PROTECTION AND CONTROL EQUIPMENT

In electrical systems for the generation, distribution and use of electrical energy considerable control equipment is ne­cessary. It can be divided into two classes: a) equipment used at the generating and distributing end; b) equipment used at the receiving end of the system.

Safety switches are used at the point where the power en­ters a building. They are of the knife type and are usually en­closed in metallic boxes.

A magnetic contactor is used to make and break the circuit at the points where considerable power is used.

An automatic starter is a device which is used to keep the current from being excessive while the motor is obtaining full speed. It is a kind of a resistance inserted in series with the direct current armature. As the motor obtains speed it gradu­ally removes.

Answer the questions:

TEXT 16

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CHARACTERISTICS AND USAGE OF COMPUTERS

A computer is faster and more accurate than people, but unlike most people it must be given a complete set of instructions that tells it exactly what to do at each step of its operation. This set of instructions, called a programme, is prepared by one or more persons for each job a computer is to do. These programmes are placed in the computer’s memory unit in binary-coded form, with each instruction having unique code.

Computers are often used in application where the results of their calculations are required immedi­ately to be used controlling a process. These are called real-time applications; they are often found in industrial process control in industries such as paper mills, oil re­fineries, chemical plants and many others. The measur­ing systems send their signals to the computer which processes them and responds with appropriate control signals to be sent back to the process.

Computers in present use range considerably: from tiny things to big fellows. The microcomputer, for one, is the smallest and the newest member of the com­puter family. It usually consists of several integrated circuit chips, including a microprocessor chip, memory chip, and input/output interface chip which are a result of tremendous advances in large-scale integration.

Answer the following questions:

1. Where are computers often used?

2. What do we call a real-time application?

3. What is a microcomputer?

TEXT 17

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COMPUTER ELEMENTS

Most of the computer principles and concepts are common to all categories of computers, although there can be tremendous variations from computer to com­puter.

A question sometimes arises whether computers are able to think. As a matter of fact they do not think. The computer programmer provides a programme of instructions and data which specifies every detail of what to do, how to do and when to do it. The computer is simply a high-speed machine which can manipulate data, solve problems and make decisions, all under the control of the program. If the programmer makes a mistake in the program or puts in the wrong data, the computer will produce wrong result.

Every computer contains at least five essential elements or units: the arithmetic logic unit, the memory unit, the control unit, the input unit and the output unit.

The arithmetical logic unit is the area of the computer in which arithmetic and logic operations are performed on data.

The memory unit stores groups of binery digits (words) that can represent instructions (program) which the computer is to perform and the data that are to be operated on by the program.

Answer the questions:

1. What can you say about the computer principles and concepts?

2. Are computers able to think?

3. What can computers do?

TEXT 18

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COMPUTER LANGUAGES – HIGH LEVEL AND LOW LEVEL

Do we actually need high level languages such as C++ and PASCAL when we work with computers in control application? No! Not only high level languages are often unnecessary but they can interfere with microcomputer performances. The alternative, low level languages, give you greater control over the process and hardware and reduce the cost of the system.

Assembly language is called low level because it is very close to machine operation. The resident pro­gram called the assembler, translates only on a one-to-one basis, so the user must instruct the machine, what to do.

Low level languages use less English-like mne­monics, such as WPM. As it was mentioned a low level mnemonics instruction translates via the resident pro­gram into one machine instruction.

A FIN assembly instruction, for instance, would fetch a particular piece of data from memory.

Typically the microprocessors program memory can cost about 25% more with a high level language than it might cost if the program had been written in the microprocessor assembly language.

A microprocessor is the central processing unit of a microcomputer.

Answer the following questions:

1. Why don't we need high level languages such as PASCAL working with microcomputers in control application?

2. Why is assembly language called low level?

3. What do low level languages use?

TEXT 19

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WHAT IS THE MICROCOMPUTER?

Although small, the microcomputer can be as powerful as a computer that once filled a room. It's still a general purpose digital computer, but it's composed of large scale integrated circuits instead of transistors or vacuum tubes. At its heart is the microprocessor - a single integrated circuit that is the central processing unit. Additionally, the microcomputer has some memory 1/0 (input/output) capability.

The capability of a microcomputer is usually measured by its microprocessor. And the microprocessor's sophistication is usually determined by its word length, given in bits. Microprocessors currently have word length of 32 or 64 bits. In other words, an 8-bit numbers with a single "add" instruction. But two in­structions are needed to add two 16-bit numbers. (These instructions use up memory).

Microprocessors with four bits were calculators type processors. Unlike other microprocessors which use binary arithmetic, 8-bit processors use binary coded decimal arithmetic Microcomputers with 8-bit processor now contain the processor and the memory on one chip.

The 8-bit microprocessor is the most popular and widely available microprocessor on the market. Eight bits is enough for most data and character handling and it's also a multiple of 16 or 24 if higher pression arith­metic is necessary. Most 8-bit processors, such as Na­tional's SC/MP, can also perform decimal arithmetic for process calculating.

Answer the following questions:

1. What is the microcomputer composed of ?

2. What is at its heart ?

3. Why were microprocessors with four bits calculator type processors ?

TEXT 20

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WHAT IS THE MODEM?

The word “Modem” is an acronym for “modulator— demodulator”, .the name of a piece of electronic equipment that converts the signals from your computer to tones that can be transmitted over phone lines, allowing your computer to "talk" to another, by "whistling" messages back and forth.

A modem was cigar box-like device, with two foam cups. You took telephone receiver and stuck the earpiece into one cup and the mouthpiece into the other. Such a unit was an acoustic modem.

Today, most modems are the size of a textbook and have several red lights on their faces. On these, you snap the modulator plug out of your telephone and into the modem and by avoiding the acoustic computing to the above – mentioned antique, you are able to communicate at higher speed. There are modems as small as a matchbox with no lights (which evolution in electronics has rendered less necessary); and same even built into the computer.

Next you’ll be asked what speed you want: 300, 1200, 14400, 2400, 9600 baud. The “baud rate” describes how fast a modem can send and receive. The most common speed today is 33600. It depends on the quality of telephone communication.

Answer the following questions:

1. What is "modem" an acronym for?

2. What allows your computer to “talk" to another, by "whistling" messages back and forth?

3. What was a modem like?

Для спеціальності ОМР

TEXT 16

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