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'[OT} Water level Sensor for PIC project'
2000\01\18@231354 by Alan Williamson

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Hi,

Slightly off topic ...  I am looking for a sensor that I can
attach to the outside of my Spa that will give me a signal I can
input to my PIC based Spa controller.  I have heard of
'capacitive' or perhaps 'mass' based units but cannot locate them.

Any pointers or ideas would be appreciated.

thanks,   Alan

2000\01\19@102500 by jamesnewton

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I think you want
http://www.qprox.com
see:
204.210.50.240/techref/default.asp?url=io\sensor\h2o.htm
and
http://204.210.50.240/techref/default.asp?url=io\sensors.htm

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James Newton spam_OUTjamesnewtonTakeThisOuTspamgeocities.com 1-619-652-0593
http://techref.homepage.com The Technical Details Site.
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{Original Message removed}

2000\01\19@170700 by p.cousens

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Alan Williamson wrote:
> Slightly off topic ...  I am looking for a sensor that I can
> attach to the outside of my Spa that will give me a signal I can
> input to my PIC based Spa controller.  I have heard of
> 'capacitive' or perhaps 'mass' based units but cannot locate them.

Omron E2K-C25ME1
10 to 40 volts DC, NO NPN output, ajustable sensetivity via trimmer on
rear,
About #90.

I have used them to replace faulty sensors on a Spa
as long as the baths not metal it will work
--
Peter Cousens
email: .....p.cousensKILLspamspam@spam@cwcom.net  or  p.cousensspamKILLspamvirgin.net
smail: 48, Yarmouth Cresent, London, N179PQ, England.

2000\01\20@051931 by Craig Peacock

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Alan,

> Slightly off topic ...  I am looking for a sensor that I can
> attach to the outside of my Spa that will give me a signal I can
> input to my PIC based Spa controller.  I have heard of
> 'capacitive' or perhaps 'mass' based units but cannot locate them.
>
> Any pointers or ideas would be appreciated.

A solution is only limited to your imagination.

Normally you don't want to put anything around the outside of the spa,
as it gets dirty, looks terrible and normally doesn't perform very good.
As soon as the blower comes on, results go haywire with all the waves
and air pockets. Put a little to much bromine in the water, and it goes
throthy. Sensors have a hard time dealing with this, and life
expectancy and reliability isn't all that flash.

What you want to do is tap a little capillary tube in somewhere and
bring it up under the shell. This will work on gravity, and provided you
use a fine opening will not fluctuate very much. However if you do use a
too fine opening it gets clogged!

Then what you do under the shell is totally up to you. Capacitive
Sensors don't tend to go to well with the chemicals. You are really
seeking a totally sealed control system. You can use a float sensor
(Farnell) which gives a digital output. These are a sensor with a magnet
in one end and a reed switch. Place this in a tube (Storm Water Pipe
capped at one end) and connect up the capillary tube. Depending upon how
many levels you want you could add several of them. You could try a
analog type float arrangement but once again they are unreliable and
will normally stick at one level or rust away totally.

These level sensors can set you back a small fortune, and take up a
little real estate under your shell. Another option is a small pipe
with a magnetic float in the top. This will float up and down based
on water level and magnetic sensors / hall effect devices can be used
to pick up it's location. Taking this further, use clear pipe and use
light sensors to pick up where the "marble" float is. These rely on
just a bit of flexible pipe and are relatively inexpensive. The clear
pipe will age over time and generally isn't that reliable.

If you want an analog output try connecting up an differential pressure
sensor. However the membranes in these sensors normally get clogged,
thus
keep it above water level. Then if this isn't high tech enough, try
ultrasonic down a tube of water and measure the time taken for the
signal to bounce back. I can remember a rain water tank sensor done
this way, however once again the sensor at the top of the tube
although above water level, collects quite a bit of humidity and
moisture. The rain water gauge used a small globe at the top to
combat this. How well is another thing.

Anything I've mentioned about can be sought from Farnell or your
local hardware & electronics store. My perference is first, with a
sealed Float Sensor and StormWater Pipe. Very Reliable and you
normally only want a maximum and minimum limit. Mind you these
limits change quite a bit with a few people aboard.

A word of advice with your PIC and Sensors. Try to make it as least
acceptable to noise as you can. I had a comercial spa controller (Not
mine!) which everytime there was lightning in the area, or a small hicup
in the power supply, the two pumps and blower would turn on full speed.
Great while your sleeping at night and really annoys the neighbours
when you are not home during the day!

Regards,

Craig Peacock

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