I. Translate the following sentences:

1. The digital display directly indicates a quantity as a number, there is no risk of parallax causing an error when viewing a reading.

2. A multimeter can be a handheld device useful for basic fault finding and field service work or a bench instrument which can measure to seven or eight and a half digits of accuracy.

100. Вольтметр - это прибор для измерения разницы потенциалов между двумя точками в электрической цепи.

4. As the resistance of the voltmeter is very high, the current passing through it is very small.

5. The construction of a voltmeter and a ammeter may be the same. Each meter has a pointer which is deflected according to the current passing and the scale of ammeter is marked in amperes.

6. С помощью универсального измерительного прибора можно измерять напряжение, ток и сопротивление в электрической цепи.

7. The final reading of the meter depends upon the strength of the current in the power supply line.

II. Translate the following information in to Russian:

Electricity meters.

F ig. 2 shows a motor-type ampere-hour meter. It is in effect a small direct-current motor. The armature, or rotor, is an aluminum disc mounted in the field of a permanent magnet. The disc contains three coils which are supplied with current from a com­mutator consisting of three sectors. The current to the rotor coils is proportional to the total current passing through the consumer installation, from which it is branched off. Since the field strength of the permanent magnet is

Fig.2 Motor type meter

constant, the speed of rotation of the rotor is proportional to the current strength. The counting mechanism connected to the rotor shaft counts the revolutions, which cor­respond to the product I.t. If, instead of the permanent magnet, an electromagnet is used to produce the magnetic field, and if the consumer voltage V is applied to this coil, then the speed of rotation of the rotor is proportional both to V and to I, and therefore to the product V. I. In that case the counting mechanism directly records the energy V.l.t. The ampere-hour meter has thus become a true watt-hour meter.

The kind of meter nowadays generally used for alternating current is the induction meter (Fig. 3). It has no commutator. There are two electromagnets. The coil of one of these is energised by the consumer current; the other magnet coil is connected to the consumer voltage. If the current and the voltage in the consumer circuit are in phase with each other , then the current in the voltage coil, and therefore the magnetic field of this coil, will have a lag of one-quarter period (90°) in relation to that of the current coil. The interaction of the two coils produces a moving magnetic field which induces eddy currents in the light aluminum rotor disc. These currents cause the disc to rotate in the direction of motion of the moving field. The speed of rotation of the disc is pro­portional to the strengths of the two magnetic fields, but it is also dependent upon the phase displacement of these fields (and therefore upon the power factor cos ф). This will readily be understood when one considers the case where the consumer installation has a 90° phase displacement between V and I (i.e., cos ф = 0); when this happens the two magnetic fields in the meter will be in phase, so that the rotor will then cease to rotate. The braking magnet (on the right in Fig. 3) constantly produces eddy currents in the rotor; these damp the rotation and thereby ensure that the rotor stops instantly when the consumer current ceases to flow.

F ig.3. Induction meter