From: Joerg Hansmann (info_at_jhansmann.de)
Date: 2001-05-17 22:08:44
Hi,
----- Original Message -----
From: JBilderback <jiva_at_humboldt1.com>
To: <buildcheapeeg_at_yahoogroups.com>
Sent: Thursday, May 17, 2001 4:39 PM
Subject: [buildcheapeeg] optocoupler isolation
> >
> > The other option would be to use the RS232 port and some optocouplers.
> > Does anybody know what isolaton voltage is common in eeg equipment ?
> > I think the brainmaster has about 160V which sounds quite low to me.
> > Does anybody know types of optocouplers normally used in medical equipment ?
> > Another idea is to built an optocoupler by ourselves using phototransistors and
> > IR LEDs. That would probably also result in a very high isolation voltage.
> >
>
> the til111 used in Bernd Porr's preamp design posted by john anand specs
> at 1500v.
>
> http://www.isocomoptocouplers.com/isocom/til111.htm
1500V is _not_ sufficient if we want a IEC601-1 certification.
3750Vrms or 5300Vpeak (or better 5500Vpeak) (@50/60Hz) seems to be the
standard for EEGs.
e.g.:
www.sensoriuminc.com/manual.pdf
"EPA-6 Electro-Physiology
Amplifier
Reference Manual
...
Isolation: 3750 Vrms, 60Hz,continuous
...
The low pass filter stage is followed by
an isolation amplifier. The isolation element
consists of a LED emitter coupled through a
servo circuit with a photodiode. A second
photodiode detects the amplitude of light.
Optical isolation..."
In this professional device the isolation is done with
discrete IR-emitters and photodiodes. The reason
for using a discrete solution is probably, that
integrated optoisolators for the required voltage
are not available.
Regards,
Joerg
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