ABSTRACT
At the end of this chapter you should be able to: • recognize the importance of testing and measurements in electric circuits
• appreciate the essential devices comprising an analogue instrument
• explain the operation of an attraction and a repulsion type of moving-iron instrument
• explain the operation of a moving coil rectifier instrument
• compare moving coil, moving iron and moving coil rectifier instruments
• calculate values of shunts for ammeters and multipliers for voltmeters
• understand the advantages of electronic instruments • understand the operation of an ohmmeter/megger • appreciate the operation of multimeters/Avometers /Flukes
• understand the operation of a wattmeter
• appreciate instrument ‘loading’ effect • understand the operation of an oscilloscope for d.c. and a.c. measurements
• calculate periodic time, frequency, peak to peak values from waveforms on an oscilloscope
• appreciate virtual test and measuring instruments • recognize harmonics present in complex waveforms • determine ratios of powers, currents and voltages in decibels
• understand null methods of measurement for a Wheatstone bridge and d.c. potentiometer
• understand the operation of a.c. bridges • understand the operation of a Q-meter • appreciate the most likely source of errors in measurements
• appreciate calibration accuracy of instruments
10.1 Introduction
Tests andmeasurements are important in designing, evaluating, maintaining and servicing electrical circuits and equipment. In order to detect electrical quantities such as current, voltage, resistance or power, it is necessary to transform an electrical quantity or condition into a visible indication. This is done with the aid of instruments (or meters) that indicate the magnitude of quantities either by the position of a pointer moving over a graduated scale (called an analogue instrument) or in the form of a decimal number (called a digital instrument).
