Google Answers Logo
View Question
 
Q: measuring temperature and airflow with heated thermistor ( No Answer,   2 Comments )
Question  
Subject: measuring temperature and airflow with heated thermistor
Category: Science
Asked by: eur-ga
List Price: $5.00
Posted: 22 Jul 2002 02:17 PDT
Expires: 21 Aug 2002 02:17 PDT
Question ID: 43651
LS

I need schematics and calculations for measuring air flow in the 0.1
.. 3m/s range by heating a thermistor. I need the temperature too,
accurate to 0.1C. Temp range: -25C to 50C (-13 to 122F)

The space to measure this is in an air channel 13 mm wide (1/2") and
50 mm high (2").

I can spend 1W to do this, preferably not more than 100 ms or so. I
have a PIC16F877 to do the measurements and calculations. I need to
measure 4 air speeds and temperatures and have 4 analog inputs (10
bit) available.
Answer  
There is no answer at this time.

Comments  
Subject: Resources
From: ulu-ga on 22 Jul 2002 08:16 PDT
 
This paper would probably help.  It lists the formulas needed.
http://www.agrsci.dk/jbt/gqz/pub/rv96-2vm.pdf
Subject: Re: measuring temperature and airflow with heated thermistor
From: rotrayeclipse-ga on 01 Aug 2002 16:23 PDT
 
1) Your accuracy requiremnts combined with the wide ranges to be
covered make this an ambitious specification
2) Measuring temperature will be straightforward-all you need to do is
to measure the thermistor's resistance using a bridge. Time response
may be a problem at or near your lowest flow rates since the body of
the thermistor will  take longer then to reach equilibrium with the
air-stream temperature
3) Measuring air flow will need  a further two thermistors both heated
by the same current-one of these to be placed in the air stream whose
velocity is to be measured and the other in ambient air (this second
one is to compensate for changes in ambient air temperature). A bridge
will measure how much cooler is the thermistor that is in the air
stream and finally in-situ calibration will be needed to convert that
information into air flow rates.
4) A good supplier of thermistors will be happy to give you diagrams
and recommendations to interface the above arrangemnt to your computer
system

Important Disclaimer: Answers and comments provided on Google Answers are general information, and are not intended to substitute for informed professional medical, psychiatric, psychological, tax, legal, investment, accounting, or other professional advice. Google does not endorse, and expressly disclaims liability for any product, manufacturer, distributor, service or service provider mentioned or any opinion expressed in answers or comments. Please read carefully the Google Answers Terms of Service.

If you feel that you have found inappropriate content, please let us know by emailing us at answers-support@google.com with the question ID listed above. Thank you.
Search Google Answers for
Google Answers  


Google Home - Answers FAQ - Terms of Service - Privacy Policy