Triggering on entering or leaving a defined window
| A user defined number of analogue signal channels are continuously
monitored at the selected sample rate. If its signal leaves a user programmed window,
defined by a higher and lower threshold level, then a valid trigger is seen
and acted upon so that recording starts. The green trace shows when the condition
has been met for a valid trigger. During recording further trigger events are
ignored until the recording period has completed. Programmed window levels
are simply made in the appropriate code register of the driver software.
The level is defined in millivolts allowing for fine adjustment.
|Alternatively the window trigger also works for situations where the
incoming trigger signal enters the defined window, this choice is
made by the programmer in the appropriate register.
|Note that in both diagrams above the "Start" indicates the point
at which the card was armed ready to receive triggers, here the start occurred when the
trigger condition was already fulfilled, so instantly the card starts to record.
The start could be at any point in time as determined by the user and the application.
|The window triggering can be combined with a pulsewidth control. Take for
example the case described at the top of the page where a trigger is seen and
acted upon when it leaves a defined window. With the pulsewidth an extra control
is implemented. Every time the signal leaves the window a pulsewidth counter
is started. If the pulsewidth counter stops and the signal is still outside
the window, the trigger event will be detected.
If the signal enters the window again before the pulsewidth counter
has stopped, no trigger will be detected.
An example where this could be useful is in avoiding false triggers caused by
fast transients. Other combinations of window trigger and pulsewidth control
can be chosen and the pulsewidth counter can set a maximum period that a trigger
can be valid. Now only short period events could intitiate a trigger.
|Window trigger mode can be combined with AND or OR logic from
other sources, e.g. a software trigger (such as key press), a signal
from the card's digital (LVTTL/TTL) trigger I/O input, or optional BASEXIO TTL inputs.
The above is just a summary of the window and pulsewidths versatile features.
Full details can be found in the user manual.
Images courtesy of Spectrum GmbH
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Last modified by DataQuest Solutions Ltd 23.04.19