From: Joerg Hansmann (info_at_jhansmann.de)
Date: 2001-06-13 13:27:51
Hi,
----- Original Message -----
From: frans smith <f.smith_at_c...>
To: <buildcheapeeg_at_yahoogroups.com>
Sent: Thursday, January 01, 1998 2:34 AM
Subject: [buildcheapeeg] GROUNDING EEG/PC
>Hi all,
>Most PC-users are not aware of the fact that the pc does not
>uses power supply like other electronical stuff (TV, radio etc).
>The PC don''t make use of "transforming" the net-power by
>means of a transformator. In fact, pc is directly attached to the
>NET !!!!!
PCs use primary switched power supplies. That means, that
230V AC is rectified, giving ca. 325V DC on a capacitor.
The DC voltage is converted to 40kHz (and higher) AC, that
is transformed with a HF (ferrite core) transformer which
provides isolation between line voltage and the 5V/12V DC
used on the mainboard.
However unlike most radios and TVs (at least in Germany)
PCs have a connection from protection earth to mainboard
GND and all metal parts of the computer.
>Should whe not warning user of rs2332 "to ground the pc"
Protection earth is a good thing if the transformer isolation
breaks down. In this case it can save your life.
>Most PC users use there PC in a room where there is no
>grounding.
This is not true for Germany.
What countries do not use PE ? (I know of Danmark, Netherlands ?)
>In The netherlands grounding is only in the kitchen
>or badroom. Grounding the PC and thus the EEG could help
>at least to minimize the effects of accidents.
The EEG must _never_ be grounded.
In fact the EEG circuit _must_ have an isolation against all PC-signals
(including PE or GND) that can withstand ca. 6kV according to IEC601-1.
In the RS232EEG circuits this is done by the digital part, that transports
RS232-data via optoisolators and by a powersupply powered by batteries
or a DCDC converter.
>Question to Joerg,
>In electronics whe used special tranformation 220v tot 220v,
>(i don't know the englisch name for it) so as to protect the
>technician when working in for example an TV.
>could the same safety-set-up be used when working with an
>PC ?.
An isolation transformer could be used for additional safety. However
the isolation could easily be corrupted by peripheral devices like printers
or modems etc.
Regards,
Joerg
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