Water Level Sensor Circuit

Question

I am designing a water level controller with discrete components. But when I use DC sensing, the probes are getting corroded... I want to eliminate the corrosion completely, perhaps using either AC or Pulsating DC. Can anyone please suggest me with examples?

Answer 1

Actually, if you just need discrete high/low levels, float switches would work fine, are super reliable, and not expensive. Look for a sump pump type float switch. Basically a mercury switch in a sealed floating ball.

If you need actual level, one of the best systems is a 'bubbler', which uses a controlled air pressure to literally blow bubbles out of a tube, which has the endpoint at the bottom of the liquid stack. The level is measured by monitoring the air pressure and air flow supplied to the bubbler tube. Bubblers are good as they are inherently self cleaning, and give instant indication if there is a severe clog or fault in the system.

Another option for actual level would be ultrasonic. Ultrasonic rangers aren't expensive, and using ceramic transducers, the corrosion problem is eliminated.

Answer 2

Disclaimer: In the essence of time this response is an cut paste of response to a Can I use a ultrasound sensor to measure water level?. Configured the sensor detect water levels, with can be combined with a electronic valve to control the water level. If interested there are few reference to help seek additional infomation.

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Technology used in depth finder, in marine application is mostly like is the best to measure the water from the top.

To measure water level from the bottom of tank one could use a piezo electric ceramic transducer combined with an Analog Front End (AFE) and a micro-controller to measure water level. The diagram below best explains the configuration.

You can use a piezo electric ceramic transducer from Steminc, TDC1000 AFE from Texas Instrument and a MSP430 micro-controller also from Texas Instrument. There might be other configurations, but currently I am only aware of this configuration.

Piezo Electric Transducer

Analog Front End (AFE)

_{Click on image for a larger version of the image.}

Limitation: The thickness and material of the tank might be an issue. For the most part above configuration work with plastic.

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References:

• Steminc - piezo electric transducer
• Piezoelectric Modes of Vibration
• What is Radial and Thickness Mode Vibration in a Piezo Electric Ceramic Disc Transducer?
• TDC1000 Ultrasonic Sensing Analog Front End (AFE) for Level Sensing
• How to measure output of the ultrasonic transducer?

Answer 3

Water has quite a large dielectricity constant (ca. \$\epsilon_r = 80\$), i.e. the capacitance of a capacitor normaly filled by air is changed much if air is replaced by water.

You can build a capacitor consisting of a vertical tube with a wire (or rod) along its center axis (aka coaxial capacitor). Tube and wire form the two electrodes of the capacitor. Of course the tube and wire have to be conducting but they should not be in electrical contact with the water (i.e. they should be insulated because waters is conductive), therfore you don't have problems with electrolysis or other forms of corrosion:

Depending on the waterlevel inside the vertical tube capacitor its capacity changes between some base value \$C_0\$ (0% water level) and \$\epsilon_r C_0\$ (100% water level).

Use the tube capacitor as frequency determining element of an RC (or LC) oscillator in order to measure its capacity via the osciallators frequency (\$f\$~\$\frac{1}{C}\$).

Answer 4

You could put a plastic pipe into the water and connect it to a pressure sensor above the water.