MI 2893 / MI 2892 / MI 2885 Measurement methods
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trigger and post-trigger buffers. Pre and post-trigger buffers are composed of waveform snapshots
taken before and after trigger occurrence, as shown on following figure.
Record Duration = 2 sec
Record start
Record stop
Trigger point
PreTrigger = 1 sec
PostTrigger=1sec
Figure 168: Triggering and pre-triggering description
Several trigger sources are possible:
Manual trigger - user manually triggers waveform recording.
Voltage events – instrument starts waveform recorder when voltage event occur. Voltage
events are set up in EVENT SETUP menu (see 3.23.2 for details), where user defines threshold
limits for each event type: Dip, Swell and Interrupt. Each time event occurs, waveform recorder
starts recording. Instrument then capture U
Rms(1/2)
and I
Rms(1/2)
values into RxxxxINR.REC file and
waveform samples for all voltages and currents channels into RxxxxWAV.REC file. If parameter
PRETRIGGER is greater than zero, then recoding will start prior the event for defined time, and
will finish when record DURATION length is reached. On following figure voltage dip is shown,
where voltage drops from nominal value to the almost zero. When voltage drops below dip
threshold, it triggers recorder, which capture voltage and current samples from one second
before dip to one second after dip occurs. Note that if during this time period another event
occurs, (as interrupt on figure below, for example) it will be captured within the same file. In
case where voltage event last for longer time, new recording will start after first record is
finished, soon as any new event occurs (voltage ramp-up event, shown as example on figure
below).
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