The design depends on there being a difference between the air temperature
and the water temperature, which may or may not be the case in general. If
there is any risk of them being at the same temperature you could address
the problem by attaching a heater resistor to each sensor. Then the water
would cool the resistor more than the air would so you would be measuring
the difference in the specific heat of the media more than the temperature.
Wouldn't have to be much heat to work, I wouldn't think.
> ----- Original Message ----
> From: Scott <[EMAIL PROTECTED]>
> To: [email protected]
> Sent: Sunday, September 21, 2008 8:29:12 AM
> Subject: [Owfs-developers] Thoughs on a temp sensor based liquid level
> monitor?
>
> I use OWFS to monitor various parameters of my saltwater aquarium. One
> of the biggest things I'd like to monitor is the approximate height of
> the water in my sump to know when additional water needs to be added,
> etc. It also gets a little bit interesting because I have baffles in
> my sump and filter floss between them to filter particulate matter as it
> goes through the baffles. As the filter floss gets plugged with debris,
> it restricts the water flow creating a difference in heights on each
> side of the baffle. I can't just monitor one side or the other and
> assume the water level because the two levels may be identical (zero
> restriction with newly replaced filter) or up to ~8 inches different
> (plugged filter in desperate need of replacement). I need to know the
> level on both sides and average it to get a true standard volume baseline.
>
> I've thought about using an array of float switches and a GPIO chip to
> monitor which switches are open/closed to deduce the water level, but
> there's several reasons why I haven't gone that route: reliability,
> space, and resolution to name a few. The other day I came up with an
> alternative - use an array of temp sensors to monitor the differential
> temperature between the air and water to approximate the water level. I
> already track both those temps, giving me a sort of calibration standard
> for comparison. As long as the temp sensors are spaced at a known
> distance, and the starting height is known, I just write a script to
> read and compare all the temps. The water height should be between the
> two adjacent sensors with temps matching the known air/water temps. The
> resolution of the array would be determined by the distance between and
> number of temp sensors in it.
>
> I'm I computer guy, but definitely no EE so I thought I'd bounce this
> design off the list to see if there's anything I should add to the
> circuits I'm not thinking of. I'd probably (since I already have a slew
> of them) use DS18B20 chips all wired in parallel with a network branch
> (DS2409) to separate the two sides and logically segregate the arrays
> from the general temp probe population. Each array of temp probes would
> be wired up and then completely encased in epoxy to protect it from the
> water. I've already done this with TO-92 form factor temp sensors and
> it works quite well.
>
> Here's a diagram I put together with my design. Let me know if anyone
> has thoughts, etc on it:
>
> http://bytality.com/offsite/OWTemp_depth_sensor.png
>
> -Scott
>
>
>
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