Saturday 16 March 2013
DEFINITIONS IN A WAVE FORM
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The sinusoidal waveform of figure 1 with its additional notation will now be used as a model in defining a few basic terms. These terms, however, can be applied to any alternating waveform. It is important to remember as you proceed through the various definitions that the vertical scaling is in volts or amperes and the horizontal scaling is always in units of time.
Waveform
The path traced by
a quantity, such as the voltage in figure 1, plotted as a function of some
variable such as time (as above), position, degrees, radians, temperature, and
so on.
Instantaneous value
Peak amplitude
The maximum
value of a waveform as measured from its average, or mean, value, denoted by
uppercase letters (such as Em for sources of voltage and Vm for the voltage
drop across a load). For the waveform of figure 1, the average value is zero
volts, and Em is as defined by the figure.
Peak value
The maximum
instantaneous value of a function as measured from the zero-volt level. For the
waveform of figure 1 the peak amplitude and peak value are the same, since the
average value of the function is zero volts.
Peak-to-peak value
Denoted
by Ep-p or Vp-p, the full voltage between positive and negative peaks of the
waveform, that is, the sum of the magnitude of the positive and negative peaks.
Periodic waveform
A
waveform that continually repeats itself after the same time interval. The
waveform of figure 1is a periodic waveform.
Period (T )
The time
interval between successive repetitions of a periodic waveform (the period T1 =
T2 = T3 in figure 1, as long as successive similar points of the periodic
waveform are used in determining T.
Cycle
The portion of a
waveform contained in one period of time.The cycles within T1, T2, and T3 of
Fig.1 may appear different in figure 2, but they are all bounded by one period
of time and therefore satisfy the definition of a cycle.
Frequency ( f )
The number
of cycles that occur in 1 s. The frequency of the waveform of Fig. 3(a) is 1
cycle per second, and for Fig. 3(b), 2(1/2) cycles per second. If a waveform of
similar shape had a period of 0.5 s [Fig. 3(c)], the frequency would be 2
cycles per second.
The unit of measure for
frequency is the hertz (Hz), where
1hertz
= 1 cycle per second
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