for my university project, i have to design a liquid leakage sensor. the sensor will be placed somewhere on the floor of a room and it must monitor the variation in liquid if spillage or leakage occurs

The problem now is that the output of the sensor must be analogue - it must monitor the height of the liquid up until 5mm. when the liquid level reaches 5mm, the alarm will trigger. The sensor also must be designed using the following specifications:

- height: 5mm
- width & length: 10mm
- must be able to detect conductive and non conductive liquid (eg: water, oil, petrol, sulphuric acid etc)
- not too expensive
- able to detect the liquid within 1m2 area around the sensor

i have been trying to use capacitance with the liquid as dielectric material but i'm not sure if it might work. if also thought about using potential dividers but it may become problematic when using liquids with low conductivity.

 

Almeg Controls has a level sensor box that sits on the floor with adjustable pin height for level. It is used in machine rooms to protect motor installations.

The control box is DIN rail mount – conductive type with a sensitivity adjustment of 0 to 50 kilo ohms. It sends a low voltage 10 VAC signal to the box with a 0.5 mA current. The controller c/w a 240V 5A relay and is power up by 110V.

http://www.almegcontrols.com/ I don’t believe a picture is online. You can email from the site if you require pricing and a drawing.

Thanks Bob Hogg

 

Also you could use a system with a float. Take apart an old POT and use it in conjunction with the float to vary an output voltage. The float doesn't care what type of fluid it is; it will work. You can even buy an automotive carburetor float from ANY parts store that will be impervious to gas/oil.

 

John,

Seems like a tough job - but a few questions first.
Analog - is it supposed to output analog signal relative to spill level 0-5mm ? if not, it is just discrete (to the ouside world - regardless of its inner operating mode). Area of detection - seems the toughest spec topic if sensor itself is limited to 5x20x20 mm size - unless floor is flat and level and can be construed as passive part of the sensor.

Now let's review the physical principles that can be used - or not.
Float - can be but sensitivity depends on fluid's specific gravity
Optical - depends on fluid's index of refraction and transmisivity
Air pressure - can be a candidate - look at how a spill is prevented in a washing machine (air in tube trapped with large diafragm pressure switch at the top. Might not work for only 5 mm height - unless you find a very sensitive solid state pressure sensor. Look also into the McLeod vacuum gauge to learn a nice pressure sensing trick.

These were my thoughts for you. As this is a university project, you don't expect us to solve the problem for you - just some helpful guidance.

Meir