Bumpless transfer circuits for process control systems

Claim 2

For controlling the magnitude of current supplied to a control element, a system comprising: a. a plurality of subsystems for alternatively controlling the current, each of said subsystems including an amplifier having a first input terminal, a second input terminal which is electrically connected to a system common terminal, and an output terminal, and a feedback capacitor having one terminal connected to said first input terminal; b. a system feedback path forming a feedback connection between the controL element and each of said feedback capacitors; c. system switching means for simultaneously connecting the output terminal of the amplifier in one of said subsystems to the control element, connecting the first input terminal of each amplifier in the remaining subsystems to the common terminal whereby the feedback current charges each of said feedback capacitors in each of the remaining subsystems to a voltage directly proportional to the current through the control element, and disconnecting the first input terminal of the amplifier in said one subsystem from the common terminal.

Claim 3

For controlling the magnitude of current supplied to a control element, a system including: a. an automatic control subsystem comprising one or more process controllers, each of which includes an amplifier having a first input terminal for receiving a signal representative of a deviation between a predetermined characteristic for the process and a setpoint for that characteristic, a second input terminal connected to a system common terminal, and an output terminal, and a feedback capacitor having one terminal connected to said first input terminal; b. a manual control subsystem including an amplifier having a first input terminal, a second input terminal connected to the system common terminal, and an output terminal, and a feedback capacitor having one terminal connected to said first input terminal; c. a system feedback path connected between the control element and the other terminal of each of said feedback capacitors; and d. system switching means for simultaneously connecting the output terminal of an amplifier in a first of said subsystems to the control element, connecting the first input terminal of each amplifier in the second of said subsystems to the system common terminal whereby each feedback capacitor in said second subsystem is charged to a voltage proportional to the current through the control element, and disconnecting the first input terminal of each amplifier in said first subsystem from the system common terminal.

Claim 4

For controlling the magnitude of current supplied to a control element, a system including: a. an automatic control subsystem comprising one or more process controllers, each of which includes an amplifier having a first input terminal for receiving a signal representative of a deviation between a predetermined characteristic for the process and a setpoint for that characteristic, a second input terminal connected to a system common terminal, and an output terminal, and a feedback capacitor having one terminal connected to said first input terminal; b. a manual control subsystem including an amplifier having a first input terminal, a second input terminal connected to the system common terminal, and an output terminal, and a feedback capacitor having one terminal connected to said first input terminal; c. a system feedback path connected between the control element and the other terminal of each of said feedback capacitors; and d. system switching means for simultaneously connecting the output terminal of an amplifier in a first of said subsystems to the control element, connecting the first input terminal of each amplifier in the second of said subsystems to the system common terminal whereby each feedback capacitor in said second subsystem is charged to a voltage proportional to the current through the control element, and disconnecting the first input terminal of each amplifier in said first subsystem from the system common terminal.

Claim 5

A system as recited in claim 2 wherein said manual control subsystem further includes a voltage source comprising: a positive voltage source; a negative voltage source; contact means for connecting a selected one of said sources to the first input terminal of the amplifier in said manual control subsystem to control the current supplied to the first input, said contact means having a normal non-connecting position from which it must be moved to effect the connection.

Claim 6

A system as recited in claim 2 wherein said system feedback path includes a high impedance amplifier having an input terminal connected in circuit with the control element and an output terminal connected electrically to each of said feedback capacitors in each of said subsystems.

Claim 7

A system as recited in claim 3 wherein said system feedback path includes a high impedance amplifier having an input terminal connected in circuit with the control element and an output terminal connected electrically to each of said feedback capacitors in each of said subsystems.

Claim 8

A system as recited in claim 2 wherein said automatic control subsystem includes output selector circuitry responsive to a predetermined characteristic of amplifier output to pass the amplifier output having the most extreme value of that characteristic while effectively open circuiting amplifiers having outputs of less extreme values.

Claim 9

A system as recited in claim 6 wherein said output selector circuitry includes a plurality of diodes, each having a first terminal connected to the output terminal of one of said amplifiers and a second terminal connected in common with the second terminals of the other diodes to the system switching means.