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How Does A Liquid Level Switch Work

How Do Optical Liquid Level Sensors Work?

If you are looking for a reliable and robust solution for an industrial point level sensing application, optical liquid level sensors may be the answer to your problems. Optical liquid level sensors are solid state, meaning they have no moving parts to cause unreliability. They use infra-red light and can be used in environments where a traditional float switch would not be suitable.


How do they work?

Optical liquid level sensors do not measure the liquid level, instead they detect the presence or absence of liquid.

Optical liquid level sensors consist of two main parts: an infra-red LED and phototransistor that is accurately positioned at the base of the sensor tip.

When the tip is in air, infra-red light reflects internally round the tip of to the phototransistor providing strong optical coupling between the two. When the sensor tip is immersed in liquid, the infra-red light escapes from the tip causing a reduction in the amount of light at the phototransistor which makes the output change state.

Advantages and Disadvantages of Optical Liquid Level Sensors

The main selling points for an optical liquid level sensor is their compact size, their solid state design, their low cost and reliability. However, while extremely accurate for point level sensing in high pressure, temperature and at times corrosive environments, they are less useful for continuous level measurement applications.


Optical liquid level sensors from SST Sensing

SST offers a range of optical liquid level sensors that can operate in almost any type of liquid. If you think an optical liquid level sensor would be suitable for your application, consider the following level sensors from SST.


Optomax Digital Liquid Level Sensors

The Optomax Digital liquid level sensors are ideal for applications with restricted space that require a miniature, low power and low cost sensing solution. They are available in polysulphone and trogamid materials that can handle most liquid types.


Optomax Industrial Glass Liquid Level Sensors

For more aggressive and corrosive environments, the Optomax Industrial Glass liquid level sensors can operate in high pressure, high temperature environments due to their stainless steel and glass tip design while offering industrial supply voltages and outputs that can directly drive loads.


For applications with more specific requirements, SST can offer a customisation service where we will design a solution specifically to suit your requirements. For more information, please contact


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