A level sensor is a device designed to monitor, maintain and measure the level of liquid. Once the level is detected, the sensor converts the sensed data into an electrical signal. Liquid level sensors are mainly used in the manufacturing and automotive industries, but can also be found in many household appliances, such as coffee machine, water cooler, water dispenser etc.
There are two main types of liquid level sensors: point level sensors and continuous level sensors. The point sensor is designed to indicate if the liquid has reached a particular point in the container. On the other hand, continuous level sensors are used for accurate level measurement. The level sensor can be further divided into intrusive and non-contact sensors. The intrusive sensor is in direct contact with the substance being tested, while the non-contact sensor is using sound or microwave.
Continuous level sensors are non-contact, it has ultrasonic type and microwave type. The ultrasonic level sensor emits sound waves, while the "radar" sensor emits microwaves. The time interval between emission and reflection is proportional to the liquid level.
There are many different types of point sensors, but they are all immersion. One of the most basic point sensors is the "floating switch". When the liquid level rises or falls in the container, it forces the switch to open or close the circuit. The optical level sensor consists 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 reflected back to the photodiode. The capacitance level sensor measures the change in capacitance (the ability to store charge) to determine the level in the tank. The Tuning Fork sensor uses the difference in pressure and vibration to measure the level.