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Oscilloscope isolation

  1. Mar 29, 2010 #1
    Hai all,
    Could you please explain the need for isolating the oscilloscope. If not isolated what will happen?
  2. jcsd
  3. Mar 29, 2010 #2


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    Staff: Mentor

    A regular oscilloscope will have a 3-prong plug (at least in the US), and all of the external metal on the 'scope, including the ground shield and clip of the probes will be connected to chassis ground. So you cannot connect the ground clip of your 'scope to Neutral or Hot when working with powerline measurements.

    To work with powerline voltages, you either need to use an isolation transformer on the mains power, or use a battery-powered (floating) oscilloscope.

    Does that address your question? What is the context of your question?
  4. Mar 30, 2010 #3

    Thanks. I can understand. But still I've some doubts. Is it enough to disconnect earth connection? If isolation transformer is to be used, how it protects the device?
  5. Mar 30, 2010 #4


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    Science Advisor
    Gold Member

    http://en.wikipedia.org/wiki/Isolation_transformer" [Broken]
    Last edited by a moderator: May 4, 2017
  6. Mar 30, 2010 #5


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    Science Advisor

    Hopefully you wouldn't need to float the whole oscilloscope.

    Dual trace oscilloscopes have two vertical inputs which you can usually invert or add with front panel switches.

    So, if you want to measure the voltage drop across a resistor in a mains circuit or anywhere else (and assuming you do this with great care) you put one probe on one side of the resistor and one on the other. Then invert one of the inputs and add the two inputs.

    This is the same as subtracting one of the inputs from the other.
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