Flowserve 1400 Valtek Logix User Manual
Page 17
46-17
Flowserve Corporation, Valtek Control Products, Tel. USA 801 489 8611
LOAD_EE_DEFAULTS) are maximum gain = 2.0, mini-
mum 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 recom-
mended 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 which may prevent fully closing the valve.
Integration Summer: The integral summer within the
Logix 1400 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 sum-
mer 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 which 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 be-
comes 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:
• 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.
Figure 17: Logix 1400 Digital Positioner Block Diagram
Table I: Factory Tuning Sets
.
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f
M
g
n
i
n
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T
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I
A
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1
0
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2
5
0
.
0
0
1
5
2
B
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r
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t
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0
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1
5
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2
5
0
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0
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4
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3
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7
7
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1
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3
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0
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0
5
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t
3
2
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0
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1
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1
5
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0
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1
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t
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3
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3
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1
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1
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6
1
4
R
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2
5
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2
5
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0
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1
7
3
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t
7
2
5
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5
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2
6
.
3
5
0
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0
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1
5
7
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t
8
4
6
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0
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4
0
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5
5
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0
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1
9
0
1
Stem
Position
Sensor
Tubed ATO
Sensor
Air Supply
Modulator
Coil Current
Inner Loop
Spool Control
Inner-Loop
Hall Sensor
Output
D/A Output
Percentage
Control
Algorithm
Deviation
Position
P
max
P
min
G
mult
Integration Summer
Inner Loop Offset
XD
AO
+
Control
Command
(CMD_USED)
(GAIN_UPPER)
(HALL_SENSOR)
(GAIN_LOWER)
(GAIN_MULTI)
(IL_OFFSET)
Linear Mode
Characterization
Soft Limits
MPC