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    Isolated probe for inverter measurements needed?

    HI ,
    i have DSO TBS2072b from tektronics (ground is not isolated )
    will the DSO will get damage if i check mosfet oputput without using isolated probe (using normal probe).??
    Actually i am buying this oscilloscope so during demo the marketing team told me about this so i am confused coz i never herd of such things before . Or is it just just there marketing trick to sell me an isolated probe as well?
    Last edited by FvM; 15th April 2017 at 09:42. Reason: New topic, moved to new thread

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    Re: Isolated probe for inverter measurements needed?

    Mains supplied oscilloscopes like TBS2072 have the ground tied to protective earth. Respectively you must not connect the probe ground to a mains supplied inverter without isolation transformer.

    High voltage differential probes are a standard tool of power electronics development. You can get less expensive types from third parties.


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    Re: Isolated probe for inverter measurements needed?

    what is this isolation transformer??
    can u please explain with the help of a diagram on how to use isolation tranformer while testing mosfert output with normal probe.

    thanks in advance for your help
    Last edited by Akshaydpal; 15th April 2017 at 11:46.



    •   Alt15th April 2017, 11:40

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    Re: Isolated probe for inverter measurements needed?

    Isolation transformer isolates the 230V inverter power supply.


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    Re: Isolated probe for inverter measurements needed?

    If your circuit is battery-powered so no problems at all, you can measure freely. If your circuit uses isolated power supply (i.e. power adapter with 2 pins for mains and a trasformer inside), again no restrictions. But if your power supply connects 0V rail (GND) to protective earth (PE), you can connect alligator clips of the probe ONLY to 0V rail in your circuit. But you're still able to check your circuit (mosfet) and can measure voltage relative to 0V rail. If in this case you try to connect the alligator clip to a point that has a potential other than 0V, you'll make low-resistance path with non-zero voltage that may lead to disasterous results because of large current.


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    •   Alt15th April 2017, 19:58

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    Re: Isolated probe for inverter measurements needed?

    At work, we use some very expensive LeCroy diff probes.

    At my home lab, I use the much less expensive ProbeMaster 4232

    They have many models, depending on your budget and your requirements.

    http://probemaster.com/differential-probes/
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    Re: Isolated probe for inverter measurements needed?

    You can use a 220V/220V isolation transformer with 100W power. You may get this from any small term transformer manufacturer.



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    Re: Isolated probe for inverter measurements needed?

    if i use 220/220v isolation transformer with 100W power. the connections will be like ine side of transformer will be connected to probe + and gnd . and the other side will serve as testing points . Then no need to worry about connections gets accidently reversed ?? I hope this is what u ment .

    Image is attached as per my understanding


    http://obrazki.elektroda.pl/2401855700_1492407904.jpg



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    Re: Isolated probe for inverter measurements needed?

    The schematic seems to connect the isolation transformer between the device under test and the oscilloscope probe. This won't work for the intended purpose and will in case of doubt damage the device under test.

    The suggestion was to isolate the inverter power supply.

    There's also a theoretical option to isolate the oscilloscope supply, but it involves a hazardous contact voltage at the oscilloscope case and controls and thus can't be suggested.


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    •   Alt17th April 2017, 07:31

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    Re: Isolated probe for inverter measurements needed?

    then how am i suppose to use isolation transformer please help me . it would be great if u prove me with a pictorial example.



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    Re: Isolated probe for inverter measurements needed?

    An isolation transformer has a plug, which you connect to the wall outlet; and a connector which you connect to the device under test.

    Check for instance: http://www.ebay.com/itm/STANCOR-ISOL...wAAOSww3tY7qk0

    NOTE: I'm not promoting this product or vendor. I only used it as an example, because it has good images.
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    Re: Isolated probe for inverter measurements needed?

    Quote Originally Posted by schmitt trigger View Post
    An isolation transformer has a plug, which you connect to the wall outlet; and a connector which you connect to the device under test.

    Check for instance: http://www.ebay.com/itm/STANCOR-ISOL...wAAOSww3tY7qk0
    .
    but i did not understand how to use this while testing an inverter circuit if possible can you please elaborate using an image



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    Re: Isolated probe for inverter measurements needed?

    Very simple:
    Instead of connecting the inverter directly to your wall outlet, connect it first to the isolation transformer.
    Then connect the isolation transformer to the wall outlet.

    In plain English, the isolation transformer will be between the wall outlet and the device you are testing.
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    Re: Isolated probe for inverter measurements needed?

    but inverter im testing will be powered by the battery



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    Re: Isolated probe for inverter measurements needed?

    Quote Originally Posted by Akshaydpal View Post
    but inverter im testing will be powered by the battery
    You should have started by telling us this in the first place.

    If the inverter is ONLY powered from the battery, and NOT CONNECTED IN ANY WAY to the AC mains or physical GROUND, then it is effectively floating.
    You don't require an isolation transformer.
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    Re: Isolated probe for inverter measurements needed?

    so that means while testing mosfet i dont need diffrential probe either



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    Re: Isolated probe for inverter measurements needed?

    It depends. Grounding a circuit node through the probe ground clip can affect circuit operation in different ways, even if it's isolated. If you e.g. ground a bridge output node to measure high side transistor Vgs or Vds, you superimpose a high frequent common AC voltage to the complete inverter which may cause all kind of problems.


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    Re: Isolated probe for inverter measurements needed?

    You can safely measure low side mosfets.
    As FvM has explained, a high side mosfet, may cause erratic behavior.


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    •   Alt22nd April 2017, 17:04

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    Re: Isolated probe for inverter measurements needed?


    http://obrazki.elektroda.pl/8203938900_1493439663.jpg
    this is my current inverter testing set up probe is normal probe
    in this case do i need any isolation transformer to keep my dso safe . if i need sonthing please guide me how to keep my dso safe im using tbs2072



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    Re: Isolated probe for inverter measurements needed?

    is there any one who can help me please i need it



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