Anti-reset windup proportional and integral controller

In a process control system having a proportional control loop including sensor means for monitoring a controlled variable and for providing a linearly changing command signal indicating deviations of the controlled variable from a system set point, and actuator means responsive to the command signal to control a manipulated variable to effect a change in the controlled variable to return the controlled variable to the set point, a proportional plus integral controller means comprising proportional means responsive to said command signal to provide a first signal that is proportional to said command signal, integral means having an input and an output, circuit means including integrating capacitor means connected between said input and said output, said integral means being operable when enabled to be responsive to said command signal to permit said capacitor means to charge to a value related to time changes of said command signal whereby said integral means provides a second signal that is proportional to the time integral of the command signal, summing means for summing said first and second signals to provide a modified command signal, and control means responsive to said modified command signal and operable to control said integral means to limit the amplitude of the second signal to a value which enables said summing means to normally provide a modified command signal of an amplitude that is between predetermined first and second values which define a proportional band for the controller means, and said control means disabling said integral means thereby permitting said capacitor means to discharge to cause the potential at said input and said output to decrease to substantially zero for reducing said second signal to zero whenever the amplitude of the modified command signal exceeds either one of said first and second predetermined values.

In a process control system having a proportional control loop including sensor means for monitoring a controlled variable and for providing a linearly changing command signal indicating deviations of the controlled variable from a system set point, an actuator means responsive to the command signal to control a manipulated variable to effect a change in the controlled variable to return the controlled variable to the set point, a proportional plus integral controller means comprising proportional means including proportional amplifier means responsive to said command signal to provide a first signal which is proportional to the command signal, integral means including integrating amplifier means having an input and an output, and integrating capacitor means connected between said input and said output of said integrating amplifier means, said integrating amplifier means being operable when enabled to permit said capacitor means to be charged by said command signal to provide a second signal that varies in proportion to the time integral of the command signal, summing amplifier means for summing said first and second signals to provide a modified command signal for said actuator means, and signal comparator means including reference means for providing a reference signal, and at least one signal comparator amplifier means for comparing said modified command signal with said reference signal and operable in response to a first predetermined difference between said modified command signal and said reference signal to control said integrating amplifier means to respond to said command signal to provide said second signal, and said signal comparator amplifier means being operable in response to a second predetermined difference between said modified command signal and said reference signal to disable said integrating amplifier means to permit said capacitor means to discharge to zero to thereby permit the potential at said input and said output of said integrating amplifier means, and thus the amplitude of said second signal to decrease to zero.

In a process control system having proportional control loop including sensor means for monitoring a controlled variable and for providing a linearly changing command signal indicating deviations of the controlled variable from a system set point, and actuator means responsive to the command signal to control a manipulated variable to effect a change in the controlled variable to return the controlled variable to the set point, a proportional plus integral controller means comprising proportional amplifier means responsive to said command signal to provide a first signal which is proportional to the command signal, integrating amplifier means operable when enabled to be responsive to said command signal to provide a second signal that varies in proportion to the time integral of the command signal, summing amplifier means for summing said first and second signals to provide a modified command signal for said actuator means, said integrating amplifier means comprising a programmable operational amplifier means having an integrating capacitor means connected between an output of said operational amplifier means and an input of said operational amplifier means, and input network means for extending said command signal to said operational amplifier means to permit said integrating capacitor means to charge to a value related to time changes of said command signal whenever said operational amplifier means is enabled, said output of said operational amplifier means being connected to an input of said summing amplifier means to permit said second signal to be extended to said summing amplifier means and for providing a discharge path for said capacitor means, and signal comparator means including reference means for providing a reference signal, and at least one signal comparator amplifier means for comparing amplifier means said modified command signal with said reference signal, said operational amplifier means having a control input, and said signal comparator amplifier means being operable to normally extend an enabling signal to said control input for enabling said first operational amplifier means in response to a first predetermined difference between said modified command signal and said reference signal, said signal comparator amplifier means being operable to extend a disabling signal to said control input for disabling said operational amplifier means in response to a second predetermined difference between said modified command signal and said reference signal to disable said programmable operational amplifier means to permit said capacitor means to discharge over said discharge path.

In a process control system having a proportional control loop including sensor means for monitoring a controlled variable and for providing a linearly changing command signal indicating deviations of the controlled variable from a system set point, and actuator means responsive to the command signal to control a manipulated variable to effect a change in the controlled variable to return the controlled variable to the set point, a proportional plus integral controller means comprising proportional means responsive to the said command signal to provide a first signal proportional to said command signal, integral means operable when enabled to be responsive to said command signal to provide a second signal that varies in proportion to the time integral of the command signal, summing means for summing said first and second signals to provide a modified command signal for said actuator means, and control means for normally enabling said integrating means, said control means including a first and a second signal comparator means and a first and a second reference means for supplying first and a second reference signals to said first and second signal comparator means respectively, said first and second comparator means being operable to compare said modified command signal with the reference signal extended thereto and to disable said integral means in response to a predetermined difference between said modified command signal and said reference signal, said first signal comparator means being operable to effect disabling of said integral means whenever said modified command signal is a predetermined amount greater than said first reference signal, and said second signal comparator means being operable to effect disabling of said integral means whenever said modified command signal is a predetermined amount less than said second reference signal.

In a process control system having a proportional control loop including sensor means for monitoring a controlled variable and for providing a linearly changing command signal indicating deviations of the controlled variable from a system set point, and actuator means responsive to the command signal to control a manipulated variable to effect a change in the controlled variable to return the controlled variable to the set point, a proportional plus integral controller means comprising proportional means responsive to said command signal to provide a first signal proportional to said command signal, integral means comprising a programmable operational amplifier means having an integrating capacitor means connected between a first input and an output of said operational amplifier means, input means connected between said first amplifier input and an output of said sensor means for extending said command signal to said operational amplifier means to permit said integrating capacitor means to charge to a value related to the time integral of said command signal whenever said operational amplifier means is enabled to permit said integral means to provide a second signal that varies in proportion to the time integral of the command signal, summing means for summing said first and second signals to provide a modified command signal for said actuator means, and control means having a first means for providing at least one reference signal, and a second means for comparing said modified command signal with said reference signal, said programmable operational amplifier means having a control input connected to an output of said second means, said second means normally providing a first output to said control input for enabling said programmable operational amplifier means, and said second means being operable to provide a second output to said control input for disabling said programmable operational amplifier means in response to said predetermined difference between said modified command signal and said reference signal.

In a process control system having a proportional control loop including sensor means for monitoring a controlled variable and for providing a linearly changing command signal indicating deviations of the controlled variable from a system set point, and actuator means responsive to the command signal to control a manipulated variable to effect a change in the controlled variable to return the controlled variable to the set point, a proportional plus integral controller means comprising proportional amplifier means responsive to said command signal to provide a first signal which is proportional to the command signal, integrating amplifier means operable when enabled to be responsive to said command signal to provide a second signal that varies in proportion to the time integral of the command signal, said integrating amplifier means comprising a first programmable operational amplifier means having a control input, an integrating capacitor means connected between an output of said first operational amplifier means and an input of said first operational amplifier means and input network means for extending said command signal to said first operational amplifier means to permit said integrating capacitor means to charge to a value related to time changes of said command signal whenever said first operational amplifier means is enabled, summing amplifier means for summing said first and second signals to provide a modified command signal for said actuator means, and signal comparator means including reference means for providing a reference signal, a second operational amplifier means, a first input means for extending said modified command signal to a first input of said second operational amplifier means and second input means for extending said reference signal to a second input of said second operational amplifier means, said second operational amplifier means having an output connected to said control input of said programmable operational amplifier means, said second operational amplifier means being operable to compare said modified command signal with said reference signal and to normally provide a signal to said control input for enabling said first operational amplifier means in response to a first predetermined difference between said modified command signal and said reference signal, and to extend a signal to said control input for disabling said operational amplifier means in response to a second predetermined difference between said command signal and said reference signal.