From: Joerg Hansmann (info_at_jhansmann.de)
Date: 2002-03-27 11:30:43
Hi Andreas, Sar Saloth ,scottelofson
----- Original Message -----
From: sleeper75se <sleeper75se_at_yahoo.se>
To: <buildcheapeeg_at_yahoogroups.com>
Sent: Tuesday, March 26, 2002 5:29 PM
Subject: [buildcheapeeg] Re: temperature feedback
...
> Hi Joerg,
> there seems to be a problem with the .asc file. It is almost empty...
It is really quite short: 3282 bytes.
I have zipped it and put it into the attachment again.
...
> RS Components (and others I'm sure) has NTC resistors in 0805
> packages. Small enough? :-) Time constant is 4 seconds, B=4100, R =
> 22k.
That looks nice :-)
> They also sell bead-shaped resistance-temperature curve matched
> NTC's that are easier to use, time constant is 10 seconds, 2.4mm in
> diameter.
----- Original Message -----
From: Sar Saloth <sarsaloth_at_yahoo.com>
To: <buildcheapeeg_at_yahoogroups.com>
Sent: Tuesday, March 26, 2002 5:26 PM
Subject: Re: [buildcheapeeg] temperature feedback
> I have seen people use beads and not disks for breath.
I really intended temperature feedback of the hands.
> 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)
Only two thin wires made from differnet materials should be
very fast.
However IIRR the thermo voltage per 1 Kelvin difference between
the hot and the cold side gives somewhat in the range of
10uV. In order to resolve 1/1000 K, the amplifier would have to resolve
10nV what is not much compared to offset drift and noise.
> 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.
They use pyroelectric film sensors. However they sell only to physicans.
> 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.
For monitoring air-flow this is a good idea.
>
> Thermocouples can be made fairly small. Accuracy isn't important for your
> application.
> ...
----- Original Message -----
From: scottelofson <scottelofson_at_yahoo.com>
To: <buildcheapeeg_at_yahoogroups.com>
Sent: Wednesday, March 27, 2002 12:16 AM
Subject: [buildcheapeeg] Re: temperature feedback
> --- In buildcheapeeg_at_yahoogroups.com, "Joerg Hansmann" <info_at_jhansmann.de> wrote:
> [...]
> > Does anyone know where to get very small NTC resistors ?
>
> I like YSI Temperature [www.ysi.com/temperature.htm].
These here could be very useful:
YSI 081 Typical Time Constant: 1.1 seconds
YSI 082 Typical Time Constant: 0.3 seconds
Any idea what these sensors cost ? I did not find any
price information.
Regards,
Joerg
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