ABSTRACT
At the end of this chapter you should be able to:
• recognize the in electric circuits
• appreciate the instrument
• calculate values of for voltmeters
• understand the
• understand the
• appreciate the
• understand the
• appreciate
• understand the 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
• appreciate the most likely source of errors in measurements
• appreciate calibration accuracy of instruments
Tests and measurements 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). The digital instrument has, in the main, become
the instrument of choice in recent years; in particular, computer-based instruments are rapidly replacing items of conventional test equipment, with the virtual storage test instrument, the digital storage oscilloscope, being themost common.This is explained later in this chapter, but before that some analogue instruments, which are still used in some installations, are explored.
