PicoScope 7 Software
Available on Windows, Mac and Linux
Windowing with PWQ trailing edge trigger
Windowing with PWQ trailing edge trigger
I don't understand why for a window trigger with PWQ the trigger occurs on the trailing edge of the window. Why not as soon as the pulse width is exceeded? The magnitude window's trigger condition is satisfied on the rising edge of the pulse so that as soon as the pulse width is satisfied the AND of the window trigger and pulse width trigger are satisfied, so then why not issue the official trigger at that point rather than waiting until the pulse falls back to the threshold on the trailing edge?
This becomes a problem for long duration pulses with short PWQ conditions. For example, say I have a 1000us pulse, but the minimum pulse width threshold is 10 us. So the trigger doesn't occur until after 1000us past the leading edge! It also means that the pretrigger capture is not based on the beginning of the pulse but on the ending of the pulse which so very much unconventional. So for a set of pulses of varying duration, I have to set the pretrigger sample period based upon the worse case duration and the number of samples before the pulse's leading edge varies from pulse to pulse. This is all so very much unconventional.
I believe I see how Pico has implemented window trigger with PWQ: (1) The PWQ starts counting when the window threshold is exceeded (in the absolute value sense) BUT the level trigger is not set; (2) When the pulse width is exceeded, only then does the level trigger get enabled; (3) subsequently after enabling the level trigger, the AND of the PW trigger and the level trigger is not true until the signal re-enters the window on the trailing edge of the pulse. That explains why the only level trigger direction that works with PWQ is 'INSIDE'.
IMHO, the proper way to implement window trigger with PWQ is to set the level trigger immediately upon going outside the window regardless of the PWQ. The PWQ begins counting pulse width with the setting of the level trigger. The ANDed trigger of the window and PW is set true immediately upon the PW exceeding its threshold (since the level trigger has been already set).
This becomes a problem for long duration pulses with short PWQ conditions. For example, say I have a 1000us pulse, but the minimum pulse width threshold is 10 us. So the trigger doesn't occur until after 1000us past the leading edge! It also means that the pretrigger capture is not based on the beginning of the pulse but on the ending of the pulse which so very much unconventional. So for a set of pulses of varying duration, I have to set the pretrigger sample period based upon the worse case duration and the number of samples before the pulse's leading edge varies from pulse to pulse. This is all so very much unconventional.
I believe I see how Pico has implemented window trigger with PWQ: (1) The PWQ starts counting when the window threshold is exceeded (in the absolute value sense) BUT the level trigger is not set; (2) When the pulse width is exceeded, only then does the level trigger get enabled; (3) subsequently after enabling the level trigger, the AND of the PW trigger and the level trigger is not true until the signal re-enters the window on the trailing edge of the pulse. That explains why the only level trigger direction that works with PWQ is 'INSIDE'.
IMHO, the proper way to implement window trigger with PWQ is to set the level trigger immediately upon going outside the window regardless of the PWQ. The PWQ begins counting pulse width with the setting of the level trigger. The ANDed trigger of the window and PW is set true immediately upon the PW exceeding its threshold (since the level trigger has been already set).
Re: Windowing with PWQ trailing edge trigger
The reason it is programmed this way is that until you get the edge you haven't received a pulse, so it can't be qualified.
Have you looked at the dropout triggers which will fire after the given time.
Have you looked at the dropout triggers which will fire after the given time.
Martyn
Technical Support Manager
Technical Support Manager
Re: Windowing with PWQ trailing edge trigger
Understood, but disagree.