From: Jim Meissner (jpmeissner_at_mindspring.com)
Date: 2002-01-11 22:20:15
Dear Joerg:
> Now since you are the chief engineer and you state that there
> "shall be no batteries", I will work with you.
>
> Otherwise not ? ;-)
I think you may have misunderstood my statement. As chief engineer you must provide leadership and set a direction. If you set up rules that state "NO batteries" then I will try to be helpful in that direction. My purpose on this list is to be of help.
> And what would be the possible error mechanisms that lead to isolation
> failure in such a ferrite core transformer ?
A normal transformer design calls for tight coupling between primary and secondary. At high frequencies this is even more important so usually there is very little spacing between windings. The picture you show of your converter transformer looks very, very good. The main failure mode would be arcing through from primary winding to core and core to the secondary winding. As more and more spacing is used for safety purposes the efficiency drops. I have used transformers that had more than an inch air spacing betweenprimary and secondary, but that was with 60 Hz. It used one torroid and aseparate EI lamination at 90 degrees to the torroid. The name of the company may have been Isotech, I am not sure. I know that there are 60 Hz triple shielded medical grade isolation transformers available that will meet the 10 microamp leakage spec.
> What would be the price for a ferrite donut core transformer
> isolating 6kV according to IEC601-1 ?
I am sorry, but I cannot be much help to you with this. It was too many years ago.
+++++++++++++++++++++++++
> And your 4x 4N35 based isolator has prevented this reliably.
> (Viso=3550V DC ?, AC rms ? )
I was sharing what worked for me, not dictating what you should do. If hadto build this again, I would like the fiber optic or spaced transmitter-receiver design as Andreas has suggested.
I am really impressed with the simulation tools that you have available. In my day you had to build something and test it and put it in the environmental chamber to do temperature runs.
I started designing with germanium transistors. I guess transistors have come a long way where you don't have to worry about leakage current.
Juergen P. (Jim) Meissner
Check out my Website at www.MeissnerResearch.com
Read about the benefits of the Brain State Synchronizer sounds for improving your life and health.
----- Original Message -----
From: Joerg Hansmann
To: buildcheapeeg_at_yahoogroups.com
Sent: Friday, January 11, 2002 3:37 PM
Subject: Re: [buildcheapeeg] Re: Input protection
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 askedyou, 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
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This archive was generated by hypermail 2.1.4 : 2002-07-27 12:28:36 BST