Rockwell Automation RSLogix 5000 Fuzzy Designer - Manual (Page 55)

Publication LOGIX-UM004A-EN-P - March 2007
FuzzyDesigner Component Library 55
Zero crossing dead band control stops changing control variable (ΔCV
= 0) when the process variable crosses the setpoint. The control
variable is not changed as long as the process variable remains within
the dead band interval. Zero crossing dead band control can be
written as follows:
Once PV reaches SP (E = 0) and as long as PV∈ DBI , use ΔCV = 0
(consider E = 0)
No zero crossing dead band control stops changing control variable
immediately when approaching the setpoint and crossing the band
limits. The control variable is not changed as long as the process
variable remains in the dead band interval. No zero crossing dead
band control can be written as follows:
IF (PV∈ DB) THEN ΔCV = 0 (consider E = 0)
When the gain parameters of the PID controller are supervised by
fuzzy rules, rapid changes of premise rules variables may cause rapid
changes of controller gains. To avoid these changes the gain forgetting
factor g can be used. The value of g has to be in the interval [0.001 1].
Value g = 1 corresponds to exact parameter tracking (no forgetting
factor is applied) and g = 0.001 corresponds to very slow parameter
tracking. The default value is 1.
Connections
The Input links of the PID component can be connected to all
components providing crisp values, such as:
• Input Port component.
• Output Takagi-Sugeno Variable component.
• Output Linguistic Variable component.
• PID component (theoretically).
The output link of the PID component can be connected to all
components expecting a crisp value, such as:
• Output Port component.
• Input Linguistic Variable component.
• Output Takagi-Sugeno Variable component (theoretically).
• PID component (theoretically).