US3882368A
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Apparatus and method for automatic or manual process control
Assignee: Westinghouse Electric Corp
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Filing: 1972-07-14
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Granted: 1975-05-06
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Expires: 1992-07-14
Abstract
Abstract Apparatus and a method for achieving bumpless transfer between the manual and automatic modes in either single or multiple loop process control systems. The last stage of the process controller is an integrator which generates the final control element position signal in both the manual and automatic modes. Proportional, first derivative or second derivative actions applied to the measured variable and/or the set point in the first stage of the controller become integral, proportional and derivative actions, respectively, after passing through the integrator. Since the integrator remains in the output circuit and is under control continuously in both modes, bumpless transfer between the manual and automatic modes is achieved without the necessity of matching signals. When two controllers are used in cascade, the speed signal generated by the first stage of the inner loop controller is applied to the integrator stage of the outer loop controller so that it tracks the measured variable of the inner loop while the inner loop is in the manual mode. Only integral action is applied to the set point inputs of the controllers so that the rate of change of the set point signal is not critical.
Inventors
- 👤 James T Carleton
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-24 22:29
CPC Classifications
G; G05; G05B; G05B7/00; G05B7/02
Claims Analysis
Total Claims: 21
Claim 1
Independent Claim
109 words
A process control system including: measurement means for generating a feedback signal representative of a selected process variable, set point means for generating a signal representative of a desired value of the measured variable, controller means for generating a control signal from the feedback signal and the set point signal, said controller being operative to apply selected control action including at least one form of control action other than integral action to the feedback signal and only integral action to set point signal, and a final control element responsive to the control signal to modify the process so as to drive the measured variable toward the set point value.
Claim 2
Dependent Claim
109 words
A process control system including: measurement means for generating a feedback signal representative of a selected process variable, set point means for generating a signal representative of a desired value of the measured variable, controller means for generating a control signal from the feedback signal and the set point signal, said controller being operative to apply selected control action including at least one form of control action other than integral action to the feedback signal and only integral action to set point signal, and a final control element responsive to the control signal to modify the process so as to drive the measured variable toward the set point value.
Claim 3
Dependent Claim
21 words
The apparatus of claim 1 wherein the controller includes means for applying integral and proportional control actions to said feedback signal.
Claim 4
Dependent Claim
15 words
The apparatus of claim 2 including means for applying derivative action to said feedback signal.
Claim 5
Dependent Claim
61 words
The apparatus of claim 1 wherein the controller includes means for generating an error signal as the difference between the set point signal and the feedback signal, means for applying derivative action to the feedback signal, means for summing the derivative of the feedback signal with the error signal, and a single means for applying integral action to the resultant signal.
Claim 6
Dependent Claim
57 words
The apparatus of claim 4 including means for applying derivative action to the derivative of the feedback signal to generate the second derivative of the feedback signal, and wherein the means for summing the derivative of the feedback signal with the error signal includes means for including the second derivative of the feedback signal in the sum.
Claim 7
Independent Claim
79 words
A method of controlling a process including the steps of: generating a feedback signal proportional to a selected process variable, generating a set point signal representative of a desired value of the measured variable, applying selected control action including at least one form of control action other than integral action to the feedback signal, applying only integral action to the set point signal, and modifying the process as a function of the resultant feedback signal and set point signal.
Claim 8
Independent Claim
79 words
A method of controlling a process including the steps of: generating a feedback signal proportional to a selected process variable, generating a set point signal representative of a desired value of the measured variable, applying selected control action including at least one form of control action other than integral action to the feedback signal, applying only integral action to the set point signal, and modifying the process as a function of the resultant feedback signal and set point signal.
Claim 9
Dependent Claim
45 words
The method of claim 6 wherein the step of applying selected control action to the feedback signal includes the step of applying proportional action to the feedback signal by first applying derivative action to the feedback signal and then integrating the resultant derivative feedback signal.
Claim 10
Dependent Claim
58 words
The method of claim 7 including the step of applying integral action to the feedback signal by the steps of summing the feedback signal in opposition to the set point signal to generate an error signal, summing the error signal with the derivative feedback signal to generate a desired rate signal and then integrating the desired rate signal.
Claim 11
Dependent Claim
40 words
The method of claim 7 including the additional step of applying derivative action to the derivative feedback signal prior to the step of integrating the resultant signal whereby the resultant control action applied to the feedback signal is derivative action.
Claim 12
Dependent Claim
277 words
A cascaded two loop process control system comprising: a final control element operative to a position called for by a final control element position signal for modifying the process in accordance therewith, an inner loop controller including a first integrator operative to generate said final control elemenT position signal through integration of a final control element speed signal, means for generating a director mode final control element speed signal as a function of a manual signal and means for generating a regulator mode final control element speed signal as a function of an inner loop set point signal and a first measured variable signal representative of a first selected process variable, an outer loop controller comprising a second integrator operative to generate said inner loop set point signal as a function of an inner loop set point rate signal, means for generating an inner loop set point rate tracking signal as a function of the regulator mode final control element speed signal and means for generating an inner loop set point rate control signal as a function of an outer loop set point signal and a second measured variable signal representative of a second selected process variable, and transfer means operative between a director mode wherein the director mode final control element speed signal is applied to the first integrator and the inner loop set point rate tracking signal is applied to the second integrator for manual process control, and a regulator mode wherein the regulator mode final control element speed signal is applied to the first integrator and the inner loop set point rate control signal is applied to the second integrator for automatic process control.
Claim 13
Dependent Claim
277 words
A cascaded two loop process control system comprising: a final control element operative to a position called for by a final control element position signal for modifying the process in accordance therewith, an inner loop controller including a first integrator operative to generate said final control elemenT position signal through integration of a final control element speed signal, means for generating a director mode final control element speed signal as a function of a manual signal and means for generating a regulator mode final control element speed signal as a function of an inner loop set point signal and a first measured variable signal representative of a first selected process variable, an outer loop controller comprising a second integrator operative to generate said inner loop set point signal as a function of an inner loop set point rate signal, means for generating an inner loop set point rate tracking signal as a function of the regulator mode final control element speed signal and means for generating an inner loop set point rate control signal as a function of an outer loop set point signal and a second measured variable signal representative of a second selected process variable, and transfer means operative between a director mode wherein the director mode final control element speed signal is applied to the first integrator and the inner loop set point rate tracking signal is applied to the second integrator for manual process control, and a regulator mode wherein the regulator mode final control element speed signal is applied to the first integrator and the inner loop set point rate control signal is applied to the second integrator for automatic process control.
Claim 14
Dependent Claim
47 words
The apparatus of claim 10 wherein the means for generating the regulator mode final control element speed signal and the means for generating the inner loop set point rate control signal include means for applying selected control actions, not including integral action, to the signals applied thereto.
Claim 15
Dependent Claim
39 words
The apparatus of claim 10 wherein the means for generating the inner loop set point rate tracking signal includes means for generating said signal with a polarity opposite to that of the regulator mode final control element speed signal.
Claim 16
Dependent Claim
102 words
Apparatus for generating a final control element position signal for positioning the final control element in a process control system, said apparatus comprising: a signal generator including a switch, means operative to generate an output signal having a predetermined magnitude when said switch is closed and which increases in magnitude as a function of the time that the switch remains closed and means for resetting the output signal to said predetermined magnitude upon opening of said switch, and an integrator connected to the signal generator and operative to generate the final control element position signal as a function of said output signal.
Claim 17
Dependent Claim
102 words
Apparatus for generating a final control element position signal for positioning the final control element in a process control system, said apparatus comprising: a signal generator including a switch, means operative to generate an output signal having a predetermined magnitude when said switch is closed and which increases in magnitude as a function of the time that the switch remains closed and means for resetting the output signal to said predetermined magnitude upon opening of said switch, and an integrator connected to the signal generator and operative to generate the final control element position signal as a function of said output signal.
Claim 18
Independent Claim
229 words
A method of controlling a two loop process control system by positioning a final control element, including the steps of: generating the final control element position signal by integrating a final control element speed signal, generating a director mode final control element speed signal manually, generating a regulator mode final control element speed signal as a function of an inner loop set point signal and a first measured variable signal representative of the value of a first selected process variable, generating the inner loop set point signal by integrating an inner loop set point rate signal, generating an inner loop set point rate tracking signal from the regulator mode final control element speed signal, generating an inner loop set point rate control signal as a function of an outer loop set point signal and a second measured variable signal representative of the value of a second process variable, selecting the director mode final control element speed signal to generate the final control element position signal and the inner loop set point rate tracking signal to generate the inner loop set point signal for manual control of the process, and selecting the regulator mode final control element speed signal to generate the final control element position signal and the inner loop set point rate control signal to generate the inner loop set point signal for automatic control of the process.
Claim 19
Independent Claim
229 words
A method of controlling a two loop process control system by positioning a final control element, including the steps of: generating the final control element position signal by integrating a final control element speed signal, generating a director mode final control element speed signal manually, generating a regulator mode final control element speed signal as a function of an inner loop set point signal and a first measured variable signal representative of the value of a first selected process variable, generating the inner loop set point signal by integrating an inner loop set point rate signal, generating an inner loop set point rate tracking signal from the regulator mode final control element speed signal, generating an inner loop set point rate control signal as a function of an outer loop set point signal and a second measured variable signal representative of the value of a second process variable, selecting the director mode final control element speed signal to generate the final control element position signal and the inner loop set point rate tracking signal to generate the inner loop set point signal for manual control of the process, and selecting the regulator mode final control element speed signal to generate the final control element position signal and the inner loop set point rate control signal to generate the inner loop set point signal for automatic control of the process.
Claim 20
Dependent Claim
33 words
The method of claim 14 wherein the step of generating the inner loop set point tracking signal comprises the step of reversing the polarity of the regulator mode final control element speed signal.
Claim 21
Dependent Claim
34 words
The method of claim 14 wherein selected control action not including integral action is used to generate the regulator mode final control element speed signal and the inner loop set point rate control signal.
References Cited (Backward Citations)
US2954514A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1978-05-05 | 1978-11-04 | 1979-05-06 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1982-05-05 | 1982-11-04 | 1983-05-06 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1986-05-05 | 1986-11-04 | 1987-05-06 | $7700.00 | Window Closed / Lapsed |