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Working principle of external liquid level switch: The working principle of an external liquid level switch involves the instrument measuring the ultrasonic waves emitted by the probe, as well as detecting the reflected signals from the container wall. When the liquid rises above the probe, the amplitude of these reflected signals decreases; once this change is detected by the instrument, it generates a switch signal. Based on this principle, it is possible to monitor the high and low liquid levels in storage tanks; switch signals are generated at these measurement points to promptly alert instrument maintenance personnel to stop liquid intake and addition, thereby effectively preventing safety incidents such as leaks. Applications of external level switches: The ELL-SA external level switch is a contactless level switch that utilizes \"frequency-modulated ultrasonic technology\". It is primarily used for monitoring the liquid level in storage tanks, enabling alarm functions for high and low liquid levels. With the advancement and evolution of measurement technologies, external level switches are also widely used to detect whether there is liquid in pipes. By measuring from outside the tank wall without coming into contact with the liquid inside, this type of switch represents a completely contactless method for detecting liquid levels. It can be applied in industries such as pharmaceuticals, petroleum, chemicals, power generation, and food processing for the control of liquid level processes. Commissioning conditions for external level switch instruments: 1: Requirements for the instrument 1. Complete the installation of the instrument in accordance with the installation requirements ； 2. The instrument is powered normally ； 3. No error codes displayed when the instrument is powered on ； 4. Magnetic pen ； 5. 24 hours after the probe installation is completed. II. Operating Conditions 1. The current liquid level is more than 200 mm above or below the probe height ； 2. Tank wall thickness data (plate thickness at the probe installation location). Possible problems encountered during debugging and their solutions. Phenomenon 1: Debugging proceeds normally, but the circuit system gives an alarm. Reason: The normally open and normally closed settings of the instrument do not match the system configuration settings. Solution: Reverse the user parameter 20# for setting the gauge; 01 indicates a liquid level alarm, while 00 indicates no liquid level alarm. Phenomenon 2: Debugging is normal; check parameter 7, values 12–15, of the project parameters. Reason: The receiving probe picks up an excessively weak signal. a. The probe cable is too long, resulting in significant signal attenuation. b. The probe mounting surface is not polished or coated with coupling agent. Solution: a. The probe cable should not be longer than 30m; b. Clean the probe mounting surface and reinstall the probe. Precautions for installing external level switches: 1. How to ensure the strongest adsorption force of the probe’s magnetic ring. 1.1 The grinding area of the tank wall should be larger than the size of the magnetic ring, to prevent paint or impurities from reducing the suction force. 1.2 Rotate the magnetic ring so that it protrudes above the sealing ring, preventing it from being recessed inside the sealing ring. 1.3 The sealing ring and sealant are used to seal the probe, preventing water ingress and rust. 1.4 The protective tube of the probe should not experience large torsional forces. 2. How to ensure a clean and stable signal. 2.1 The amount of coupling agent applied should not be too little; it should have a thickness of at least 1.5 mm. 2.2 The tank wall at the probe installation location should be polished smooth. 3. How to ensure measurement accuracy. The two probes are installed at the same height, at the same level as the alarm point.