Description of the level meter and tank measurement technology

The level measuring device is used to determine the height of the fluid and/or particulate solids in the tank, container, silo or any other suitable container. Recently, the VDC market research company found that the global market value of industrial process level measurement equipment in 2004 was 1.32 billion US dollars, of which the tank measurement system accounted for about 327 million US dollars. A large number of detection techniques are used to measure the level - a widely measured process variable.

    Level measuring sensors are divided into two categories: point switches and continuous level meters. Some techniques are used on both types of sensors. Point refers to the arrival of a material above or below a specific point in the container. This type of device is used to indicate whether the container is full, empty, or somewhere in the middle. A continuous level gauge provides information on where the material is located anywhere in the container.

    Compared to process control, tank measurement (ITG) refers to the level measurement of applications such as inventory storage and custody transfer. Many ITG systems have a larger measurement range and higher measurement accuracy than process level measuring instruments.

    Different technology shipment scenarios

    Here, the shipped process equipment includes continuous and point measurement equipment, but does not include vibrating products that can only provide point measurement.

    The static pressure level gauge is by far the largest amount of process level measurement equipment in the world, and most of them are continuous measuring equipment. The simplest of these devices is the static pressure probe device, which measures the pressure in the open tank by measuring the pressure at the bottom of the tank, because the density is known at any point in the liquid. The height above the liquid is determined.

    On the other hand, differential pressure equipment is the most common continuous level measurement equipment. In the application, the high pressure portion of the differential pressure sensor is connected to the bottom of the tank, and the low pressure portion is connected to the vacant portion of the closed tank top. If the liquid density is constant, the measured pressure difference is indicative of the actual liquid level. If the liquid density is not constant, changes in the liquid composition or operating temperature will cause some of the gravity to change, resulting in erroneous readings, which will need to be corrected.

    For the next five years, VDC expects the global market share of hydrostatic equipment to decline, but not much. Pressure sensing is expected to remain the dominant technology in the field of process level measurement. This technology has been used for a long time, and even some major suppliers are worried that it will be replaced, but it is not so fast.

    Static pressure level measurement technology continues to dominate, depending on the application, this can be attributed to many factors. Some attractive features of hydrostatic level measurement include:

    1) lower product and / or maintenance costs;

    2) Easy to install;

    3) sturdy and durable;

    4) High reliability (long-term verification);

    5) wider media compatibility;

    6) User familiarity

    Among them, cost may be the most important factor. For example, in 2004, only sonic/ultrasonic products, which accounted for 1% of the global continuous level measurement market, had lower average selling prices, while other products cost relatively higher.

    Non-contact microwave/radar products account for the largest share of the global ITG market. In 2004, shipments of such equipment in marine and non-maritime applications accounted for more than 60% of the total shipments of ITG equipment worldwide, while static pressure storage The shipment amount of the tank meter is less than 6%.

    Since its introduction and application on the tanker by Saab Marine Electronics in 1976, non-contact microwave/radar products have been used in a wide variety of ITG applications. For example, in 1991, these products accounted for about 10% of the US ITG market, reaching about 14% in 1997 and 22% in 2002.

    The technology's market share in the US and throughout North America is much lower than its global market share. This is mainly because the ITG systems shipped in the maritime industry are mainly used in newly built ships, while the current shipbuilding is mainly concentrated in other parts of the world, especially in Asia and the Pacific Rim countries and regions. In 2004, ITG systems shipped less than 2% of global market share in North American shipping applications. Shipments in the Asia Pacific region accounted for almost 73% of total global shipments, with the rest being mainly in the European market.

    A non-contact microwave/radar level measuring device is mounted on the top of the tank, which sends a microwave signal down to the surface of the material in the tank, and the receiver receives the reflected signal. Based on the difference between the transmitted and received signals, the system can calculate the level in the tank.

    Here are two modulation methods:

    1) The pulse system measures the time from the transmission of the pulse to the receipt of the echo. The level can be directly calculated by the delay between the transmitted and received pulses;

    2) The frequency modulated continuous wave (FMCW) transmission scheme mixes the echo signal whose frequency has been changed with the transmitted microwave signal. Because of its different frequency (because of frequency modulation), the frequency of the mixed signal is proportional to the distance from the surface of the material.

    The microwave frequency used has a large impact on the performance of the radar level gauge. High-frequency, short-wavelength signals that are extremely sensitive to steam, foam, and contaminants. At a frequency of 24 GHz, even a small amount of water vapor can absorb microwave signals. The low frequency long wavelength and wide beam angle signals return many interfering echoes from the tank wall and the agitator. The best frequency is known to be around 10 GHz.
Non-contact microwave/radar equipment is completely or relatively inaccessible to measurement problems that many other technologies may face, such as:

    3) related to material density;

    4) related to the dielectric constant of the material;

    5) susceptible to dust;

    6) high maintenance strength;

    7) can not work under vacuum;

    8) susceptible to stress;

    9) susceptible to the environment between the medium and the sensor (such as foam and varying density of steam, etc.);

    10) susceptible to range effects;

    11) It is susceptible to temperature and so on.

    The non-contact properties of this technology are especially suitable for measuring rough or corroded materials. To date, most ITG systems have been used in the oil and gas industry for sea-based and land-based applications, including refining. In the global ITG system market in 2004, these applications accounted for more than 87% of the total, and most of the products shipped were based on non-contact microwave/radar technology.

    The high price of non-contact microwave/radar technology equipment is an obstacle to preventing it from being used more widely. This is especially true for process level measurement applications, which accounted for only about 6% of global shipments in 2004. However, its price is declining to meet the application of process and ITG systems; it is expected that the average selling price of products using this technology will be greatly reduced over the next five years.

    Influencing factors include the use of low-cost devices, the provision of simplified features, and increased production of low-priced products. Increasing production will lead to greater economies of scale. In addition, more manufacturers are entering this market, which further increases the pressure of price competition.

    High growth market

    Non-contact microwave/radar products are expected to be the fastest growing products in process level measurement and ITG applications. Contact/guided microwave/radar products and sonic/ultrasonic systems in the ITG market are even expected to grow even higher. However, sonic/ultrasonic technology now accounts for only a small share of the global ITG market (less than 1%).

    In 2004, contact/guided microwave/radar products accounted for approximately 4% of the global level measurement equipment market and approximately 3% of the global ITG market. This is a new level measurement technology that has only recently been introduced. VDC was the first to recognize the use of Bindicator and Krohne's products in process level measurement in 1997, and the application of Barton Instrument System's products to ITG in 2002.

    Contact/Guide Microwave/Radar Level Measurement Equipment measures the level of liquids, pastes, slurries, powders and other special particulate materials. In 2004, this technology accounted for 8.8% and 3.1% of global shipments of process solids and liquid level measurement applications, respectively.

    Such products (some known as radio frequency or time domain reflectometers) are mounted on the top of the tank and emit radio or low frequency microwave signals along transmission lines or waveguides inserted into the material in the tank. Like non-contact microwave/radar level measurement devices, contact microwave/radar devices are available in both pulse and frequency modulation types.

    Compared to non-contact products, contact microwave/radar level meters operate at lower radio and microwave frequencies at lower cost, but have many of the same advantages. In addition, they often have greater installation flexibility and lower installation costs, and their use is not subject to licensing by similar regulatory agencies in the US Federal Communications Commission or other countries.

    This all-electronic device measures ultra-short or long distances and is less susceptible to dust, air movement, temperature or pressure fluctuations.

    On the other hand, heavy objects pressed on the transmission line or waveguide can also cause false readings. In addition, such products are difficult to measure the level of plastic materials (such as EPS beads) with extremely low dielectric constants. However, it measures the plastic balls and plastic sheets very well.