Showing posts with label PROM. Show all posts
Showing posts with label PROM. Show all posts


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.

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.

Modules of Alarm Measuring System

The typical electronic system comprises modules which are designed for mounting in the control room desk or in a cabinet front. Here are standard modules: alarm measuring module, display module, selector module, bridge panel, cabin and mess panel, power distribution unit, central unit for data logging and alarm print-out.

These modules are identical in electrical and mechanical design. The modules are made of sheet steel and are provided with ventilation holes. The internal wiring is provided with a printed circuit backplate, i. e. the "mother board", and ribbon cable. The front can be removed, and the electric boards can be inserted from the front.

Each module has a circuit board for stabilizing the supply voltage to the electronics. The modules are interconnected by ribbon cable — the system bus — used for internal communication in the system. Process signals and the power supply are connected to terminals at the rear of the module on the terminal board.

Alarm and measuring modules. They are designed with space for several analog or on/off channel boards. In front of each channel is a transparent legend plate on which the name of the channel is engraved, and a push-button for visual alarm acknowledgement and manual measuring.

The channel boards, which can be located in these modules according to the customer's requirements, are:
  1. On/off alarm board, for adapting the on/off transducer signals.
  2. Analog channel board, for adapting the analog transducer signal.
  3. Average board, for calculation of mean values.
  4. Group alarm board, for generation of group alarm signals.
  5. Blocking board, for adapting the blocking transducer signals of internal blocking signals.
Display module. It is designated for presentation of analog values on a digital display. Two switches are mounted in the front, and these can be used to determine whether the measured value or one of the set limits is to be displayed when measuring.

Apart from the electronics for interfacing the display, the module includes circuits for generating start signals to the sirens and the rotating lights. The front is equipped with a push button for audible alarm acknowledgement.

Selector module. It is used for the selection of the engine room status, attended or unattended, and an engineer on duty. The module is equipped with one circuit board per engineer, and switches and indicating lamps in the front. The unit also provides call of the engineers.

Central unit. Systems with alarm print-out or data logging include the central unit. The control unit is connected to the system via the system bus.

Such systems are programmable bus-oriented electronic systems comprising a number of standard units. The functions in the system are controlled from a central processing unit based on a microcomputer.

The functions are determined by a program — the system software — stored on a PROM semi-conductor memory. In addition to the basic functions of the central unit the use of the microcomputer and software make such alarm systems easily expandable to more complex functions.

Typical optional functions available are: presentation of process data on a display, telex transmission of measured values, trend analyses, condition monitoring of the machinery.

The central unit is fitted in a cubicle. The front of the cubicle includes the printer for alarm print-out.

Data Logging

The data logging function is controlled from the control unit. The measured, values are printed out at regular intervals, e. g. every four hours, or by depressing the print-out button.

The central unit addresses the measuring channels with a binary code via the system bus. The address is decoded in each module and one channel is addressed. Signal connections to the system bus, scaling and conversion, are carried out in the same way as during manual measuring.

However, the display is extinguished. The central unit receives the measured value in code and the information on the number of decimals, processes the input signals and controls the typewriter, where the measured values are printed out. The data and time are recorded on each print-out.