Principles of various liquid level sensors suitable for household appliances

- Jan 12, 2020-

Most of the water tanks of household appliances need to detect the water level, such as those in air conditioners, dehumidifiers, humidifiers, dishwashers, water purifiers, mopping machines, mobile air conditioners, etc. According to the different water tanks, different level liquid sensors can be used. There are two main types, contact level sensors and non-contact level sensors. The contact type liquid level sensor mainly includes a floating ball type liquid level switch, and the non-contact type liquid level sensor includes a capacitive liquid level sensor, a photoelectric liquid level sensor, an ultrasonic sensor. EPT Sensor produces various types of liquid level sensors. The products and specifications are as follows:

Float-type liquid level sensor:

Float-type liquid level sensor is mainly composed of magnetic reed switch and magnetic floating ball. One or more magnetic reed switches are set in a sealed non-magnetic metal or plastic tube, and then the tube runs through one or more floating ball with a ring magnet inside, and the fixed ring is used to control the floating ball and the reed switch at the corresponding positions. The floating ball rises or falls with the liquid, and the magnet inside the ball is used to attract the contacts of the reed switch to generate the switch action to achieve liquid level control or indication (the switch is turned on when the float approaches the magnetic spring, the switch is turned off when it leaves).


Photoelectric water level switch:
The photoelectric water level switch uses the principle of total reflection, which is based on the total reflection or penetration of light as the output level of the liquid level alarm. Because the refractive index of the material at the front end of the sensor is very different from that of air, when light enters the air from the sensor and the incident angle is greater than the critical angle of total reflection, total reflection will occur and the light can be transmitted to the receiver; Otherwise, when the medium is changed into a liquid, because the refractive index of the liquid is similar to the material of the sensor front, almost all light will penetrate the sensor front. Using this principle, a light transmitter and receiver are designed in the photoelectric water level switch, which can detect and determine the total reflection or penetration of light at the front of the sensor, and drive the output of the alarm circuit for back-end system equipment applications.


Capacitive liquid level sensor
The capacitive level sensor uses advanced signal processing technology and high-speed signal processing chip to break through the influence of the wall thickness of the container and realize the true non-contact detection of the liquid level in the closed container. The liquid level sensor (probe) is installed above and below the outer wall of the tested container (high and low level of the liquid level). The non-metallic container does not need to be opened a hole, the installation is easy. It can detect the level of various toxic substances, strong acids, strong alkalis and various liquids in high-pressure closed containers. The liquid level sensor has no special requirements for liquid media and can be widely used.


The above-mentioned several liquid level sensors are developed and manufactured by EPT Sensor. EPT Sensor is a professional sensor research and development manufacturer, which mainly supplies products such as level switches, level sensors, water level switches, and water tank control switches, flow sensor, tilt switch.