I saw a variation of this on the 'net. It uses the filament of a #47
light bulb (with the glass carefully broken and removed) as a
temperature sensor. A constant current source heats up the filament and
a comparator measures the resistance across it.
The filament resistance drops with cool airflow and rises without any
airflow, causing the comparator to trip.
http://www.aaroncake.net/circuits/airflow.asp
It's pretty ingenious but I might just go with the microswitch-vane
method to keep it simple.
Thanks for all the suggestions.
73 de Hugh VA3TO
www.va3to.com
>Date: Thu, 12 Apr 2007 08:03:27 +0100
>From: Steve Thompson <g8gsq@eltac.co.uk>
>Subject: Re: [Amps] 8877 blower requirement -airflow switch
>To: amps@contesting.com
>Message-ID: <461DD9BF.8090406@eltac.co.uk>
>Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
>I've used a ptc thermistor - the sort that changes from low to high
>resistance abruptly at a set temperature. Run some current through it so
>it self heats, the airflow cools it so it stays below the trip point.
>The thermistor is about the size of a match head, so the mechanics are easy.
>
>Many years ago a friend tried a variation on this - putting the sensor
>in the output air so it tripped if the air got too hot, whether that was
>from lack of flow or excess dissipation.
>
>Steve
>
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|