Instruments and Measurements

Electricians are responsible for measurement of different electrical quantities. Some must be measured as part of the inspection and testing of an installation (e.g. insulation resistance). The most common quantities that we often come across¹ are shown in the table given below

 

Quantity	Instrument
Current Voltage Resistance Power	Ammeter Voltmeter Ohmmeter Wattmeter

 

But before using any meter, we must always ask ourselves these questions:

· Have we chosen the correct instrument?

· Is it working correctly?

· Has it been set to the correct scale?

· How should it be connected?

Although we know a multimeter to be used for measuring different quantities including current, the actual name for an instrument that measures current is an ammeter. Ammeters are connected in series so that the current to be measured passes through them. The circuit diagram in Figure 3 illustrates this. Consequently, they need to have a very low resistance or they will give a false reading.

Fig. 3. Ammeter in circuit

 

If we now look at the same circuit, but use a correctly set multimeter, the connections would look as in Figure 4.

Fig. 4. Multimeter in circuit

 

For general purposes we can use a multimeter to measure voltage, but the actual device used for measuring voltage is called a voltmeter. It measures the potential difference between two points (for instance, across the two connections of a resistor). The voltmeter must be connected in parallel across the load or circuit to be measured as shown in Figure 5.

Fig. 5. Voltmeter in circuit

 

If we now look at the same circuit, but use our correctly set multimeter, the connections would look as in Figure 6. The internal resistance of a voltmeter must be very high if we wish to get accurate readings.

 

Fig. 6. Multimeter measuring circuit

 

There are many ways in which we can measure resistance. However, in the majority of cases we do so by executing a calculation based upon instrument readings (ammeter/voltmeter) or from other known resistance values. Once again we can use our multimeter to perform the task, but we refer to the actual meter as being² an ohmmeter. The principle of operation involves the meter having its own internal supply (battery). The current, which then flow through the meter, must be dependent upon the value of the resistance under scrutiny³. However before we start our measurement, we must ensure that the supply is off and then connect both leads⁴ of the meter together and adjust the meter’s variable resistor until full-scale deflection⁵ (zero) is reached.

 

Notes

¹ come across – зустрічати

² as being – який є

³ under scrutiny – який досліджується (вимірюється)

⁴ lead – вивід

⁵ full-scale deflection – відхилення на всю шкалу

 

2. Now read the text once again looking up any word you do not understand in a dictionary and answer the following questions.

1. What does an ammeter measure in the circuit?

2. How must it be connected?

3. What does a voltmeter measure?

4. How must a voltmeter be connected across the circuit?

5. What do we use an ohmmeter for?

6. What must be done before we start the measurement by means of an ohmmeter?

7. What can a multimeter be used for?

8. How is a multimeter set correctly?

 

3. Decide if these statements are true or false. Quote from the text to support your decisions.

1. Different instruments are used to measure electrical quantities.

2. It does not matter how to connect electrical instruments in the circuit.

3. Both an ammeter and voltmeter must have a very low resistance.

4. There is only one way which can be used to measure resistance.

 

Pronounce correctly

 

4. Read the words given below paying special attention to wh:

[w] when, what, why, where, whether, which, while, white;

[h] who, whose, whom, whole, whoever, wholly.

 

5. Read the words paying attention to the stress l:

 

l Ÿ testing power voltage series figure reading meter value

Ÿ l below involve supply adjust until

l Ÿ Ÿ measurement instrument actual illustrate general difference parallel accurate variable scrutiny

Ÿ l Ÿ responsible correctly dependent resistor

Increase your vocabulary

 

6. Find these words and word combinations in the text and try to remember them:

 

accurate ammeter choose (chose, chosen) come across (came, come) consequently correct deflection ensure execute in parallel

in series inspection installation involve lead meter quantity responsible scale variable

 

Suffixes say a lot

7. What part of the speech are these words? Translate them and use some of them in your own sentences.

Quantity, majority, electricity, gravity, quality, density, popularity, productivity, complexity, activity, responsibility, capability, necessity, humidity, changeability, durability, falsity, possibility.

 

8. Read the text below. Use the word given in italics at the end of some of the lines to form a word that fits in the space in the same line.

Example

 

Although instruments exist to measure individual	individually
Although instruments exist to measure ____ electrical quantities, most electricians think that a cost-effective (економічно ефективний) ____ is to use a digital multimeter. Digital meters are ____ capable of measuring current, ____ and voltage, both in a.c. and d.c. circuits and across a wide range of values. Modern multimeters are considered to be reliable due to their accuracy and ____.	individually solve general resist durable

 

9. Match the words in A with the words which have similar meaning in B.

A. Inspection, to come across, to choose, correct, to set, purpose, majority, to perform, to involve, to ensure, scrutiny.

B. Aim, to fulfill, to select, to meet, examination, right, investigation, to guarantee, to adjust, most of, to include.

 

10. Match a word in A with its definition in B.

A

B

1. Ammeter     2. Multimeter     3. Ohmmeter   4. Voltmeter     5. Wattmeter

a. an electrical instrument that measures electrical resistance   b. an instrument for measuring the electric power in watts of any given circuit   c. an instrument used for measuring electrical potential difference between two points in an electric circuit   d. a measuring instrument used to measure the electric current in a circuit   e. an electronic measuring instrument that combines several measurement functions in one unit

 

11. Complete the passage using the following words and word combinations.

 

a. numeric values b. semiconductors c. have used d. circuits

e. accurate f. calibrated scale g. display

Meter Displays (Analogue and Digital)

There are two types of display, analogue and digital. Analogue meters have a needle moving around a (1)____, whereas digital tend to show results, as (2)____, via a liquid crystal or LED (3)____. For many years electricians (4)____ the analogue meter. A continuity tester (тестер для перевірки на обрив кола) and an insulation resistance tester are still of the analogue style. However, their use is slowly being replaced by the digital meter. Most modern digital meters are based on (5)____ and consequently have very high impedance, making them ideal for (6) ____ readings and good for use with electronic (7)____.

 

Word range

12. Which sentence best illustrates the use of the word in italics taken from the text?

1. If we now look at the same circuit, but use our correctly set multimeter, the connections would look as in Figure 6.

a. There is a TV set in front of the sofa.

b. The device must be set in the right way.

c. This set of tools can be dangerous if you use them improperly.

d. Your set of responsibilities includes being able to speak English.

2. There are many ways in which we can measure resistance.

a. This way, please.

b. Could you tell me the way to the railway station?

c. There are two ways of connecting batteries.

d. I can ensure that he is a good specialist in many ways.

3. The circuit diagram in Figure 3 illustrates this.

a. The circuit of the city walls is three miles.

b. The larger the planet’s orbit, the more time it takes the planet to complete a full circuit around the sun.

c. The circuit is the path along which the electricity moves.

 

Revise your grammar