CONTROL OF A PROCESS VARIABLE BY A COMPUTER AND A CONTROLLER WHICH REPLACES THE COMPUTER

• US 3,665,172 A
• Filed: 06/25/1969
• Issued: 05/23/1972
• Est. Priority Date: 06/25/1969
• Status: Expired due to Term

• Current Assignee: Aart Bijl, Klaas Spaargaren
• Original Assignee: Aart Bijl, Klaas Spaargaren
• Inventors: Spaargaren, Klaas, Bijl, Aart
• Primary Examiner(s): Botz, Eugene G.
• Application Number:
  US04/836,463
• Time in Patent Office: 1,063 Days
• Field of Search: 235/151.1,150.1 318/20.075,20.240,20.245
• US Class Current: 700/75
• CPC Class Codes: G05B 15/02 electric
• CPC Class Codes: G05B 9/03 with multiple-channel loop, i.e. redundant control systems
• CPC Class Codes: G11C 27/00 Electric analogue stores, e.g. for storing instantaneous values
• CPC Class Codes: G11C 27/026 associated with an amplifier G11C27/028 takes precedence

Abstract

A method and apparatus for controlling a process variable wherein the variable is controlled primarily by a digital computer but where a part of the control function is performed by an analog controller. When the control is by the computer, an output signal is passed intermittently from the computer to a memory amplifier, the output signal of which is a control signal that may be used for correcting the process variable. When control is by the controller, the memory amplifier operates as a summing amplifier for negative feedback control.

Claims

1. A system for controlling a process variable of a process, comprising:

a meter for measuring said process variable, said meter being operatively connected to said process and adapted to generate an output signal proportional to the measured value of said process variable;

a digital computer operatively connected to said meter so as to receive the output signal thereof, said computer being adapted to produce an intermittent output signal proportional to changes that must be made in said process;

a signal generator adapted to generate a signal proportional to the set value of said process variable;

circuit means having input means connected to the output of said computer, to the output of said signal generator, and to the output of said meter, said circuit means including 1. an operational amplifier having an input and an output;

2. a plurality of impedances;

3. switching means, said switching means being connected between said impedances and the input of said operational amplifier and adapted to operate such that when said switching means are in one position the operational amplifier receives an output signal from the computer and said process is controlled by said computer but when said switches are in another position, said process is controlled by said operational amplifier in combination with a portion of said impedances such that said set value signal and said measured value signal are supplied to the input of said operational amplifier with opposite polarities;

4. separate feedback impedance means included in the plurality of impedances and connecting the output of the operation amplifier to its input when the switching means is in said one position or said other position; and

a correcting unit connected between the output of said circuit means and said process, said process, said correcting unit being adapted to control said process variable in accordance with the output signal of said operational amplifier.

2. The system of claim 1 wherein said circuit means comprises:

a capacitor included as one of the separate feedback impedance means;

a first switch included in said switching means having a first and second position, the series combination of said capacitor and said first switch being connected between said input and output of said operational amplifier;

a first impedance means included in said plurality of impedances as one of the separate feedback impedance means;

a second switch included in said switching means, said first impedance means and said second switch being serially connected between said input and said output of said operational amplifier, only one of said first and second switches being closed at one time;

a second impedance means included in said plurality of impedances, said second impedance means connected between the output of said signal generator and the common node between said first impedance means and second switch;

a third switch included in said switching means, said third switch connected between the input of said operational amplifier and said computer output.

3. The system of claim 1 wherein said computer output signal comprises a series of current pulses with defined charge contents, each pulse representing a calculated alteration of the control signal.

4. separate feedback impedance means included in the plurality of impedances and connecting the output of the operation amplifier to its input when the switching means is in said one position or said other position;

and a correcting unit connected between the output of said circuit means and said process, said process, said correcting unit being adapted to control said process variable in accordance with the output signal of said operational amplifier.

5. The system of claim 1 wherein said signal generator includes a circuit comprising an operational amplifier, a capacitor, and a switch, said capacitor and switch connected serially between said input and said output of said operational amplifier, said switch having two positions, one position connecting said capacitor in a completed circuit between said input and said output of said amplifier, the other position of said switch grounding said capacitor.

6. The system of claim 2 wherein said second impedance means comprises a resistance;

and, said third impedance means comprises the parallel combination of a resistance and a capacitance.

7. The system of claim 1 wherein said circuit means comprises:

a capacitor included in said plurality of impedances as one of the separate feedback impedance means;

a first switch included in said switching means having a first and second position, the series combination of said capacitor and said first switch being connected between said input and output of said operational amplifier;

a first impedance means included in said plurality of impedances as another of the separate feedback impedance means;

a second switch included in said switching means, said first impedance means and said second switch being serially connected between said input and said output of said operational amplifier, only one of said first and second switches being closed at one time;

a second impedance means included in said plurality of impedances, said second impedance means connected between said signal generator and the common node between said first impedance means and second switch;

a third switch included in said switching means, said third switch connected between the input of said operational amplifier and said computer output; and

, wherein said signal generator is connected in series between said meter and said second impedance means in such a manner that said meter output signal is subtracted from said signal generator signal.

8. The system of claim 7 wherein said computer output signal comprises a direct current the output of which corresponds with a calculated value of the control signal.

9. The system of claim 7 wherein said signal generator comprises a source of dc power connected across a rheostat;

said first impedance means comprises a series combination of a resistance and a capacitance; and

, said second impedance means comprises a resistance.