Could I use leaf wetness sensors such as this:
http://www.hobby-boards.com/store/products/Leaf-Wetness-Sensor.html
?
Peter
On Sun, Jul 7, 2013 at 8:00 AM, Peter Hollenbeck <[email protected]> wrote:
> 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 <[email protected]> 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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