Sandaysoft

BigDave:

The sensor that you recommend lies on the conductivity of the waters being sensed, since the user wants a "Early Alert" after a potential flooding can occur, the sensor must have very high reliability.

If the waters are contaminated with debris or something else the sensor maybe not be able to detect the waters, hence opening the possibility of flooding.

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Marco-Luis
YV1HX
Cabimas, Zulia, Venezuela
http://www.twitter.com/meteoven

This is true, and should indeed be a consideration.

The sensitivity of the sensor however is quite high. I understand that it relies on some form of comparator, meaning that even a highly resistive connection between the two terminals would trigger the relay. In fact, on reflection, I think that some means to prevent rainwater from above from bridging the contacts might be necessary.

On further thought though, I'm not too sure how well the contacts of this sensor type would hold up to permanent immersion in water. As far as I am aware, they're not stainless steel so will probably corrode (but I don't know that for a fact). These sensors are really designed to be "normally dry" as far as I am aware, but I'm sure that versions exist which are designed to be permanently (or nearly permanently) immersed.

Not sure that contamination in the water course would prevent a device which works by conductivity from working though. What particular contaminants did you have in mind which might prevent it from working?

I agree with you.



The sensor body can be made from water resistant plastic or polymer, see below.



There is sensors available to be permanently water immersed, like this:





This sensor was spare from a project that I´m was partner a few years ago, this sensor particularly, was installed inside a telecom cabinet, about two centimeters near the floor, then connected to the on cabinet remote alarm system, to give us an alarm in the Network Control Center in case of cabinet flooding. (We have also other alarms: fire, open doors, power systems fail, etc..)



In a natural water course there is a plenty of "contaminants" can gave problems to a contact sensor: algae, fishes, floating leaves...even stones..to pinpoint a few..

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Marco-Luis
YV1HX
Cabimas, Zulia, Venezuela
http://www.twitter.com/meteoven

Thanks for your reply.

Of course you are right, a natural watercourse will contain all sorts of contaminants, and I suspect that algae would be the worst one in this case as it would tend to grow in such a way as to continue to short the contacts after the water level recedes, at least until the algae dries out.

What mechanism does the sensor type you show in your post use to determine that water is present? It rather looks like the type used for Air-Con plant condensation drip trays, whereby it has a floating part inside which floats up and triggers a reed switch. If so, presumably this too could be fouled by algae, fish etc?

Is there any reason why some sort of float/arm/potentiometer arrangement could not be employed? Apart from the need to weatherproof the actual potentiometer, and perhaps some sort of backup "limit" sensor (maybe a contact based one, as it would only get wet in a flood situation) I think this mechanism could have real 'potential' (no pun intended!)

What are your thoughts?

This sensor doesn't have any moving parts for detecting the waters, works from a optical principle, please note the small round window in the image below.



The sensor can work fully submerged, in fact, the sensor body is made from die cast.



Reliability....



The moving arm devices has been used for years in tanks facilities...Years ago, they was mature enough to be used in some hazardous facilities (gasoline, fuel oil, petroleum, etc...), but now the state-of-art is mature enough to bring us ultrasonic (and even radar!) based sensors at relatively low cost and a superior reliability than any comparable mechanical based device.

_________________
Marco-Luis
YV1HX
Cabimas, Zulia, Venezuela
http://www.twitter.com/meteoven

Yup personally here like the ultrasonic means. That said I have had a project on the back burner and will probably finish it soon. I have to soften my water here with a water softner. That said I never really pay attention to the salt levels in the container which keeps the salt for the softner. Its kind of a pain.

So will be doing the folowing (which I believe is very similiar to the above mentioned endeavor).

http://cocoontech.com/forums/topic/4666-how-to-measure-salt-level-in-your-water-softener/page__hl__%2Bwater+%2Bsoftner+%2Blevels

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- Pete

http://longboatkey.golffan.us/ - Fine Offset

http://lockport.golffan.us/ - Davis Vantage Vue