Cascade control system

Claim 2

direct to the process operator element a control signal corresponding to said automatic output signal produced by said secondary controller (which automatic output signal had during the preceding independent mode been maintained equal to said separate signal whereby the process operator element will remain unaffected at the instant of switchback to automatic mode); and

Claim 3

direct to said process operator element a control signal corresponding to said separate signal;

Claim 4

direct to said process operator element a control signal corresponding to said separate signal;

Claim 5

In a cascade process control system of the type including a primary controller arranged to receive both primary measurement and primary set point signals and to provide an intermediate output signal to serve as a set point signal for a secondary controller arranged to receive a secondary measurement signal for comparison with the secondary set point signal, said secondary controller serving to provide an automatic control signal to adjust the setting of a process operator element such as a valve or the like so as to maintain the primary measurement at its set point value, and wherein the system is transferable between automatic and independent (e.g. manual) control modes and for that purpose includes a selectively activatable means operable in independent mode for producing a separate signal, in the form of a manual signal or the like, for controlling the process operator element in place of said automatic control signal; that improvement in said control system for effecting bumpless, balanceless transfer from independent mode to automatic mode which comprises, in combination: transfer switch means selectively operable into automatic or independent status and serving in independent status to:

Claim 6

In a cascade process control system of the type including a primary controller arranged to receive both primary measurement and primary set point signals and to provide an intermediate output signal to serve as a set point signal for a secondary controller arranged to receive a secondary measurement signal for comparison with the secondary set point signal, said secondary controller serving to provide an automatic control signal to adjust the setting of a process operator element such as a valve or the like so as to maintain the primary measurement at its set point value, and wherein the system is transferable between automatic and independent (e.g. manual) control modes and for that purpose includes a selectively activatable means operable in independent mode for producing a separate signal, in the form of a manual signal or the like, for controlling the process operator element in place of said automatic control signal; that improvement in said control system for effecting bumpless, balanceless transfer from independent mode to automatic mode which comprises, in combination: transfer switch means selectively operable into automatic or independent status and serving in independent status to:

Claim 7

In a cascade process control system of the type including a primary controller arranged to receive both primary measurement and primary set point signals and to provide an intermediate output signal to serve as a set point signal for a secondary controller arranged to receive a secondary measurement signal for comparison with the secondary set point signal, said secondary controller serving to provide an automatic control signal to adjust the setting of a process operator element such as a valve or the like so as to maintain the primary measurement at its set point value, and wherein the system is transferable between automatic and independent (e.g. manual) control modes and for that purpose includes a selectively activatable means operable in independent mode for producing a separate signal, in the form of a manual signal or the like, for controlling the process operator element in place of said automatic control signal; that improvement in said control system for effecting bumpless, balanceless transfer from independent mode to automatic mode which comprises, in combination: transfer switch means selectively operable into automatic or independent status and serving in independent status to: 1. direct to said process operator element a control signal corresponding to said separate signal; 2. maintain said secondary controller functioning to produce an automatic output signal corresponding to said separate independent signal; 3. maintain said primary controller functioning, with a constant set point, to produce an intermediate output signal corresponding to the secondary measurement signal; said transfer switch means serving when switched back to automatic status to: 1. direct to the process operator element a control signal corresponding to said automatic output signal produced by said secondary controller (which automatic output signal had during the preceding independent mode been maintained equal to said separate signal whereby the process operator element will remain unaffected at the instant of switchback to automatic mode); and 2. release said primary controller from the effective influence of said secondary measurement signal and return it to normal operation under the influence of said primary measurement and set signal, whereby the primary controller will not alter the functioning of the secondary controller so as to upset the process but will, after switchback to automatic, readjust the set point of the secondary controller to whatever extent is required for the purpose of automatically controlling the primary process condition to its set value.

Claim 8

In a cascade process control system of the type including a primary controller arranged to receive both primary measurement and primary set point signals and to provide an intermediate output signal to serve as a set point signal for a secondary controller arranged to receive a secondary measurement signal for comparison with the secondary set point signal, said secondary controller serving to provide an automatic control signal to adjust the setting of a process operator element such as a valve or the like so as to maintain the primary measurement at its set point value, and wherein the system is transferable between automatic and independent (e.g. manual) control modes and for that purpose includes a selectively activatable means operable in independent mode for producing a separate signal, in the form of a manual signal or the like, for controlling the process operator element in place of said automatic control signal; that improvement in said control system for effecting bumpless, balanceless transfer from independent mode to automatic mode which comprises, in combination: transfer switch means selectively operable into automatic or independent status and serving in independent status to: 1. direct to said process operator element a control signal corresponding to said separate signal; 2. maintain said secondary controller functioning to produce an automatic output signal corresponding to said separate independent signal; 3. maintain said primary controller functioning, with a constant set point, to produce an intermediate output signal corresponding to the secondary measurement signal; said transfer switch means serving when switched back to automatic status to: 1. direct to the process operator element a control signal corresponding to said automatic output signal produced by said secondary controller (which automatic output signal had during the preceding independent mode been maintained equal to said separate signal whereby the process operator element will remain unaffected at the instant of switchback to automatic mode); and 2. release said primary controller from the effective influence of said secondary measurement signal and return it to normal operation under the influence of said primary measurement and set signal, whereby the primary controller will not alter the functioning of the secondary controller so as to upset the process but will, after switchback to automatic, readjust the set point of the secondary controller to whatever extent is required for the purpose of automatically controlling the primary process condition to its set value.

Claim 9

maintain said secondary controller functioning to produce an automatic output signal corresponding to said separate independent signal;

Claim 10

maintain said secondary controller functioning to produce an automatic output signal corresponding to said separate independent signal;

Claim 11

Apparatus as claimed in claim 1, wherein said selectively activatable means comprises a manual signal unit having means for manually controlling the magnitude of a signal for the process operator element.

Claim 12

release said primary controller from the effective influence of said secondary measurement signal and return it to normal operation under the influence of said primary measurement and set signal, whereby the primary controller will not alter the functioning of the secondary controller so as to upset the process but will, after switchback to automatic, readjust the set point of the secondary controller to whatever extent is required for the purpose of automatically controlling the primary process condition to its set value.

Claim 13

release said primary controller from the effective influence of said secondary measurement signal and return it to normal operation under the influence of said primary measurement and set signal, whereby the primary controller will not alter the functioning of the secondary controller so as to upset the process but will, after switchback to automatic, readjust the set point of the secondary controller to whatever extent is required for the purpose of automatically controlling the primary process condition to its set value.

Claim 14

maintain said primary controller functioning, with a constant set point, to produce an intermediate output signal corresponding to the secondary measurement signal; said transfer switch means serving when switched back to automatic status to:

Claim 15

maintain said primary controller functioning, with a constant set point, to produce an intermediate output signal corresponding to the secondary measurement signal; said transfer switch means serving when switched back to automatic status to:

Claim 16

Apparatus as claimed in claim 1, wherein said primary controller includes a reset element to produce reset action in the intermediate output signal; and adjusting means operable in independent mode responsive to said secondary measurement signal for adjusting the activation of said reset element to maintain said intermediate output signal equal to said secondary measurement signal.

Claim 17

Apparatus as claimed in claim 3, wherein said primary and secondary controllers are of the pneumatic force-balance type; said reset element comprising a pressure-responsive element arranged to apply a force to the balanceable device of the controller in accordance with the pressure developed in said reset element by said adjusting means.

Claim 18

Apparatus As claimed in claim 4, wherein said adjusting means comprises a pneumatic force-balance transfer unit adapted to receive and compare pressure signals corresponding to the secondary measurement signal and said intermediate output signal, respectively, and to produce a controlling pressure signal for said reset element of such a magnitude as to a maintain equal said secondary measurement signal and said intermediate output signal.

Claim 19

Apparatus as claimed in claim 5, wherein said transfer unit comprises a planar element pivoted at an intermediate point and supplied on opposite surface on one side of said pivot point with pressures corresponding to said secondary measurement signal and said intermediate output signal.

Claim 20

Apparatus as claimed in claim 1, wherein said secondary controller includes an activatable reset element to introduce reset action in the output signal from the secondary controller; and adjusting means operable in independent mode and responsive to said separate signal for adjusting the activation of said reset element so as to maintain the output signal equal to said separate signal.

Claim 21

Apparatus as claimed in claim 7, wherein said secondary controller is of the pneumatic force-balance type; said reset element comprising a pressure chamber adapted to receive a pressure signal to be applied to the force-balanceable element of the controller in accordance with the separate signal directed to said process operator element.

Claim 22

Apparatus as claimed in claim 8, wherein said secondary controller comprises a laminar sandwich structure including a pivotally mounted planar element serving as said force-balanceable element; said sandwich structure including walls defining pressure chambers adjacent respective sections of said planar element; means to supply secondary measurement and secondary set pressure signals to two of said chambers to produce oppositely-directed torques on said planar element about its pivot axis; a position detector associated with said planar element to detect small changes in the position thereof responsive to unbalance in forces thereon about said pivot axis; and means controlled by said detector for adjusting the pressure in at least a third chamber so as to maintain the torque, on said planar element in balance.

Claim 23

Apparatus as claimed in claim 9, wherein said planar element comprises at least two separate segments on the same side of said pivot axis, each of said segments being movable together about said axis in response to any unbalance in torques about said axis.

Claim 24

Apparatus as claimed in claim 10, wherein said sandwich walls define a pressure chamber adjacent one of said segments and separate from the other segment, whereby said one segment is individually activatable in accordance with a respective pressure.

Claim 25

Apparatus as claimed in claim 11, including a seal along the pivot axis to provide for independent pressures on opposite sides of the pivot axis, said planar element extending through said seal and being pivoted about said axis while maintaining the pressure integrity on opposite sides thereof.

Claim 26

Apparatus as claimed in claim 12, wherein said position detector comprises a pneumatic nozzle mounted adjacent said other segment to sense changes in the pivotal position of said planar element about said axis.

Claim 27

Apparatus as claimed in claim 13, wherein said other segment extends out through said seal and beyond the exterior wall of said sandwich structure, whereby said other segment and said nozzle are located in atmospheric pressure at all times.

Claim 28

Apparatus as claimed in claim 9, including further means controlled by said detector for adjusting the pressure in a fourth chamber in response to changes in the pivotal position of said planar element.

Claim 29

Apparatus as claimed in claim 15, wherein said further means includes means to alter the pressure in said fourth chamber in such a manner as to introduce reset action in the output signal of said secondary controller.

Claim 30

Apparatus as claimed in claim 16, wherein said reset introducing means includes an adjustable restrictor in the pressure line leading to said fourth chamber.

Claim 31

Apparatus as claimed in claim 17, wherein said first two chambers are located adjacent respective opposite surfaces of said planar element which are on one side of said pivot axis; and said other two chambers are located adjacent respective opposite surfaces of said planar element which are on the other side of said axis; said planar element being formed with an additional segment which moves with the planar element about its pivot axis; said additional segment being remote from any of said four pressure chambers so as not to be directly affected by the pressures therein; and a position detector adjacent said additional segment to sense any unbalance in forces about said pivot axis.

Claim 32

Apparatus as claimed in claim 8, wherein said adjusting means includes a non-restrictive conduit of relatively large flow capacity for directing a pressure signal to said reset pressure chamber corresponding to the signal being sent to the process operator element.

Claim 33

Apparatus as claimed in claim 19, wherein said transfer switch means includes a pneumatically-operated switch for opening said non-restrictive conduit when the system is conditioned for non-automatic (independent) mode of operation.

Claim 34

In a cascade process control system of the type including a primary controller arranged to receive primary measurement and set point signals and to provide an intermediate output signal to serve as a set point signal for a secondary controller arranged to receive a secondary measurement signal for comparison with the secondary set point signal, said secondary controller serving to provide an automatic control signal to adjust the setting of a process operator element such as a valve or the like so as to maintain the primary measurement at its set point value, and wherein the system is transferable between automatic and independent (e.g. manual) control modes and for that purpose includes a selectively activatable means for producing a separate signal, in the form of a manual signal or the like, for controlling the process operator element in place of said automatic control signal; the method of conditioning the control system to prepare it for bumpless, balanceless transfer from independent mode to automatic mode which comprises the steps of: maintaining the automatic output signal of said secondary controller equal to said separate signal; and maintaining the intermediate output signal of said primary controller equal to the secondary measurement signal without altering the primary set point.

Claim 35

In a cascade process control system of the type including a primary controller arranged to receive primary measurement and set point signals and to provide an intermediate output signal to serve as a set point signal for a secondary controller arranged to receive a secondary measurement signal for comparison with the secondary set point signal, said secondary controller serving to provide an automatic control signal to adjust the setting of a process operator element such as a valve or the like so as to maintain the primary measurement at its set point value, and wherein the system is transferable between automatic and independent (e.g. manual) control modes and for that purpose includes a selectively activatable means for producing a separate signal, in the form of a manual signal or the like, for controlling the process operator element in place of said automatic control signal; the method of conditioning the control system to prepare it for bumpless, balanceless transfer from independent mode to automatic mode which comprises the steps of: maintaining the automatic output signal of said secondary controller equal to said separate signal; and maintaining the intermediate output signal of said primary controller equal to the secondary measurement signal without altering the primary set point.

Claim 36

The method of claim 21, wherein said primary controller is of the reset type; said intermediate output signal being maintained equal to said secondary measurement signal by adjusting the reset signal of said primary controller.

Claim 37

The method of claim 21, wherein said secondary controller is of the reset type; said automatic output signal being maintained equal to said separate signal by adjusting the level of the reset signal in said secondary controller.

Claim 38

The method of claim 23, wherein the reset signal in said secondary controller is maintained equal to the separate signal, and the measurement and set signals of said secondary controller are maintained equal.

Claim 39

The method of claim 24, wherein said primary controller is of the reset type; said intermediate output signal and said secondary set point signal being maintained equal to said secondary measurement signal by adjusting the level of reset activation in said primary controller.