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. Window trigger. Diagram an trigger input signal leaving an amplitude window to be recognised as a trigger event.
 
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. Window trigger. Diagram an trigger input signal entering an amplitude window to be recognised as a trigger event.
 
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. Diagram an trigger input signal entering an amplitude window to be recognised as a trigger event.
 
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.

DataQuest Solutions Ltd. | Phone: 01526 557171 | Email: info@dqsolutions.co.uk