Dynamic Response - Fisher FIELDVUE DVC6200 Instruction Manual

Instruction Manual
D103605X012

Dynamic Response

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. In firmware 2, 3, and 4 this parameter should be set to 0.
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. In firmware 2, 3, and 4 this parameter should be set to 0.
D Set Point Filter Time (Lag Time)—The 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 2, 3, and 4 this parameter should be set to 0.
Note
Set Point Filter Time (Lag Time) is available for instrument level HC, AD, and PD.
D Lead/Lag Set Point Filter—ODV devices have access to a lead‐lag set point filter that can be used to improve a valve's
dynamic response. The lead‐lag 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.
Note
Lead/Lag is only available for instrument level ODV.
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
3‐2 for typical lead‐lag filter settings.
Table 3‐2. Typical Lead/Lag Filter Settings for Instrument Level ODV
Parameter
Lag Time First order time constant. A value of 0.0 will disable the lead‐lag filter.
Opening Lead/Lag Ratio Initial response to the filter in the opening direction.
Closing Lead/Lag Ratio Initial response to the filter in the closing direction.
Lead‐Lag Boost Initial conditions of the lead‐lag filter when the lower travel cutoff is active.
Description
Configuration
February 2017
Typical Value
0.2 sec
2.0
2.0
Off
23