Two small magnetic rings unclog the narrow biliary tract
Time：2024-04-16
The liquid level meter has a good structure and installation mode, which can measure the level of strong corrosive medium, measure the level of high temperature medium, measure the level of sealed container, and has nothing to do with the viscosity, density and working pressure of the measuring medium.
Liquid level meter is a commonly used instrument in the automation industry, it can work in high temperature, high pressure, strong corrosion, crystallization environment, and anti-blocking, anti-freezing, can also measure solid powder, granular materials. Let's take a look at several commonly used level gauges.
Drop type liquid level gauge
Based on the principle that the measured hydrostatic pressure is proportional to the height of the liquid, the piezoresistive effect of the diffused silicon or ceramic sensor is used to convert the static pressure into an electrical signal. After temperature compensation and linear correction, it is converted into 4-20mADC standard current signal output. The sensor part of the submersible hydrostatic level transmitter can be directly put into the liquid, and the transmitter part can be fixed by flange or bracket, which is very convenient to install and use.
The drop type liquid level meter is made of advanced isolated diffused silicon sensitive elements, which can be directly put into a container or water body to accurately measure the height from the end of the water level meter to the water surface, and the water level value is output through 4-20mA current or RS485 signal.
Magnetic flap level gauge
The liquid level structure of the magnetic flip plate is based on the by-pass tube principle, and the liquid level in the main tube is the same height as that in the container equipment. According to Archimedes' theorem, the buoyancy and gravity balance float generated by the magnetic float in the liquid float on the liquid surface, and when the liquid level in the measured container rises and falls, The rotating float in the main tube of the level gauge is also raised and lowered accordingly. The magnetic steel in the float is flipped 180° through the red and white tilting column in the magnetic coupler drive indicator.
When the liquid level rises, the tip column turns from white to red. When the liquid level drops, the plume column turns from red to white. The white boundary is the actual height of the medium liquid level in the container, so as to realize the indication of the liquid level.
Magnetostrictive level meter
The structure part of the magnetostrictive level sensor is composed of stainless steel tube (measuring rod), magnetostrictive line (waveguide wire), movable float (with magnet) and other parts. When the sensor is working, the circuit part of the sensor will excite a pulse current on the waveguide wire. When the current propagates along the waveguide wire, the pulse current magnetic field will be generated around the waveguide wire.
A float is provided outside the measuring rod of the sensor, and the float moves up and down along the measuring rod as the liquid level changes. Inside the float is a set of magnetic rings. When the pulsed current magnetic field meets the magnetic ring magnetic field generated by the float, the magnetic field around the float changes so that the waveguide wire made of magnetostrictive material generates a torsional wave pulse at the location of the float, which is transmitted back along the waveguide wire at a fixed speed and detected by the detection mechanism. By measuring the time difference between the pulsed current and the torsional wave, the position of the float can be precisely determined, that is, the position of the liquid surface.
Radar level gauge
Radar level meter adopts the mode of transmitting - reflecting - receiving. The antenna of the radar level meter emits electromagnetic waves, which are reflected by the surface of the measured object and then received by the antenna. The time from transmission to reception of the electromagnetic wave is proportional to the distance to the liquid surface. The radar level meter records the time experienced by the pulse wave, and the transmission speed of the electromagnetic wave is constant.
In practice, there are two kinds of radar level meter, namely frequency-modulated continuous wave type and pulse wave type. The liquid level meter using frequency modulated continuous wave technology has high power consumption, four-wire system and complex electronic circuit. The liquid level meter using radar pulse wave technology has low power consumption and can be supplied with two-wire 24VDC power supply, which is easy to achieve intrinsic safety, high accuracy and wider application range.
Ultrasonic level meter
Ultrasonic level meter is a digital level meter controlled by microprocessor. In the measurement, the pulse ultrasonic wave is emitted by the sensor, and the sound wave is received by the same sensor after being reflected by the surface of the object and converted into an electrical signal. The distance between the sensor and the measured object is calculated by the time between the transmission and reception of the sound wave.
The advantages are that there is no mechanical moving part, high reliability, simple installation, convenient, belongs to non-contact measurement, and is not affected by the viscosity and density of the liquid.
The disadvantage is that the accuracy is relatively low, and the test is easy to have a blind area. Do not measure pressure vessels, do not measure volatile media.
Radio frequency admittance type liquid level gauge
Rf admittance is a new level control technology developed from capacitance, which is more reliable, more accurate and more applicable. It is an upgrade of capacitive level technology.
The so-called radio frequency admittance, the meaning of admittance is the reciprocal of the impedance in electricity, which is composed of resistive components, capacitive components and inductive components, and radio frequency is the radio spectrum of high frequency liquid level meter, so radio frequency admittance can be understood as the measurement of admittance with high frequency radio waves.
When the instrument is working, the sensor of the instrument forms the admittance value with the filling wall and the measured medium. When the level changes, the admittance value changes accordingly. The circuit unit converts the measured admittance value into the level signal output to realize the level measurement.
