CONTROL SYSTEM HAVING MEANS FOR EXPANDING THE USEFUL FREQUENCY RESPONSE

• US 3,817,651 A
• Filed: 04/20/1973
• Issued: 06/18/1974
• Est. Priority Date: 04/20/1973
• Status: Expired due to Term

• Current Assignee: Elliot Turbomachinery Company Incorporated
• Original Assignee: Donald E. Neill, John Law
• Inventors: Law, John, Neill, Donald E.
• Primary Examiner(s): Husar, C. J.
• Application Number:
  US05/353,057
• Time in Patent Office: 424 Days
• Field of Search: 415/1,30,36
• US Class Current: 415/1
• CPC Class Codes: F01D 17/24 electrical
• CPC Class Codes: F05D 2200/11 Sum
• CPC Class Codes: G01P 1/103 by comparing the value of the measured signal with one or several reference values in general G01R17/00

Abstract

A control system for a steam turbine includes a speed sensor providing a signal to actuate a monostable multivibrator. The output from the multivibrator is integrated and conditioned to control the fluid flow through the turbine. When the integrated output from the multivibrator reaches a predetermined magnitude, a feedback signal is provided to vary the current passing to the multivibrator in a manner which reduces the duration of the output pulses therefrom, so that the useful input frequency response of the multivibrator is expanded. Two means of establishing the turbine speed are disclosed wherein a manual setpoint signal is summed with a function of the control signal output from the multivibrator to provide an error signal, and a process control signal may additionally be employed to vary the current supplied to the multivibrator to produce a corresponding variation in the output pulse duration thereof and a corresponding variation in the error signal magnitude.

Claims

1. A speed control system for a machine comprising:

A. sensing means for sensing a speed of operation associated with said machine and providing a speed signal having a frequency which is a function thereof;

B a monostable multivibrator responsive to said speed signal for providing an output signal comprising pulses at a frequency which is a function of the frequency of said speed signal;

(C) integrating means for integrating the output signal from the said multivibrator to provide a control signal which is a function thereof;

(D) setpoint means for generating a setpoint signal corresponding with a desired speed of operation of said machine;

(E) actuating means for adjusting the speed of operation of said machine in response to a function of an error signal functionally related to the control signal output provided from the integrating means;

(F) current source means for providing a current to the multivibrator of a magnitude which determines the duration of the output pulses therefrom; and

(G) feedback circuit means for supplying a feedback signal which is functionally related to the speed of said machine, to the current source means to vary the current provided to the multivibrator to thereby vary the duration of the output pulses produced by the multivibrator during at least high speed operation of the machine.

2. A speed control system as defined in claim 1 wherein said feedback circuit means includes a level detector for transmitting only feedback signals of a predetermined threshold magnitude to the current source means, said predetermined threshold magnitude feedback signal being indicative of a relatively high speed of operation of said machine;

and wherein said current source means includes a circuitry for varying the current supplied to the multivibrator in a direction to reduce the duration of the output pulses therefrom when the feedback signal exceeds said predetermined threshold magnitude.

3. A speed control system as defined in claim 1 wherein said setpoint means includes means for supplying a process setpoint control signal to the current source;

and wherein said current source includes circuitry for varying the current supplied to the multivibrator in response to the process signal input in a manner so as to vary the duration of the output pulses from the multivibrator to thereby vary the speed of operation of said machine in accordance with the process setpoint control signal input to the control.

4. A speed control system as defined in claim 1 including summing means for summing a setpoint signal with a function of the output signal from the multivibrator to provide an error signal for adjusting said actuating means, said circuit further including means for supplying a process setpoint control signal to the current source;

and wherein said current source includes circuitry for varying the current supplied to the multivibrator in response to the process signal input in a manner so as to vary the duration of the output pulses from the multivibrator to thereby vary the speed of operation of said machine in accordance with the process setpoint control signal input to the control.

5. A speed control system for a fluid turbine comprising:

A. sensing means for sensing a speed of rotation associated with the turbine and providing a speed signal having a frequency which is a function thereof;

B. a monostable multivibrator responsive to the speed signal for providing an output signal comprising output pulses of normally Constant duration at a frequency which is a function of the frequency of the speed signal frequency;

C. integrating means for integrating the output signal from the multivibrator to provide a control signal which is a function thereof;

D. setpoint means for generating a setpoint signal corresponding with a desired speed of operation of said turbine;

E. summing circuit means for summing the setpoint signal with the control signal from said integrating means to provide an error signal;

F. actuating means for controlling the fluid flow through said turbine in response to a function of the error signal provided from said summing means;

G. current source means for providing a current to the multivibrator of a magnitude which determines the duration of the output pulses therefrom;

H. feedback circuit means for providing a feedback signal to said current source means which is functionally related to the sensed speed of the turbine, said feedback circuit means including a level detector circuit for transmitting only feedback signals corresponding to a relatively high turbine speed to said current source means; and

I. said current source means including circuitry for varying the current supplied to the multivibrator in a manner to reduce the duration of the output pulses from the multivibrator upon the passage of a feedback signal corresponding to a relatively high turbine speed to said current source.

6. A speed control for a fluid turbine as defined in claim 5 wherein said setpoint means further includes means for supplying an externally generated process signal to the current source;

and wherein said current source includes circuitry for varying the current supplied to the multivibrator in response to the process signal input in a manner so as to vary the duration of the output pulses from the multivibrator to thereby vary the speed of operation of said machine in accordance with the process signal input to the control.

7. A method of controlling the speed of a fluid turbine comprising the steps of:

A. sensing a speed functionally related to the speed of rotation of the turbine and providing a speed signal which has a frequency which is a function thereof;

B. supplying current to a monostable multivibrator and triggering the multivibrator with said speed signal to produce output pulses corresponding with a function of the frequency of said speed signal and having a duration corresponding with the magnitude of current supplid to themultivibrator;

C. integrating the output pulses fro the multivibrator to obtain a control signal;

D. generating a setpoint signal which is a function of desired speed of operation of said turbine;

E. modifying the control signal with the setpoint signal to obtain an error signal which is a function of the desired change in fluid flow through theturbine;

F. varying the fluid flow through the turbine in accordance with a function of the error signal to obtain a desired speed of operation of the turbine; and

G. varying the duration of the output pulses from the multivibrator by varying the current supplied thereto in accordance with a function of the sensed speed of said thrbine to extend the range of input frequencies to which the multivibrator can usefully respond.

8. A method of controlling the speed of a fluid turbine as defined in laim 7 wherein the step of modifying the control signal includes varying the duration of th output pulses from the multivibrator by varying the current supplied thereto in accordance with a function of a setpoint control signal.

9. A method of controlling the speed of a fluid turbine as defined in claim 7 wherein the step of modifying the control signal with the setpoint signal comprises summing a control signal with the setpoint signal to prvide said error signal and varying the duration of the output pulses from the multivibrator by varying the current supplied thereto in accordance with a function of another setpoint contRol signal.