The liquid level switch, as the name suggests, is a switch used to control the liquid level. In terms of form, it is mainly divided into contact type and non-contact type. Non-contact types include capacitive liquid level switches, and contact types include: float-type liquid level switches, electrode-type liquid level switches, and electronic liquid level switches. Capacitive level switches can also be implemented using contact methods.
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1. Magnetic flap liquid level gauge
Magnetic plate level gauge: also called magnetic float level gauge, magnetic flip column level gauge.
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Principle: Connector principle, developed based on the buoyancy principle and magnetic coupling. When the liquid level in the container under test rises and falls, the permanent magnet in the float is transmitted to the magnetic flip column indication panel through magnetic coupling, causing the red and white column to flip. Flip 180°. When the liquid level rises, the flip column turns from white to red. When the liquid level drops, the flip column turns from red to white. The junction of red and white on the panel is the actual height of the liquid level in the container, thereby realizing liquid level display. .
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2. Float level gauge
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Principle: The structure of the float level gauge is mainly designed and produced based on the principles of buoyancy and static magnetic field. The position of the float with a magnet (referred to as the float) in the measured medium is affected by buoyancy: changes in the liquid level cause changes in the position of the magnetic float. The magnets and sensors (reed switches) in the float ball change the number of components (such as fixed-value resistors) connected in series to the circuit, which in turn changes the electrical quantities of the instrument circuit system. That is to say, changes in the position of the magnetic float cause changes in electrical quantities. The liquid level in the container is reflected by detecting changes in electrical quantities.
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3. Steel strip liquid level gauge
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Principle: It is designed and produced using the principle of mechanical balance. When the liquid level changes, the original mechanical balance will reach a new balance through the movement of the steel strip when the float is disturbed by the buoyancy force. The liquid level detection device (float) drives the steel belt to move according to the liquid level. The displacement transmission system drives the transmission pin to rotate through the movement of the steel belt, and then acts on the counter to display the liquid level.
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4. Radar level gauge
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Principle: Radar level gauge is a measuring instrument based on the time travel principle. Radar waves run at the speed of light, and the running time can be converted into level signals through electronic components. The probe emits a high-frequency pulse and propagates along the cable probe. When the pulse encounters the material surface, it is reflected back and is received by the receiver in the instrument, which converts the distance signal into a material level signal.
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5. Magnetostrictive liquid level gauge
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Principle: When the sensor of the magnetostrictive level gauge works, the circuit part of the sensor will excite a pulse current on the waveguide wire. When the current propagates along the waveguide wire, a pulse current magnetic field will be generated around the waveguide wire. There is a float outside the sensor rod of the magnetostrictive liquid level meter. This float can move up and down along the rod as the liquid level changes. There is a set of permanent magnetic rings inside the float. When the pulsed current magnetic field meets the magnetic ring magnetic field generated by the float, the magnetic field around the float changes, causing the waveguide wire made of magnetostrictive material to generate a torsional wave pulse at the position of the float. This pulse moves along the direction of the float at a fixed speed. The waveguide wire is transmitted back and detected by the detection mechanism. By measuring the time difference between the pulse current and the torsional wave, the position of the float, that is, the position of the liquid level, can be accurately determined.
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6. Radio frequency admittance level meter
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Principle: The radio frequency admittance level meter consists of a sensor and a control instrument. The sensor can be installed on the top of the silo using a rod, coaxial or cable probe. The pulse card in the sensor can convert the change in material level into a pulse signal and send it to the control instrument. After calculation and processing, the control instrument converts it into an engineering quantity and displays it, thus realizing continuous measurement of the material level.
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7. Tuning fork level meter
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Principle: The working principle of the tuning fork level controller is to make the tuning fork vibrate at a certain resonance frequency through a pair of piezoelectric crystals installed on the tuning fork base. When the tuning fork comes into contact with the medium being measured, the frequency and amplitude of the tuning fork will change. These changes are detected, processed and converted into a switching signal by the intelligent circuit.
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8. Glass plate liquid level gauge
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Principle: The glass plate liquid level meter is connected to the container through a flange to form a connector. The liquid level in the container can be directly read through the glass plate.
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9. Pressure level transmitter
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Principle: The pressure type liquid level gauge adopts the principle of static pressure measurement. When the liquid level transmitter is put into a certain depth of the liquid to be measured, the pressure of the liquid is introduced into the sensor through the gas-conducting stainless steel while facing the pressure on the liquid surface. The positive pressure chamber of the sensor is connected to the atmospheric pressure Po on the liquid surface and the negative pressure chamber of the sensor to offset the Po on the back of the sensor, so that the pressure measured by the sensor is: ρ.g.H. By measuring the pressure P, the liquid level can be obtained depth.
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10. Capacitive liquid level meter
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Principle: Capacitive liquid level gauge measures the level of liquid level by measuring changes in capacitance. It is a metal rod inserted into a liquid container. The metal rod serves as one pole of the capacitor and the container wall serves as the other pole of the capacitor. The medium between the two electrodes is the liquid and the gas above it. Since the dielectric constant ε1 of the liquid is different from the dielectric constant ε2 on the liquid surface, for example: ε1>ε2, when the liquid level rises, the total dielectric constant value between the two electrodes of the capacitive level meter increases. Therefore the capacitance increases. On the contrary, when the liquid level drops, the ε value decreases and the capacitance also decreases. Therefore, the capacitive level gauge can measure the level of the liquid through the change in capacitance between the two electrodes.
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11. Intelligent electric float level gauge
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Principle: The intelligent electric float level gauge is a liquid level measuring instrument designed based on Archimedes' law and the principle of magnetic coupling. The instrument can be used to measure liquid level, boundary level and density, and is responsible for outputting upper and lower limit alarm signals.
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12. Buoy level gauge
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Principle: It is designed and produced using the principle of mechanical balance. When the liquid level changes, the original mechanical balance will reach a new balance through the movement of the steel belt (rope) when the float is disturbed by the buoyancy force. The liquid level detection device (float) drives the steel belt (rope) to move according to the liquid level. The displacement transmission system drives the on-site indication device through the movement of the steel belt (rope), and then displays the liquid level on the display device.
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13. Float level transmitter
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Principle: The buoy is immersed in the liquid in the buoy chamber and is rigidly connected to the torque tube system. The force endured by the torque tube system is the net value of the weight of the buoy minus the buoyancy force on the buoy. Under the action of this combined force, the torque tube twists at a certain angle. Changes in the position, density or boundary level of the liquid in the buoy chamber cause changes in the buoyancy force of the buoy immersed in the liquid, thus causing the twist tube angle to change accordingly. This change is transmitted to the sensor rigidly connected to the torque tube, causing the sensor output voltage to change, which is then amplified by the electronic component and converted into a 4-20mA current output. The float level transmitter uses a microcontroller and related electronic circuits to measure process variables, provide current output, drive LCD display and provide HART communication capabilities.
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14. Electric contact liquid level meter
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Principle: The electric contact water level meter is designed according to the different resistivities of water and steam. The impedance of the electrode of the measuring cylinder to the cylinder is small in the water. The impedance to the cylinder in steam is large. As the water level changes, the number of electrodes in the water changes. Converted into a change in resistance value. It is transmitted to the secondary instrument to realize water level display, alarm, protection interlocking and other functions.
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15. Magnetic sensitive two-color electronic liquid level gauge
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Principle: The magnetic-sensitive electronic two-color liquid level gauge is made of high-quality stainless steel and imported electronic components. The display part uses high-brightness LED two-color light-emitting tubes to form a columnar display. Through the red and green changes of the LED light column, the upper and lower limit alarms of the liquid level can be realized. and control.
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16. External liquid level gauge
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Principle: The external liquid level meter is an instrument that uses the sonar ranging principle and "micro-vibration analysis" technology to measure the liquid level from outside the container. Two compact external liquid level gauge ultrasonic sensors are installed on the bottom of the tank and the other on the side wall of the tank to compensate for density changes. The signal from the external liquid level gauge sensor is converted by the microprocessor and output to the local display or user control system. The height of the liquid in the tank and the volume of the liquid in the tank can be calculated.
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17. Hydrostatic liquid level gauge
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Principle: Hydrostatic liquid level transmitter encapsulates a diffused silicon oil-filled core in a stainless steel housing. The front protective cap protects the sensor diaphragm and allows the liquid to smoothly contact the diaphragm, waterproof wires and housing. Sealed connection, the vent pipe is connected to the outside world within the cable, and the internal structure is designed to prevent condensation.
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18. Ultrasonic liquid level meter
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Principle: Ultrasonic liquid level gauge/level gauge is composed of a complete ultrasonic sensor and control circuit. The ultrasonic waves emitted by the ultrasonic sensor are reflected by the liquid surface, and the time required for return is calculated. The temperature effect during the ultrasonic transmission process is corrected by the temperature sensor, and converted into the distance between the liquid surface and the ultrasonic sensor. The liquid crystal displays and outputs 4mA- 20mADC analog signal enables remote reading of field instruments.
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19. Differential pressure level gauge (double flange level gauge)
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Principle: The differential pressure level transmitter is an electrical component that measures the difference between high and low pressure and then converts it into a current signal by a conversion component and transmits it to the control room. Differential pressure level gauge is mainly used for liquid level measurement in closed pressure vessels. The size of the differential pressure also represents the size of the liquid level. Use a differential pressure meter to measure the differential pressure between the gas and liquid phases to determine the liquid level.
