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Introduction and selection analysis of common oil tank level gauge

Time: 2012-09-26 10:42:27 source: Author:

Oil tank is the storage equipment commonly used in oil refineries, oil depots, oil terminals and petrochemical enterprises. For the liquid medium (petrochemical products) in the tank, the parameters such as liquid level, temperature, density and pressure (pressure storage tank) should be measured to calculate the volume and mass storage of liquid. Oil tanks are generally divided into two categories: intermediate tank and trade tank. Intermediate tank only monitors the parameters such as liquid level, temperature and pressure (tank with pressure), so as to prevent accidents such as roof fall and vacuum pumping. It is not necessary to monitor and measure the liquid level, temperature, density, volume and quality of the medium in the trade tank, and the accuracy requirements are very high. Different types and sizes of tanks used Liquid level meter Therefore, according to the needs of users and investment requirements, reasonable selection of liquid level gauge, in order to achieve a more reasonable performance price ratio.
1. Performance characteristics of common level gauge

1.1 manual measuring ruler:
Measure the temperature and weight of the oil tank by immersing it into the scale and measuring the volume. This is an old and still widely used tank measurement method in the world. It can be used as a reference for field inspection of other measuring instruments. The accuracy of manual liquid level measurement is generally considered to be the accuracy of the scale steel ruler plus the artificial reading error of ± 2mm.

1. 2 magnetic level gauge
UHZ type Magnetic level gauge According to the principle of buoyancy, the float in the magnetic flap is in the main body (connected with the container), and floats up and down with the rise and fall of the liquid level of the measured medium. The magnetic component of the inner float is used to attract the indicator in the turnover plate to directly and conspicuously indicate the liquid level change in the measured container. It can be equipped with remote transmitter to realize remote display alarm control function.
Characteristics of magnetic level gauge

(1) It is suitable for measuring liquid level and interface of liquid medium in container. In addition to on-site indication, it can also be equipped with remote transmitter, alarm switch and complete detection function.
(2) The direction of the indicator can be observed according to the user's needs
Change the angle.
(3) The measurement range is large and not limited by the height of the tank.
(4) The indicating mechanism is completely isolated from the measured medium, with good sealing performance, high reliability and safe use.
(5) It has the advantages of simple structure, convenient installation, convenient maintenance, corrosion resistance, no power supply and explosion-proof.

Float level gauge

Floating ball level gauge It is composed of floating ball and inserting rod. The floating ball liquid level gauge is installed on the top of the container through the connecting flange. The floating ball floats on the liquid surface according to the principle of equal volume of liquid in the row. When the liquid level of the container changes, the floating ball also moves up and down. Due to the magnetic effect, the dry spring of the floating ball liquid level gauge is attracted by magnetism, and the liquid level position is changed into electrical signal. The actual position of the liquid is displayed by digital display instrument The liquid level can be detected and controlled remotely.
characteristic:
It is basically the same as the magnetic flap level gauge, but if it is an indoor storage tank, it is a little limited. The floating ball level gauge is top mounted and inserted at the top. If it is indoor, there is a roof. The distance from the bottom of the tank to the roof limits the height of the float ball level gauge. However, holes can be opened on the roof, but the actual situation on site should be considered.


1.4 radar level gauge

??? Radar level gauge It is a kind of intelligent measuring instrument. It adopts modular structure and fieldbus technology to realize full digital processing (DSP). It has good compatibility and openness, and has the ability of self-calibration and self diagnosis. Its principle is to measure the time difference between the electromagnetic wave transmitted and reflected and calculate the propagation distance of the electromagnetic wave by using the reflected wave after the microwave incident on the liquid surface It is a new non-contact liquid level measuring instrument
(1) the liquid level gauge is not in contact with the medium and has no movable parts. It works very reliably with low failure rate and wide application range. It is especially suitable for liquid level measurement of high viscosity and high corrosive medium;
(2) the measurement accuracy is high, and the installation is simple. However, there must be no blocking objects between the bottom and the bottom, otherwise the microwave transmission and reception will be affected, so it can only be installed on the top of the tank;
(3) the relative permittivity of the measured medium, the turbulence state of the liquid level and the size of the bubbles in the medium will affect the measurement results. In general, heavy oil only needs to consider the influence of oil and gas in the tank and the installation position, while light oil needs to focus on the dielectric constant of the medium, and the radar level gauge has higher requirements on the dielectric constant;
(4) the price is generally on the high side.

1.5 hydrostatic level gauge
The working principle of the static pressure type liquid level gauge is: the pressure is the product of liquid level height and liquid density to measure the pressure and obtain the liquid level. Therefore, the mass, volume, density and liquid level of the medium can be measured. The simple HTG (hydraulic tank gagings) system only has one transmitter. The weight of the liquid can be obtained by multiplying the measured pressure by the area of the tank. The early static pressure transmitter has low measurement accuracy and is greatly affected by the ambient temperature, so it is not widely used in the early stage. In recent years, due to the development of transmitter and computer technology, it is now welcomed to a certain extent. Its use has the following characteristics:
(1) simple installation, no moving parts, reliable operation and small daily maintenance;
(2) the density and quality accuracy of measuring medium is high, and the accuracy of measuring liquid level is general;
(3) The air pressure change caused by strong wind will affect the measurement accuracy;
(4) It can not be used to measure the layered storage tank;
(5) It is especially suitable for remote signal and monitoring.

1.6 magnetic level gauge
??? Magnetostrictive liquid level gauge is a new type of non-contact liquid level gauge. It can be installed on the top or side of oil tank. Its working principle is to use magnetic field pulse wave. When measuring, the head of liquid level meter sends out current "inquiry pulse". This pulse generates magnetic field at the same time and runs downward along the induction line in the wave tube. Outside the tube of the liquid level gauge is equipped with float The float is equipped with a set of permanent magnets. When the magnetic field meets the magnetic field generated by the pulse, a new electromagnetic "return pulse" is generated, and then a new electromagnetic "return pulse" is generated. Therefore, the magnetostrictive liquid level gauge takes the float as the measuring element and transmits it to the indicator through the change of magnetic a, so that the indicator can clearly indicate the height of the liquid level. The liquid level meter is equipped with a liquid level alarm and a liquid level transmitter. The alarm can realize the upper and lower limit control and limit alarm of liquid level, and the liquid level transmitter can convert the change of liquid level into a certain intensity current signal. The characteristics of the liquid level gauge are as follows:
(1) The movable part only has float, so the maintenance is small, the installation is simple and the precision is high;
(2) It can measure the liquid level and temperature of medium, but it is not suitable for heavy oil;
(3) In the actual installation of the project, the problem of fixing the bottom often occurs, and the longer the measurement range, the more complex the actual installation;
(4) The price is very high.
1.7 ultrasonic level gauge
External use Ultrasonic level gauge It is mainly used for liquid level measurement of railway tank car, automobile tank car and horizontal tank. The principle of ultrasonic liquid level gauge is that the ultrasonic wave penetrates the tank wall and liquid outside the tank, and the liquid level height is measured by receiving the echo signal of liquid surface. This kind of liquid level meter adopts 712mhz crystal oscillator and autocratic thyristor. It has high transmitting power and high receiving sensitivity. It can receive ultrasonic information reflected back after penetrating the metal tank wall and liquid twice. It has sound and light alarm when the liquid level exceeds the upper limit or lower limit, and has good anti shock, anti-corrosion, lightning protection and explosion-proof performance; In order to prevent the interference of the liquid level meter a and the liquid crystal screen from the interference of the high-temperature electric current and the liquid crystal screen in our country, it is designed to prevent the interference of the high-voltage liquid crystal meter and the liquid crystal screen in the normal working condition. The ultrasonic liquid level meter used outside the tank is especially suitable for the supervision and control of the filling amount in the process of liquid filling of railway tank cars, so as to ensure that the liquid capacity filled by users in the tank car is controlled in the safe transportation capacity of the railway tank car, but its high price is difficult to achieve popularization and application.


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