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 watt meters, 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 also be necessary to employ a wattmeter to determine the to tal 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 limitati ons of the basic types of electrical measuring instruments, coupled with the theory of circuit operation is most essential in servicing and maintaining electrical equipment.

Duties of electricians on the vessels. Who is an electrician on a vessel?

1. Electricians are directly responsible to electrical engineers (ETO).

2. Marine electricians are to know the construction, the principle of operation, characteristics and the use of shipboard electrical equipment.

3. They are to know in detail the procedure used in diagnosing a troubleshooting and the steps recommended to trace the fault.

4. They are to list some of the causes, e. g., why the motor may fail to start, detect the trouble and remedy the fault when found.

5. They must know the consequencies which may result from poor and careless operation. They must be able to operate all sorts of shipboard electrical equipment.

6. Besides, they are to know the operational and constructional features of all units of the shipboard electrical installation.

7. They are to know how to use fire-fighting devices especially in the engine-room.

8. They are to take part in maintaining and repairing all shipboard electrical equipment.

9. They are to adhere strictly to all the regulations and instructions concerning maintenance of electrical equipment and safety rules.

10. They are to keep watches according to the schedule on board ship with electrical propulsion. The most important items of electrical equipment are subjected to their supervision:

Technical Documentation of Electrical Equipment

Prior to the commencement of supervising the manufacture of the electrical equipment the following documentation is to be submitted for consideration:

1) description of the principle of operation and main characteristics;
2) material specification (list of products) which is to contain elements, instruments and materials used and their technical characteristics;
3) assembly drawing with sections;
4) circuit diagram;
5) test programme;
6) mechanical rotor shaft calculations, as well as drawings of fastening of poles, magnetic circuit stackings, commutator, etc., and detailed drawings of elements welded to the shaft;
7) for distribution switchboards — calculation of thermal and electrodynamic strength of busbars under short-circuit conditions and choice of apparatus to fit these conditions where current rating of a generator or generators running in parallel exceeds 1,000 A.