3
sine wave shape of utility power. A waveform of this type is
suitable for most AC loads, including linear and switching
power supplies used in electronic equipment, transformers, and
motors. This waveform is much superior to the square wave
produced by many other DC to AC inverters.
The modified sine wave produced by the PROwatt 250 is de-
signed to have a RMS (root mean square) voltage of 115 volts,
the same as standard household power. Most AC voltmeters
(both digital and analog) are sensitive to the average value of
the waveform rather than the RMS value. They are calibrated
for RMS voltage under the assumption that the waveform meas-
ured will be a pure sine wave. These meters will not read the
RMS voltage of a modified sine wave correctly. They will read
about 2 to 20 volts low (i.e. about 100V) when measuring the
output of the PROwatt 250. For accurate measurement of the
output voltage of the PROwatt 250, a
true RMS
reading volt-
meter such as a Fluke 87, Fluke 8060A, Beckman 4410, or
Triplett 4200 must be used.
