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MIL-I-19028E(OS)
4.4.5 .1.2.2 DC input current.  Measure and record the input current,
using a 0-50 ampere dc ammeter (4.4.3.3).
4.4.5.1.2.3 AC output voltage.  Measure and record the three ac output
line-to-line voltages as near the inverter terminals as possible, using
a 0-150 volt rms voltmeter (4.4.3.2.2) calibrated at 400 Hz. These volt-
ages shall meet the requirements of 3.3.1.3.2.
4.4.5.1.2.4 Output frequency.  Measure and record the phase AB fre-
quency, using the electronic frequency counter (4.4. 3.5 ). This frequency
shall be within the limits of 3.3.1.3.3.
4.4.5.1.2.5 Total ac output watts.  Use two wattmeters (4.4.3.4) with
0-100 volts rms, 400 Hz voltage circuits and 0-5 ampere, 400 Hz current
circuits.  Connect plus or minus voltage and current terminals together
on each wattmeter.  Place the current circuit of one wattmeter in output
line A, and place the current circuit of the other wattmeter in output
line B, with the plus or minus markings on the inverter side. Join the
remaining voltage circuit terminals together and connect them to output
line C.  Add the wattmeter readings for total watts output. See Figure
5.
4.4.5.1.2.6 Efficiency.  Efficiency shall be not less than the limits
specified in 3.3.1.4 when calculated according to the following formula,
using the data taken in 4.4.5.1.2.1, 4.4.5.1.2.2, and 4.4.5.1.2.5:
4.4.5.1.2.7 Modulation.  Measure across the AB phase, using a calibrated
oscilloscope (4.4.3.7) as follows:
4.4.5.1.2.7.1 Set the oscilloscope so that at least 25 plus or minus
5 Hz peak-to-peak of the 400 Hz output voltage can be seen. Use suffi-
cient vertical gain so that the trace very nearly fills the screen.
Using the oscilloscope calibrator, measure and record the maximum peak-
to-peak voltage.  This reading shall be called E max.
4.4.5.1.2.7.2 Adjust the trace vertical position control and the vertical
gain control on the oscilloscope so that only about one quarter of the pos-
itive half of the waves can be seen on the screen.  Using the oscilloscope
calibrator, measure and record the maximum difference noted between the
voltage peaks on the screen.  This reading shall be called E. See Figure
6.
4.4.5.1.2.7.3 Modulation limit.  Modulation shall not exceed the limit
specified in 3.3.1.3.7 when calculated according to the following formula
and using the data of 4.4.5.1.2.7.1 and 4.4.5.1.2.7.2.
17

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