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10/01/2013

Digital Computer Integrated Automation Systems

Digital Computer Applications. There are such applications of minicomputers as: Supervision of plant operating data with alarm recording, data logging and process monitoring of the process.
Digital Computer Integrated Automation Systems
Automation and control systems can be conveniently integrated with minicomputer digital processors. Interface units apt to handle all inputs and outputs problems from the process to the computer (Fig. 1) are available, depending on the type of solution contemplated.


Fig. 1. Process of the computer

On demand digital display of plant variables. Event recording: print out of the various plant variables on occurrence of an event, with the chronological history of groups of events in their exact sequence.

Recording of the value of the various plant variables in the time intervals preceeding the occurrence of a fault condition.

Trend recording: recording of the tendency of a variable to exceed set-point value over a short and medium term.

Recording of the maximum off-normal drift of a variable from threshold value.

Sequence control: for groups of variables.

Optimization of complex automation systems with set-point value correction by the computer.

Plant efficiency and performance calculations.

Operator guide: processing of the data collected by comparison with the optimum memorized operating program in order to furnish guidance to the operator.

Information storage: collection of data relating to plant operation. Formulation of consents and locks based on complex programs including non-linear functions of plant parameters.

Data communication: local processing of the variables by the peripheral microcomputers with data transmission to the central microcomputer. Microcomputer. The microcomputer is a control unit with extremely flexible program; modern electronic technology has made this facility available for application in the solution of control problems which heretofore had to be handled by wired logic or relay logic.

Easily expandable high speed programs include complex arithmetic and logic operations.

The microcomputer itself comes as a conventional electronic unit mounted on standard racks apt to contain several plug-in type modules. The following modules are fitted in the standard rack:
  1. Central Processor Unit (CPU). CPU performs arithmetical and logical calculations at high speed with 8 bit words: it performs all the processing functions and is capable of addressing itself up to 64 memory bits.
  2. Electronic type programmable memory (PROM) or fixed memory (ROM).
  3. Memory module for electronic type data.
  4. Input module connecting the CPU with the process.
  5. Output module, to dispatch the microcomputer information toward the process.
  6. Interface module, to adapt the input signals and input/output card capacity to the multiplexing and demultiplexing units and for A/D to D/A conversion.
Computer Hardware

The heart of the system is the Central Processing Unit (CPU), which holds both program and data, an Arithmetic-Logic Unit (ALU), which contains processing circuitry such as an adder, shifter, and a few fast registers for holding the operands, and the instruction currently being processed (Fig. 2). The program counter would also be included in the ALU.

One part of the CPU is a set of routing circuits which provide path between storage and the ALU and input/output controllers or channels. Many storage or input devices may be wired to one channel; but only one device per channel can be transmitting information from or to main storage at any one time.


Fig. 2. General organization of a computer system

In general, large computers may be thought of as having four distinct parts: a high-speed calculating unit, a memory unit, an input device and an output device.