PPA5xx/15xx user manual
8-2
8.2 Inrush current
Measurement of inrush current (surge) requires very fast
sampling to catch the highest instantaneous value.
Measurements must be made under conditions of manual
ranging and with the voltage applied to the instrument.
Then when the load is switched on the highest peak value
can be detected. In inrush mode, the PPA5xx/15xx
samples and analyses every sample at the full sample rate
of 1Msamples/s to catch even very fast peaks.
When performing analysis of inrush current of a product
such as a transformer or the input stage of a switched
mode power supply, “range up only” (found in the RANGE
menu) can provide a useful method for determining an
appropriate range for the inrush tests if the current
consumption of the product during an inrush event is
unknown.
However, precautions should be taken regarding the
range-up only function as this functionality is generally
intended for use when monitoring gradual load current
changes, such as when a motor load is gradually increased
over time.
Ideally, before performing an inrush test the range setting
in the PPA would be manually selected and fixed using the
“manual” setting in the range menu. This setting will
reflect the maximum peak current you expect the device
under test to draw from the voltage supply.
*It is important that the voltage supply signal is always
present at the voltage input terminals of the PPA, do not
turn the source on and off to perform inrush current tests.
The voltage source should be disconnected and
reconnected to the device under test using safe working
practices.
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