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.

Measuring Instruments and Alarms

Given below is a minimum list of measuring instruments that are to be provided in order to ensure permanent and direct indication of the system parameters: 1) an ammeter in the main current circuit; 2) a voltmeter in the main current circuit; 3) an ammeter in the field circuit for adjustable excitation system; 4) a voltmeter in the field circuit for adjustable excitation system; 5) a tachometer for propulsion motors or propeller shafts; 6) a rudder angle indicator.

For a-c systems the following is to be provided additionally: 7) a frequency indicator; 8) a synchronizer for generator paralleling.

The electric propulsion plant system is to be equipped with an insu lation resistance measuring instrument. Continuous insulation resistance measuring is to be provided in the main current circuits, with visual and audible alarms to operate in the event of inadmissible decrease of the insulation resistance.

Where a control desk or a control panel incorporates measuring in struments with oil, steam or water supply to them, suitable measures are to be taken to prevent the possibility of any of the above agents gaining access to live parts if the instruments or piping connections are damaged.

Basic electrical measuring instruments are essential for diagnosing and analyzing electrical systems. Here are some commonly used instruments:

1. Multimeter

• Function: Measures voltage (AC/DC), current (AC/DC), and resistance.
• Types: Analog and digital.
• Usage: Can also test diodes, continuity, and sometimes capacitance and frequency.

2. Voltmeter

• Function: Measures electrical potential difference between two points in an electric circuit.
• Types: Analog and digital.
• Usage: Connected in parallel with the circuit.

3. Ammeter

• Function: Measures electric current in a circuit.
• Types: Analog and digital.
• Usage: Connected in series with the circuit.

4. Ohmmeter

• Function: Measures electrical resistance of a component.
• Types: Analog and digital.
• Usage: Connected to a component when the circuit is de-energized.

5. Oscilloscope

• Function: Visualizes varying signal voltages, usually as a two-dimensional plot of one or more signals as a function of time.
• Types: Analog and digital storage oscilloscopes (DSO).
• Usage: Diagnoses and analyzes signal properties in complex circuits.

6. Clamp Meter

• Function: Measures current without the need to break the circuit.
• Usage: Clamped around a conductor to measure current flow.

7. Wattmeter

• Function: Measures the electrical power (in watts) of a circuit.
• Usage: Connected in series with the circuit for current measurement and parallel for voltage measurement.

8. LCR Meter

• Function: Measures inductance (L), capacitance (C), and resistance (R) of electronic components.
• Usage: Commonly used in the testing of passive components.

9. Frequency Counter

• Function: Measures the frequency of an electrical signal.
• Usage: Connects to a signal source to count the number of cycles per second (Hertz).

10. Insulation Tester (Megger)

• Function: Measures the insulation resistance of electrical wiring and motor windings.
• Usage: Applies a high voltage to test the integrity of insulation.

11. Phase Meter

• Function: Measures the phase difference between two or more electrical signals.
• Usage: Used in power systems to determine the phase relationship between voltage and current.

12. Function Generator

• Function: Produces various types of electrical waveforms over a wide range of frequencies.
• Usage: Used for testing and development in circuits.

Key Points:

• Safety: Always follow safety procedures to prevent injury or damage.
• Calibration: Regularly calibrate instruments to ensure accuracy.
• Reading Manuals: Understand the manufacturer's instructions for proper use.

These instruments are foundational for electrical engineers, technicians, and hobbyists to effectively troubleshoot, repair, and design electrical systems.