2—10+Ю points for 5 correctly written sentences per 24 minutes get you an excellent mark.
10+7+8 per 26 minutes — good; 9+6+7 per 27 minutes — satisfactory.
UNIT 2
SHIPBOARD ELECTRICAL EQUIPMENT AND BASIC ELEMENTS OF AUTOMATION
SECTION I (2+1+2)
Basic Electrical Measuring Instruments
The first class period
Review of “Duties of Electricians”. 10
Topical content: Basic electrical measuring instruments. 10
Grammar item: Participle.
Text
Basic Electrical Measuring Instruments
1. In the field of electricity, as well as in all other physical sciences, accurate quantitative measurements are essential. This involves two important items — numbers and units. Simple arithmetic is used in most cases, and the units are well defined and easily understood. The standard units are those of current, voltage and resistance.
2. The operator commonly works with ammeters, voltmeters and electron-tube analyzers; but he may also have many occasions to use wattmeters, watt-hour meters, power-factor meters, synchroscopes, frequency meters and capacitance-resistance-inductance bridges.
3. Electrical equipment is designed to operate at certain efficiency levels. A good understanding of the functional design and operation of electrical instruments is important. In electrical service work one or more of the following methods are commonly used to determine if the circuits of an equipment are operating properly.
a) Use an ammeter to measure the amount of current flowing in a circuit.
b) Use a voltmeter to determine the voltage existing between two points.
c) Use an ohmmeter or megger to measure circuit continuity and total or partial circuit resistance.
4. It may alsd be necessary to employ a wattmeter to determine the total power being consumed by certain equipment. If we wish to measure the energy consumed by certain equipment or certain circuits, a watt-hour or kilowatt-hour meter is used.
5. For measuring other quantities such as power factor and frequency it is necessary to employ the appropriate instruments. In each case the instrument indicates the value of the quantity measured, and in this information helps to understand the way the circuit is operating.
6. Occasionally the operator will need to determine the value of a capacitor or an inductor. Inductance or capacitance bridges may be employed for this purpose.
7. A thorough understanding of the construction, operation and limitations of the basic types of electrical measuring instruments, coupled with
the theory of circuit operation is most essential in servicing and maintar ining electrical equipment.