Water level Sensor

Hi Guys.
I am shortly going for a project of automatic motor control
(i.e. always top-up the water in the roof-top tank by pumping water from underground reserve)

Just for the fun of it, I would like to also display (maybe in a line of LEDs) the % of water remaining. But its not absolutely necessary

I need to have a sensor that senses the level of water.

In my last attempt at the project using just relays and transistors, I diped two probes of wire and used Transistor amplifier, but the wires would soon corrode (bad water here) and I often got false triggering due to high humidiy. Pherhaps I made the amplifiers badly!

Now, since I am PICMICRO, I am eager to give a uC twist.

The simple way, use a float switch and avoid the corrosion. Even circuits designed to use AC on the probes to avoid corrosion get corrosion. Using a few mechanical float switches will work fine. When tank drops to a set level, fill tank to another preset level.

The fancy way, use a float ganged mechanically to a pot and let the pot drive an LM3914 dot/bar display.

If you are entering a love affair with the PIC then let the pot drive the analog input to a PIC. That or embed a series of magnetic reed switches in a tube with a floating magnet in a donut. As the magnet travels up and down the tube it can provide a digital input to pins on the PIC.

Use your imagination.

Ron

If you can salvage a gas tank float from a junk car, that might work. They typically have a variable resistance output corresponding to the float position.

Might be a bit overkill but you can also use a pressure transducer to measure fluid level. This appnote gives some info' on it.

https://www.electro-tech-online.com/custompdfs/2011/05/AN1516.pdf

Some washing machines have a good water level sensor that you could use like the Fisher and Paykle which i had a fiddle with recently.

Brief post here......................

**broken link removed**

Otherwise you can get off the shelf pressure sensors that can read the hydrostatic pressure of a column of fluid.

Pete.

Use a ring magnet from a speaker with a foam float. Use a glass tube with reed switches to detect the 3 levels.

I was thinking of some electronic solution such as maybe IR range finder or such . The reason is I have poor hands at doing mechanical things like fixing float sitches or managing to 'gang' float to a Pot. (;

Also, I am pretty surprised to learn that there can be no corrosion free sensor solution that employes directly the waters' conductivity?

geko said:

Might be a bit overkill but you can also use a pressure transducer to measure fluid level. This appnote gives some info' on it.

https://www.electro-tech-online.com/custompdfs/2011/05/AN1516-1.pdf

Click to expand...

Kind of a tangent but I just have to say that this is a very interesting app note. I was looking into using a sensor from this family a while ago for a liquid level sensing application. So, I wrote Freescale's tech support to ask a few questions and this is what they told me:

Unfortunately, we do not recommend all our sensor (MPXV2010DP) to become in
direct contact with any kind of liquid substance which would damage the gel and
cause the sensor to become out of specification.

The strain gauge and the electronic circuitry for calibration and compensation
are protected by a nitride layer but the aluminum bonding pads which provide
electrical connections between the leadframe and the gauge are not protected, in
order to make the bonding feasible. The complete die is also protected with a
silicone gel. This gel is not fully hermetic, although we use much better gel
for our newer types of pressure sensors, water or any other fluid can penetrate
the gel and can reach the die. When the sensor die is in contact with water
e.g., oxydoreduction reactions between Al/Al3+ and water start as soon as the
sensor is biased. After some working hours, or maybe days, the aluminum pad of
the supply pin is definitely destroyed, so that an open circuit on the Vcc pin
occurs. This is an aluminum corrosion phenomena. But the corrosion phenomena is
stopped when the sensor supply voltage is switched off. There are also some
other failure causes like galvanic corrosion, but the Mean Time To Failure
(MTTF) due to these other causes much longer than the MTTF caused by
electrocorrosion of the Vcc pad. Therefore electrocorrosion is the major failure
cause, and they are permanent.

Click to expand...

The sensor I was looking at isn't the exact one in the app note but it's from the same family and I would expect, has the same limitations. Granted, in the app note the pressure sensor is exposed to air pressure but that's air trapped inside a tube with water at the bottom. I'd think that trapped air would be very humid and water would likely condense inside the sensor at some point. It seems weird that Freescale wrote an app note using their sensor this way when it seems to me this family of sensors is only suited for dry environments. Oh well, maybe I'm just too cautious.

I ended up going with a **broken link removed** because of what tech support told me. Unfortunately, they were more expensive. Just my $.02 if you decide to go the pressure sensing route. The app note does have some good info. I'd just use a different sensor though.

For a float device, how about an oil tank float (IIRC ~$45 at Home Depot). It will translate a large height/volume swing into a smaller height swing. From there you could adapt it to many pickups (pot, IR, hall effect, etc.). I'm hoping to attach a magnet to one and use a ratiometric hall effect sensor for the Volume to Voltage conversion.

Why do I have this urge to take apart the wife's new washing machine suddenly?

Ron

PICMICRO said:

Also, I am pretty surprised to learn that there can be no corrosion free sensor solution that employes directly the waters' conductivity?

Click to expand...

I have been thinking of playing with microchips capSense for water level monitoring. It does not have the same set of problems as conductivity. My application is monitoring the levels in a fish pond filtration system.

Hi PICMICRO,

some people call me a "pea counter" which I guess I'm not. I'm just thorough and precise.

41 one of my pilot comrads were no "pea counters" and that's the reason why I had to escort them on their way to the funeral.

I'm presently building my "dream house" which includes water supply using several pumps and two water wells.

The main tank will be a stainless steel tank of 2.88m height and 88cm diameter. The roof of the building management room has a height of 3.20 - not enough room to lower any metallic rods into the tank to be used for probes.

Besides having to overcome problems being caused by corrosion, metallic probes cause a second problem of electrolytic effects, dissolving in water pretty quickly (some months).

My approach is very simple: I'll be using a differential pressure sensor measuring the pressure of the water column against atmospheric pressure.

Since the pressure sensor is temperature compensated the measured water column is always true with changing atmospheric pressure.

The only downside of that method is a leaking pressure hose being fitted between tank bottom and the pressure sensor well above maximum water level. (That problem won't exist using PU-hosing (PU=PolyUrethane)). Getting abnormal tank readings you just have to disconnect the hose from the sensor and blow air through the hose until air bubbles ascend. (Best using a three-way valve)

My design includes an MCU which allows tank readings of water height in cm, inches, liters and USgallons, and programmable "pump-on/pump-off" setpoints. (Pump-off is self explanatory, but it is required for different tank sizes to make the circuit universal)

The circuit also includes an audible alarm output in case the water well has run dry and the tank is not being filled within a presetable time with automatic shut-off of the pump.

If you are interested in the circuit just drop me a PM.

Regards

Boncuk

why not use this conductivity sensor. Ive purchased it from the guy and it does the trick. It measures conductivity and provides relay output or 5vdc output for microprocessors.
**broken link removed**