From: Doug Sutherland (wearable_at_earthlink.net)
Date: 2001-12-18 06:25:28
Hi Yaniv,
> everybody says that the optocouplers are in compliance to
> the iec601 standard for medical safety. <snip>
> if badly designed ( for example bad layout ) it could not
> be really isolated. does bad assembly can affect this?
I think it would have to be a really big mistake in layout
to be not isolated. Same goes for assembly.
> what are the ways to verify the total design is safe from
> this point (high voltage from pc)?
I have no idea what the regulations are, but the sensors
mag article I referred to said that manufacturers of bio
amplifiers, especially EEG and ECG, provide up to 10^12
ohms isolation.
http://www.sensorsmag.com/articles/0199/iso0199/main.shtml
I don't think we can achieve that with opto-couplers, but
then I don't know that it's really necessary either. I am
personally comfortable with using simple opto-couplers on
my body, but then I'm not planning on asking anyone else
to do the same. Here's what I would like to know: what
kind of opto-couplers are inside brainmaster, waverider,
procomp, etc? I wish I still had my commerical brainmaster
(I sold it) or I would take a look.
> what are the costs asociated?
It seems that the isolators that provide 10^12 ohms of
isolation are expensive, like $100. But then the simple
phototransistor method or IR would achieve the same for
a lot less money. The other issue is AC/DC ... I wonder
if there are regulations on these adapters. Does that
TMA0505S DC/DC converted provide safety if something
goes wrong with an AC/DC adapter?
> are they are needed for each device going out to market?
> or not, just for the prototype?
Good question. Again, it would be interesting to look
inside some commercial units and see what's in there.
I think brainmaster always runs on batteries, even when
plugged into AC, but I'm not sure how they did that.
> please assume, like i myself doing here, that this
> safety issue should be 100% for each device on market!
> this is a very very critical point, we don't want
> somebdoy to die !!!
Someone mentioned that nobody has ever been electrocuted
by an EEG, arguing that opto-isolation was not needed,
but I don't think electrocution is the only threat.
According to that sensors mag article "A normally harmless
60 Hz current can cause cardiac arrest under certain
circumstances". It seems to me that the only way to
guarantee protection is to run on DC (batteries) all
the time. But that implies built-in charging to be a
viable solution. People won't want to swap batteries.
I know that brainmaster is usable while plugged into
AC and charging, the question is: what safety measures
are there to prevent injury if something were to go
wrong with the AC/DC adapter?
-- Doug
This archive was generated by hypermail 2.1.4 : 2002-07-27 12:28:35 BST