Solidat Guided Wave Radar Level Meter Features and Applications - Taking the Bottom of Oil Tanks as an Example

Solidat Guided Wave Radar Level Meter Features and Applications - Taking the Bottom of Oil Tanks as an Example

Abstract: This article mainly introduces the application principles of guided wave radar level meters as one of the level measurement technologies, the characteristics of microwave radar and guided wave radar respectively, as well as the application of the SLDL5500 series guided wave radar level meter products launched by Solidat in the actual field of bottom oil tanks.

Keywords: Level Meter; Guided Wave Radar; Microwave; Radar; Bottom Oil Tanks

1. Overview

With the iterative upgrading of industrial technology, the level measurement technology has undergone multiple innovations, evolving from manual operation-based methods such as weight-type and scale-type measurement to intelligent and high-precision measurement. Nowadays, advanced technologies such as radar measurement and nuclear radiation measurement have been widely applied in industrial scenarios. However, nuclear radiation measurement has certain limitations due to its technical sensitivity and high safety control requirements. Among various level measurement technologies, radar measurement technology derived from military radar, with its outstanding performance and wide applicability, is gradually becoming the core choice in the industrial level measurement field.

Radar level measurement technology is mainly divided into two categories: microwave radar (non-contact type) and guided wave radar. Microwave radar level measurement benefits from cost advantages and excellent performance in complex conditions, earning the favor of many users. However, each technology has its applicable boundaries, and microwave radar may not be able to meet the measurement requirements for all media. Guided wave radar technology, with its unique measurement principle and technical characteristics, effectively fills the gap of microwave radar in specific measurement scenarios, becoming an important supplement to level measurement technologies.

2. Characteristics of Radar Technologies

2.1 Characteristics of Microwave Radar

· Large measurement range: High-frequency electromagnetic wave signals facilitate long-distance transmission, enabling measurement of a large range of levels.

· Not affected by gas phase conditions: Not affected by changes in gas phase conditions in space, able to operate stably in complex gas-phase environments.

· Non-contact measurement: No need for direct contact with the medium, reducing equipment wear and maintenance costs.

2.2 Characteristics of Guided Wave Radar

· Low energy consumption: When operating, Solidat guided wave radar outputs a very small amount of signal energy to the waveguide probe, approximately 10% of the energy emitted by non-contact radar. This is due to the waveguide structure, which builds an efficient signal transmission channel. During the signal transmission from the emission end to the surface of the medium, the attenuation is controlled to the minimum, significantly reducing energy demand and achieving low-energy operation.

· Strong signal: During signal transmission, the waveguide plays a key role, ensuring signal transmission is not disturbed by liquid surface fluctuations or obstacles in the storage tank. Therefore, the final received signal from the instrument is strong, approximately 20% of the emitted energy. This stable and high-intensity signal reception ensures the accuracy and reliability of measurement data.

· Wide range: For the measurement of low dielectric constant media, Solidat guided wave radar performs exceptionally well. Taking its guided wave radar products as an example, the lowest dielectric constant that can be measured is as low as 1.4, capable of precisely meeting the measurement requirements of various low dielectric constant media, significantly expanding the application scope and playing an important role in numerous complex industrial environments.

· Strong anti-interference: The dielectric constant change has no impact on measurement performance. Whether it is the surface of hydrocarbons (dielectric constant 2 - 3) or the reflection of water (dielectric constant 80), the propagation time is the same, only the signal amplitude varies. Microwave radar needs to filter signals based on the characteristics of the medium to obtain accurate measurement values, and the signal strength change during reception is prone to interference; while guided wave radar has concentrated energy, it can effectively avoid interference. · Not affected by density: Although changes in the density of the medium will affect the buoyancy force exerted on the immersed object, it has no impact on the propagation of electromagnetic waves in the waveguide.

· Minimal influence of adhesion: The adhesion of the medium on the probe/cable has a negligible effect on the level measurement. The adhesion mainly takes two forms: film-like and bridging. In the case of film-like adhesion, as the material level decreases, a uniform covering of high-viscosity medium forms on the probe, which has almost no impact on the measurement; while bridging adhesion may lead to significant measurement errors. Therefore, when choosing a dual-rod/cable type conductor, the viscosity of the medium needs to be fully considered.

3. Principles of Microwave Radar and Guided Wave Radar

3.1 Microwave Radar:

Microwave radar measures the level by emitting and receiving high-frequency (GHz) electromagnetic waves. The level is calculated based on the time it takes for the electromagnetic waves to reach the surface of the measured object and be reflected back to the receiving antenna. Since the propagation of electromagnetic energy is not overly restricted by the properties of the propagation space, it can be transmitted in high/low pressure (vacuum) or in the presence of vaporizing media, and the gas fluctuations have little impact on its propagation. However, the antenna of a common microwave radar level measurement instrument radiates relatively weak energy, approximately 1mW. When the signal propagates in the air, the energy decays rapidly. Moreover, when the microwave signal reaches the surface of the measured object and is reflected, the signal intensity (amplitude) is closely related to the dielectric constant of the medium. For non-conductive media with extremely low dielectric constants, such as hydrocarbon liquids, the reflected signal is extremely weak. After the attenuated signal returns to the top receiving antenna, it further loses energy. The microwave radar level meter receives the returned signal energy, which is only about 1% of the emitted signal energy. Under these conditions, the performance of the contact-type microwave radar level meter will significantly decline, and it may even fail to work properly.

3.2 Guided Wave Radar:

To overcome the limitations of contact-type radar level meters, guided wave radar level meters emerged. The working principle of guided wave radar is similar to that of traditional radar, based on the time-domain reflection TDR (Time Domain Refectory) and ETS (Equal Time Sampling) principles. For a long time, TDR technology has been used to detect the ends of buried cables and cables embedded in walls. When detecting cable ends, the electromagnetic pulse signal emitted by the TDR generator propagates along the cable, and when it reaches the end, a measurement reflection pulse is generated. At the same time, a preset impedance change corresponding to the total length of the cable is set in the receiver to trigger a reference pulse. By comparing the reflection pulse with the reference pulse, the position of the end can be accurately determined. Applying this principle to level measurement, the TDR generator generates tens of thousands of energy pulses per second and conducts them along the waveguide. When the pulse reaches the medium surface, it produces a level reflection original pulse. At the same time, a preset value impedance is set at the top of the probe to generate a reliable reference pulse, namely the baseline reflection pulse. The radar level meter detects the level reflection original pulse and compares it with the baseline reflection pulse to obtain the level measurement value, which is the working process of the guided wave radar level meter.

The ETS (Equal Time Sampling) principle is used to measure high-speed, low-power electromagnetic signals and is the key to the application of TDR liquid level measurement technology. Due to the difficulty of short-distance measurement of high-speed electromagnetic signals, ETS can capture the electromagnetic signals (UIS) in real time and reconstruct them within an equivalent time to better apply advanced technologies for measurement.

With the development of level measurement technology to date, a variety of mature and reliable level measurement instruments have emerged, each with its unique performance and application range, playing an important role in different liquid level measurement scenarios, such as pressure/differential pressure measurement liquid level method, radio frequency conductivity/ capacitance level meters, ultrasonic level meters, and float level meters, etc. These instruments have decades of successful application experience in the industrial field.

4. Introduction and Application of Solidat Guided Wave Radar Level Meter

Solidat, as a well-known automation equipment supplier in the industry, has achieved remarkable success in the research and manufacturing of level measurement instruments. The company always adheres to the concept of innovation and is committed to providing customers with high-quality and high-performance level measurement solutions.

The SLDL5500 series guided wave radar level meter launched by the company is specifically designed for corrosive liquids, high-temperature liquids, and high-pressure liquids. The FlexScan guided wave radar emits high-frequency microwave pulses that propagate along the detection component (steel cable or steel rod). When encountering the measured medium, due to the sudden change in dielectric constant, a reflection occurs, and some of the pulse energy is reflected back. The time interval between the transmitted pulse and the reflected pulse is proportional to the distance of the measured medium. The FlexScan includes SLDL5521 ordinary type, SLDL5522 anti-corrosion type, SLDL5523 coaxial type, SLDL5524 high-temperature type, SLDL5525 steam compensation type, and SLDL5526 double-cable type. Among them, the SLDL5525 series has steam compensation function and can correct the influence of saturated steam on measurement, suitable for use in high-temperature and high-pressure measurement conditions such as steam drum, high and low pressure feed water heaters, and condensers.

Key technical features include:

4.1 Temperature and Pressure Resistance: SLDL525 has steam compensation function and has excellent temperature and pressure resistance performance (275bar@450℃, 413bar@80℃)

4.2 Multiple Communication Methods: Supports HART, Modbus, Profibus PA, Foundation Fieldbus, GPRS/CDMA remote communication methods.

The SLDL5500 series has a dynamic range of 120 dB (compared to 96 dB for 26 GHz), enhancing reliability in extreme conditions such as 1.5-meter-thick foam (animal feed factory), condensation or adhesion environments (oil regeneration reactor), and supporting penetration of glass/container walls for measurement (such as in the distillation process).

4.3 Coaxial structure: SLD5523/5525 have a coaxial structure, ensuring no measurement blind zone

4.4 Installation ease: Simple debugging, no need to load the container or empty it, saving time

4.5 Medium adaptability: Using FlexScan echo processing technology, measurement is not affected by external interference such as foam, steam, powder, etc., or by suspended materials. Measurement is not affected by changes in medium density, dielectric constant, pressure, temperature, or container shape.

Taking a large-scale tank bottom oil factory as an example, this factory has various specifications of oil tanks storing different media such as crude oil and refined oil. Before using the Solidat guided wave radar level gauge, the traditional measurement method had limited measurement accuracy and was extremely unstable in complex conditions such as when there was steam or foam in the tank. This often led to production scheduling errors, material overflow or shortage, and such situations occurred frequently. After introducing the Solidat guided wave radar level gauge, the situation was greatly improved. It can easily adapt to complex conditions, even when the tank environment is harsh, and can stably output high-precision level data. Moreover, the measurement blind zone is small, meeting the measurement requirements of different oil tanks. The installation process is simple and convenient, and the maintenance cost is also low, saving a lot of manpower and material resources for the oil factory. In the application of crude oil storage tanks, it can monitor the liquid level in real time, stably and reliably, providing precise data support for the production scheduling of the oil factory, helping to optimize the production process, effectively avoiding material waste and supply shortages, and bringing significant economic benefits and security guarantees to the oil factory.

In conclusion, the Solidat guided wave radar level gauge, with its advanced technology, outstanding performance and reliable quality, demonstrates significant advantages and application potential in the field of level measurement, providing strong support for the intelligent development of various industries.