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Thread: 0-5V Air Flow Sensor
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face BY : Montaigne, Mike - NRC email (remove spam text)



       Hi:

       I am using a PIC for a simple gas flow check on an air sampler.  My
crude first run at this was to use a Radio Shack 271-110A 10K@25 degrees C
Thermistor, 5 min epoxied to a 82 ohm resistor which was connected to 5
volts.  The thermistor was connected in series with a 5K resistor to 5V and
the middle junction point connected to a meter (eventually a a/d ip on a
PIC).  I got 1.72V (a/d 88) at 25C room temp, 3.28V (a/d 168) with no
airflow (63C), and 2.78V (a/d 142) with some airflow (50C).  The a/d numbers
are what I figure I'll get in my PIC with 256 bit resolution.

       So my questions............

       I can't find a cheap airflow sensor.  A pressure switch won't work
as it could still read OK if there was a blockage.  This sensor would cost
me about $3. and I need 20 or so.

       My airflow is 20L/min and I have not tested at that exact airflow
yet.  I'm hoping there will be enough cooling to give me a significant
change in my a/d reading.  How many counts change between no airflow and
20l/min should I attempt to design for to give me reliable operation.  Is
there another approach I should be looking at?

       I know there are lots of gurus out there who are a lot smarter at
this than I am.  I'm just trying a seat of the pants approach and this is
where I am at, after my first run at this.

       tks

       Mike Montaigne
       Montaigne Audio
       Pembroke Ontario
       spammontaigmRemoveMEspamspam_OUTnrtco.net

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