Five Types of Liquid Level Sensors


Liquid level sensors are essential to both monitor and regulate liquid levels within a confined space. They have a wide range of industrial applications and are used in liquid storage tanks to ensure they don’t overflow. Beyond industrial use, liquid-level sensors can also be found in vehicles to monitor fuel, power steering, and oil levels. Even coffee machines have liquid level sensors.

Liquid level sensors can detect when the liquid level is too high or too low to ensure the safety of the equipment and liquid in the container. There are various types of liquid level sensors available, but here are the five most common options.

1. Float

Float switches are the most classic style of liquid level sensor, and they are both effective and affordable. They consist of a hollow float, which sits on top of the liquid and moves up and down as the liquid rises and falls. There is an arm that connects to the float, which links to a switch. When the arm reaches a specific position, then it will trigger the switch either on or off. A float sensor may also connect to a gauge that lets the user know how full the container is. They are versatile since they can be used with any liquid and don’t require a power source to operate them.

2. Optical

Optical liquid level sensors use infra-red LED light with a phototransistor that senses the presence of that light. When the sensor is not in liquid, the light is constant and intense. Once submerged in liquid, much of the LED light disperses before hitting the sensor, thus triggering the switch. Optical sensors can typically only detect whether there is liquid or not rather than giving variable levels.

3. Conductive

Conductive sensors use at least two metal rods, or electrodes, which will trip a switch when the liquid reaches a preset level. One electrode has a low voltage and is at a low point in the container, and the other, which is non-conductive, is placed at the required fluid height. When the liquid reaches the top electrode, it will complete the circuit between the two electrodes, and the switch will trip. The measured liquid must be conductive for this switch to function correctly.

4. Capacitive

Similar to conductive sensors, capacitive sensors also use electrodes to identify liquid levels. The difference is that a capacitive switch features two electrodes, which are both conductive. They are placed closer together, and both sit at the required liquid level or the top of the container. When the electrodes are both immersed in water, they make a circuit, which trips the switch.

5, Diaphragm

Lastly, is the diaphragm liquid level sensor, sometimes called pneumatic. These sensors use air pressure to move a diaphragm until it reaches a preset level and trips the switch. As the liquid in a container rises, the air pressure will increase as well. Similarly, once the liquid level drops, the air pressure will drop. The switch doesn’t require a power source, and since it doesn’t come into contact with the liquid, it is long-lasting.

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