Volume of Alarm Signal per IEC 60601-1-8

R

raymond02302

#1
hello everybody

I am newcomer here.I have one question about the alarm signal.
according to the standard,the sound pressure level is measured
with sound press level meter complying with the requirement of IEC 60651
at the location complying with ISO 3744.

If the location with ISO 3744 is a must? test on the open site without reflecting object is ok?

hope your reply?

thanks in advance!
 
Elsmar Forum Sponsor
V

vijay_840

#3
Hi Thanks for above link.

Can you Please let me know how to measure
IEC 60601-1-8: The relative sound pressure level of the harmonic components should be within 15 dB above or below amplitude at the PULSE FREQUENCY.

Best Regards,
Vijay
 

Peter Selvey

Staff member
Super Moderator
#4
Most sound level meters have a output which allows the signal to be viewed on an oscilloscope.

Most modern digital oscilloscopes have a "FFT" or "spectrum" mode which allows you to view the frequency spectrum, so you can see the frequency content of the waveform. Typical alarm sounds are very "tonal" so you should see sharp peaks for the pulse frequency and a range of harmonics. They usually show the spectrum in dB, so you just find the pulse frequency and measure everything relative to that point.

There are some tricks to make sure the frequency resolution is adequate. Also you need to trigger to get the core part of the sound pulse, and capture multiple cycles of the waveform in the time domain.

You can experiment by making a simple sound source e.g. 1kHz beep for 1s, and checking that you get a nice sharp peak at 1kHz.
 
R

RednBlack

#5
Does 60601-1-8 specify that the harmonic content must be measured using a microphone? I only ask because I had our NB test engineer ask me how to connect his oscillosope directly to the speaker terminals to perform this test on our last product. Is this test method allowed by the standard? I would have thought that the characteristics of the speaker itself and the product enclosure would strongly influence the spectral content.
 

Peter Selvey

Staff member
Super Moderator
#6
The standard requires measurement by microphone (amendment 1 also partially specifies also the position as being 1m in front).

But this is technically wrong ...

The harmonic content is heavily influenced by the point in space where the measurement is taken, due to reflections (e.g. from the floor) and also due to the physical shape of the device: it is not a point source, so even in a perfect anechoic chamber there will be interference patterns and focal points just coming from the panels of the device under test. These patterns are different for each frequency so just moving the sound level meter by a few cm can significantly change the harmonic content.

So, although the standard says measure by sound level meter, I think the NB approach to measure at the speaker is good way at least to create some repeatability in the test.

It would be good if the standard allowed this as a method, but with a tighter definition of a harmonic (e.g. +/-10dB not +/-15dB), and as long the speaker's specification shows the 3dB bandwidth includes the harmonics.
 
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