B+K precision Sefram DAS1800, Руководство пользователя, Страница: 29 / 73

Sefram CHAPITRE 3. GETTING STARTED
F
IGURE
3.11 : Setting recording frequencies
You can customize the information displayed using the displayed columns field (1) , and filter the channel display
using the Filter by name field (2) . 4 different sampling frequencies can be set (3) .
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The same measurement can be recorded at a single frequency. Two measurements of the same
channel can have different sampling frequencies.
In the example shown in the table above, the direct voltage measurement of channel 1 is recorded at 1MHz, while
the RMS measurement of channel 1 is recorded at 5kHz. Channel 2 forward voltage is recorded at 100Hz. All the
other measurements shown in the table can be viewed in real time, but are not recorded, as they are not activated
in a frequency group.
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The sampling frequency is limited and depends on the acquisition card used (1MSa/s for the univer-
sal card). It is independent of the recording frequency. For example, if a recording is set to 1kSa/s
on a universal card, the trigger will still be accurate to 1µs. Calculations are based on all samples
present in the period
∆ t .
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Depending on the type of measurement recorded and the acquisition card used, a maximum re-
fresh rate is calculated in column
(5)
. If the user-defined recording frequency is higher than this va-
lue, the measurement will be oversampled. The same measurement point will be sampled several
times, which can lead to a "plateau" effect on the measurement curve. It is therefore recommen-
ded not to exceed this limit. Depending on the configuration, an optimum recording frequency is
proposed by default to avoid this behaviour.
DAS User manual 29