Fisher FIELDVUE DVC6200 Instruction Manual page 49

Parameter
Lag Time
Opening Lead/Lag Ratio
Closing Lead/Lag Ratio
Lead-Lag Boost
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).
Dynamic Response (1-2-2-5)
D SP Rate Open—Maximum rate (% of valve travel
per second) at which the digital valve controller will
move to the open position regardless of the rate of
input current change. A value of 0 will deactivate this
feature and allow the valve to stroke open as fast as
possible.
D SP Rate Close—Maximum rate (% of valve travel
per second) at which the digital valve controller will
move to the close position regardless of the rate of
input current change. A value of 0 will deactivate this
feature and allow the valve to stroke close as fast as
possible.
Note
Lag Time is available for instrument
level HC, AD, and PD.
D Lag Time—Slows the response of the digital
valve controller. A value ranging from 0.2 to 10.0 can
be used for noisy or fast processes to improve closed
loop process control. Entering a value of 0.0 will
deactivate the lag filter.
September 2010
Table 4-6. Typical Lead/Lag Filter Settings
Description
First order time constant. A value of 0.0 will disable the
lead-lag filter.
Initial response to the filter in the opening direction.
Initial response to the filter in the closing direction.
Initial conditions of the lead-lag filter when the lower
travel cutoff is active.
Detailed Setup
Note
Lead/Lag is only available instrument
level ODV.
D Lead/Lag—ODV devices have access to a
lead-lag input filter that can be used to improve a
valve's dynamic response. The lead-lag input filter is
part of the set point processing routine that reshapes
the input signal before it becomes travel set point.
Lead-lag filters are characterized by lead and lag time
constants.
When the valve is in its active control region (off the
seat), the lead-lag filter improves small amplitude
response by momentarily overdriving the travel set
point. This is useful when the actuator is large and
equipped with accessories. As a result, any volume
boosters that are present will be activated. The longer
the lag time, the more pronounced the overdrive.
Since the lead-lag input filter is used to enhance the
dynamic response of a control valve, filter parameters
should be set after the tuning parameters have been
established.
When the valve is at its seat, the lead-lag filter also
has a boost function that sets the initial conditions of
the filter artificially low so that small amplitude signal
changes appear to be large signal changes to the
filter. The boost function introduces a large spike that
momentarily overdrives the instrument and activates
any external volume boosters that may be present.
The lead-lag boost function is normally disabled
except for those cases where the valve must respond
to small command signals off the seat. By setting the
lead/lag ratio in the opening and closing directions to
1.0, the boost function can be enabled without
introducing lead-lag dynamics in the active control
region. See table 4-6 for typical lead-lag filter settings.
Alerts (1-2-3)
The following menus are available for configuring
Alerts. Items on the menus may be changed with the
instrument In Service. Protection does not need to be
removed (no need to set to None). Alerts are not
processed when a Diagnostic is in progress. Select
Typical Value
0.2 sec
2.0
2.0
Off
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