Application differences, functional distinctions between servo level gauges and radar level gauges, as well as their selection and use in tank farms

Additional note: Generally, the instruments installed in spherical tanks mainly consist of switch valves, level gauges, thermometers, and pressure gauges. As required, two sets of continuous level measurement instruments equipped with tank edge indicators shall be installed on the tank top; one set is used to set the high and low level alarms in the control system. The main purpose of measuring the liquid level in a spherical tank is to monitor the level of the medium inside the tank. Instruments commonly used for continuous level measurement in storage tanks include radar level gauges, servo level gauges, magnetostrictive level gauges, and hydrostatic level gauges. Servo level gauges can not only measure the liquid level but also parameters such as interfaces, density, or the tank bottom, and they are widely used for high-precision level measurement in spherical tanks. The advantages of servo level gauges are very evident: they have powerful functions and high measurement accuracy, capable of achieving ±1mm with a repeatable accuracy of ±0.1mm. The main drawback of servo level gauges is their relatively complex structure; due to long-term use, mechanical wear inevitably occurs between components such as linear motors, which leads to increased maintenance costs in the future. Furthermore, since it is a floating-type measurement method, high requirements are placed on the stability of the liquid level and the medium inside the spherical tank; when the liquid level fluctuates significantly, the measurement can be greatly affected. To address the above issues, a servo level gauge with a process interface size of 6\" can be selected; the size of the guide tube is also set at 6\". The openings in the tube are arranged in two rows, with the holes in each row offset from each other by 150 mm, and the spacing between holes in a single row is 300 mm. The inside of the guide tube is smooth without burrs, and its verticality should not exceed the specified vertical deviation value. The purpose of this design is to ensure the stability of the liquid within the guide tube, while also meeting the requirements regarding the verticality of the magnetic float. This helps to prevent collisions caused by fluctuations in the liquid level, thereby ensuring the accuracy and reliability of the level gauge’s measurements. A radar level gauge uses electromagnetic waves transmitted via an antenna to the liquid surface of the container being measured; when these electromagnetic waves hit the liquid surface, they are reflected back. The instrument calculates the liquid level height by detecting the time difference between the transmitted wave and the echo. Since radar level gauges use a contactless radar measurement method, with no moving parts entering the interior of the spherical tank and thus no contact with the medium, they require almost no maintenance, do not suffer from material accumulation, have a long service life, and are easy to install and calibrate. It is simple to operate, not easily affected by fluctuations in liquid level, and is particularly suitable for measuring spherical tanks. However, radar level gauges also have disadvantages: if the dielectric constant of the liquid in the storage tank is low, the radar reflection waves are weakened, or if there is severe disturbance to the liquid in the tank, this will **affect the accuracy of the measurements**. To reduce the interference of these factors on the measurement accuracy of radar level gauges, a guide wave tube can be installed inside the storage tank, with a radar antenna placed within this guide wave tube to ensure the precision of the radar level gauge’s measurements. To avoid the occurrence of false reflections, a reflector plate can be used to process overly strong false reflection signals in order to improve the measurement accuracy. Based on the standard waveguide dimensions, the reflector plate can be removed from the waveguide freely, preventing interference with the normal operation and maintenance of the equipment.

Each type of level gauge has its advantages and disadvantages. The best choice depends on the specific operating conditions, in order to achieve optimal results.

1. The servo level gauge can not only measure the liquid level of the medium, but also perform functions such as density measurement, oil-water interface detection, as well as measurement of the average density and density distribution of the medium. However, when the viscosity of the medium being measured is high, and it exhibits wall-adhesion and viscosity-related properties, servo level gauges yield significant measurement errors; they are not suitable for measuring the level of such media, and moreover, these level gauges are relatively expensive. 2. Radar level gauges have numerous advantages: they can measure liquids, solid media, volatile liquids, etc., and are not affected by factors such as noise, steam, dust, or vacuum. They are also unaffected by changes in the density or temperature of the medium. Additionally, they feature high measurement accuracy, a small blind zone, easy maintenance, and strong stability.