> expressed as 'dmax', the maximum relative voltage change, measured as an
> r.m.s. value over the worst half-cycle, starting from the zero-crossing.
While I suppose there are sophisticated oscilloscopes
that will make this measurement at the touch of a button,
I wonder how many colleagues would know how to make this
measurement without such a tool?
I don't know how to do it without an oscilloscope. A
storage oscilloscope would be nice.
The first problem is how to identify and capture that
particular half-cycle. I would first need to look at
the start-up waveform for the first 5 cycles or so to
identify the specific worst half-cycle. I would
probably put the current waveform on the other channel
and observe both traces; the maximum current should
correspond to the maximum relative voltage change.
This effort alone requires either a storage scope or a
scope camera. Then, I would want to change the sweep
speed so as to capture just the desired half-cycle and
make it full-screen (for the best resolution).
With a digital scope, this part should be easy. It is
also possible with an analog scope, but it would take
a bit of trial-and-error.
Doing the RMS requires manipulating a graphic image of
the waveform. To get the image, I would use a digital
scope with a printer, or an analog scope with a camera.
Then comes the fun of graphically determining the rms
value of the half-cycle. I would divide the half-wave
into equal increments. Then, measure the amplitude at
the center of each increment. How many increments
before entering the realm of diminishing returns?
Then, square each value, sum them, and take the square
root. Does anyone remember how to do this by hand?
Anyone still have the CRC math tables for getting the
square root?
Using such methodology and now having a value, is the
value within the resolution required by the standard?
Or, is the measurement fully dependent on a sophisticated
oscilloscope?
I often wonder whether being able to measure a
phenomenon means that we should therefore control
that phenomenon. Phenomena such as flicker and EMC
have been observable long before the advent of suitable
measuring equipment. Clearly, in the absence of the
ability to measure any phenomenon, we cannot control it.
But, do we sometimes control it because we can measure
it?
Best regards,
Rich
> From owner-emc-p...@ieee.org Wed Mar 14 13:51:14 PST 2001
> Received: from hpsdlo.sdd.hp.com (hpsdlo-sw.sdd.hp.com [15.80.36.40])
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> Received: by ruebert.ieee.org (8.9.3/8.9.3) id QAA05731; Wed, 14
> Mar 2001 16:49:31 -0500 (EST)
> Message-ID: <mp9gsaamk7r6e...@jmwa.demon.co.uk>
> Date: Wed, 14 Mar 2001 18:03:56 +0000
> To: "Wagner, John P (John)" <johnwag...@avaya.com>
> Cc: EMC-PSTC <emc-p...@ieee.org>,
> "Colgan, Chris" <chris.col...@tagmclarenaudio.com>
> From: John Woodgate <j...@jmwa.demon.co.uk>
> Subject: Re: Flicker problem
> References:
> <4203d61676d0ae468aa5cea90a891c13235...@cof110avexu4.global.avaya.com>
> In-Reply-To:
> <4203d61676d0ae468aa5cea90a891c13235...@cof110avexu4.global.avaya.com>
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>
> <4203d61676d0ae468aa5cea90a891c13235...@cof110avexu4.global.avaya.com>,
> Wagner, John P (John) <johnwag...@avaya.com> wrote:
> > I think this refers to Amendment 1of IEC 61000-3-3 published January
> 2001.
> > Apparently it has not yet been transposed into an EN.
> It was dual-voted, so it will be.
> > The amendment (at
> > least as it effects me) deals primarily with requirements and limits
> for
> > inrush current.
> >
> Well, inrush current is dealt with in the unamended standard, but
> neither that or the amendment deal with it directly. Limits are
> expressed as 'dmax', the maximum relative voltage change, measured as an
> r.m.s. value over the worst half-cycle, starting from the zero-crossing.
>
> The amendment goes into much more detail about this, and gives relaxed
> limits for some types of equipment. The main problem with inrush current
> is where there is a lot of equipment in one location, and there is a
> power outage. When the power comes back on, cumulative inrush current
> may reach many tens of times normal load current, causing protective
> devices to operate and restore the 'outage'! In some cases, protective
> equipment has been damaged.
> --
> Regards, John Woodgate, OOO - Own Opinions Only. Phone +44 (0)1268 747839
> Fax +44 (0)1268 777124. http://www.jmwa.demon.co.uk Foxhunters suffer from
> tallyhosis. PLEASE do not mail copies of newsgroup posts to me.
>
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