Emerson Fisher FIELDVUE DVC6000, Инструкция по эксплуатации, Страница: 71 / 162

Detailed Setup
September 2013 4-11
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 (1-2-2-4)
Select Custom Characterization Table from the
Response Control menu and follow the prompts to
define a custom input character.
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)
SP Rate Open (Minimum Opening Time in
firmware 2
−
6)—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. In firmware 10 and below this parameter
should be set to 0.
SP Rate Close (Minimum Closing Time in
firmware 2
−
6)—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. In firmware 10 and below this parameter
should be set to 0.
Note
Set Point Filter Time (Lag Time) is only
available for instrument level HC, AD,
and PD, firmware 7, 9, 10, and 11.
Set Point Filter Time (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.
In Firmware 7, 9, and 10 this parameter should be set
to 0.
Note
Lead/Lag is only available for
instrument level ODV.
Lead/Lag Set Point Filter—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 4-7 for typical lead-lag filter settings.
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