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Oscilloscope EXT. INPUT , source Channel#2

Discussion in 'General Electronics Chat' started by Billy Mayo, Dec 11, 2013.

  1. Billy Mayo

    Billy Mayo Member

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    No , I had to use channel#1 as the AC output which has a polarity switch to go from 0 to 180 degrees
    Channel#2 I had to put 115vac 400hz and on the O-scope set it to SOURCE on channel 2

    This allowed me to view the AC waveform at either 0 or 180 degrees

    I used the Channel#2 as a SOURCE REFERENCE

    Can't I put 115VAC on the EXT. INPUT on the O-scope and use this as a SOURCE REFERENCE ?

    I'm just not sure if i can put an AC waveform input on the EXT INPUT on the O-scope and how much voltage can I put into it?

    Why can't I put 115VAC at 400hz on the EXT INPUT on the O-scope? so that channel#1 and channel#2 can SOURCE to the ext input
     
  2. Billy Mayo

    Billy Mayo Member

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    What have you guys done in the past or in general when using Channel#2 to be the reference and having channel#1 Source to channel#2?

    What have you guys done in the past or in general when using the EXT input? using reference waveforms or what kind of references
     
  3. Reloadron

    Reloadron Well-Known Member Most Helpful Member

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    First of all I haven't a clue what scope you are using or its capabilities. I will tell you this. Most scopes share a common. If you try and run 115 VAC (Line Voltage) into the external trigger in and have line and neutral reversed things will get ugly real quickly.

    What exactly are you trying to do? Exactly meaning define in detail.

    I left you with this link in the other phase related thread. Did you try it?

    Ron
     
  4. dave

    Dave New Member

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  5. Billy Mayo

    Billy Mayo Member

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    So what can I put into the External trigger INPUT?

    Can I put 115 VAC in the External trigger input? or will it get damaged?

    I'm not sure if I can put an AC signal or voltage into the External Trigger Input

    Are Channel#1 and Channel#2 , isolated grounds? or the tied together to ground?
     
  6. Billy Mayo

    Billy Mayo Member

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    No, I'm not trying to measure to different AC waveforms , and trying to measure the phase shift or time between them
     
  7. chemelec

    chemelec Well-Known Member

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    The Channel-1 and Channel-2 are on a "DUAL TRACE" SCOPE.
    Channel-2 is NOT the Same as an EXT INPUT.

    BILLY, You have a LOT TO LEARN
     
  8. Billy Mayo

    Billy Mayo Member

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    .

    Yes I know that

    But you can use channel#2 as a reference and Source Channel#2 to channel#1

    This is a form of Triggering right?

    Why Can't you use the EXT INPUT like this?
     
  9. Reloadron

    Reloadron Well-Known Member Most Helpful Member

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    The link shows how to measure phase shift. Thus the title of Oscilloscope Phase Shift Measurements.

    I told you, nobody here knows what scope you are using. I have no idea if the in/out share the same common but most general purpose scopes do. Furthermore, most scopes allow for line triggering so if the 115 VAC you plan to inject into the external trigger jack is line voltage just use the line trigger function.

    Ron
     
  10. Billy Mayo

    Billy Mayo Member

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    Can I inject 115VAC at 400hz into the External trigger jack?

    I will get the model names tomorrow at work , I don't them off hand sorry
     
  11. Reloadron

    Reloadron Well-Known Member Most Helpful Member

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    Read the manual for the scope. The scope manual will tell you the limitations for external trigger in.

    Ron
     
  12. Billy Mayo

    Billy Mayo Member

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    Ok, but what have you used this for ? bench check or tested a circuit in the past or in general

    Give examples please so I can learn how to use the external trigger input
     
  13. ChrisP58

    ChrisP58 Well-Known Member

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    The only times I have ever used the External trigger input on a scope was when I need to see the timing of two signals with respect to a third signal. And that was for square waves in a digital circuit, so I only needed to know where the edges were. One big problem that I see with trying to use the Ext input to measure phase of something like a sine wave, is that you can't actually see the waveform, which makes it difficult to know where to make your timing reference from.

    Why do want to use the External input instead of the two regular channels?
     
  14. Billy Mayo

    Billy Mayo Member

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    1.) So I can have more channels to display inputs and outputs and not use up a channel
    2.) I think using the External input would LOCK SYNC the reference 115VAC 400hz AC waveform with Channel#1

    Using Channel#2 as the Reference at 115VAC 400hz AC waveform doesn't SYNC , so you don't know where the beginning of the waveform is on channel#1 , I have to use the trigger level to find a starting point

    Doesn't the External Input SYNC up better when used as a reference?

    This is the same problem I'm having when using Channel#2 as the reference source
     
  15. ChrisP58

    ChrisP58 Well-Known Member

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    You only need two channels to check the phase of two signals. Why do you need a third?
    Yes, but at what threshold voltage?
    If you want to sync to the signal on channel #2, you set the trigger source to Ch #2. And yes, you set the trigger level to whatever threshold you want to use as the a reference point. For an AC sinewave you would typically use zero volts to get the zero crossing point. Please note, for phase measurements, you trigger on only one channel. You then use your eyes and the cursor to find the same point on the waveform showing on the second channel.
    I can't imagine why. My experience is that the ext input has fewer trigger options.
    Are you saying you can't see the waveform on the 2nd channel? If so, you have it setup wrong, or a broken scope.
     
  16. Billy Mayo

    Billy Mayo Member

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    What Threshold voltage would an AC 115 VAC be? at what threshold hold voltage?

    Well how do you get the threshold hold to be at zero volts?

    The AC waveform moves from left to right when you move the Trigger level - or +

    Why does it make it difficult to make the timing reference using the EXT INPUT?
     
  17. ChrisP58

    ChrisP58 Well-Known Member

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    I would choose zero volts, to set the zero time reference at the zero crossing point.

    My Tek TDS5034 has a display that shows what the trigger voltage is, so I set the level at 0.0V. I don't know about your scope.

    As it should. You are changing the voltage of the trigger point, so of course the waveform will change position.

    I don't know the details of your scope, so I really shouldn't speculate. But why don't you just make it easy on yourself and do it the simple way?[/quote]
     
  18. Billy Mayo

    Billy Mayo Member

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    On channel#1 or on Channel#2? which channel do you do this for?
     
  19. ChrisP58

    ChrisP58 Well-Known Member

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    It really does not matter. You can use either channel as the reference, since you are only looking for a time difference.
     
  20. Billy Mayo

    Billy Mayo Member

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    Yes i know

    for the reference channel do you set the Trigger level to Zero? or the other channel?

    Why do you think the EXT. INPUT is limited and has limited triggering?

    Why do you think using a Channel as a reference is better than using the EXT. INPUT?

    Can you put in DC or AC waveforms into the EXT. INPUT?
     
  21. ChrisP58

    ChrisP58 Well-Known Member

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    Whichever channel you are using as a trigger source. Again, for measuring a time difference it doesn't matter which is which.

    Again, without knowing the details of YOUR scope, I can't say.
     

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