US 4,344,128 AGranted

Automatic process control device

OwnerRobert C. Fryeinventor

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Abstract

Automatic Process Control Device having input transistors to receive process and set point signals; a subtractive amplifier to compare the process and set point signals and produce one of two amplified deviation signals which are limited to maximum values by zener diodes; capacitors to receive, time-integrate and store the amplified and limited deviation signals, and produce a neutral output if the time-integration of the amplified and limited deviation signals is in balance, and one of two trigger signals if the time-integration of the amplified and limited deviation signals is positive or negative; and relay switches connected to discharging circuits and in series with zener diodes to receive the trigger signals and operate a controlling device upon the process to urge the process toward its desired set point, and simultaneously produce a corresponding tripping signal which urges the capacitors toward a status to produce the neutral output, such that as the controlling device is operating upon the process the Automatic Control Device is simultaneously being urged toward its neutral position, and the response of the controlling device is time-integrated to the accumulative deviation of the process. In use, the disclosed Automatic Control Device virtually eliminates "hunting", and it can also accomodate and control extreme and sudden changes ("bumping") in either the process variable or the set point without damage to the Automatic Process Control Device or its operation.

Claims23

Dependent claims

Automatic process control device comprising, in combination:

first input means for receiving a first signal proportional to a measured variable;
second input means for receiving a second signal proportional to the desired set point of said measured variable;
control means to selectively urge said measured variable toward a pre-selected desired value;
reference signal generating means to provide a reference signal reflective of the difference between said first signal and said second signal;
deviation signal generating means to receive said reference signal and produce a first or a second deviation signal, each proportional to the reference signal;
voltage clipping means having input means adapted to receive said first and second deviation signals to limit said first and second deviation signals to selected maximum values;
deviation signal time-integration and storage means to receive said first and second limited deviation signals and to integrate said first and second limited deviation signals on a time basis and provide a first signal from said deviation signal time-integration and storage means when said time integration of said first and second limited deviation signals is between a pre-selected minimum and a pre-selected maximum value, a second signal from said deviation signal time-integration and storage means when said time integration of said first and second limited deviation signals exceeds said pre-selected maximum value, and a third signal from said deviation signal time-integration and storage means when said time-integration of said first and second limited deviation signals is below said minimum value;
and
switching means responsive to said second and third signals from said deviation signal time-integration and storage means and operably connected to said control means to operate said control means to adjust said measured variable to minimize the difference between said first and second signals and simultaneously urge said time-integration of said first and second limited deviation signals toward a mid-point between said pre-selected maximum and minimum values of said time integration of said first and second deviation signals to produce said first signal from said deviation signal time-integration and storage means.

6 more elements

Method of controlling a process variable, comprising the steps of:

receiving a first and a selected one of one or more second signals where said first signal is reflective of the value of a process variable which is desired to be controlled and said second signals are reflective of one or more desired values of said process variable;
converting said first and second signals into a first reference signal proportional to said first signal and a second reference signal proportional to said second signal;
reversing the polarity of said second reference signal to produce a third reference signal equal to but of opposite voltage to said second reference signal;
algebraically comparing said first reference signal and said third reference signal to produce one of two deviation signals, said first deviation signal being produced if said first reference signal and said third reference signals are in a first algebraic relation and said second deviation signal being produced if said first reference signal and said third reference signal are in a second algebraic relation;
amplifying said first and said second deviation signals to produce first and second amplified deviation signals;
limiting the maximum value of said first and second amplified deviation signals each to a maximum selected value;
integrating said first and second amplified and limited deviation signals on a time basis and storing said first and second amplified and limited deviation signals in deviation signal time-integration and storage means, the discharge value of which is selected to substantially equal said maximum value of said first and second amplified and limited deviation signals, said deviation signal time-integration and storage means arranged to provide a first signal from said deviation signal time-integration and storage means which will not cause discharge of said deviation signal time-integration and storage means when said first and second signals are in a first relation of substantially equivalent value and said time-integration of said first and second amplified and limited deviation signals is substantially equal, and provide a first trigger signal from said deviation signal time-integration and storage means when said first and second signals are in a second relation and said time-integration of said first and second amplified and limited deviation signals are in a second relation to permit said first amplified and limited deviation signal to discharge said deviation signal time-integration and storage means and produce said first trigger signal, and provide a second trigger signal from said deviation signal time-integration and storage means when said first and second signals are in a third relation and said time-integration of said first and second amplified deviation and limited signals is in a third relation to permit said second amplified and limited deviation signal to discharge said deviation signal time-integration and storage means to produce said second trigger signal;
and
receiving said first and second trigger signals to operate control means upon said process variable in a first direction when said first trigger signal is produced and simultaneously produce a first tripping signal to urge said deviation signal time-integration and storage means toward a status to provide said first signal from said deviation signal time-integration and storage means and to operate said control means upon said process variable in a second direction when said second trigger signal is produced and simultaneously produce a second tripping signal to urge said deviation signal time-integration and storage means toward a status to provide said first signal from said deviation signal time-integration and storage means.

6 more elements

Dependencies are inferred from the claim text.