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:

1. Where is considerable control equipment necessary?

2. What classes can it be divided in?

3. Where are the safety switches used?

Для спеціальностей соі, прг, окс 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?