Airpax Dimensions MIL-24X26UVQ Owner's Manual - page 24
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Chart H:
Waveform Discussion
Pure sine waveform electrical power is the world's standard waveform for the electrical
utility grid (see figure a below). This waveform is the naturally occurring waveform that
is emitted from a rotating electrical generator, so it was a logical decision to make this
the standard. This is commonly called alternating current or AC.
The other common type of electricity is direct current or DC, which is emitted from
batteries. A limited number of electrical products will operate from DC versus a large
number from AC. Inverters are devices that convert DC to AC electronically, or statically,
without the use of a rotating generator.
It is very difficult to produce a pure sine waveform electronically. The original inverters
produced a square waveform output that was cheaper and easier to produce. These
inverters are very limited in the equipment they will operate and are typically used for
resistive AC loads. They cannot be U.L. listed.
Newer inverters output a more usable waveform called quasi-sine waveform by
Underwriters Laboratory U.L. (see figure b below). Other names for this waveform are
modified sine wave, rectangular wave, or modified square wave. A correct version of
this quasi-sine waveform can be granted U.L. approval. This waveform can operate most
equipment and will not harm other U.L. listed equipment.
The newest inverters output pure sine waveforms (Figure a). These inverters will
operate any load within their power rating range, but usually do not have the motor
starting capability of quasi-sine inverters. There are several electrical products that
require a pure sine waveform to operate correctly. A partial list of them is provided
below. See chart D on page 22 also.
• Microprocessor controlled tools and equipment
• Phase controlled devices such as ceiling fan speed controls, incandescent lamp
dimmers, and power supplies.
• Transformless capacitive powered devices such as DC tool battery chargers,
compact fluorescent light, and smoke detectors.
a) Pure sine wave form
b) Quasi-sine wave form
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