106 AWT420 | UNIVERSAL 4-WIRE, DUAL-INPUT TRANSMITTER | OI/AWT420-EN REV. B
…Appendix D PID control
…Control action
Dual-acting control
• Two control outputs (Base Output and Acid Output)
• P or P+I (Base Controller)
• Base Output increases as Process Value deviates below
Base Setpoint
• Base Output is zero if Process Value is greater than
Base Setpoint
• Base proportional band is positioned below Base setpoint
• P or P + I (Acid Controller)
• Acid Output increases as Process Value deviates above
Acid Setpoint
• Acid Output is zero if Process Value is less than Acid Setpoint
• Acid proportional band is positioned above Acid Setpoint
Figure 40 Dual-acting control
Manual Reset (proportional band offset)
A Manual Reset Reverse or Direct-acting
controllers when the integral term is disabled (i.e., Control Type
is configured for P, or P+D).
When the process variable is equal to the control setpoint, the
output value is equal to the Manual Reset
changes the position of the proportional band.
Figure 41 Manual Reset (proportional band offset)
100 %
Output
Base controller
output
Acid controller
output
Proportional
band (Base)
Proportional
band (Acid)
Setpoint
(Base)
Setpoint
(Acid)
0 %
PV
100 %
100 %
100 %
Output
Output
Output
Proportional
band
Proportional
band
Proportional
band
Setpoint
Setpoint
Setpoint
0 %
0 %
0 %
50 %
PV
PV
PV
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