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Understanding the working principles, advantages, and disadvantages of different level sensors helps us choose a more suitable one. Below are the detection principles of commonly used level sensors today. 1 Laser level sensor: A laser level sensor is a non-contact, high-precision level sensing device with excellent performance. Its working principle is very similar to that of ultrasonic level sensors, with the difference being that light waves are used in place of ultrasonic waves. The laser beam is very thin, so it can function properly even when the liquid surface is extremely rough. Laser level sensors have a very wide range of operation; they generally use near-infrared light. It processes the laser emitted by the light flow by using a semi-transmitting mirror. One part is fed as a reference signal to the time transmitter, while the laser from the semi-transmitting mirror is processed by an optical system to become a parallel beam of a certain width, which is then directed at the surface of the object. The reflected wave reaches the sensor’s receiving unit and is then converted into an electrical signal. Since the time from irradiation to reception is very short, a sampling circuit is used to expand it to the nanosecond range, which facilitates signal processing and time measurement. A microcomputer is used for data processing to generate an analog output signal with a digitally displayed liquid level value; software is then employed to check the reliability of this signal, and an alarm is issued if a fault occurs in the measurement system. This type of sensor is suitable for applications in monitoring lakes, rivers, reservoirs, open channels, tides, and urban water levels. 2 Radar level sensors: Radar level sensors offer the same advantages as laser measurement methods; they are not affected by the medium being measured, are less susceptible to external environmental influences, and do not require repeated calibration. However, their measurement range is generally limited to within 6 meters. They are particularly suitable for measuring inside large containers that use heated steam, such as in applications related to the monitoring of residue oil and asphalt. 3 Ultrasonic level sensor: An ultrasonic level sensor works by measuring the time difference between the emission and reflection of ultrasonic waves in order to determine the liquid level. It is simple to install and offers high flexibility, but it is susceptible to losses in the energy of the ultrasonic waves as they travel; therefore it is not suitable for use in environments where sound is absorbed, such as those with foam, dust, steam, etc. 4 Hydrostatic level sensor: The measurement principle of a hydrostatic level sensor is to obtain pressure values by installing a pressure sensor at the bottom. Converting to a liquid level height has the advantage of being unaffected by the height of the liquid surface; however, the higher the height, the greater the precision required of the liquid level sensor, and calibration is necessary after long-term use or when changing the liquid. It is widely used in monitoring applications in cities, such as water supply and drainage, sewage treatment, reservoirs, rivers, and the ocean. 5 Float-type level sensor: The float-type level sensor measures changes in liquid level by the rise and fall of a float; it is a mechanical detection method with poor repeatability accuracy. It is not suitable for viscous liquids or those containing impurities, as this can easily lead to blockage of the float. Float-type level sensors have a wide range of applications and are cost-effective; they are commonly used in areas such as sump pits, fire water tanks, and sewage treatment for level monitoring, but they are not suitable for use in the food hygiene industry. 6 Tuning fork vibration level switch – The tuning fork vibration level switch is widely used in industrial control systems and is suitable for almost all applications related to liquid level monitoring. For example, continuous monitoring of liquid levels in things such as factory coolant tanks and lubricant tanks. The principle is as follows: when a liquid or bulk material fills the two vibrating forks, a change in the resonance frequency occurs, and a switch signal is generated by detecting this frequency change. The output is digital; continuous height cannot be measured. There is also the photoelectric refraction measurement method: a light source is emitted from within the sensor, and this light is totally reflected back to the sensor’s receiver through the transparent resin. However, when it encounters the liquid surface, part of the light is refracted into the liquid; the sensor then detects the decrease in the amount of light that is reflected back in order to monitor the liquid level. The photoelectric refractive method is only applicable to the level measurement of transparent liquids. Having understood the measurement principles of the various liquid level sensors mentioned above, and by considering the properties and conditions of the liquid that needs to be measured, we can select the appropriate liquid level sensor.