Process control system

Abstract

An electronic process control system including a digital computer, a computer interface that is easily replaceable in order to change computer types; a logic module for grouping the computer and controller signals and converting between digital and analog representations; and a control unit interface for generating analog signals for a control unit in response to computer commands and adapting the analog control unit to communicate with a digital computer.

Claims

2. The control system of claim 1 further including:

address lines connected to the individual control unit interfaces, and

means for demultiplexing an address signal from the digital computer by activating one of the address lines.

3. The control system of claim 2 wherein the control unit interface means includes:

gating means for receiving the series of pulses in parallel with other unit interfaces, the gating means allowing the signals to pass only upon the presence of a properly activated address line.

4. The control system of claim 3 wherein the control unit interface further includes:

a plurality of memory means for storing analog values related to the series of pulses passed; and

switching means for determining which of the memory means are to be activated by the analog value upon command from the computer.

5. A DDC process interface system for use with a digital computer having computer interface circuitry for translating between the digital format of the computer and a prearranged digital format including command, address, digital output value, and digital input value information, and a plurality of devices cooperating with the process to be controlled, the interface system comprising:

a plurality of control unit interfaces for transmitting analog signals to the devices;

a plurality of address lines each connected to an individual control unit interface;

an address decoder for activating individual address lines based on the address information;

a plurality of command lines connected in parallel to interfaces for transmitting the command information;

a command code register associated with each control unit interface operable to record the present status of the command lines when activated by the corresponding address line;

a pulse line connected to the analog control unit interfaces;

a pulse generator assembly for generating a series of pulses on the pulse line based on the digital output value information;

a pulse enabling gate associated with each control unit interface for passing the pulses on the pulse line when activated by the corresponding address line;

a pulse converter associated with each gate for converting the pulses into an analog value for transmission to the devices cooperating with the process to be controlled;

an analog input value line associated with each control unit interface for collecting analog value information related to the corresponding control unit;

an analog multiplexer to which all analog input value lines are connected, the multiplexer being connected to the address decoder and activated thereby to multiplex the analog input value line corresponding to the address line activated; and

an anlog to digital converter for converting the analog value on the analog input value line to digital input information for the computer.

6. The DDC process interface system of claim 5 with setpoint tracking, further comprising;

a second pulse converter associated with each gate for converting pulses into a second analog value for transmission to the devices cooperating with the process to be controlled; and

a setpoint/output switch inserted between the pulse enabling gate and the first and second pulse converter of each control unit interface for directing the pulses to one of these converters according to the status of the command code register associated with the same control unit interface, whereby the first analog value may be utilized as a computer generated output value and the second analog value utilized as a computer generated setpoint value.

7. The DDC system of claim 6 wherein the first pulse converter in each control unit interface comprises:

a pulse shaper for generating a predetermined pulse shape in response to each pulse received on the pulse line; and

an integrator for storing and integrating the predetermined pulse shapes to generate the first analog value.

8. The DDC system of claim 7 wherein the second pulse converter in each control unit interface comprises:

a pulse counter for generating a digital value related to the number of pulses received; and

a digital to analog converter for generating the second analog value.

9. The DDC system of claim 5 with remote/local setpoint switching, further comprising:

a remote/local switch in each control unit interface for receiving the second analog value and another analog value and transmitting one of these analog values to the devices cooperating with the process to be controlled according to the status of the command code register associated with the same control unit interface, whereby the computer may choose between the setpoint value locally generated by the computer and another setpoint value remotely generated.

10. The DDC process interface system of claim 5 with absolute/incremental ability, further comprising:

an absolute/incremental switch associated with each pulse generator for receiving the digital output value information and another digital output value signal and transmitting one of these digital values to the pulse generator according to the command code information; and

means for combining the digital output value information from the computer to the digital input information from the analog to digital converter to generate the other digital output value signal for the absolute/incremental switch, whereby the analog value transmitted to the devices cooperating with the process to be controlled may be either the absolute value determined by the computer or an incremental value related to the difference between the absolute value and a present value.

11. The DDC system of claim 5 further comprising: a digital multiplexer associated with each analog multiplexer for combining digital status information regarding the present status of the control unit interface and the devices with the output of the analog to digital converter to form composite digital input value information.

12. The DDC system of claim 5 further comprising:

a legal code decoder for determining the validity of the present combination of information on the command code lines.

13. The DDC system of claim 5 wherein the control unit interfaces are arranged in sub-systems of a maximum of a predtermined number of units each, further comprising:

an additional set of address decoders, pulse generators, analog multiplexers, and analog to digital converters for each sub-system beyond one..Iadd. 14. In a system for controlling a complex industrial process having a large number of different process conditions, said system comprising a plurality of closed-loop control units, each unit being for a respective process condition; said control units comprising analog controllers, said controllers including means for producing analog control signals to operate respective process devices which determine the magnitudes of corresponding process variables thereby to effect the desired control of the process conditions, said analog controllers being provided with analog set-point signals, indicating the value of the process condition to be established, and corresponding analog measurement signals indicating the actual value of the process conditions, said analog controllers including means for comparing the respective set-point signal with the corresponding analog measurement signal and developing from such comparison the required control signals for the respective process device to maintain each affected process condition at its set-point value;

said control system further comprising a central station with a digital computer which is supplied with information signals respecting the controlled process, including the values of selected process conditions, for producing from such information signals various instructional signals to be transmitted to equipment associated with said analog controllers for directing the functioning of the corresponding process devices in accordance with predetermined characteristics pre-set in the digital computer; said analog controllers and associated equipment being located remotely from said central station computer;

the improvement in such a process control system wherein said equipment associated with said analog controllers comprises:

at least one input/output subsystem assigned to a set of said analog controllers for operation therewith;

a cable extending from said digital computer to said input/output subsystem for carrying digital signals in both directions therebetween;

said input/output subsystem including a set of controller interfaces with each such interface being coupled to a respective controller of said set of analog controllers;

each of said controller interfaces including digital-to-analog converter means responsive to digital signals developed from instructional signals sent over said cable by said computer and representing instructional data for the corresponding analog controller, or the process device associated therewith;

said digital-to-analog converter means at each controller interface including output circuit means operable to produce an output analog signal corresponding to the applied digital signal and to direct such output analog signal to the analog controller corresponding to that controller interface, or to the process device associated with said analog controller, for effecting control of said associated process device;

memory means for each of said digital-to-analog converter means to store signals representing the instructional data directed to the respective converter means by said computer, said memory means being coupled to said corresponding analog controller or to said associated process device whereby such instructional data remains available for use by the corresponding analog controller or the associated process device while said computer is communicating with other of said controller interfaces or is performing other tasks; and

analog-to-digital converter means forming part of said input/output subsystem for converting analog signals to corresponding digital signals to be sent through said cable to said digital computer..Iaddend..Iadd. 15. Apparatus as claimed in claim 14, wherein said memory means comprises a digital register to store a digital number representing the value of a set-point signal for the corresponding analog controller;

the output of said register being coupled to the input of the corresponding digital-to-analog converter means to produce at the output thereof an analog set-point signal for said corresponding analog controller..Iaddend..Iadd. 16. Apparatus as claimed in claim 14, wherein said memory means comprises an integrator producing an analog signal representing the value of an output signal to be directed to the process device associated with the corresponding analog controller..Iaddend..Iadd. 17. Apparatus as claimed in claim 16, wherein said input/output subsystem includes means to produce a series of pulses the number of which reflects the value of an output signal for said associated process device; and

means to direct said series of pulses to the input of said integrator..Iaddend..Iadd. 18. Apparatus as claimed in claim 14, wherein said input/output subsystem includes digital register means to store a binary signal specifying whether the output of said digital-to-analog converter means is to represent a set-point value for the corresponding analog controller or an output value for the associated process device;

first and second lines respectively for conducting set-point signals to said analog controller and for conducting output signals for the associated process device;

multiplex means; and

means responsive to the binary signal stored in said digital register for controlling said multiplex means to selectively activate said digital-to-analog means to direct an output thereof to said set-point line or said output signal line..Iaddend..Iadd. 19. Apparatus as claimed in claim 18, wherein each controller interface includes first and second digital-to-analog converters;

means coupling the output of said first converter to the set-point line of the corresponding controller;

means coupling the output of said second converter to the output line for the associated process device;

said multiplex means having an input arranged to receive a digital signal representing a value for either set-point or output;

said multiplex means having first and second outputs selectively activatable by said binary signal to connect said digital signal, at the input of said multiplex means, to one or the other of said digital-to-analog converters..Iaddend..Iadd. 20. Apparatus as claimed in claim 14, wherein each controller interface includes a set-point signal line for directing set-point signals to the corresponding analog controller;

digital register means at said input/output subsystem to store a digital signal specifying whether the set-point signal for an analog controller is to be supplied from said digital-to-analog converter means or is to be supplied from a remote source;

a multiplex means having its output coupled to at least one of said set-point signal lines;

a first input for said multiplex means coupled to the output of one of said digital-to-analog converter means;

a second input for said multiplex means coupled to a line from a remote source of set-point signal; and

means under control of the digital signal stored in said digital register to activate said multiplex means to selectively connect to said set-point signal line either the output of said one digital-to-analog converter means or a signal from said remote source..Iaddend..Iadd. 21. Apparatus as claimed in claim 14, wherein at least one of said controller interfaces includes an automatic/manual line leading to the corresponding analog controller to furnish to that controller an automatic/manual signal for shifting the controller from one to the other of those two modes of operation;

a digital register forming part of said input/output subsystem adapted to store a binary signal derived from the computer instructional signals and indicating whether said one controller is to be operated in automatic or manual mode; and

means coupling the output of said digital register to said automatic/manual line..Iaddend..Iadd. 22. Apparatus as claimed in claim 14, wherein said input/output subsystem includes a digital register having sections for storing three groupings of a digital instruction signal developed from signals transmitted by said computer, wherein the first grouping contains the command instructions respecting the actions to be carried out, the second grouping contains an address identifying the specific controller interface which is to be affected by the command instructions, and the third grouping contains the value of a change to be effected;

operating means coupled to said digital register responsive to said first signal grouping and operable to activate portions of said input/output subsystem to carry out the specified command;

address means coupled to said digital register responsive to said second signal grouping for activating a corresponding controller interface in accordance with the specified address data; and

means coupled to said digital register responsive to said third signal grouping for directing a corresponding digital signal to the digital-to-analog converter means of the activated controller interface to produce an analog signal representing the value of the change to be effected through the activated interface..Iadd. 23. In a system for controlling a complex industrial process having a larger number of different process conditions, said system comprising a plurality of closed-loop control units, each unit being for a respective process condition; said control units comprising analog controllers, said controllers including means for producing analog control signals to operate respective process devices which determine the magnitudes of corresponding process variables thereby to effect the desired control of the process conditions, said analog controllers being provided with analog set-point signals, indicating the value of the process condition to be established, and corresponding analog measurement signals indicating the actual value of the process condition, said analog controllers including means for comparing the respective set-point signal with the corresponding analog measurement signal and for developing from such comparison the required control signals for the respective process devices to maintain each affected process condition at its set point value;

said control system further comprising a central station with a digital computer which is supplied with information signals respecting the controlled process, including the values of selected process conditions, for producing from such information signals various instructional signals to be transmitted to equipment associated with said analog controllers for directing the functioning of the corresponding process devices in accordance with predetermined characteristics pre-set in the digital computer; said analog controllers and associated equipment being located remotely from said central station computer;

the improvement in such a process control system wherein said equipment associated with said analog controllers comprises:

a plurality of input/output subsystems each assigned to a corresponding set of said analog controllers for operation therewith;

a cable connecting said digital computer to all of said input/output subsystems in parallel, for carrying digital signals in both directions between said computer and said input/output subsystems;

each of said input/output subsystems including a set of controller interfaces with each such interface being coupled to a respective controller of the corresponding set of analog controllers;

each of said input/output subsystems including digital-to-analog converter means responsive to digital signals developed from instructional signals sent over said cable by said computer and representing instructional data for any of said analog controllers or the associated process devices;

said digital-to-analog converter means including circuit means to direct the output analog signal to a selected analog controller, or to the process device associated therewith, for effecting control of said associated process device;

memory means for each of said input/output subsystems to store signals representing instructional data directed to that subsystem by said computer, said memory means being coupled to a corresponding analog controller or an associated process device, whereby such instructional data remains available for use by said corresponding analog controller or associated process device while said computer is performing tasks unrelated to such corresponding analog controller or associated process device; and

each of said input/output subsystems including an analog-to-digital converter responsive to analog signals from the corresponding analog controller or associated devices and operable to produce corresponding digital signals for transmittal through said cable back to said digital

computer..Iaddend..Iadd. 24. In a system for controlling a complex industrial process having a large number of different process conditions, said system comprising a plurality of closed-loop control units, each unit being for a respective process condition; said control units comprising analog controllers, said controllers including means for producing analog control signals to operate respective process devices which determine the magnitudes of corresponding process variables thereby to effect the desired control of the process conditions, said analog controllers being provided with analog set-point signals, indicating the value of the process condition to be established, and corresponding analog measurement signals indicating the actual value of the process condition, said analog controllers including means for comparing the respective set-point signal with the corresponding analog measurement signal and for developing from such comparison the required control signals for the respective process devices to maintain each affected process condition at its set-point value;

said control system further comprising a central station with a digital computer which is supplied with information signals respecting the controlled process, including the values of selected process conditions, for producing from such information signals various instructional signals to be transmitted to equipment associated with said analog controllers for directing the functioning of the corresponding process devices in accordance with predetermined characteristics pre-set in the digital computer; said analog controllers and associated equipment being located remotely from said central station computer;

the improvement in such a process control system wherein said equipment associated with said analog controllers comprises:

at least one input/output subsystem assigned to a set of said analog controllers for operation therewith;

a cable connecting said digital computer to said input/output subsystem for carrying digital signals in both directions between said computer and said input/output subsystem;

said input/output subsystem including a set of controller interfaces with each such interface being coupled to a respective controller of said set of analog controllers;

said input/output subsystem including digital-to-analog converter means responsive to digital signals developed from instructional signals sent over said cable by said computer and representing instructional data for any of said analog controllers or the associated process devices;

circuit means for directing output analog signals of said digital-to-analog converter means to selected analog controllers or the process devices associated therewith, for effecting control of such associated process device;

memory means for each of said controller interfaces to store signals representing instructional data directed to said digital-to-analog converter means by said computer for a selected interface and its corresponding analog controller or associated process device, said memory means being coupled to said corresponding analog controller or said associated process device whereby such instructional data remains available for use by the corresponding analog controller or associated process device while said computer is performing tasks unrelated to such corresponding analog controller or associated process device;

said input/output subsystem including analog-to-digital converter means responsive to analog signals from the corresponding analog controllers or associated devices and operable to produce corresponding digital signals for transmittal through said cable back to said digital computer; and

means responsive to digital signals transmitted over said cable by said computer for controlling the functioning of said analog-to-digital converter means to produce said corresponding digital signals under the command of said computer..Iaddend..Iadd. 25. Apparatus as claimed in claim 24, wherein said means responsive to digital signals includes multiplex means for selecting an analog signal from a particular controller interface as the input to said analog-to-digital converter means..Iaddend..Iadd. 26. Apparatus as claimed in claim 25, wherein said multiplex means includes means to select one of a plurality of analog signals from a selected controller interface..Iaddend..Iadd. 27. In a system for controlling a complex industrial process having a large number of different process conditions, said system comprising a plurality of control units for respective process conditions and having means for producing analog control signals to operate respective process variables thereby to effect the desired control of the process conditions; said control units being provided with applied signals for determining the values of the control signals produced by the respective control units;

said control system further comprising a central station with a digital computer which is supplied with information signals respecting the controlled process, including the values of selected process conditions, for producing from such information signals various instruction signals to be transmitted to equipment associated with said control units for directing the functioning of the corresponding process device in accordance with predetermined characteristics pre-set in the digital computer; said control units and associated equipment being located apart from said central station computer;

the improvement in such a process control system wherein said equipment associated with said control units comprises;

at least one input/output subsystem assigned to a set of said control units for operation therewith;

signal transmission means extending from said digital computer to said input/output subsystem for carrying digital signals in both directions therebetween;

said input/output subsystem including a set of control unit interfaces with each such interface being coupled to a respective control unit of said set of control units;

said input/output subsystem including digital-to-analog converter means for all of said control unit interfaces and responsive to digital signals developed from instructional signals sent over said signal transmission means by said computer and representing instructional data for a corresponding control unit;

said digital-to-analog converter means including output circuit means operable to produce an output analog signal corresponding to the applied digital signal and to direct such output analog signal to the corresponding control unit for effecting control of said associated process device;

memory means for each of said control units to store signals representing the instructional data directed to the converter means by said computer, said memory means being coupled to the corresponding control unit whereby such instructional data remains available for use by the corresponding control unit while said computer is communicating with other of said control unit interfaces or is performing other tasks; and

analog-to-digital converter means forming part of said input/output subsystem for converting analog signals to corresponding digital signals to be sent through said signal transmission means to said digital

computer..Iaddend..Iadd. 28. Apparatus as claimed in claim 27, wherein said input/output subsystem includes a digital register having at least one section for storing a corresponding signal grouping of a digital instruction signal developed from signals transmitted to said input/output subsystem and representing an address identifying the specific control unit interface which is to be affected by the command instructions; and

address means coupled to said digital register responsive to said signal grouping for activating a corresponding control unit interface in

accordance with the specified address data..Iaddend..Iadd. 29. Apparatus as claimed in claim 28, wherein said digital register includes a second section for a second signal grouping of the digital instruction signal;

said second signal grouping containing the command instructions respecting the action to be carried out by the input/output subsystem and associated elements; and

operating means coupled to said digital register responsive to said second signal grouping to activate portions of said input/output subsystem to carry out the specified command..Iaddend..Iadd. 30. Apparatus as claimed in claim 29, wherein said digital register includes a third section for a third signal grouping of the digital instruction signal identifying a signal magnitude for a specified command instruction to be carried out; and

digital signal means coupled to said digital register responsive to said third signal grouping for directing a corresponding digital signal to the digital-to-analog converter means of the activated control unit interface to produce an analog signal representing said signal magnitude for the activated control unit interface..Iaddend..Iadd. 31. Apparatus as claimed in claim 30, wherein said digital signal means comprises means for developing a signal corresponding to a change to be effected in an analog signal produced by the activated control unit interface..Iaddend..Iadd. 32. Apparatus as claimed in claim 30, wherein said digital signal means comprises means for developing a signal corresponding to an analog signal level to be developed by the activated control unit interface..Iaddend..Iadd. 33. Apparatus as claimed in claim 30, wherein said memory means comprises a storage capacitor storing an analog signal representing the output of said digital-to-analog converter..Iaddend..Iadd. 34. Apparatus as claimed in claim 30, wherein said memory means comprises digital register means the output of which is coupled to said digital-to-analog converter..Iaddend..Iadd. 35. Apparatus as claimed in claim 34, wherein said memory means comprises a counter for developing a digital signal responsive to the number of received pulses; and