A level sensor is a device that is designed to monitor, maintain, and measure liquid (and sometimes solid) levels. Once the liquid level is detected, the sensor converts the perceived data into an electric signal. Level sensors are used primarily in the manufacturing and automotive industries, but they can be found in many household appliances as well, such as ice makers in refrigerators.
There are two main classifications for level sensors: point level sensors and continuous level sensors. Point level sensors are designed to indicate whether a liquid has reached a specific point in a container. Continuous level sensors, on the other hand, are used to render precise liquid level measurements. Level sensors can be divided further into invasive and non-contact sensors. Invasive sensors make direct contact with the substance they are measuring, while non-contact sensors use sound or microwaves.
There are many different types of point level sensors, but they are all invasive. One of the most basic point level sensors is the “float switch.” When a liquid level rises or falls in a container, it forces the switch to open or close a circuit. Optical level sensors are comprised of an infrared (IR) emitter and a photodiode. As photoelectric proximity sensors, they detect the presence of liquid by measuring the amount of infrared light that is reflected back into the photodiode. Capacitance level sensors measure change in capacitance (the ability to store electric charge) to determine liquid levels in tanks. “Tuning fork” sensors use differences in pressure and vibration to measure liquid level.
Unlike point level sensors, the two main types of continuous level sensors (ultrasonic and microwave) are non-contact. Ultrasonic level sensors emit sound waves, while “radar” sensors emit microwaves. The time interval between wave emission and reflection is directly proportional to the liquid level.