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An external ultrasonic level switch is a contactless level detection instrument that combines various ultrasonic detection technologies. External ultrasonic level switches, thanks to their special probe design and non-submersion detection mechanism, are particularly suitable for use in applications with strict hygiene requirements, as well as in high-pressure, radioactive, toxic, or corrosive environments. The externally mounted ultrasonic level switch, with its simple installation method and high protection rating, ensures that the entire unit can operate for extended periods in harsh environments. The externally mounted ultrasonic level switch is simple to adjust and easy to operate; it is a very user-friendly instrument. In the past, when using ultrasonic principles to measure the liquid level in a container, the residual ultrasonic vibration signals in the container walls were often regarded as a negative factor, as they increased the measurement blind spots. This effect was particularly pronounced when the wall thickness was large and the echo signals were weak. It is a difficult task to suppress the influence of residual vibration signals. After years of research and experimentation, it has been found that the attenuation characteristics of the ultrasonic residual vibration signals in the container wall are closely related to the liquid level in the container. By utilizing this principle, external-mounted ultrasonic level switches can easily enable non-invasive, fixed-point level detection using ultrasonic waves. Compared with other non-invasive methods for detecting fixed liquid levels, this method possesses significant advantages. An external ultrasonic level switch is a new type of liquid level monitoring and alarm device. It is mainly used for monitoring the liquid level in storage tanks, to provide upper and lower limit alarms, or to detect whether there is fluid in a pipeline (dry-state protection). Ultrasonic level switches mounted on the outside can be applied to the level control processes in industries such as pharmaceuticals, petroleum, chemicals, power generation, and food processing. The high-frequency ultrasonic pulses generated by the externally mounted ultrasonic level switch sensor (probe) can penetrate the container wall; these pulses travel through the container wall and the liquid, and are also reflected back. By detecting and calculating these reflection characteristics, it is possible to determine whether there is liquid inside the container at the monitoring point. At the same time, the level controller can output relay signals to subsequent electrical devices or other equipment; an external ultrasonic level switch can be used to monitor or control the liquid level.