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Ext trigger on analogue scope
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Ext trigger on analogue scope

by Myrmidon on Sat Jul 17, 2010 3:39 pm

Greetings.

I have a Hitachi v-525 50MHz analogue scope. But my question covers a lot of analogue scopes.

What is the purpose and point of the external trigger? I'm having difficulty understanding this and the manual and research i'v done haven't enlightened me at all.

At first i thought that maybe an external trigger would provide some kind of snapshot ability and the manual alludes to this. I was thinking that given a pulse that was non-periodic, when the pulses triggered the set level, the beam would kind of loop this pulse train, but i'm beginning to think i'm way off.

Can someone then, explain the point of the external trigger, and maybe even give some examples?

:roll:
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Re: Ext trigger on analogue scope

by mikeselectricstuff on Sat Jul 17, 2010 9:21 pm

The main use is to be able to display 2 signals while triggering on a third, so you don't waste a trace on a signal you don't need to look at.

It's a very cheap way to give more useable traces in _some_ situations. I can't think of anything you could do with ext trig that you couldn't also do by triggering off a channel, except maybe in the case of very high speed measurements, where the delay from the ext trig may be less than that though the analogue amplifiers, although better fast analogue scopes signal have delay lines to overcome this.
I suppose another example would be where you are looking at a system where you are poking both probes randomly all over the place to look at different signals, but they are all related to a single trigger event that you can permanently connect to the ext trig input.

There are probably also a few applications where you want to DC couple the trigger but AC couple the trace, or vice versa.

Some scopes have a 'trig view' mode which gives a third trace, for a limited rage of input amplitudes.
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Re: Ext trigger on analogue scope

by Myrmidon on Sun Jul 18, 2010 7:46 am

Ah, thanks for that. That clears up things quite a bit.

Looks like i need to get saving for a digital storage scope. :shock:
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