> Something like this can work, but you'll have a real hard
> time to measure the cooling time...


I'm thinking if it isn't better  measuring the "warming time" instead of "cooling time"..

For example, using a thermistor and a PIC with a comparator.
First step, measure the fluid temperature (same method as reading a potentiometer).
Second step, measuring the time the thermistor took to warm to a definite threshold.
If necessary (fluid flow is very variable) the internal voltage reference may be adjusted on the fly for an adapted  threshold.


regards
Marco




---------- Initial Header -----------

>From      : piclist-bounces@mit.edu
To          : piclist@mit.edu
Cc          : 
Date      : Wed, 1 Nov 2006 11:04:36 -0300
Subject : Re: [EE]Flow Sensor possibilities







> Genome wrote:
> 
> > Maybe you can use 1 LM35 temp sensor then tie a heating coil around it
> > and cover it with maybe some epoxy. Measure the initial temperature of
> > the water.. then heat the lm35 through the coil a few degrees above the
> > initial reading and then wait for the time it took for the LM35 to cool
> > back.. the time elapsed would be a good indication of flow speed
> > change.. you just have to calibrate it with some empirical
> > measurement... this way its cheap though maybe not be too accurate..
> 
> Something like this can work, but you'll have a real hard time to measure
> the cooling time. It's an inverse exp function, and it slowly smoothes down
> to 0. It's not easy to measure the exact point in time when it goes below a
> certain threshold. The error (in time) can easily become bigger than
> desired. 
> 
> Gerhard
> 
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