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Optical Water Level Sensors

Waterline Controls level sensors provide a better solution to the optical water level sensors. Read more to compare our key points and see what makes us unique.

Theory of operation

The optical sensor derives it’s name from the fact that it uses an infrared light source in conjunction with a reflective prism to detect the liquid level. The infrared light source is generated by an infrared LED in then is directed down to one face of a right angle prism, across the prism to the other face and then reflected up to an infrared receiver. When a liquid covers the external surface of the prism, the light is then deflected through the prisms face into the liquid and none (or very little) is reflected back to the receiver.  The liquid level detection is at only one level and the output is either ON or OFF.

Design Challenges

Internal component placement is important to ensure that the light from the LED transmitter, the receiver and the prism alignment are correct. The prism material is generally made of glass. The type of glass is important to ensure correct reflectivity as well as the non-reflectivity when the glass is immersed in the liquid media to be detected. It is also important to ensure that the liquid not adhere to the surface of the prism.


Optical sensors are generally small and require minimal power. Outputs can be of many forms; all designed to meet the specific requirements of the customer. They are precise in the level of detection, will not contaminate the liquid, and may be configured in several locations to allow for the advantage of multilevel detection.


For multilevel detection requirements, several optical level sensors need to be purchased and installed, thus increasing the cost. With multiple sensors, the connection to a control unit becomes more challenging.  If the liquid being detected has a tendency to adhere to the surface of the prism, a false reading will occur. The optical sensor will only function with liquid media.