Using the “At./Norm.” button you can switch between automatic trigger level selection (At) and normal, manual trigger level selection (Norm.). The trigger level in automatic mode equals the level during groundline crossing, in this simulation that is 0 V. The trigger level in manual mode can be set using the “Level” wheel located below the “At/Norm.” button. Using that wheel, voltage values larger than the amplitude of the signal can be set, too. However, as the signal level will never reach that (higher) trigger level, the signal will not be triggered in that case at all.
To make sure that the simulation allows demonstration of this function even for high input voltages, an algorithm has been implemented that does not use the voltage of a signal: In the simulation a signal is always triggered as long as the trigger wheel is rotated within a range of -90° and +90° from its center position, outside this range it is not triggered. In reality the maximum trigger level would equal 100 V, and the trigger range would be based on the true voltage of the signal. After production of the simulation this limitation has shown to be reasonable: For small input voltages on a real oscilloscope minor moves of the wheel influence the trigger level strongly. Such small movements cannot be executed by a simulation user with his mouse exact enough to implement them in the simulation.
If a signal is triggered on ascending or descending flank can be set using the “+/-“ button.
The following images show examples for different trigger settings:
The “At/Norm.” button is off (=automatic level selection),
the “+/-“ button is off (=trigger on ascending flank)
The “At/Norm.” button is on (=manual trigger level setting),
the “Level” wheel is turned to a position lower than the lowest voltage of the signal,
therefor the signal cannot be triggered, the screen remains empty.