Classification and principle of liquid level switch

What types of level switches are there? What is the principle of the level switch? Please see below 1. Float level switch The float level switch structure is mainly designed and produced based on the principles of buoyancy and static magnetic field. The position of the float with a magnet (abbreviated as float) in the measured medium is affected by buoyancy: changes in the liquid level lead to changes in the position of the magnetic float. The magnet in the float and the sensor (reed switch) act to generate the switching signal. 2. Tuning fork liquid level switch The working principle of the tuning fork liquid level switch is to make the tuning fork vibrate at a certain resonance frequency through a pair of piezoelectric crystals installed on the base. When the tuning fork of the tuning fork level switch is in contact with the measured medium, the frequency and amplitude of the tuning fork will change. These changes of the tuning fork level switch are detected by the intelligent circuit, processed and converted into a switch signal to reach the liquid level. for alarm or control purposes. To allow the fork to reach into the tank, a flanged or threaded process fitting is usually used to mount the fork switch to the side or top of the tank. 3. Capacitive liquid level switch The measuring principle of capacitive liquid level switch is: the change of the level of the solid material causes the size of the area covered by the probe to change, which leads to the change of the capacitance value. The probe and the tank wall (made of conductive material) form a capacitor. When the probe is in air, a small initial capacitance value is measured. When material is injected into the tank, the capacitance value will increase correspondingly with the increase of the area of ​​the probe covered by the material, and the switch state will change. 4. External measurement liquid level switch External measurement liquid level switch, also known as externally attached liquid level switch, externally attached ultrasonic liquid level switch, is a non-contact liquid level switch realized by 'frequency conversion ultrasonic technology', which is widely used in various liquid detection of liquids. The measuring probe is installed on the outer wall of the container, and belongs to a complete non-contact detection instrument for detecting the liquid level from outside the tank. The measuring probe of the instrument emits ultrasonic waves and detects its residual vibration signal in the container wall. When the liquid flows over the probe, the amplitude of the residual vibration signal will become smaller. After this change is detected by the instrument, a switch signal is output to reach the liquid level. The purpose of the bit alarm. 5. Radio frequency admittance liquid level switch radio frequency admittance level control technology is a level control technology developed from capacitive level control technology, which is anti-hanging, more reliable, more accurate and more applicable. The meaning of 'admittance' in 'nano' is the reciprocal of impedance in electricity, which is composed of resistive, capacitive and inductive components, and 'radio frequency' is high frequency, so radio frequency admittance technology can be understood as using high Frequency measurement admittance. The high-frequency sinusoidal oscillator outputs a stable measurement signal source, and uses the bridge principle to accurately measure the admittance of the sensor installed in the container to be measured. In the direct action mode, the output of the instrument increases with the increase of the material level. Increase. The difference between RF admittance technology and traditional capacitance technology lies in the diversity of measurement parameters, the driving three-terminal shielding technology and the addition of two important circuits. RF admittance technology introduces measurement parameters other than capacitance, especially resistance parameters, which increases the signal-to-noise ratio of the instrument's measurement signal, greatly improving the resolution, accuracy and reliability of the instrument. The diversity of measurement parameters is also powerful. It expands the reliable application field of the instrument. 6. The anti-rotation effect of the material on the rotating blade of the resistance-rotating liquid level switch causes the overload detector of the switch to act, and the relay sends out on and off switching signals, so that the external control circuit sends out a signal alarm and controls the feeder at the same time. For example, when the switch is used as a high-level control: when the material touches the blade, the switch sends an alarm signal and stops the feeder at the same time. When the switch is used as a low-level control, when the material leaves the blade, the switch sends out an alarm signal and starts the feeder at the same time. 7. Electromagnetic liquid level switch Electromagnetic proximity switch, also known as inductive proximity switch, when energized, the oscillating circuit (coil, etc.) emits electromagnetic waves forward with the assistance of the magnetic core CORE, and then returns to the proximity switch, when the front end of the proximity switch When there is metal, because the metal absorbs the electromagnetic, the proximity switch is converted into a switch signal through the attenuation of the electromagnetic, and the output is controlled after the signal processing is completed. 8. Electronic liquid level switch The working voltage of the electronic liquid level switch is DC5V-24V. The water level is detected by the built-in electronic probe, and then the detected signal is processed by the chip. When the liquid level of the tested liquid reaches the action point, the output DC5V-24V, can be used directly with PLC or with control board, so as to control the liquid level. 9. Photoelectric liquid level switch The photoelectric liquid level switch uses infrared detection, using the principle of refraction and reflection of light, the light will produce reflection or refraction at the interface between two different media. When the measured liquid is at a high level, the measured liquid and the photoelectric switch form an interface; when the measured liquid is at a low level, the air and the photoelectric switch form another interface.These two interfaces make the reflected light intensity received by the light-receiving crystal inside the photoelectric switch different, that is, corresponding to two different switching states. 10. Ultrasonic liquid level switch The fork-shaped probe of the piezoelectric crystal inside the ultrasonic liquid level switch is separated by air. A crystal vibration frequency of 1.5MHz transmits the sound signal to the middle of the air gap. When the probe is immersed in the liquid, the crystal and the sound wave are coupled, and the ultrasonic liquid The bit switch changes state.
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