristic = Linear
Input Characteristic = Equal Percentage
Input Characteristic = Quick Opening
100
0
−
25
125
T
ravel T
arget,
%
100
0
−
25
125
Ranged Set Point, %
T
ravel T
arget,
%
100
0
−
25
125
Ranged Set Point, %
A6535-1/IL
Figure 4-2. Travel Target Versus Ranged Set Point, for Various
Input Characteristics (Zero Control Signal = Closed)
4