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How to identify lead or lag on oscilloscope

Discussion in 'General Electronics Discussion' started by electronicsLearner77, Oct 5, 2020.

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  1. electronicsLearner77

    electronicsLearner77

    152
    1
    Jul 2, 2015
    I am trying to understand the lead and lag on an oscilloscope, this is one of the images explained in the book
    upload_2020-10-5_19-17-25.png
    I understood that the phase difference is 144deg as it is 2 divisions and the complete cycle is 5 divisions for 360 Deg. I am only confused how to identify the lead and lag, the book says 'e' leads 'i' by 144Deg, on what basis it was concluded? Because if you see from the beginning the 'e' is leading but if you take some other position the 'i' is leading. For me which curve meets the 0 value in positive slope first will be leading.
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    11,160
    2,548
    Nov 17, 2011
    My interpretation:
    You can't tell from the scope image alone. The scope image tells you that there is a phase difference of 144 ° between e and i --- or 216 ° between i and e. How you interpret the data depends on the circuit and the points where you measure. If you have a capacitive circuit, e follows i as the current takes time to charge the capacitor, thereby changing the voltage across the capacitor.
    If you have an inductive circuit, i follows e as the change in current through the inductor follows the change in voltage across the inductor.
     
  3. electronicsLearner77

    electronicsLearner77

    152
    1
    Jul 2, 2015
    But the circuit we cannot say can have only inductor and capacitor it can have many more components, then it is difficult to predict, in that case how to know? And also if we want to confirm if a particular signal is leading by X degrees on the scope, how do I confirm? Can we use other tools, differential probe etc?
     
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