Test Exercise

Write the letter of the right choice:

2. Permanent magnets for field poles are used in:

   1. medium-size motors

   2. large-size motors

   3. very small motors

1. The construction features of the shunt, series and compound motors are.

   1. quite similar

   2. differ slightly

   3. differ considerably

C. Retell the text

V. METERS

attract, v. - притягивать (ся)

body, n. - тело

capacitance, n. - емкость

concentric, adj. - концентрический

electrostatic, adj - электростатический

electro-thermal, adj. - электротермический

function, n. - функция

function, v. - функционировать

galvanometer, n. - гальванометр

indication, n. - указание

inductance, n. - индуктивность

linear, adj. - линейный

measure, v. - измерять

measurement, n. - измерение

meter, n. - измерительный прибор, счетчик

ammeter, n. - амперметр

dynamometer, n. - динамометр

moving-coil meter, n. - магнитоэлектрический

прибор moving iron-vane meter, n - электромагнитный прибор с

листком

ohrameter, n. - омметр

voltmeter, n - вольтметр

wattmeter, n. - ваттметр

obtain, v. - получать, достигать

oxide, adj. - оксидированный, окисленный

polarity, n. - полярность

precautions, n. - предосторожность

protect, v. - защищать, предохранять

quantity, n. - количество

radial, adj. - радиальный

range, n. - диапазон, уровень

rectifier, n. - выпрямитель

repel, v. - отталкивать

scale, n. - шкала

sensitivity, n. - чувствительность

shunt, n. - шунт

an external shunt - внешнее шунтирование

an internal shunt - внутреннее шунтирование

shunt, v. - шунтировать

similar, adj. - похожий, схожий

thermo couple, n. - термопара

thermo instruments - термические приборы

unit, n. - единица

versatile, adj - разносторонний

voltmeter method - метод вольтметра

Part I

1. Read and translate the following words and word combinations:

galvanometer, electrostatic meters, electro-thermal, electromagnetic, moving-coil meters, permanent magnet, a moving iron-vane meter, thermocouple, dynamometer, rectifier, ammeter, voltmeter, shunt, range, ohmmeter, wattmeter.

2. Form as many word combinations as you can:

a)

a permanent magnet a concentric a radial a low a high

to damage an electrostatic a complex-scale an electromagnetic a low-range moving-coil a moving-iron moving iron-vane an electrodynamometer

(the) meter

scale

b)

capacitance inductance resistance current voltage a unit of

measurement

c)

high low to take voltage the centre the galvanometer

readings

of circuits of circuit elements

3. Change the following word combinations using the pattern:

measurements of capacitance =>

capacitance measurements

1. measurement of inductance

2. measurements of resistance

3. the value of resistance

4. the range of an ammeter

5. the variations in voltage

6. the method of voltmeter

7. the range of a voltmeter

8. the range of an ammeter

9. a voltmeter with low sensitivity

Part II

1. Choose another word or phrase with the same meaning:

an electromagnetic instrument, to take readings, an electro dynamometer meter, a voltmeter, complex scale meters, to obtain measurements, an electrodynamometer, a moving-iron Instrument, an instrument for measuring voltage, instruments with two or more multiple scales.

2. Put In the missing preposition or adverb if necessary:

The current which may safely be led... an ammeter mechanism is limited... the current-carrying capacity ...the coil... the moving element. To increase the range ... such instruments, shunts and current transformers are used, the former ... direct currents, the latter… the alternating currents (into, by, of, in, of, with, with)

3. Make questions using the pattern:

Electrostatic meters are used

for measuring high voltages =>

What are electrostatic meters used for?

1. The electrostatic mechanisms are used for electrical indications

2. The electrostatic voltmeters are used in a-c circuits

3. The permanent-magnet moving-coil mechanisms are used in most galvanometers.

4. The concentric and radial types of the moving-iron vane are generally used for measuring alternating currents.

5. The electrodynamometer meters are used for a-c as well as d-c measurements.

4. Answer the questions (see suggestions in brackets):

1. What is the principle of operation of the copper oxide rectifier? (сопротивление току в напряжении от окиси к меди очень низкое, а в обратном направлении сопротивление току очень высокое)

2. How is the ammeter protected when readings are not being taken? (переключатель закрыт и подсоединен к амперметру)

3. How is a voltmeter connected in a circuit? (вольтметр подключается непосредственно в цепь)

4. What is the difference between an internal and an external shunt? (шунт, постоянно подсоединенный внутри амперметра и шунт, употребленный для увеличения диапазона амперметра)

5. What precautions are necessary in using combination meters? (надо проверить до включения в цепь положение всех переключателей)

5. Translate the following words and word combinations into English:

измерительный прибор, принцип действия, электромагнитный прибор, магнитоэлектрический прибор, медно-закисный выпрямитель, амперметр, высокая (низкая) чувствительность прибора, отсчеты вольтметра, снимать показания, низкие величины тока, высокое сопротивление, метод вольтметра, меры предосторожности, ваттметр, внешнее (внутреннее) шунтирование

6. Read and translate the text with a dictionary:

Electrical instruments are essential in order that the amount of voltage, current, resistance, power, etc., in a circuit can be measured, adjusted, or controlled.

Voltage and current are the two quantities most generally measured, as it is possible to calculate other quantities such as resistance and power by using these two values.

The basis mechanism in practically all meters is the galvanometer, which may be defined as a sensitive instrument used for detecting and/or measuring very small amounts of electric current

Meters may be classified according to their principle of operation as: (1) electrostatic, (2) electro-thermal, and (3) eleclro-magnetic.

Electrostatic meters are used for measuring high voltages and are based on the theory that charged bodies of like polarity repel one another and those of unlike polarity attract one another. The electrostatic mechanism is the only one used for electrical indications that functions because of the presence of a voltage.

Hot-wire meters depend upon the expansion and contraction of a wire carrying an electric current. The expansion of the wire is proportional to the heat.

The practical application of the thermal effect of electron flow is obtained by using the principle of the thermocouple. Thermo instruments measure the effective values of current and therefore can be used with both direct and alternating currents.

Most commercial meters are based on the electromagnetic principle. These meters may be further classified as (1) permanent magnet, (2) iron vane, (3) dynamometer. The operation of the permanent magnet movable coil meter depends upon the presence of a magnetic field which acts upon a movable element. This type of meter is applicable only to d-c measurements.

If two similar adjacent iron bars are similarly magnetized, a repelling force is developed between them which tends to move them apart. In the moving iron-vane mechanism, this principle is used by fixing one bar in space and pivoting the second so that it will tend to rotate when current flows through the coil. The movable iron-vane may be of the radial type or of the concentric type. The radial vane is the more sensitive and has almost a linear scale.

The electrodynamometer-type meter is composed of two stationary coils and a movable coil which also supports the pointer. This type of meter can be used for a-c as well as d-c measurements. It is the most versatile of all the basic mechanism, since it can be used to indicate current, voltage, or power for either alternating current or direct current.

7. Answer the following questions:

1. Why are electrical instruments essential to the study of electricity?

2. What is a galvanometer?

3. What are the uses of the galvanometer?

4. How many electrical instruments to classified in terms of their principle of operation?

5. What is the principle of operation of an iron-vane meter?

6. What type of electromagnetic meter is most versatile?

8. Ask your fellow-student:

what two possible types of movable iron vane may be;

which of the two types of movable iron vane is more sensitive;

what elements the electrodynamometer type meter is composed of;

how this type of meter can be used;

if the electrodynamometer-type meter can be used only for direct current or not.

9.

a) Explain the principle of operation of the permanent-magnet

moving-coil meter.

b) Explain the principle of operation of an iron-vane meter.

c) Define galvanometer.

d) Describe this figure (the basic principle of the electrostatic voltmeter)

10. Learn the dialogues by heart:

I

Prof.: Name the types of electromagnetic instruments, will you, Comr. Ivanov?

Comr. I.: They are of permanent magnet, iron vane and dynamometer types.

Prof.: Correct. Could you possibly name the most versatile type as well?

Comr. I.: I'll try to. It's a... an electrodynamometer-type meter.

Prof.: Thank you.

II

A 1-st Year Student: I am interested to know all about the so-called electrostatic meters.

An Electrical Engin.: All? Oh, you don't mean to say that! O.K., though. I'll share my scraps of knowledge with you

A 1-st Year Student: Are those instruments based on a certain principle?

An Electrical Engin.: Sure. They are based on the theory of polarity: like charged bodies repel, while unlike charged bodies attract

A 1-st Year Student: I see. This was the only thing I meant to ask you about. All the rest I suppose I'll manage to learn for myself not to annoy you working here any longer.

An Electrical Engin.: And the right thing you will do.

Test Exercises

Write the number of the right choice or choose the right letter

A.

1. Most commercial meters arc based on

1. the electromagnetic principle

2. the theory of polarity

3. the heat expansion

1. The electrodynamometer-type meter can be used for

   1. d-c measurements only

   2. a-c measurements only

   3. a-c as well as d-c measurements

B.

1. ... a circuit (l.at, 2.on, 3.in)

2. meters are classified ... their principle of operation

(1. -, 2. in, 3. according to)

3 it is based ... the theory (1. in, 2. on, 3. at)

4. to depend ... the expansion (1. from, 2. -, 3. upon)

5. proportional ... the heat (l. -, 2. into, 3. to)

Part III

A. Read the following text without a dictionary.

Rectifier - Type Meters

Rectifier-type meters are used for measuring alternating currents and voltages of small magnitude. They are used in telephone, telegraph and signal systems.

A rectifier is a device that changes an alternating current to a direct current. It operates on the principle that resistance to current flow is high in one direction and low in the opposite direction. Metallic rectifiers used for instrument are usually of the copper oxide-type. Resistance to current flow from-oxide to copper is very low, while the resistance to current flow in the opposite direction is very high. This type of instrument can be used as a voltmeter by connecting a resistance in series with the line to limit the current to the rating of the rectifier unit and the galvanometer.

B.

Test Exercise

Write the letter of the right choice:

1. Rectifier-type meters are used for measuring:

1. d-c currents

2. a-c currents

3. resistance

1. Rectifier-type meters are used in:

   1. telephone (telegraph)

   2. radio

   3. television

C. Retell the text