I like the idea of using cheap ICs. Can you suggest one for me to consider?
Thank you,
Peter
On Sun, Jul 7, 2013 at 7:21 AM, Jan Kandziora <j...@gmx.de> wrote:
> Am 07.07.2013 15:49, schrieb Peter Hollenbeck:
> > I don't really understand why that works,
> >
> Usually, there is air between the heater and heat sensor. This will heat
> the sensor, but only marginally as
>
> * heat conduction through air is nearly always insignificant
> * heat convection through air is insignificant if the air flow is
> neglible or laminar (small gap between the two -> laminar flow at most)
> * heat radiation is insignificant at room temperature unless your
> heatsink is something really cold (e.g. night sky)
>
> So the heat sensor will report room temperature if there's air between
> it and the heater.
>
> If there's a water drop between the heater and the sensor, heat
> conduction is about 25 times better than with air, allowing the heater
> to effectively heat the sensor. The sensor will report the higher
> temperature almost immediately.
>
>
> That's also a good method checking the presence of non-polar liquids
> like gasoline or kerosene where moisture sensors depending on electrical
> conductivity will fail.
>
> ---
>
> Another possible method working with both water and non-polar liquids is
> checking the dielectrical permittivity, same method as a capacitive
> touchscreen uses. There are really cheap ICs for that purpose out there,
> but they all have to be calibrated carefully and in your installation, I
> doubt the calibration data needed is stable enough in the long run.
>
> Kind regards
>
> Jan
>
>
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