>
> Dear Group,
>
> 2.4.2 of UL1950 defines the upper current limit for Limited Current Circuits
> when the frequency is above 1kHz as 0.7mA multiplied by the frequency in
> kilohertz (up to 70mA peak). Since the limit increases (up to
> 70mA) as the frequency goes up, one can assume that the human body is less
> susceptible to higher frequencies (i.e. the limit at 1001Hz is 0.7007mA, and
> at 10kHz it is 7mA, etc.).
>
> My question arises when the waveform is not a nice, regular sine/square/etc.
> wave. I've attached an jpg illustration to make the asking of the question
> easier (if
> anyone has any problems viewing this, I'll try to put the whole question
> into words). If one assumes that one cycle is the portion denoted by the
> letter A, the frequency is 11.56kHz and the limit is 11.56 X 0.7 = 8.09mA.
> Now, if one chooses to use the part labeled B, the frequency is 47.62kHz and
> we now have a limit of 33.3mA. The current for this example is 33.8 V/ 2000
> ohm = 16.9 mA. Obviously, one interpetation results in a failing result,
> and the other a passing one. Which is correct?
>
> I must add that if one chooses the "A" waveform as the correct one,
> visualize a pure sine wave at the same frequency, and superimpose it over
> the attached waveform. There seems to be more energy (RMS wise), in the
> pure sine wave yet the limit is the same.
>
> Your comments and opinions will be appreciated.
>
> Sincerely,
>
> Frank F. Goto
> A-pex International Co., Ltd.
> 1st Engineering Department
> 248-1 Kusube-cho
> Ise-shi, Mie-ke 516-0014
> Japan
> Tel: +81-596-24-6717
> Fax:+81-596-27-5631
> [email protected]
> http://a-pex.co.jp
>
Hi Frank:
You have one answer of using a spectrum analyzer and measuring the
current at each frequency. Unfortunately, this is still difficult
and you don't know how to add up the various components.
My answer is: Measure the current using the IEC 990 network.
This network fully compensates the frequencies and their effect on
the human body. You get one number which is not multiplied by
frequency. Just use the value of current measured using the IEC
990 network and an ordinary VOM (as specified in IEC 990).
The limit value using this network is 0.5 mA rms (0.7 mA peak).
Best regards,
Rich
ps: If a waveform is not a pure sine wave, then it has harmonics
in it. Any waveform can be synthesized with sinusoid waveforms.
With regard to energy, we must also consider the voltage wave-
form. Watt = voltage x current. Joule (energy)/second = watt.
Supposedly, the body is sensitive to the peak value of the
current, not the rms value. This doesn't translate well to
energy (joules).
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Richard Nute Quality Department
Hewlett-Packard Company Product Regulations Group
San Diego Division (SDD) Tel : 619 655 3329
16399 West Bernardo Drive FAX : 619 655 4979
San Diego, California 92127 e-mail: [email protected]
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