Micro Float Switch

Try McMaster-Carr; they sell a lot of these things.

Ing. Robert Forbus

There are many types about, have you thought of using a light refraction sensor? these are extremely sensitive and could easily give you an 1/8 inch change in level...

In case they are called something else the type I'm referring to is the one which has a LED beam up to a lens which reflects the beam back to an integral light sensor. When the water covers the lens the beam is not reflected back to the sensor....

John.

Try GEMS, they specialize is level switches and sensors GEMSsensors.com

Try RedE Parts http://www.redeparts.com/index.cfm

Most answers so far are on the usage on on-off type of sensor. Is this what you need or a sensor with an analog output?

How small do you need?

We built thermistor based sensors with a length of 15/16in, 10-32 threads and 5/16 hex. For these you need some electronics drive and decode the signal into a usefull output.

I have used plastic fiberoptic based sensors witch take minimal place (1-3mm diameter) at the process point but a small elecrtronic module is needed elswhere in your setup. Depending on the temperature and turbidity of the liquid, this a very interresting aproach. Glass fiber sensors can be even smaller.

You could also consider ultrasound sensors, with on-off or analog output.

Please contact us if you need further assistance.

Eric Girard

Try this indiginous swich I am using to stop my Water pump when Water-tank is filled

2 SS rods [1/8" dia] pierced through a rubber Cork, separated >1/3", Tips extruded 1/8" at difference can be used by hanging [mounted vertically] in the water tank while the longer rod's tip just touching the water. Electronic circuit will be needed to indicate/ switch on a light.

A ===============

| 1/8" |

B ====================

Wires connected to ends A & B to be connected to Circuit.

Other ends hanging downwards, tip of B just touching water

Check out Aquahub magnetic reed switches: http://www.aquahub.com/store/index.html

for a limited range application, small ultrasonic sensors on a chip have become very inexpensive. E.g. the Ping sensor used for robotics hoobyisrs has a range of 0.75-10 inches for $30. http://www.hobbyengineering.com/H2951.html

Less expensive waterproof units can be found in electronic component shops online fro just $2-4.