10 | SAMLEX AMERICA INC.
2.2 OUTPUT VOLTAGE WAVEFORMS
TIME
180
160
140
120
100
80
60
40
20
0
20
40
60
80
100
120
140
160
180
Modified Sine
Wave sits at
ZERO for some
time and then
rises or falls
V
PEAK
= 169.68V
Modified Sine Wave
Sine Wave
Pure Sine Wave
crosses Zero Volt
instantaneously
V
PEAK
= 140 to 160V
V
RMS
= 120 VAC
VOL
T
S
(+)
VOL
T
S
(–)
16.66 ms
Fig. 2.1: Pure and Modifi ed Sine Waveforms for 120 VAC, 60 Hz
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also shows Modifi ed Sine Waveform for comparison.
In a Sine Wave, the voltage rises and falls smoothly with a smoothly changing phase
angle and also changes its polarity instantly when it crosses 0 Volts. In a Modifi ed Sine
Wave, the voltage rises and falls abruptly, the phase angle also changes abruptly and
it sits at zero V for some time before changing its polarity. Thus, any device that uses a
control circuitry that senses the phase (for voltage / speed control) or instantaneous zero
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Modifi ed Sine Waveform.
Also, as the Modifi ed Sine Wave is a form of Square Wave, it is comprised of multiple
Sine Waves of odd harmonics (multiples) of the fundamental frequency of the Modifi ed
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frequency harmonic content in a Modifi ed Sine Wave produces enhanced radio interfer-
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MJLFIBOEUPPMTSFGSJHFSBUJPOBJSDPOEJUJPOJOHDPNQSFTTPSTQVNQTFUD5IFIJHIFS
frequency harmonics also produce overloading effect in low frequency capacitors due to
lowering of their capacitive reactance by the higher harmonic frequencies. These capaci-
tors are used in ballasts for fl uorescent lighting for Power Factor improvement and in
single-phase induction motors as Start and Run Capacitors. Thus, Modifi ed and Square
Wave inverters may shut down due to overload when powering these devices.
SECTION 2 |
General Information
