Honeywell VPR100 User Manual page 114

Programming Function Blocks and Features
Prompt
SOFT PID YES, NO
SP INC SLEW LIMIT & Enter a number
SP DEC SLEW LIMIT
SP LOW LIMIT & OFF or number
SP HIGH LIMIT
SP1 TRACKING SP2, NONE
SUPPRESS YES, NO
OVERSHOOT
ATTENTION
Regardless of the setting of this SUPPRESS OVERSHOOT selection, overshoot is not suppressed when the process
disturbance causes an initial deviation (PV-SP) value between -0.7 and +0.7 engineering units. Consequently,
overshoot may not be suppressed in applications which require numerically small control loop PV ranges such as
carbon potential where this range is typically 0.0 to 2.0 engineering units.
WILD VARIABLE
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Table 4-10 Loop Prompts (continued)
Range/Selections
VPR & VRX – User Manual
Definition
Soft PID action (YES) causes the control algorithm to not
calculate proportional output corresponding to errors
resulting from changes to setpoint. The algorithm will adjust
its Reset (Integral) term to a value required to maintain the
present output when the setpoint is changed. Normal
proportional action should occur for all changes and
variations to the controlled variable.
Working setpoint slew limits for increasing and decreasing
slew rates. (Variable slew limits are available by
programming a constant's Destination with IS or DS. See
Program Constants, Section 4.16.)
Limits will be imposed on the working setpoint value,
regardless of source. A setpoint value above or below the
limits will be entered into the loop at the limit value. OFF
entry will assume process variable limits. (Variable limits are
available by programming a constant's Destination with HS or
LS. See Program Constants, Section 4.16.)
A selection of Setpoint #2 will cause the Setpoint #1 value to
be set to the Setpoint #2 value on a transfer from Setpoint #2
to Setpoint #1. Setpoint #1 adjustment may be made after
the transfer.
This parameter set to YES limits overshoot of the Setpoint
(SP) by the Process Variable (PV) after a disturbance in the
process such as a load or SP change. Through fuzzy logic,
the working SP of the control loop is dynamically modified by
the control algorithm to reduce or eliminate overshoot.
Enter an analog input (AIn OV) or calculated value (CVn OV)
parameter that represents a second input signal applied to
the ratio control loop whose value will be multiplied by the
RATIO SETPOINT multiplier. The product of this
multiplication may be specified as the ratio control loop's
working set point and can be biased by specifying a RATIO
BIAS value. This input parameter is referred to as the "WILD
VARIABLE" since the ratio loop has no control over its value
whatsoever. In the fuel-air ratio control examples used in
RATIO SETPOINT AND RATIO BIAS, fuel flow was for all
intents and purposes the WILD VARIABLE.
Note that the typical function block diagram one will use to
represent a ratio control loop is illustrated in Figure 4-1.
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