Process control method and apparatus

• US 3,912,913 A
• Filed: 04/08/1974
• Issued: 10/14/1975
• Est. Priority Date: 04/09/1973
• Status: Expired due to Term

• Current Assignee: James William Bunting
• Original Assignee: James William Bunting
• Inventors: Bunting, James William
• Primary Examiner(s): Botz, Eugene G.
• Application Number:
  US05/458,464
• Time in Patent Office: 554 Days
• Field of Search: 235/151.1,151.12 236/46F,15B,78D 318/601
• US Class Current: 700/78
• CPC Class Codes: G05B 15/02 electric
• CPC Class Codes: G05B 19/075 for delivering a step function, a slope or a continuous function G05B19/06 takes precedence
• CPC Class Codes: G05D 23/1917 using digital means

Abstract

A method for controlling changes in the value of a process variable includes the steps of producing electrically a digital number signal representing the desired value of the variable, periodically adding to or subtracting from that number a digital number representing a required change in the variable, to produce an updated desired value signal, and comparing the latter signal or an analogue of it electrically with a signal representing the measured value of the variable to obtain a control signal for regulating the value of the variable. The method is applicable to the control of many industrial processes, for example the control of temperature in a dyebath, temperature cycles in baking ovens, pottery firing ovens and metal treatment furnaces, rates of flow of gases and liquids, tool movements in contour machine tools, and '"'"''"'"''"'"''"'"'loss of weight'"'"''"'"''"'"''"'"' feeding systems. Apparatus for carrying out the process is also described, comprising a first shift register for storing a binary number representing a desired value of the variable, a second shift register for storing a binary number representing a change to be made to the desired value in a predetermined time, programme means for receiving programme instructions and periodically transferring numbers to the second shift register, means for periodically combining the numbers in the two registers to produce an updated number and means for transferring periodically updated number signals to a comparator stage for comparison with electric signals representing the measured value of the variable to produce control signals for influencing the variable.

Claims

1. A method for controlling changes in the value of a process variable including the steps of producing electrically a digital number signal representing the desired value of the variable, adding to that number at successive equal intervals of time the positive or negative digital number representing the magnitude of a required change in the variable, to produce an updated desired value signal, and comparing the latter signal or an analogue of it electrically with a signal representing the measured value of the variable to obtain a control signal for regulating the value of the variable.

2. A method according to claim 1 wherein the digital number signals are binary numbers.

3. A method according to claim 1 wherein the digital number signals are binary coded decimal numbers.

4. A method according to claim 1 including the step of periodically comparing the signal representing the desired value of the variable with a signal representing the final value it is to achieve and thereby producing a further signal determining automatically whether the said number representing the required change is to be added to or subtracted from the desired signal value.

5. Apparatus for controlling a process variable comprising a first shift register for transient storage of a binary number representing a desired value of the variable, a second shift register for momentarily storing a binary number representing a chaNge to be made to the desired value in a predetermined time, programme means for receiving programme instructions and periodically transferring numbers to the second shift register, means for periodically combining the numbers in the two registers to produce an updated number and means for transferring periodically updated number signals to a comparator stage for comparison with electric signals representing the measured value of the variable to produce control signals for influencing the variable.

6. Apparatus according to claim 5 wherein the means for combining the numbers in the two registers comprises a serial adder for adding the number stored in the second shift register to that stored in the first shift register.

7. Apparatus according to claim 6 wherein the programme means includes means responsive to a programme instruction indicating the final value to be achieved by the variable to produce an electric signal representing the final value and the comparator stage includes means for comparing periodically the desired value with the final value for producing a '"'"''"'"'subtract'"'"''"'"' signal when the desired value exceeds the final value, including inversion means responsive to the said '"'"''"'"'subtract'"'"''"'"' signal for feeding the complement of the number stored in the second shift register to the serial adder instead of that number itself.

8. Apparatus according to claim 7 wherein the electric signal representing the final value is a digital signal and the means for comparing it with the desired value signal is a digital device.

9. Apparatus according to claim 7 wherein the electric signal representing the final value is an analogue signal, including a digital-to-analogue converter for receiving the said updated numbers and producing analogue signals representing the said numbers, the means for comparing the desired value with the final value being an analogue device.

10. Apparatus according to claim 5 including an analogue sensor for measuring the actual value of the variable and producing a voltage signal representing this measured value, and an analogue-to-digital converter for producing a digital signal representing the measured value, the comparator stage including a digital device.

11. Apparatus according to claim 5 including an analogue sensor for measuring the actual value of the variable and producing a voltage signal representing this measured value, a digital-to-analogue converter for receiving the said updated numbers and producing analogue signals representing the said numbers, the comparator stage including an analogue device.