ADD mode used for on the Oscilloscope

Discussion in 'General Electronics Chat' started by DexterMccoy, Feb 20, 2014.

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  1. DexterMccoy

    Thread Starter New Member

    Feb 19, 2014
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    What is the ADD mode used for on the oscilloscope?

    What kind of troubleshooting would you use the ADD mode on the oscilloscope for?

    What kinds of tests would you use the ADD mode for on the oscilloscope?
     
  2. WBahn

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    Mar 31, 2012
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    For adding two signals.

    Troubleshooting that would be aided by adding to signals.

    Tests that needed signals added together.


    Perhaps Billy Mayo could get with you offline and explain things to you.
     
  3. alfacliff

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    Dec 13, 2013
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    It can be used to test whether two signals are timed the same. by adding them, it makes it obvious if they are simultaneous or not. also, you can test delay through a circuit the same way. it also makes it stand out if there is distortion in an amplifier or system.
     
  4. DexterMccoy

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    Feb 19, 2014
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    Yes I know the signals need to be added together
    But i need examples of when and how , what kind of circuits would use the ADD mode on the oscilloscope

    Do you have any examples of when you have used the ADD mode to add signals together to make a measurement or to do troubleshooting?
     
  5. DexterMccoy

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    Feb 19, 2014
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    O-scope channel#1 on the Clock input of IC chip#1?
    O-scope channel#2 on the Clock input of IC chip#2?
     
  6. MrChips

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    Oct 2, 2009
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    Some scopes have ADD function but no SUBTRACT.

    If you want to measure the current pulse on the high side of a power supply by monitoring the voltage drop across a series resistor,

    connect CH1 probe to one end of the resistor,
    connect CH2 probe to the other end of the resistor,
    set CH2 to INVERT,
    select ADD function.
     
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  7. WBahn

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    I've used the ADD mode lots of times, usually in combination with the inversion mode of one of the channels so as to effectively subtract them. Can you think of any cases where it might be nice to subtract two signals?

    Or, if you want to see the common-mode of two signals you add them together.
     
  8. DexterMccoy

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    Why would you want to measure the "current pulse" of a power supply?

    You mean the high frequency pulse for switching power supplies?

    Does the series resistor have to be 1 ohm? or can it be any value?

    Both O scope ground clips would have to be floating and not used right?
     
  9. DexterMccoy

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    Can you give examples of when you used them, so i can learn from them please?
     
  10. WBahn

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    They call them ground clips for a reason. They are not floating to begin with.
     
  11. DexterMccoy

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    Yes , but if you use the O scope ground clips while do a differential voltage drop, it will be referenced to ground and you don't want that. You want the ground clips not to be used so there is no reference to ground
     
  12. WBahn

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    Your scope probes (unless they are specifically differential probes, which tend to be rare and expensive) measure a voltage relative to the scope's ground reference. Which means you want your circuit to be referenced to the scope's ground reference. That's what the scope's ground clips are for. Of course, you need to be aware of what point in your circuit, if any, is otherwise ground referenced and be sure to be consistent with that.
     
  13. WBahn

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    No. I can't. I haven't done much bench diagnostic work in the last decade or so and I certainly don't recall specific examples of how I made some specific measurement on some specific chip a dozen years ago or so.
     
  14. MrChips

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    I didn't specify what kind of load the power supply is driving or the type of power supply. This is simply an example of making a current measurement.

    The resistor can be of any appropriate value.

    The oscilloscope ground clips would be connected to the GROUND of the circuit being tested.
     
  15. ErnieM

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    Apr 24, 2011
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    It's an example of when you would need such a measurement.

    Mebby he means that, mebby not. He made an example of a differential signal where the value across an element is measured, not the voltage from one point to ground.

    It could be any element in any circuit where you want to watch the voltage directly across something.

    Any. It's an example. It's an imaginary example to illustrate where you would want to make such a measurement.

    Nope. Best if both clips go to the ground of the circuit under test, keeps the signals as faithful as they can be that way.

    Don't over think this, just remember it and one day when worrying out a problem you'll remember the technique and use it and enjoy troubleshooting bliss.
     
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