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On traditional proportional plus integral controls, the
amount of correction becomes too large if the system
load exceeds the capacity of the equipment. When
the actuated device (valve or damper) is fully open or
closed and the setpoint still cannot be reached, the
integration error continues to grow. The result is
called integral windup. The S350P avoids integral
windup with a patented circuit that puts a dynamic
ceiling on the integrator. This circuit resets the
integration error when the sensor goes just above the
calculated setpoint plus the throttling range (in DA
mode) or just below the calculated setpoint minus the
throttling range (in RA mode). This allows the process
to recover from an out-of-range condition without a
large overshoot.
The S350P has three field-selectable integration
constants and an off position. The integration DIP
switch selects the integration constant. (Refer to
Figure 2 for location.) The field-selectable integration
constants include:
Proportional
Offset
S350P
Calculated
Setpoint
Proportional
Offset = 0
S350P
Calculated
Setpoint
Figure 6: Operation of Proportional Only vs. Proportional Plus Integral Control
Add-On Modules—S350P Proportional Plus Integral Temperature Stage Module Product/Technical Bulletin 5
Proportional Only Control
Load Change
Error
Time
Proportional Plus Integral Control
Load Change
Error
Time
Off (Switch 1 to On position, all others Off)
Provides proportional only operation.
Slow (C3) (Switch 2 to On position, all others
Off) This is the slowest integration constant
(equal to 26 minutes) and is suitable for most
proportional plus integral applications. Slow is the
recommended initial setting.
Medium (C2) (Switch 3 to On position, all
others Off) Selects a 13-minute integration
constant. If the rate of system recovery to setpoint
is sluggish with the control set to slow, and if the
system has enough capacity to drive the process
to setpoint at a faster rate, the medium setting
may be used.
Fast (C1) (Switch 4 to On position, all others
Off) This is the fastest integration constant
(equal to 6.5 minutes). Use the fast setting only in
instances where the rate of change at the sensor
is extremely rapid and system capacity can
compensate for that rapid change.
System Load
Control Point
Follows the Load
System Load
Integration adjusts the
setpoint regardless of load.
Throttling
Range
proportional output to
bring the process to
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