Flowserve 3400MD Digital Positioner - Manual (Page 21)

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Logix 3400MD Digital Positioner FCD LGENIM3404-08-AQ – 5/15
flowserve.com
7.13.2 Control and Tuning
Setting P + I Parameters
Using the Host configurator, you can set individual tuning parameters.
A few key points are mentioned below (see Figure 11.)
GAIN_UPPER, GAIN_LOWER, and GAIN_MULT: These three
parameters are related by the following formula.
Proportional Gain = Maximum Gain - | deviation | x Gain Multiplier
If Proportional Gain < Minimum Gain, then Proportional Gain =
Minimum Gain
This algorithm allows for quicker response to smaller steps yet stable
control for large steps. Setting the gain multiplier to zero and max
gain = min gain results in a typical fixed proportional gain.
The higher the gain multiplier, the larger the required deviation before
the gain increases. Default values upon initiating a RESET to factory
defaults (under LOAD_EE_DEFAULTS) are maximum gain = 2.0,
minimum gain= 1.0, and gain multiplier= 0.05. These values will allow
stable control on all Valtek control product actuator sizes.
Integral Gain (IGAIN): The integral gain is primarily for deviations due
to temperature drift within the inner loop spool control. The factory
default value is 10. Although higher numbers can speed the time it
takes to reach zero deviation, it can add overshoot if too large. It is
recommended that maximum and minimum gains be adjusted while
leaving integral gain fixed at 10. Integration is disabled below a stem
position of 3 percent and above a stem position of 97 percent. This
is to prevent integration windup from calibration shifts due to lower
pressure or a damaged seat that may prevent fully closing the valve.
Integration Summer: The integral summer within the Logix 3400MD
digital positioner is clamped at +20 percent and -20 percent. If the
integration summer is fixed at +20 percent or -20 percent, it usually
indicates a control problem. Some reasons for a clamped integration
summer are listed below:
• Stroke calibration incorrect
• Any failure which prevents stem position movement: stuck spool,
handwheel override, low pressure
• Incorrect inner loop offset
• Loss of air supply on a fail in place actuator
Writing a zero to integral gain (IGAIN) will clear the integral summer.
The integral gain can then be returned to its original value.
Inner loop offset (IL_OFFSET): Three control numbers are summed
to drive the inner loop spool position control: proportional gain,
integral summer, and inner-loop offset.
Inner-loop offset is the parameter that holds the spool in the ‘null’
or ‘balance’ position with a control deviation of zero. This value is
written by the positioner during stroke calibration and is a function of
the mechanical and electrical spool sensing tolerances. However,
if it becomes necessary to replace the driver module assembly or the
software RESET calibration constants has been performed, it may be
necessary to adjust this value. The method below should be used to
adjust inner-loop offset.
Or simply perform a new stroke calibration.
From the fieldbus configurator:
• Set transducer block to OOS
• Enable Diagnostic Variable access in TEST_MODE
• Send a 50 percent command
• Set integral to zero
• Locate the DAC_PERCENT
• Write this percentage value to IL_OFFSET
• Write original value to Integral
These tuning sets can be used to obtain initial values for Flowserve
products and comparable actuator sizes. The user may need to adjust
this tuning to achieve optimal performance for a particular application.
Mfg. Tuning Set
Gain
Lower
Gain
Upper
Gain
Multi
lgain
Compa-
rable size
(in 2 )
Valtek
VFactory_A 1 2 0.05 10 25
VFactory_B 1 2.5 0.05 10 50
VFactory_C 2 3 0.05 10 100
VFactory_D 4 5 0.05 10 200
VFactory_E 4 7 0.05 10 300
Trooper 48 0.4 0.5 0.05 25 31
Trooper 49 3 4 0.05 10 77.5
Kammer
Trooper 48 0.4 0.5 0.05 25 31
Trooper 49 3 4 0.05 10 77.5
Automax
R1 0.3 0.5 0.05 10 3 to 5
R2 1 1.5 0.05 10 9 to 12
R3 1.3 2 0.05 10 16 to 19
R4 2 2.5 0.05 10 27 to 37
R5 2.5 3.6 0.05 10 48 to 75
R6 4 5 0.05 10 109
Table 10: Factory Tuning Sets
7.14 Alerts
7.14.1 FINAL_VALUE_CUTOFF
The FINAL_VALUE_CUTOFF or tight shutoff feature of the
Logix 3400MD digital positioner allows the user to control the level
at which the command signal causes full actuator saturation in the
closed or open position.