oscilloscope triggerring

Discussion in 'General Electronics Chat' started by mghg13, Sep 20, 2013.

  1. mghg13

    Thread Starter Member

    Jul 17, 2013
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    Hello

    can any one explain What is meant by oscilloscope triggerring?
     
  2. BillB3857

    Senior Member

    Feb 28, 2009
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    The sweep (the line across the screen) becomes synchronized with the signal being viewed. The triggering happens when the signal amplitude matches the level set by the trigger level control. The sweep simply waits until the proper trigger event happens. Older bargain scopes did not have triggered sweep, but instead used a free running saw tooth generator. There was usually a SYNC control that attempted to cause the free running saw tooth to match the frequency of the signal being viewed.
     
  3. MrChips

    Moderator

    Oct 2, 2009
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    Imagine a juggler juggling three balls.

    You take a sequence of still photos using a high speed camera that can capture multiple frames in succession.

    If you examine each frame, the juggling balls will all be at random positions.

    The same thing would happen on the oscilloscope screen if the scope was not synchronized to the waveform.

    Now if the high speed camera was somehow synchronized to the action of the juggler, then each frame would show the balls in almost the same position. That is, you would be able to "freeze" the position of the balls from sequence to sequence.

    How could one do this? You could use the action of, say, the left hand to "trigger" the camera.

    In the same way, we use the waveform (or some other event) to "trigger" the scope so that the waveform recording is in sync with the "phase" of the waveform. This results in a "stationary" view of the waveform.
     
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  4. bertus

    Administrator

    Apr 5, 2008
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  5. mghg13

    Thread Starter Member

    Jul 17, 2013
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    well I guess I should have explained where I need this oscilloscope triggerring....Because I'm not able to get your points...So here it is:

    I have an audio oscillator producing a sound of 3.4KHz. This signal is fed to an AM Modulator in order to obtain an amplitude modulated waveform with a 450KHz carrier.
    This modulated waveform is fed to an amplifier in order to be transmitted through an antenna.

    In order to observe the modulated waveform, I connect the probe of an oscilloscope to the output of the amplifier. This should be sufficient (according to me) to observe the waveform.

    But I was told that 'it may be helpful to trigger the oscilloscope from the audio signal', i.e. the output of the audio oscillator!!! What does this mean???
     
  6. #12

    Expert

    Nov 30, 2010
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    Connect the audio signal to the trigger input channel (A) and then watch the modulated output on the other channel (B).

    You don't have a 2 channel 'scope? Maybe you should tell us what you have.
     
  7. MrChips

    Moderator

    Oct 2, 2009
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    Your scope should have CH1 and CH2 inputs. It should also have and EXT TRIG input.
    Tell us which make and model scope you are using.

    Connect the 3.4kHz audio signal to any one of those three inputs.

    Go to the trigger selection of the scope and select the trigger input to the one that you connected the 3.4kHz audio signal.
     
  8. mghg13

    Thread Starter Member

    Jul 17, 2013
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    This, I have understood....but what is the purpose of doing this??? I can't understand your explanations
     
  9. MrChips

    Moderator

    Oct 2, 2009
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    Because your signal has two components, a low frequency component and one of higher frequency. You want to trigger on the lower of the two frequencies otherwise your scope cannot get into sync with the signal.

    Imagine the earth rotating once per day on its axis and revolving around the sun once a year.
    If an interstellar observer wanted to see the position of the earth in the same position (in sync) w.r.t. the sun then he would have to synchronize to the annual orbit around the sun not the daily rotation.
     
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  10. mghg13

    Thread Starter Member

    Jul 17, 2013
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    thanks MrChips...I've got it!!!
     
  11. w2aew

    Member

    Jan 3, 2012
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    To learn more about oscilloscope triggering, and scopes in general, you may want to visit my YouTube channel. I have a lot of tutorial videos there on scopes, circuits, etc.

    http://www.youtube.com/w2aew

    There is a playlist for the scope tutorials.
     
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  12. bug13

    Well-Known Member

    Feb 13, 2012
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    Learn something everyday! Thanks
     
  13. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Oh boy, two analogy explanations from Mr Chips in one day. Spot-on with a high level of clarity. Well done, Sir!
     
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  14. MrChips

    Moderator

    Oct 2, 2009
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    Thanks. I like to use analogies whenever I can to explain more abstract concepts.
     
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  15. MrChips

    Moderator

    Oct 2, 2009
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    Another good example is the old stroboscopic effect. If you have a strobe light shining on the spokes of a wheel as you dial the reptition rate of the strobe you can make the spokes of the wheel appear to be stationary.

    You get the same stroboscopic effect with timing lights shining on timing marks of an automobile engine. In this case the strobe light is triggered by the ignition coil of the engine.
     
    Last edited: Sep 20, 2013
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