>-----Original Message-----
>From: pic microcontroller discussion list
>[mailto:PICLIST@MITVMA.MIT.EDU] On Behalf Of Gerhard Fiedler
>Sent: 21 August 2004 13:42
>To: PICLIST@MITVMA.MIT.EDU
>Subject: Re: ] Flow sensing (fwd)
>
>
>> This is why you have two sensors, one exposed to the moving
>water and
>> one to measure the temperature of the water, but not actually within
>> the water (e.g. on the outside of a metal pipe).  You then have a
>> feedback circuit the attempts to keep a constant temperature
>> difference between them by heating the sensor exposed to the moving
>> water.
>
>Most of the time you have both sensors in the medium but heat
>only one. Sensors on the outside of the pipe are usually not
>so good, as the temperature they measure depends also a lot on
>the temperature around the pipe. Changing the ambient
>temperature would then give you some "phantom flow" :)

The temperature on the outside of a thinwall metal pipe would be barely
influenced by ambient temperature, unless the water flow had stopped, in
which case the water temperature will also be affected.

Mike

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