From: Sar Saloth (sarsaloth_at_yahoo.com)
Date: 2002-03-26 16:26:39
I have seen people use beads and not disks for breath. The beads can be
fairly small. Bulk thermistors will always be very slow. Film thermistors
may be faster, but they are still slow (so is regular breathing). Faster
yet are thermocouples (I think) and there is a disposable sensor made by
http://www.dymedix.com
that is extremely fast, even approaching the behaviour of nasal cannula
pressure sensors.
4mmx2mm is really too huge for reasonable response to breath, the beads
should be really tiny beads. They are available with good sensitivity. I
don't use such items any more so I can't remember the manufacturers.
On your circuit - if you don't want to zero out for each thermistor, you
could make the first stage DC coupled and handle a range and then AC couple
to the next gain stage. Of course, the Time constant must be pretty large,
but that would be less fussing.
Thermocouples can be made fairly small. Accuracy isn't important for your
application.
At 04:40 PM 2002-03-26 +0100, you wrote:
>Hi all,
>
>here (in the attachment) is a (LTspice-simulated) circuit for temperature
>feedback.
>Does anyone know where to get very small NTC resistors ?
>(e.g. with B about 3940K, R_25=22k)
>The one I have bought has disk shape with diameter=4mm and depth=2mm
>and is fairly slow.
>
>BTW:
>The "modEEGamp1_15c_std.brd" is built now.
>Next thing to do is performance testing.
>
>
>Regards,
>
>Joerg
>
>
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This archive was generated by hypermail 2.1.4 : 2002-07-27 12:28:43 BST