It is unlikely that complete plant automation will come about in big jumps It is interesting to contemplate and discuss an imagined power station with everything from control rods to switchgear under computer control, but that stage will be reached in small steps over a long period of time, just as analog control technology has developed

Lacking a charter to automate the whole plant, the engineer must select the type of control (analog, hybrid, or digital) to be applied to the constituent processes and the degree and scope of automation appropriate to those under the command of the computer Every facility has one or more process elements for which conventional control devices are inadequate, these are the prime targets for computer control 14 Next come those elements for which computer control promises a substantial cost savings either in capital investment or in greater operating efficiency Finally, there are those functions where the advantages of either digital or analog control are comparable The scope of computer applications will depend heavily on the strength and completeness of the control engineer’s system analysis Examples of the results of this stage of planning can be found in recent and current reactor plant designs, several of which are described in Sec 8-7

Up to now this section has dealt with computer control, but from here on our discussion of control equipment and software must include their other functions data acquisi tion and display. All new reactor plants will have a computer-based data-handling and data-display system, the control functions can be considered as an extended use of equipment already planned A small percentage in hardware cost will buy computer-control capability However, adding control programs raises the level of complexity of the system software in proportion to the number of functions provided

8- 5.3 Program Description

The programs discussed in this section are those necessary to perform data handling, control, and routine self checking They are called process programs and are recognized by their being always in the computer system and routinely or potentially operative when the computer is on line as a part of the operating plant A second kind, called systems programs, are those used to write and debug the process programs These include the programmers console routines, loaders, assemblers, compilers, and editors They are discussed in the section on equipment specifications because they are always part of the computer procurement

For an analog control system, the engineer can develop a set of functional specifications, most of which can be translated into equipment requirements based on a one-to — one correspondence among the set of input-data points, control-system channels, and control-signal outputs This simple relation between function and hardware is shown in Fig 8 2 However, there is no such correspondence in a computer-based system As seen m Fig 8 4, only the process interfaces can be sized according to the system functions, the rest of the hardware must be specified on the basis of the computer programs needed to perform the data acquisition and display and control tasks

So the computer-system designer starts by compiling the usual functional specification, setting forth what the system must do, and the process and operator inputs that will be needed to implement them The next step is to develop a detailed description of the computer programs required to make the hardware function as specified Th з task is the most demanding part of the design procedure If it is not done well, an adequate system procurement specification cannot be written

The program description can be developed in three stages for convenience in planning and carrying out the separate activities

1 The process software is divided into major programs The level of the division is dictated by the need for each program to have a distinct and identifiable function The number of programs on the list should be such as to make it easy to assign them to different engineers on the pro­gramming staff Too few program elements will overload the programmers, too many will make it difficult to combine them into a working whole

2 The memory required for each program is estimated An accurate estimate requires a detailed knowledge of process requirements in terms of precision and response times, the programs that provide the control functions, and how they are to be accomplished by computer-program
instructions The engineer may have to write trial routines in a typical process assembly language

3. Each program is labeled as to whether it will normally reside in core, in auxiliary memory, or partly in each The results of this step determine the proportion of computer memory which must be provided by high — and low-speed devices

Table 8.1—Major Control Programs

handled manually by the control-room staff A second reason is that a high plant-availability factor is not essential, therefore the reactor safety instrumentation can take care of computer failure. These are the cautious approaches to computer control which place little reliance on the com­puter part of the system They are becoming less evident since experience and familiarity with digital systems have

The results of the preceding three activities are sum­marized in a deceptively brief compilation similar to that shown in Table 8 1 These data, along with roughly estimated execution times, form the basis for specifying memory sizes, computation speed, and capabilities of peripherals, such as line printers and high-speed operator displays

It is important that one recognize the d’sparity in level of the different programs on the list The one titled “executive-monitor,” for example, is of the highest level It is the master program that ties all the others into a coordinated system. Its development requires the talents of the best process programmer On the other hand, programs such as the calibration routines can be handled by more junior personnel