From: Joerg Hansmann (info_at_jhansmann.de)
Date: 2002-01-11 20:37:33
Hi Jim, Andreas, etc.
----- Original Message -----
From: Jim Meissner <jpmeissner_at_mindspring.com>
To: <buildcheapeeg_at_yahoogroups.com>
Sent: Friday, January 11, 2002 8:31 AM
Subject: Re: [buildcheapeeg] Re: Input protection
>Dear Joerg:
>
>> Can you please quote the mail where I have said this ?
>> I can not really remember that I have said that opto-isolation is
>> trivial.
>
>> The reason why it may sound like we've ignored mains isolation is
>> because that it is so easy to do.
>This is an excerpt from sleeper75se Jan 07, 2002 3:28 am
>Sorry Joerg, my mistake, it was Andreas who said that!
>
>> However this implies battery operation (that I personally do not like)
>>
>
> I am very glad that you made this statement, so that I now know where you are coming from.
> Thanks for making that clear.
What I have said was in no way imperative ;-)
My likings or dislikings for a certain approach
are unimportant if patient safety would be compromised
or the required norm (IEC601-1 or IEC whatsoever for non-medical devices)
is not complied or the complience would demand too
expensive and/or complicated solutions.
>Now since you are the chief engineer and you state that there
>"shall be no batteries", I will work with you.
Otherwise not ? ;-)
> It is possible to get high isolation transformers. They are not cheap.
Ok. You said (in another mail) that you have much experience with high
isolation transformers:
What would be the price for a ferrite donut core transformer
isolating 6kV according to IEC601-1 ?
(hopefully this translation is understandable, in german it would
be "Ferrit-Ringkern-Trafo", see picture "DCDC_tmv-en.jpg" like it looks
in small)
Operating frequency should be in the 100kHz range or so.
Together with a switching regulator IC that would give a
DCDC converter built with discrete components.
And what would be the possible error mechanisms that lead to isolation
failure in such a ferrite core transformer ?
>All of the inexpensive brain monitors that I am aware of are battery operated.
ACK.
+++++++++++++++++++++++++++++++++++++++++++++++++
>> I have put emphasis on protecting the patient from input stage failures
>> in my last postings.
>> Obviously you you do not see any danger for a patient getting between
>> V+ and V- .
>
> I am very safety conscious. I was sharing my experience of getting zapped by 60 Hz
> capacitive currents.
And your 4x 4N35 based isolator has prevented this reliably.
(Viso=3550V DC ?, AC rms ? )
> I never had an input amp fail after I added the protection
> circuit.
...On the other hand Vladimir has got zapped by low voltage DC...
++++++++++++++++++++++++++++++++++++++++++++++++++++++++
[Andreas optical RS232 Receiver]
>>I looked at your receiver design. My main concern is that the base of Q2 is
>>left floating and leakage current and noise
>> Has Joerg looked at this design?
>I can see quite a few problems with the "simple" design. If you saturate Q2 without a turn
>off drive you could have usec of delay depending.....That is why I asked you, Joerg to look
>at it!
Ok. I have spent some time to simulate Andreas's circuit and I am amazed
at the unbelievable temperature independence !
With the 10k however you suggested from B to E of Q1 it gets
rather temperature dependent and the current threshold is completely
out of range.
>I would feel more comfortable with a "proven" design like QSE158 commercial part.
I will have a look at it.
>But if this simple design works then great!
The only flaw I can see at the moment is, that it will probably not work
with a standard terminal program, because RTS DTR will not have the needed polarity.
(RTS will be -12 V initially).
Regards,
Joerg
This archive was generated by hypermail 2.1.4 : 2002-07-27 12:28:36 BST