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Jim Newell

Jim has worked for Fluke for a little over 31 years working in Manufacturing production and Quality assurance for the first 15 years. In the last 15 years he has focused on technical support as a Application Engineer for all of the Electrical Industrial products such as Handheld Oscilloscopes, Digital Mulitmeters and Power Quality Analyzers.  He enjoys the challenge of helping people and the famous saying the only dumb question is the one you didn’t ask are often joked about among his customers.



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  • Hi jim,

     

    Its been a while since using an oscilloscope and I got myself loop:i.e. the question might sound a bit daft.

    I want to visualise the voltage waveforms on an induction motor and controller. Now, to measure the individual phases I would have a connect the probe to 1 or more of the phases but what do I choose as a ground? Would that be the negative of the DC input?

     

    Cheers,

Reply

  • Hi jim,

     

    Its been a while since using an oscilloscope and I got myself loop:i.e. the question might sound a bit daft.

    I want to visualise the voltage waveforms on an induction motor and controller. Now, to measure the individual phases I would have a connect the probe to 1 or more of the phases but what do I choose as a ground? Would that be the negative of the DC input?

     

    Cheers,

Children
  • in reply to mouch

    Hi Dirk,

    You have a few options, each with pros & cons:

    1) Use a differential probe to measure across each phase.

    2) Use a scope with isolated channels.  Several handheld models offer that capability, plus the Tektronix TPS2000 series instruments.

    3) Measure each phase relative to ground and use maths function on the scope, or offline ona PC) to derive the phase measurements.

     

    In any case DON'T cut your scope's ground lead and float the instrument - it's dangerous and violates numerous safety standards.

     

    Tektronix have an application note on making floating measurements.  You can download it from: http://www.tek.com/Measurement/App_Notes/3M_17773/eng/3MW_17773_0.pdf

     

    Cheers!