Phase and Phase Angle

Chapter 6.12 Phase and Phase Angle

Fundamental Electrical and Electronic Principles Third Edition Book
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Fundamental Electrical and Electronic Principles Third Edition Book

  • Alternating Quantities 213 (b) I fsd 100 μ A Iav therefore, r.m.s. value, I1 11111111111..000090 0990 06μAso, ktherefore, RRm9905090 04.k Ans The meter is therefore calibrated for the measurement of sinewaves. If any other waveform is measured, the meter reading will be in error, because the waveform will have a different form factor. Provided that the form factor is known, then the true r.m.s. value can be calculated. Worked Example 6.9 Q A moving coil meter is used to measure both a squarewave and a triangular wave voltage. The meter reading is 5 V in each case. Calculate the true r.m.s. values. A (a) The form factor for a squarewave is 1. The meter, however, has been calibrated for a form factor of 1.11. Thus the indicated reading will be too high by a factor of 1.11:1 Therefore the true valueV 54 5041111..Ans (b) If the form factor for the triangular wave is 1.15, then the meter reading will be too low, by a factor of 1.15:1.11. Therefore the true valueV 5558111111...Ans A further complication arises when the meter is used to measure small a.c. voltages. When conducting, each diode will have a small p.d. developed across it. This forward voltage drop will be in the order of 0.6 to 0.7 V. At any instant, two diodes are conducting. Thus, there will be a total forward voltage drop of 1.2 to 1.4 V across the diodes. This voltage drop is ‘ lost ’ as far as the meter coil is concerned. This effect also must be taken into account when determining the values of multipliers, for the lower a.c. voltage ranges. 6.12 Phase and Phase Angle Consider two a.c. voltages, of the same frequency, as shown in Fig. 6.17 . Both voltages pass through the zero on the horizontal axis at the same time. They also reach their positive and negative peaks at the