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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. |
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There is no answer at this time. |
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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 |
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