PPA5xx/15xx user manual
7-5
7.2 ACQU - Acquisition options
In normal acquisition mode, the window over which the
measurements are computed is adjusted to give an
integral number of cycles of the input waveform. The
results from each window are passed through a digital
filter equivalent to a first order RC low pass filter.
There are five pre-set speed options – very fast, fast,
medium, slow, and very slow – that adjust the nominal
size of the window, and therefore the update rate and the
time constant of the filter. Greater stability is obtained at
the slower speed at the expense of a slower update rate.
There is also an option to set a specific size of the window
to a value other than the preset options. In order to
synchronise to an integral number of cycles, the window
size is either reduced by up to 25% or increased as
necessary.
Note that at low frequencies, the window is extended to
cover a complete cycle of the input waveform even if this
is a longer period than the nominal update rate.
There are two time constants for the smoothing filter,
normal or slow, or the filter can be deselected. The
nominal values are:
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