106AW T4 2 0 | U N I V E R S A L 4 - W I R E , D U A L- I N P U T T R A N S M I T T E R | O I/A W T4 2 0 - E N R E V. B…Appendix D PID control…Control actionDual-acting control• Two control outputs (Base Output and Acid Output)• P or P+I (Base Controller)• Base Output increases as Process Value deviates belowBase Setpoint• Base Output is zero if Process Value is greater thanBase Setpoint• Base proportional band is positioned below Base setpoint• P or P + I (Acid Controller)• Acid Output increases as Process Value deviates aboveAcid Setpoint• Acid Output is zero if Process Value is less than Acid Setpoint• Acid proportional band is positioned above Acid SetpointFigure 40 Dual-acting controlManual Reset (proportional band offset)A Manual Reset value* is available on Reverse or Direct-actingcontrollers when the integral term is disabled (i.e., Control Typeis configured for P, or P+D).When the process variable is equal to the control setpoint, theoutput value is equal to the Manual Reset value – this effectivelychanges the position of the proportional band.* By default the manual reset value is zero.Figure 41 Manual Reset (proportional band offset)100 %OutputBase controlleroutputAcid controlleroutputProportionalband (Base)Proportionalband (Acid)Setpoint(Base)Setpoint(Acid)0 %PV100 %100 %100 %OutputOutputOutputProportionalbandProportionalbandProportionalbandSetpointSetpointSetpointManual Reset = 0 %Manual Reset = 50 %Manual Reset = 100 %0 %0 %0 %50 %PVPVPV
