Abstract:
An electronic process controller comprises a digital computer programmed to digitally simulate the functions of each of a plurality of conventional analog and discrete control blocks and a process operator&#39;s panel for selecting and arranging these simulated blocks into a simulated control circuit configuration. The operator&#39;s panel provides means for direct operator selection of: (1) the input signal to be processed by the computer; (2) the arrangement of simulated blocks for processing the input signal in order to derive an output process control signal; and (3) the output control device to which the output signal is directed. This controller permits assembly and modification of simulated analog process control configurations in a manner analogous to the assembly of conventional hard wire control circuits without the expense of wiring, breaking, and rewiring of hard wire interconnections. At the same time, it permits the operator to use a computer for providing analog control functions without knowledge of a specialized programming language.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an electronic process controller having simulated analog control functions. 
     Present systems for controlling complex industrial processes are relatively inflexible. Programmable logic controllers such as those described in U.S. Pat. No. 3,686,639 issued to W. B. Fletcher et al. and U.S. Pat. No. 3,829,842 issued to D. H. Langdon et al. are useful logic controllers for controlling the relatively straightforward operation of switch-operated machines, but they are of only limited utility in more complex processes where optimal control cannot be predicated on simple on-off decisions. 
     Control of complex processes requiring analysis of analog as opposed to simple digital signals has typically required the use of hardwired control circuits or specially programmed general purpose computers. 
     The control circuit approach involves physically interconnecting mechanical or electrical control blocks into the proper configuration for controlling the process in question. Each control block is a separate piece of hardware, such as a circuit board; and the blocks are interconnected into the desired circuit by hard wire. This approach is relatively inflexible in that modification of the process control requires breaking and rewiring of the hard wire connections. In addition, relative to the process control system described herein, the control circuit approach is: 
     1. expensive in medium to large size systems due to the cost of control blocks; 
     2. time consuming due to the labor required to mount and interconnect the blocks; 
     3. limited in accuracy of control; and 
     4. limited in the variety of control methods available. 
     An alternative approach to controlling complex processes involves the use of a general purpose computer specifically programmed to control the process in question. See, for example, U.S. Pat. No. 3,761,692 issued to E. G. Cope and U.S. Pat. No. 3,681,782 issued to F. T. Scanlon. 
     While the use of a specially programmed general purpose computer offers advantages in accuracy and variety of control as compared with the control circuit approach, it nonetheless comprises a relatively inflexible process control system. The programs required for specific process control are typically long, complex, and internally interrelated. They are written in specialized computer languages such as FORTRAN and BASIC or even Assembly Language. As a consequence, control systems using such computers cannot be readily modified by industrial engineers who are not specialists in computer programming. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention relates to an electronic process controller for controlling processes of the type requiring data processing of analog input signals indicative of the status of the process. The primary components of the controller are a digital computer, input means, output means, and a process operator&#39;s panel. 
     More specifically, the digital computer is coupled to the operator&#39;s panel, the input means, and the output means. The computer is programmed to digitally simulate the functions of each of a plurality of conventional analog and discrete process control blocks familiar to control engineers and to simulate a control circuit comprising a selected arrangement of selected ones of these control blocks. 
     The operator&#39;s panel is coupled to the digital computer. It includes means, in the form of keys, permitting selection of one or more analog process input signals to be processed by the computer. It also includes keys permitting selection of one or more simulated analog control blocks to process the selected input signals, and keys permitting selection of one or more output paths whereby process control signals derived from processing the input signals are directed to selected process control devices. 
     The input and output means include terminals for permitting connection to each of a plurality of process sensing and control devices, respectively, and input and output paths for coupling these devices to the computer. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The advantages, nature, and various features of the invention will appear more fully upon consideration of the various illustrative embodiments now to be described in detail in connection with the accompanying drawings. In the drawings: 
     FIG. 1 is a block diagram of a typical electronic digital process controller in accordance with the invention; 
     FIG. 2 is a schematic diagram showing the circuitry of an analog input module in greater detail; 
     FIG. 3 is a schematic diagram showing the circuitry of a discrete input module in greater detail; 
     FIG. 4 is a schematic diagram showing the circuitry of an analog output module in greater detail; 
     FIG. 5 is a schematic diagram showing the circuitry of a discrete output module in greater detail; 
     FIG. 6 illustrates a preferred process operator&#39;s panel in accordance with the invention; 
     FIGS. 7A through 7Y are flow charts of preferred function block simulation programs and related programs useful in the practice of the invention; 
     FIG. 8 is a schematic diagram showing the circuitry of the process operator&#39;s panel in greater detail; and 
     FIGS. 9A and 9B are illustrations of a simple process and a simulated control circuit by which it is controlled in accordance with the invention. 
    
    
     DETAILED DESCRIPTION 
     Referring to the drawings, FIG. 1 is a block diagram of a typical electronic digital process controller in accordance with the invention. The primary components of the controller comprise a digital computer 10, input means 17, output means 21, and a process operator&#39;s panel 30. 
     The Structure Of The Computer 
     The structure of general operation of digital computers are well-known in the art. See, for example, Berkeley et al., Computers: Their Operation and Application, Reinhold Publishing Company, New York, New York (1956). In the preferred embodiment of the present invention, the computer 10 comprises a central processing unit 11 which includes a removable programmer panel 12 (optional), a read only memory 13, a programmable read only memory 14, and a random access memory 15. The precise composition of the memory used in a particular configuration depends upon the complexity of the process to be controlled and the importance of retaining data during power outages. Preferably, the central processing unit and each of the memories is modular so that the unit and its memories can be interconnected through a bus 16. In the preferred embodiment, central processing unit 11 is a small, but complete real-time, multiprogrammed computer, provided with standard features including 74 instruction execution capability, two microsecond cycle time, eight vectored interrupts, a crystal-controlled, real-time clock, power failure shutdown and restart capability, parity error detection, memory data save, and &#34;watchdog&#34; timer protection. With these features, many different programs of the type used in process control can be run concurrently in different time frames and at different priorities, and high speed response to critical process events is not compromised. 
     The following table (Table 1) is a list of commercially available components comprising a preferred digital computer for use in the invention, listed by reference element number (refer to FIG. 1), descriptive name, manufacturer, and part number. 
     
                       TABLE 1______________________________________Number Description     Manufacturer Part No.______________________________________11     Central Processing Unit                  Intel Corporation                               8080                  Santa Clara,                  Calif.13     Read Only Memory                  Intel Corporation                               830814     Programmable Read                  Intel Corporation                               2708  Only Memory15     Random Access Memory                  Intel Corporation                               2107B-6______________________________________ 
    
     The Function And Structure Of The Input And Output Means 
     The controller comprises input means 17 for receiving output signals from a plurality of analog and digital process sensing instruments and for coupling these signals, in suitable form, to the computer. In substance, the input means 17 comprises one or more analog input modules 18 provided with a plurality of terminals (not shown) for (1) receiving analog differential electrical input signals from analog process sensing devices, (2) operating in conjunction with digital-to-analog converter 19 to convert the analog input signals into digital form, and (3) transmitting the signals to the computer over a plurality of respective paths. A preferred module which can accept eight or more analog signals having a voltage range from 0-10 volts (or alternatively 1-5 volts) and a current range from 4-20 milliamps is illustrated in FIG. 2. 
     The analog input module illustrated in FIG. 2 comprises, in substance, a plurality of attenuators 200 for receiving a respective plurality of analog signals and limiting the voltage thereof to levels acceptable by the subsequent circuitry. The outputs of the attenuators are applied to a selector 201 which selects one of the plurality of signals in response to a command from control logic 202. The selected signal is passed through amplifier 203 to comparator 204 wherein the numerical value of the analog signal is ascertained by a series of successive approximations. In brief, the comparator compares the analog signal with a computer estimated value from the digital-to-analog converter. If the signal is greater than the estimation, the output is 0 and if the signal is less, the output is 1. By 12 steps of successive approximations beginning at one-half of the scale voltage, the computer is able to ascertain the value of the signal to within 0.0025 volts 
     The preferred input means 17 also comprises one or more discrete input modules 20 provided with a plurality of terminals (not shown) for receiving discrete electrical input signals from discrete process sensing devices, converting the discrete input signals to appropriate levels of current and voltage, and transmitting the signals to the computer over a plurality of respective paths. A preferred module which can accept sixteen or more such signals in the form of voltages of up to 110 volts AC or DC is illustrated in FIG. 3. 
     The discrete input module illustrated in FIG. 3 comprises, in substance, a plurality of input conditioners 300 for receiving a respective plurality of discrete input signals, converting them into uniform voltages acceptable to the subsequent circuitry and providing some degree of noise filtering. The outputs of the input conditioners are applied to a bus interface 301 which, in response to commands from control logic 302, applies a selected group of the plurality of signals to the computer through the input/output bus. The bus interface comprises, in essence, a plurality of NAND gates. In addition, the lines between the respective input conditioners and the bus interface are each connected to a change detector 303 coupled to an interrupt generator 304. When one of the discrete process sensors changes state, detector 303 activates interrupt generator 304 which, in turn, sends a high priority signal to the computer. 
     The controller also comprises output means 21 for generating output control signals in response to commands from computer 10 and transmitting these control signals through respective output paths to a plurality of respective process control devices. In substance, the output means 21 comprises one or more analog output modules 22 for (1) receiving digital commands from the computer, (2) converting the commands to electrical analog control signals, and (3) transmitting these analog signals through respective paths to a plurality of analog process control devices. A preferred module which can transmit signals having a voltage range from 0-10 volts (or 1-5 volts) at a current range from 4-20 milliamps to four or more analog control devices is illustrated in FIG. 4. 
     The analog output module illustrated in FIG. 4 comprises, in substance, a multiple-position switch 400 for determining, in response to a command from the control logic 401, which of a plurality of sample-and-hold circuits 402 a signal from the digital-to-analog converter is transmitted to. In turn, the voltage signals held in the sample-and-hold circuits are transmitted to output conditioners 403 for amplifying and limiting the voltages to levels acceptable to the analog control devices. In addition, the module is provided with an override from the analog output manual panel through a two-position switch 404 and a slew circuit 405. Through this arrangement the operator can override the computer and set the value of any analog output. The manual override switch status 404 is sensed by the computer via the bus interface 407 and if the switch 404 is in manual, the value stored in the sample and hold 402 is determined by the computer through the use of comparators 406, the bus interface 407 and the D/A signal. This feedback value may be used by the computer to perform bumpless manual to automatic transfer. 
     The preferred output means 21 also comprises one or more discrete output modules 23 for (1) receiving discrete signals from the computer, (2) converting these signals to discrete control signals having appropriate levels of current and voltage, and (3) transmitting these discrete control signals through respective paths to a plurality of discrete process control devices. A preferred module which can switch currents of up to 300 milliamps at voltages of up to 50 volts for transmission to 16 or more discrete control devices is illustrated in FIG. 5. 
     The discrete output module illustrated in FIG. 5 comprises, in substance, a pair of latch circuits 500 for sampling-and-holding discrete signals from the computer through the input/output bus in response to a capture command from the control logic 501. Time multiplexing is achieved by alternatively activating the two latches. Upon receipt of a command from the control logic, the sampled, multiplexed discrete signals are transmitted to the interface circuit 502 for the discrete output manual panel where they can be manually overriden or, alternatively, transmitted to a plurality of output conditioner circuits 503 which convert them to a uniform voltages for transmission to respective discrete process control devices. 
     The input and output modules, the converter 19 and a communication interface 24 are all coupled to the central processing unit through an input/output bus 25 without intervening cable. 
     The Function And Structure Of the Manual Panels 
     Manual panels 26 through 29 are coupled to the input and output modules in order that the process control engineer may have access to the signals being received and control over those being sent out. The analog input panel 26 is provided with a plurality of meters for simultaneously displaying the value of the analog signals received at in several selected analog inputs. It is connected to the analog input module as shown in FIG. 2. 
     The analog output panel 27 is similarly provided with a plurality of meters for simultaneously displaying the value of the analog signals present at several selected analog outputs. It is also provided with switching means for manually overriding computer control of the analog output. It is connected to the analog output module as shown in FIG. 4. 
     The discrete input panel 28 is provided with indicators, such as light emitting diodes, for simultaneously displaying the state of several different discrete inputs. It is connected to the discrete input module as shown in FIG. 3. 
     The discrete output panel 29 is likewise provided with indicators for simultaneously displaying the state of several discrete outputs. It is also provided with switching means for manually overriding computer control of the discrete process control devices. It is connected to the discrete output module as shown in FIG. 5. 
     The Function and Structure Of The Process Operator&#39;s Panel 
     The process operator&#39;s panel 30, provides the primary interface between the process control engineer and the electronic process controller. In substance, the process operator&#39;s panel provides means, in the form of selectable keys, whereby the process control engineer can select one or more analog and discrete input signals to be processed by the computer, one or more digitally simulated analog and discrete control blocks to process selected input signals, and one or more output paths through which process control signals derived from processing the input signals can be transmitted to one or more selected process control devices, respectively. In addition, the panel provides means for specifying the position of each one of a plurality of selected simulated control blocks in a simulated control circuit. 
     The structure and operation of the process operator&#39;s panel 30 may be understood by reference to FIG. 6, which illustrates a preferred embodiment of such a panel comprising four classes of keys and an alphanumeric display panel 600. The four classes of keys include: 
     1. Numeric entry keys 601; 
     2. Entry control keys 602; 
     3. Miscellaneous keys 603; and 
     4. Function selection keys 604. 
     The numeric entry keys 601 include keys for the digits zero through nine, a decimal point key and a negation key. The are used primarily for the entry of numerical data. 
     The entry control keys 602 provide the user with means for ascertaining process control variables and the means for entering new values for such control variables. The READ key causes the value of a selected variable to be displayed on display panel 600. The CLEAR key clears the display panel, but it does not set the value of the variable to zero. The ENTER key can be used to enter a new value as a selected process control variable. 
     The miscellaneous keys 603 provides keys useful in programming. The key marked ↑↑= is a multi-function key. It is used to slew rapidly to the the right when reading a logic or arithmetical equation on display 600, or to enter an equals sign in defining or modifying an equation. It can be used to increase the value of any internal or output analog signal by 20% per second. Similarly, the key marked ↓↓+ is used to slew rapidly to the left in reading an equation or to enter a logical or arithmetical &#34;+&#34; sign. It can also be used to decrease the value of an analog signal by 20% per second. The key marked ↑(serves three functions. It is used to slew slowly to the right in reading an equation, or to enter a left parenthesis in modifying an equation. It is also used to increase the value of an analog signal by 2% per second. Similarly, the key ↓) slews slowly to the left, enters a right parenthesis, or decreases the value of an analog signal by 2% per second. 
     The function selection keys 604 provide input selection keys for specifying a particular input signal to be processed; output selection keys for specifying a particular output path for a process control signal derived from processed input signals, and algorithm selection keys. The input selection keys comprise an Analog In key and a Discrete In key. The Analog In key accepts analog input signals from each of a plurality of analog process sensing devices through their respective paths in the analog input modules. In the preferred embodiment, a specific analog input signal is selected for display or programming by hitting the Analog In key, the keys of the module number, the Input key and and the keys of the terminal number on the module. FIG. 7A is a flow diagram of a preferred Analog Input program, and a preferred data base configuration for the analog input is set forth in Table 2 below. This data base configuration specifies all signals to be used by the simulated terminals of this simulated control block. 
     
                       TABLE 2.______________________________________Relative Address (Bytes)             Description of Contents______________________________________Start + 0         Type is Analog Input (8)+ 1               I/O Slot *4+ 2               Number of Inputs (8)+ 4               Number of Scales (8)+ 6               Number of Zeroes (8)+ 7               Address of              Input 1 Signal+ 9               Address of              Scale 1 Signal+11               Address of              Zero 1 Signal+13               Address of              Input 2 Signal+15               Address of              Scale 2 Signal+17               Address of              Zero 2 Signal.                 ..                 ..                 .+49               Address of              Input 8 Signal+51               Address of              Scale 8 Signal+53               Address of              Zero 8 Signal______________________________________ 
    
     The Discrete In key accepts discrete input signals from each of a plurality of discrete process sensing devices through their respective paths in the discrete input modules, and it assigns each of these signals to respective logic inputs within the computer. A specific discrete input is selected for display or programming by hitting the Discrete In key, the keys for the module number, the Input key and the keys of the terminal number. FIG. 7B is a flow diagram of a preferred discrete input program, and the preferred data base configuration is for the discrete input is set forth in Table 3 below. 
     
                       TABLE 3.______________________________________Relative Address (Bytes)             Description of Contents______________________________________Start+ 0              Type is Discrete Input (2)+ 1              1/0 Slot *4+ 2              Number of Inputs (16)+ 3              Address of Input &amp; Signal+ 5              Address of Input 2 Signal+ 7              Address of Input 3 Signal.                ..                ..                .+ 34             Address of Input 16 Signal______________________________________ 
    
     The output selection keys includes an Analog Out key. By this key, respective analog output signals are selected for display or programming. A specific analog output is selected by hitting the Analog Out key, the keys for the module number, the Output key and the keys for the terminal number. FIG. 7C is a flow diagram of a preferred analog output program, and the preferred data base configuration is set forth in Table 4 below. 
     
                       TABLE 4______________________________________Relative Address (Bytes)             Description of Contents______________________________________Start +0              Type is Analog Output (17)+1                    I/O Slot *4+2                    Number of Resets (4)                 Number of Scales (4)                 Number of Zeros (4)                 Number of Outputs (4)+11                   Number of Tracks (4)                 Address of                  Reset 1 Signal+13                   Address of                  Scale 1 Signal+15                   Address of                  Zero 1 Signal+17                   Address of                  Output 1 Signal+19                   Address of                  Track 1 Signal.                     ..                     ..                     .+41                   Address of                  Reset 4 Signal+43                   Address of                  Scale 4 Signal+45                   Address of                  Zero 4 Signal+47                   Address of                  Output 4 Signal+49                   Address of                  Track 4 Signal______________________________________ 
    
     The output selection keys also include a Discrete Out key permitting selection of respective discrete output signals for display or programming. A specific discrete output signal is selected by hitting the Discrete Out key, the keys for the module number, the Output key and the keys for the terminal number. FIG. 7D is a flow diagram of a preferred discrete output program. The preferred data base configuration is set forth in Table 5, below. 
     
                       TABLE 5.______________________________________Relative Address (Bytes)             Description of Contents______________________________________Start+ 0              Type - Discrete Output (3)+ 1              I/0 Slot *4+ 2              Number of Outputs (16)+ 3              Address of                  Output 1 Signal+ 5              Address of                  Output 2 Signal+ 7              Address of                  Output 3 Signal.                ..                ..                .+34              Address of                  Output 16 Signal______________________________________ 
    
     The algorithm selection keys permit the process control engineer to select one or more digitally simulated analog and discrete control blocks and associated simulated terminals for processing selected input signals. In the preferred embodiment illustrated in FIG. 6, these keys are backlighted, and many serve multiple purposes. The upper legend on the keys identifies their control block simulation function and the lower legend, if any, indicates any simulated terminal which they also control. Several simulated blocks act as if they were analog or discrete process blocks of the type used in conventional hard wire control circuits. The simulated control blocks and their associated terminals can be selected by the following keys. 
     The Counter key permits selection of a simulated control block which will: (1) count the number of pulses that occur in a selected discrete input signal; (2) multiply the total by a scale factor entered under the Scale key; (3) add a term to the product entered under the Zero key, and (4) periodically present the sum to a selected output. FIG. 7E is a flow diagram of a preferred Counter program, and a preferred data base configuration is set forth in Table 6, below. 
     
                       TABLE 6.______________________________________Relative Address (Bytes)             Description of Contents______________________________________Start+ 0              Type - Counter+ 1              I/O slot *4+ 2              Bit number (0 - 15)+ 3              Integer count+ 5              Address of Output Signal+ 7              Address of Scale Signal+ 9              Address of Zero Signal+ 11             Address of Reset Signal______________________________________ 
    
     The Timer key permits selection of a simulated control block which provides for an output read under Output 1 a pulse output of a duration entered under the Setpoint key or provides for an output read under Output 2 a signal delay of the duration entered under the Setpoint key. FIG. 7F is a flow diagram of a preferred Timer program. A preferred data base configuration is set forth in Table 7 below. 
     
                       TABLE 7.______________________________________Relative Address (Bytes)             Description of Contents______________________________________Start+ 0              Type Designation-                  Timer (4)+ 1              Address of                  Time Signal+ 3              Address of                  Setpoint Signal+ 5              Address of                  Input Signal+ 7              Address of                  Reset Signal+ 9              Number of Outputs (2)+10              Address of                  Ouput 1 Signal+12              Address of                  Ouput 2 Signal+14              Storage Area______________________________________ 
    
     The Comparator key permits selection of a simulated control block which compares an analog input signal to a signal entered under the Setpoint key and provides a digital output signal indicating which of the two is greater when the difference exceeds an amount entered under the DEADBAND key. FIG. 7G is a flow diagram of a preferred Comparator program and a preferred data base configuration is set forth in Table 8 below. 
     
                       TABLE 8______________________________________Relative Address (Bytes)             Description of Contents______________________________________Start+ 0              Type Designation Comparator+ 1              Address of Input Signal+ 3              Address of Setpoint Signal+ 5              Address of Deadband Signal+ 7              Address of Output Signal______________________________________ 
    
     The Logic key permits the process control engineer to couple discrete signals to other discrete signals through Boolean logic equations entered under the Equation key. The logical operators available from the numeric entry and miscellaneous keys include &#34;-&#34; for logical negation, &#34;. &#34; for logical AND, &#34;+&#34; for logical OR, left and right parentheses for imbedding operations, &#34;=&#34; for logical equality, and &#34;!&#34; for the end of an equation. FIG. 7H is a flow diagram of a preferred Logic program. A preferred data base configuration is set forth in Table 9 below. 
     
                       TABLE 9.______________________________________Relative Address (Bytes)            Description of Contents______________________________________Start+ 0             Type Designation - Logic (6)+ 1             Address of                 Equation Area (start +11+2*n+ 3             Storage Area+ 5             Number of Input/Outputs (n)+ 6             Address of                 Input/Output 1+ 7             Address of Input/                 Output 2. . .           . . .+ 5+2*n         Address of                 Input/Output n+ 11+2*n        Equation Area Byte 1                Equation Area Byte 2                Equation Area Byte 3. . .           . . .+ 10+2*17*m     Equation Area Byte M______________________________________ 
    
     The Calculator key permits the process control engineer to couple analog signals to other analog signals through simple arithmetic equations entered under the Equation key. The arithmetical operators available are &#34;+&#34; for add, &#34;-&#34; for subtract, &#34;. &#34; for multiply, and &#34;÷&#34; for divide, as well as &#34;()&#34; for embedding, &#34;=&#34; for equality and &#34;!&#34; for the end of an equation. Square roots, trigonometric functions and exponential functions can optionally be provided by using recursion formulas or polynomial series. The flow diagram for the preferred calculator program is the same as that for the logic program shown in FIG. 7H. A preferred data base configuration is set forth in Table 10, below. 
     
                       TABLE 10.______________________________________Relative Address (Bytes)           Description of Contents______________________________________Start+ 1            Type Designation - Calculator (14)+ 1            Address of Equation Area                (start +11+2*n)+ 3            Storage Area+ 5            Number of Input/Outputs (n)+ 6            Address of                Input/Output 1+ 7            Address of Input/               Output 2. . .          . . .+ 5+2*n        Address of               Input/Output n+ 11+2*n       Equation Area Byte 1               Equation Area Byte 2               Equation Area Byte 3. . .          . . .+ 10+2*n+m     Equation Area Byte m______________________________________ 
    
     The Sequencer key permits selection of a simulated control block which will sequentially transmit a selected input to each of a plurality of selected outputs upon successive activation of the Strobe simulated terminal. FIG. 7I is a flow diagram of the preferred sequencer program, and a preferred data base confirguration is set forth in Table 11, below. 
     
                       TABLE 11______________________________________Relative Address (Bytes)             Description of Contents______________________________________Start+  0             Type Designation-Sequencer                  (5)+ 1              Address of Strobe Signal+ 3              Address of State Signal                 Storage Area+ 7              Number of Inputs (7)+ 9              Number of Outputs (7)+ 10             Address of Input 1+ 12             Address of Output 1+ 14             Address of Input 2+16              Address of Output 2...              ......              ...                 Address of Input n                 Address of Output n______________________________________ 
    
     The Logger key permits the process control engineer to have analog or discrete signals printed out on an accessory teletype in accordance with a predetermined format. FIG. 7J is a flow diagram of a preferred Logger program. A preferred data base configuration is set forth in Table 12, below. 
     
                       TABLE 12.______________________________________Relative Address (Bytes)             Description of Contents______________________________________Start+ 0              Type Designation-Logger (7)+ 2              Address of Reset Signal+ 8              Address of Strobe Signal+ 13             Status Bit + 4 * I/O Slot+ 14             Address of Format Data+ 16             Address of Input List+ 18             Number of Inputs (n)+ 19             Address of Input Signal 1. . .            . . .+18+2*n          Address of Signal n______________________________________ 
    
     The Rate key permits selection of a simulated control block, useful in setting up simulated control circuits, which permits specification of time between subsequent executions of each simulated control block. FIG. 7K is a flow diagram of a preferred Rate program. A preferred data base configuration is set forth in Table 13, below. 
     
                       TABLE 13.______________________________________Relative Address (Bytes)             Description of Contents______________________________________Start+ 0              Type Designator Rate+ 1              Number of Inputs (4)+ 2              Address of Input 1+ 4              Address of Input 2+ 6              Address of Input 3+ 8              Address of Input 4______________________________________ 
    
     The BCD to Bin key converts input signals comprising binary coded digital signals to analog output signals. FIG. 7L is a flow diagram of a preferred BCD to Binary program, and a preferred data base configuration is set forth in Table 14, below. 
     
                       TABLE 14.______________________________________Relative Address          Description of Contents______________________________________Start+ 0           Type Designation - BCD - BIN+ 1           Temporary Storage+ 3           Address of Output+ 5           Number of Inputs+ 6           Address of Input 1+ 8           Address of Input 2              .              .              .+ N           Address of Input N______________________________________ 
    
     The Lead-Lag key permits selection of a simulated control block which applies a lead or a lag to an analog input signal for implementation of feed-forward control, process modeling, or filtering. The amount of lead (in minutes) is entered under the Derivative key. The amount of lag in minutes is entered under the Integral key. The Lead-Lag process can be disabled by the Track key which causes the output to track the input. FIG. 7M is a flow diagram of a preferred Lead-Lag program. A preferred data base configuration is set forth in Table 15, below. 
     
                       TABLE 15.______________________________________Relative Address (Bytes)           Description of Contents______________________________________Start+ 0            Type Designation-Lead/Lag (18)+ 1            Address of Reset Signal+ 3            Address of Lead Signal+ 5            Address of Lag Signal+ 7            Address of Input Signal+ 9            Address of Output Signal+ 11           Internal Storage Area______________________________________ 
    
     The Track/Hold key permits selection of a simulated control block which receives an analog input signal and stores it in memory until it is selected by a signal entered under the simulated terminal terminal State for presentation to a selected output. A flow diagram of a preferred Track-Hold program is illustrated in FIG. 7N. A preferred data base configuration is set forth in Table 16, below. 
     
                       TABLE 16.______________________________________Relative Address (Bytes)           Description of Contents______________________________________Start+ 0            Type Designation-Track/Hold+ 1            Number of Storage cells (n)+ 2            Address of Reset Signal+ 4            Address of Track Signal+ 6            Address of Input Signal+ 8            Address of Output Signal+ 10           Number of State Signals (2)+ 11           Address of State 1 Signal+13            Address of State 2 Signal+15            Storage of Old Reset+ 16           Storage Area For Inplementation               of Memory Feature.+ 15+4n______________________________________ 
    
     The Integrator key permits selection of a simulated control block which integrates an analog input signal with respect to time. FIG. 7(O) is a flow diagram of a preferred Integrator program. A preferred data base configuration is set forth in Table 17, below. 
     
                       TABLE 17.______________________________________Relative Address (Bytes)            Description of Contents______________________________________Start+ 0             Type Designation - Integrator+ 1             Address of Input+ 3             Address of Reset+ 5             Address of Output______________________________________ 
    
     The Differentiator key permits selection of a simulated control block which differentiates an analog input signal with respect to time. FIG. 7P is a flow diagram of a preferred Differentiator program. A preferred data base configuration is set forth in Table 18, below: 
     
                       TABLE 18.______________________________________Relative Address (Bytes)           Description of Contents______________________________________Start+ 0            Type Designation - Differentiator+ 1            Address of Input+ 3            Address of Output+ 5            Address of Reset+ 7            Los value of Input______________________________________ 
    
     The Multiplexer key permits selection of a simulated control block which selects one of a plurality of input signals for presentation to the output. The selection is entered under the State key. A flow diagram of a preferred Multiplexer program is illustrated in FIG. 7Q. Table 19, below shows a preferred data base configuration. 
     
                       TABLE 19.______________________________________Relative Address (Bytes)            Description of Contents______________________________________Start+ 0             Type Designation - Multiplexer+ 1             Address of State+ 3             Address of Output+ 5             Number of Inputs+ 6             Address of Input 1+ 7             Address of Input 2+ N             Address of Input N______________________________________ 
    
     The Time/Code key generates current time information and also handles the sign-on of users, accepting the user&#39;s combination code and restricting the user to read/write access privileges specified for him. Outputs 1 through 4 provide the time of day in seconds, minutes and hours, respectively and Output 5 provides the day in the month or year in days. The user&#39;s combination code is entered under the Setpoint key and compared to the allowable combination codes entered under the Input key. The user&#39;s access privileges are entered under the Reset key. FIG. 7R is a flow diagram of a preferred Time/Code program and a preferred data base configuration is set forth in Table 20 below. 
     
                       TABLE 20.______________________________________Relative Address (Bytes)          Description of Contents______________________________________Start+ 0           Type Designation - Time/Code (11)+ 1           Address of Setpoint Signal+ 3           Number of Output Signals (5)+ 4           Address of Output 1 Signal              Address of Output 2 Signal.             ..             ..             .              Address of Output 5 Signal+ 16          Number of Input Signals (3)+ 18          Number of Reset Signals (3)              Address of Input 1 Signal              Address of Reset 1 Signal              Address of Input 2 Signal              Address of Reset 2 Signal              Address of Reset 3 Signal              Storage Area______________________________________ 
    
     The Peak Detector key permits selection of a simulated control block which samples an analog input signal, holds the value of the largest input in one or more memories and presents this value to the output. The Track key controls the sampling of the input. The State 1 keys select which of a plurality of memories which the detected peak is to be stored and the State 2 keys select which of a plurality of memories is to have its contents presented at output. A flow diagram of a preferred Peak Detector program is illustrated in FIG. 7S. Table 16, infra, illustrates a preferred data base configuration. 
     The Averager key permits selection of a simulated control block which can average an analog or a digital input signal. The Averager operates on a signal during a period controlled by the Track key. The State 1 keys control which of a plurality of memories the averaged input is to be stored in and the State 2 keys control which of the memories whose contents are to be presented at the output. The average can be multiplied by a factor entered under the Scale key before it is presented to the output. FIG. 7U is a flow diagram of a preferred Averager program. A preferred data base configuration is set forth in Table 21, below. 
     
                       Table 21.______________________________________Relative Address (Bytes)           Description of Contents______________________________________Start+ 0            Type Designation - Averager+ 1            Number of Storage Cells(n)+ 2            Address of Track Signal+ 6            Address of Input Signal+ 8            Address of Output Signal+ 10           Number of State Signals (2)+ 11           Address of State 1 Signal+ 13           Address of State 2 Signal+ 15           Address of Scale Signal+ 17           Address of Time Signal+ 19           Storage Area For Internal Time+ 23           Storage Area For Integration                Interval+ 27           Storage For Old Reset+ 28           Current For Old Reset+ 29           Storage Area For Input and                Integration Values+ 28+8n______________________________________ 
    
     The Function key permits storage of a table of values for a function of one or two variables and, for current input signals corresponding to these variables (x,y), interpolates to find the value of the function f(x,y) and presents this value to the output. FIG. 7V is a flow diagram of a preferred Function program. In the interpolation portion of the program, K,L,U, and V are defined by the relations: 
     
         X.sub.K ≦ Input 1 &lt; X.sub.K + 1; 
    
     
         y.sub.l ≦ input 2 &lt; Y.sub.L + 1; ##EQU1## A preferred data base configuration is set forth in Table 22, below. 
    
     
                       TABLE 22.______________________________________Relative Address (Bytes)           Description of Contents______________________________________Start+ 0            Type Designation - Function+ 1            Numbers of X entries (NX)+ 2            Number of Y entries (NY)+ 3            Address of Input 1 Signal+ 5            Address of Input 2 Signal+ 7            Address of Output Signal+ 9            Address of state 1 Signal+ 11           Address of state 2 Signal+ 13           Address of setpoint Signal+ 15           Reference MemoryCell (Cell)+ 19           Reference Number (NREF)+ 23           Intermediate storage of Floating               Point Numbers (X, P, Q, R, U, V)+ 47           Intermediate storage of B1, B2,               and B3.+ 50           Storage of table of X, Y, and               F (X,Y) valves.______________________________________ 
    
     A preferred data base configuration for the area of the memory which includes the data bases for the various simulated control blocks is set forth in Table 23 below. 
     
                       TABLE 23______________________________________1.     Special processing program address pointer.2.     Simulated control block directory address  pointer.3.     Process Operator&#39;s Panel key identification  number for terminal.4.     Terminal type information, including offset - information,  interleave level, required terminals  special processing and type of signals.5.     Process Operator&#39;s Panel key identification6.     Terminal Type information.   . . .7.     Addresses of simulated control blocks.8.     Data base configurations for each  respective simulated control block.______________________________________ 
    
     It should be noted that item 8 of Table 23 includes each of the control block data bases set forth in Tables 2 through 22. 
     A preferred circuit arrangement for coupling the process operator&#39;s panel to the computer is illustrated in FIG. 8. In substance, the keys of keyboard 800 are connected to keyboard encoder 801. The keyboard encoder converts the hitting of each separate key into a separate ASCII character which is presented to bus interface circuit 802. In addition upon receipt of a key hit signal, the keyboard encoder activates an interrupt generator 803 which sends a high priority message to the computer over the input/output bus. Upon receipt of such an interrupt signal, the computer commands the control logic 804 to effect a scan of the bus interface so that the computer may ascertain which key has been hit. When a backlighted key is hit, the computer, through lamp controller 805, commands backlighting of the appropriate keyboard lamp 806. When a display response is called for, the computer through to display controller 807, commands display 808. In a preferred embodiment, the display is a unit commercially marketed by the Borroughs Company under the product name Self-Scan Display. 
     The Operation Of The Process Operator&#39;s Panel In the Signal Mode 
     In the preferred embodiment of the invention, the process control engineer can operate the process operator&#39;s panel in two different modes. The first mode, referred to as the Signal Mode, is primarily concerned with the processing of signals within the various simulated function blocks; and the second mode, referred to as the System Mode, is primarily concerned the interconnections among the various simulated function blocks. In this embodiment the controller remains in the first of these modes, the Signal Mode, unless the System key is hit. 
     In the Signal Mode, the process control engineer can utilize the process operator&#39;s panel to inspect, enter and change various process variables used within the simulated control blocks. FIG. 7W is a flow diagram of a preferred program for permitting inspection, entry and modification within the Signal Mode. The operator can also inspect, enter and change logic and arithmetic equations within the logic and calculator simulated control blocks, respectively. FIG. 7X is a flow diagram of a preferred program for permitting inspection, entry and modification of logic and arithmetic equations. 
     The operation of the process operator&#39;s panel in the Signal Mode may best be illustrated by reference to the following specific examples. 
     EXAMPLE 1 
     Examination of a Process Variable 
     To examine a process variable, e.g. the setpoint on the first simulated comparator block, perform the following steps. 
     
         ______________________________________Step                 Purpose______________________________________1. Hit the keys of the            Selects simulated blocksimulated function block            in question, e.g.with which the process            Comparator number 1variable is associated, e.g.hit the Comparator and 1keys.2. Hit the key of the            Selects the simulatedsimulated terminal with            terminal to which thewhich the process variable            process variable inis associated, e.g. hit            question is applied,the Setpoint key.            e.g. the setpoint            terminal. Displays signal name.3. Hit the Read key.            Effects a display of            the current value of            the process variable            applied to the selected            terminal if the user,            identified by his sign-            on code, has security            access to read the variable.______________________________________ 
    
     EXAMPLE 2 
     Changing The Value of a Process Variable 
     To enter or change the value of a process variable after performing the steps of Example 1, perform the following steps. 
     
         ______________________________________Step                 Purpose______________________________________1. Hit the Clear key            20 delete the old            value, if any, for the            variable in question.2. Enter the new value            Selects new value.for the process variable3. Hit the Enter key.            Effects entry of the selected            new value if the user has            security axis to change the            variable.______________________________________ 
    
     EXAMPLE 3 
     Inspecting An Equation 
     To inspect a logic equation, e.g. equation for output 2 of simulated logic block number 6, perform the following steps: 
     
         ______________________________________Step                Purpose______________________________________1. Hit the keys identifying            Selects particular logicthe particular logic block,            block in which equation located.e.g. the Logic and 6 keys.2. Hit the keys identifying            Selects equation.the particular equationto be inspected, e.g. thethe Equation, 2, and Enterkeys.3. Hit the Read key.            Effects a display of the            equation. To read the whole            equation, use the slew keys.______________________________________ 
    
     An arithmetic equation is read by substantially the same steps, substituting the Calculator key for the Logic key. 
     EXAMPLE 4 
     Entering An Equation 
     To enter a logic equation, e.g. to specify that the condition of the seventh output terminal is the logical inversion of the the signal on the first input terminal, perform the following steps: 
     
         ______________________________________Step                 Purpose______________________________________1. Perform the steps of            Selects a specific logic block andExample No. 3    a specific equation &#34;terminal&#34; for            entry of equation.2. Hit Clear, 7=-1!, and            Effects entry and Enter andRead keys.       display of equation setting            the 7th output as inverted with            respect to the condition of the            first input.______________________________________ 
    
     EXAMPLE 5 
     Changing An Existing Equation 
     To change an existing arithmetical equation after inspecting it, e.g. to change the equation for output 27 from the product of in puts 9 and 29 to the product of input 9 and the sum of inputs 29 and 7, perform the following steps: 
     
         ______________________________________Steps                 Purpose______________________________________1. Using the slew keys, place             Selects position29 at the right edge of the             for subsequent operation.display.2. Hit the Clear, (29 &amp; 7). 9             Replaces oldEnter and Read keys.             portion of equation             with new.______________________________________ 
    
     The Operation of The Process Operator&#39;s Panel In the System Mode 
     The process operator&#39;s panel is further provided with means for selecting an arrangement of the above-described simulated control blocks whereby the computer simulates a control circuit comprising the selected arrangement. This selection takes place in the System Mode. 
     The primary means for arranging the simulated control circuit is the System key which, can be used in conjunction with a plurality simulated &#34;internal signal wires&#34; to permit the configuration, inspection and modification of a simulated control circuit. 
     The simulated internal signal wires are specified in a portion of the computer memory referred to as the Master Signal Directory (or MSD). For each such &#34;wire&#34;, memory space is reserved for recording; (1) the type of signal to be carried, i.e. discrete or analog; (2) the data carried; one byte for discrete signals, four bytes for analog signals; (3) the engineering unit of the signal; (4) the access security of the &#34;wire&#34;, which can be high, medium or low for read and write, respectively; and (5) the name of the signal in one to 11 characters. Each internal signal wire is uniquely identified by its number in the Master Signal Directory. 
     FIG. 7Y is a flow diagram of a operation of the process operator&#39;s panel in the system mode. This operation may best be illustrated by reference to the following specific examples. 
     EXAMPLE 6 
     Connection Of An Input To A Simulated Control Block To An Output 
     To connect the fourth analog input of the second analog input module to the compute block, square the input and apply it to the third terminal of the seventh analog output module, perform the following steps: 
     
         ______________________________________Step                Purpose______________________________________1. Hit System key         Places the controller in System Mode         which permits the process operator to         &#34;connect&#34; and &#34;disconnect&#34; simulated         internal signal wires.2. Hit Analog In, 2,         Selects the second analog input moduleInput, 4 and Enter keys         and the fourth input terminal thereof.3. Hit Read key         Effects a display of the         number of any simulated internal         signal wire already connected to the         specified terminal or &#34;Not Used&#34; if         none connected.4. Hit Clear, 119,         Disconnects any previously connectedand Enter keys.         &#34;wire&#34; and one end of connects &#34;wire&#34;         119 to the specified terminal.         The name of signal 119 is displayed.5. Hit Calculator 1,         Selects a specific simulated inputInput, 17 and Enter         terminal (the 17th) on a specifickeys          calculator control block (the first).6. Hit Read key         Effects a display of the         number of any simulated internal         signal wire already connected to         specified terminal.7. Hit Clear, 119,         Disconnects any previously connectedand Enter keys         &#34;wire&#34; and connects second end of         simulated internal signal wire number         119 to specified terminal.8. Hit Calculator,         Selects a specific simulated output1, Output, 6, Enter         terminal (the 6th) of the firstand Read keys Calculator control block and effects         a display of any simulated internal         signal wire already connected to         the specified terminal.9. Hit Clear, 5,         Disconnects any previously connectedand Enter keys.         &#34;wire&#34; and connects one end of simu-         lated internal signal wire number         5 to to the specified terminal.10. Hit Analog Out, 7,         Selects the third output terminalInput, 3, Enter, and         of the seventh analog output moduleRead keys.    and effects a display of the number         of any simulated internal signal wire         already connected thereto.11. Hit Clear, 5,         Disconnects any previously connectedand Enter keys.         &#34;wire&#34; and the connects other of         simulated internal signal wire number         5 to the specified analog output         terminal.12. Hit System key         Removes controller from the System         Mode and puts it into the Signal         Mode.13. Program first calculator block to square input 17 and presentthe result to output 6, i.e. 6=17.17!.______________________________________ 
    
     EXAMPLE 7 
     Control Of A Simple Process Involving Connection Of An Input To Two Successive Control Blocks And An Output 
     An extremely simple exemplary process for control by the invention is the process of keeping water at a constant temperature, e.g. 100° F. FIG. 9A illustrates the apparatus used in this process comprising a container of water 900, an analog sensing device comprising a temperature probe 901 and a temperature-to-voltage converter 902, a process controller 903, and a discrete process control device such as on-off voltage supply 904 connected to an electrical heater 905. 
     FIG. 9B illustrates a simulated control circuit for controlling the process of FIG. 9A comprising, in substance, a simulated comparator block 906 for receiving an analog process control signal, the comparator being coupled to a simulated logical control block 907 for receiving the output of the comparator and sending a discrete output control signal to the voltage supply 904. More specifically, an analog temperature signal from the converter 902 is connected to a terminal of an analog input module 908 of the process controller, e.g. the third terminal of the second module). This signal is, in turn, coupled by a simulated internal signal wire (e.g. number 113) to the input of a simulated comparator 906 (e.g. number 1). At the comparator, the analog input signal is compared with a setpoint corresponding to a temperature of 100° F. If the temperature signal exceeds the 100° F setpoint, the comparator generates a discrete &#34;on&#34; signal output. If the temperature signal drops below the 100° F, setpoint, the comparator turns off. 
     The output of the comparator is transmitted by a simulated internal signal wire (e.g. number 39) to an input terminal of a simulated logic control block 907 (e.g. the first input terminal of the 6th logic control block). The logic block is programmed to invert the condition of the signal on input 1 and present the result to output 7, which output is coupled to a terminal of a discrete output module 909 (e.g. the 15th terminal of module 19) by a simulated intenal signal wire (e.g. number 55). 
     Under this simulated control circuit, the voltage supply powers the heater only when the sensed voltage drops below 100° F. when the sensed voltage exceeds 100° F., the comparator is &#34;on&#34; but the comparator signal is inverted by the logic block to turn the voltage supply &#34;off&#34;. 
     In order to set up this simulated control circuit in the process controller of the invention, the following steps are performed: 
     
         ______________________________________Step                  Purpose______________________________________1. Hit the System key.             Accesses system mode.2. Hit the Analog In, 2,             Selects AI 2, Input 3 andInput, 3, Enter and Read             displays prior wires.keys.3. Hit the Clear, 113,             Attaches wire 113 to AI2,             Input 34. Hit the Comparator, 1,             Selects input of comparatorInput and Read keys.             displays prior wire.5. Hit the Clear, 113             Attaches wire 113 toand Enter keys.   comparator input.6. Hit the Comparator,             Displays prior setpointI, setpoint, and Readkeys.7. Hit the Clear, 99,             Attaches wire 99 to setpoint.and Enter keys.8. Hit the Comparator,             Selects output of1, Output, and Read keys.             comparator 1 and displays             prior wires.9. Hit the Clear, 39, and             Attaches wire 39 toEnter keys.       comparator output.10. Hit the Logic,             Selects input 1 of logic6, Input 1, Enter,             block 6 and displaysand Read keys.    prior wire.11. Hit the Clear,             Attaches wire 39 to logic39, and Enter keys.             block input.12. Hit the Logic, 6,             Selects output 7 of logicOutput, 7, Enter and             block and displays priorRead keys.        wire.13. Hit the Clear, 55,             Attaches wire 55 to logicand Enter, keys.  block output.14. Hit the Discrete Out,             Selects terminal 15 of19, Output, 15, Enter and             discrete output moduleRead keys.        19 and displays prior             wire.15. Hit the Clear, 55,             Attaches wire 55 toand Enter keys    discrete output terminal.16. Hit System key             Operator leaves the system             mode.17. Hit Comparator, Setpoint,             The current value of theRead keys         setpoint is displayed.18. Hit Clear, 100 and Enter             A 100° F setpoint has been             entered.______________________________________ 
    
     While the invention has been described in connection with a small number of specific embodiments, it is understood that these embodiments are merely illustrative of the many possible specific embodiments which can represent applications of the principles of the invention. Numerous and varied systems can be made by those skilled in the art without departing from the spirit and scope of the invention.