what is trigger in term of oscilloscope

:?:

The trigger system is that part of your oscilloscope which decides when to start displaying the signal on analogue oscilloscopes (usually the moment of triggering is the begin of the trace, in left side) or when to display the moment 0 of recorded signal for digital oscilloscopes. The trigger condition can be from the simplest (AC or DC coupled) to complex ones (ex. pattern trigger) for complex oscilloscopes.
The trigger system in analogue oscilloscopes is usually a comparator which is supplied with the input signal from one of the channels and with the trigger level which is adjustable from the front panel. The input signal can be coupled to the comparator in AC or DC, and the whole trigger system can contain several selectable filters (HF/LF reject, pulse trigger, etc.), counters for displaing video signal lines/frames.
The trigger system in digital oscilloscopes is more complex. It can be done either with comparators like in analog scopes (more precise), or implemented in software, by applying several conditions to the digitised signal (less precise, but cheaper from the implementation point of view).

/pisoiu

Here you can find more about oscilloscope triggering, including pictures for a better understanding.
**broken link removed**

it is an addition to the topic that when using external trigger for multi channel cro the default is the channel with the highest number if u didn't specify one. if the trigger isn't adjusted weell by trigger only there is in some cro a hodoff button tht mall delays to adjust trigger

say u have a series of square wave that goes from 0 to 5v and u set the trigger level at 3v, then what would that graph look like? Would it just be another squave wave graph that go from 3 to 5v? I'm trying to understand triggering.

david90 said:

say u have a series of square wave that goes from 0 to 5v and u set the trigger level at 3v, then what would that graph look like? Would it just be another squave wave graph that go from 3 to 5v? I'm trying to understand triggering.

Click to expand...

Yes, the rising slope of the first square wave you will see will go from 3 to 5v ( the others will look normal, from 0 to 5 and from 5 to 0), but only if your trigger is set on rising slope. If it is set on falling slope, you will see first a falling slope going from 3 to 0v, then the rest of the waveform.

/pisoiu

David,

The sense of trigger is just synchronizing the oscilloscope sweep with the wave you are trying to visualize.

Regarding your last question, in true life, 0-5V square signals cross all the intermediate voltages due to the dVdt may not be infinite. This means (please, don't kill yourself...) in true life square waves look like trapezoidal waves rather than square. So, setting the trigger point, for example at 3Volts, your scope will start to sweep when the signal pass over/under 3Volts, where over/ under depends on which trigger edge you have selected... take a look at the "slope" switch of your scope)

Regards