Error in meter characteristics

Discussion in 'Feedback and Suggestions' started by The Electrician, Mar 14, 2013.

  1. The Electrician

    Thread Starter AAC Fanatic!

    Oct 9, 2007
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    On this page:

    http://www.allaboutcircuits.com/vol_2/chpt_12/1.html

    about halfway down the page is found:

    "None of the meter movement technologies so far discussed inherently measure the RMS value of an AC quantity. Meter movements relying on the motion of a mechanical needle (“rectified” D'Arsonval, iron-vane, and electrostatic) all tend to mechanically average the instantaneous values into an overall average value for the waveform. "

    Iron-vane and electrostatic meters do not average instantaneous values. They are inherently RMS responding. See:

    http://www.answerbag.com/q_view/688559

    http://www.eltime.co.uk/product.php/1/Moving Iron Meters.html
     
  2. Georacer

    Moderator

    Nov 25, 2009
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    It's impromptu advertizing and/or reconnaissance for spam. Delete or leave moderated.

    EDIT: Post meant for another forum. Please disregard.
     
    Last edited: Mar 15, 2013
  3. The Electrician

    Thread Starter AAC Fanatic!

    Oct 9, 2007
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    I'm not sure what you mean. Even though the second link shows a commercial product, the reason I linked to it is because it informs the reader that iron vane meters measure RMS, which is the error in the eBook I'm trying to get corrected. That's all.
     
  4. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    Seems a bit stiff giving The Electrician a slap over the wrist for an innocuous reference to something which supports his assertion.

    What about the following as an example of advertising one's own wares ...

    http://forum.allaboutcircuits.com/showthread.php?t=82392

    Not that I would begrudge such revelation of one's [KL7AJ's] excellence in contributing something of worth to the art. I'm tempted to obtain a copy.

    However, moderators should demonstrate consistency. Perhaps this is an oversight.
     
  5. Georacer

    Moderator

    Nov 25, 2009
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    I 'm very sorry about this. This was meant to be a comment on the Mods forum. Sorry about upsetting you all.
     
  6. The Electrician

    Thread Starter AAC Fanatic!

    Oct 9, 2007
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    The error I pointed out in post #1 still exists in the E-Book.
     
  7. Wendy

    Moderator

    Mar 24, 2008
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    Generally we do a clean up once or twice a year. Christmas is still coming.
     
  8. WBahn

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    Mar 31, 2012
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    The RMS responding mechanical meters still mechanically average the instantaneous waveforms they are responding to, it's just that they are designed in such a way that the waveform they are responding to is the square of the current, not the current. In the typical D'Arsonval meter movement, what is being averaged is the product of the current and a constant magnetic field. In something like a moving iron meter, the magnetic field is simply generated by the current being measured, and hence the magnetic field is proportional to the current and, thus, the force on the needle is proportional to the square of the current. The "square root" is performed by just scaling the faceplate labeling appropriately, which is why these meters tend to have rather nonlinear scales (athough many are designed to result in a roughly linear response over a certain range of interest.
     
  9. The Electrician

    Thread Starter AAC Fanatic!

    Oct 9, 2007
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    Do you think that the E-Book text:

    "None of the meter movement technologies so far discussed inherently measure the RMS value of an AC quantity. Meter movements relying on the motion of a mechanical needle (“rectified” D'Arsonval, iron-vane, and electrostatic) all tend to mechanically average the instantaneous values into an overall average value for the waveform. "

    should left as it is?
     
  10. WBahn

    Moderator

    Mar 31, 2012
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    No. The first sentence is incorrect and the second sentence is misleading even if it can be argued that it can also be interpretted in a way that is arguably strictly correct.
     
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