(1) Tuning fork level switch
The working principle of the tuning fork level switch is to make the tuning fork vibrate at a certain resonant frequency through a pair of piezoelectric crystals installed on the base. When the tuning fork of the tuning fork level switch contacts the measured medium, the frequency and amplitude of the tuning fork will change. These changes of the tuning fork level switch are detected and processed by the intelligent circuit and converted into a switch signal to achieve the purpose of liquid level alarm or control. In order to allow the tuning fork to extend into the tank, the tuning fork switch is usually installed on the side or top of the tank using a flange or a threaded process joint.
(2) Float level switch
Float level switch is mainly designed and produced based on the principle of buoyancy and static magnetic field. The position of the float with magnet (referred to as float) in the measured medium is affected by buoyancy: the change of liquid level causes the change of the position of the magnetic float, that is, the magnet in the float and the sensor (reed switch) work together to generate a switch signal.
(3) Electrode type liquid level switch
The electrode type liquid level switch uses the conductivity of the liquid to monitor the height of the liquid level. When the liquid contacts the electrode, it will conduct electricity and output an alarm signal. This liquid level switch can be controlled at multiple points, and the control position is determined by customer needs. It has a breakthrough protection function and can effectively prevent surge interference. However, the electrode type liquid level switch is only suitable for conductive liquids, and the liquid cannot be volatile.
(4) Electronic liquid level switch
The operating voltage of the electronic liquid level switch is DC 5V-24V. The water level is detected by the built-in electronic probe, and the chip processes the detected signal. When the liquid level reaches the action point, it outputs DC 5V-24V. It can be used directly with PLC or control board to achieve liquid level control.
(5) Ultrasonic liquid level switch
Inside the ultrasonic liquid level switch, the piezoelectric crystal is formed into a fork-shaped probe with an air gap between its prongs. The crystal vibrates at a frequency of 1.5 MHz, generating sound waves that propagate into the center of the air gap. When the probe becomes submerged in liquid, the crystal and the sound waves become acoustically coupled through the medium, causing the ultrasonic liquid level switch to change its operating state.
(6) Capacitive liquid level switch
The capacitive liquid level switch operates based on the principle that variations in the level of solid material alter the extent to which the probe is covered, thereby changing the capacitance. A capacitor is formed between the probe and the tank wall, which is made of a conductive material. When the probe is exposed to air, only a small initial capacitance is detected. As material is added to the tank, the portion of the probe in contact with the material increases, leading to a corresponding rise in capacitance and triggering a change in the switch state.
(7) External liquid level switch
The external liquid level switch is a non-contact type device that utilizes frequency conversion ultrasonic technology and is extensively applied in the detection of various liquid types. Its sensing probe is mounted on the exterior wall of the container, allowing it to monitor the liquid level without direct contact. During operation, the probe emits ultrasonic waves and monitors the residual vibration signals within the container wall. When the liquid reaches and covers the position of the probe, the amplitude of these residual vibrations decreases. The instrument identifies this change and outputs a switching signal, thereby enabling liquid level alarm functionality.
(8) Electromagnetic liquid level switch
Electromagnetic proximity switch, also known as inductive proximity switch, when powered on, the oscillation circuit (coil, etc.) emits electromagnetic waves forward with the help of the magnetic core, and then returns to the proximity switch. When there is metal at the front end of the proximity switch, the metal absorbs the electromagnetic wave, and the proximity switch converts the electromagnetic wave into a switch signal through electromagnetic attenuation. After the signal processing is completed, the output is controlled.
(9) Photoelectric liquid level switch
The photoelectric liquid level switch detects liquid levels using infrared light, operating based on the principles of refraction and reflection at the boundary of different media. When the liquid level is high, an interface is formed between the liquid and the photoelectric switch; when the liquid level is low, the interface is between air and the switch. These two different interfaces cause variations in the intensity of the reflected light received by the internal photosensitive crystal, resulting in two distinct output states of the switch.
