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Views: 0 Author: Site Editor Publish Time: 2025-03-07 Origin: Site
Ultrasonic liquid flow meter and Electromagnetic Flow Meters are two common types of flow meters, each with its own advantages and disadvantages. The choice between the two should be based on actual requirements. If the liquid flow is small and the environment is harsh, an ultrasonic flow meter can be selected. If the liquid flow is large, an electromagnetic flow meter is a better choice. It is essential to conduct a detailed evaluation before use to ensure optimal performance.
(1) Electromagnetic flow meters can be used to measure industrial conductive liquids or slurries.
(2) No pressure loss.
(3) Wide measurement range, with diameters ranging from 2.5mm to 2.6m.
(4) Measures the volumetric flow rate under actual working conditions without being affected by temperature, pressure, density, or viscosity of the fluid.
(1) Limited applicability as it can only measure the flow of conductive liquids and cannot measure non-conductive media, such as gases and well-treated heating water. Additionally, the liner material needs consideration under high-temperature conditions.
(2) Electromagnetic flow meters determine volumetric flow based on the velocity of conductive liquids. However, for liquid media, mass flow should be measured, which requires considering the fluid’s density. Different fluids have different densities, which also change with temperature. If the converter does not account for fluid density and only provides volumetric flow at normal temperature, the measurement may be inaccurate.
(3) Scaling or wear inside the pipeline changes the internal diameter, affecting the predetermined flow value and causing measurement errors. For example, a 1mm change in the internal diameter of a 100mm instrument can result in approximately 2% additional error.
(4) The transmitter’s measurement signal is a small millivolt-level potential signal that includes interfering signals unrelated to flow, such as in-phase voltage, quadrature voltage, and common-mode voltage. To accurately measure flow, interference signals must be eliminated, and the flow signal must be effectively amplified. Improving the performance of the flow converter by using microprocessor-based converters can help control the excitation voltage and select excitation mode and frequency based on the fluid properties to eliminate interference. However, this makes the instrument structure more complex and increases costs.
(1) The ultrasonic liquid flow meter is a non-contact measurement instrument that can measure the flow of fluids that are difficult to access, observe, or large-diameter pipes. It does not alter the fluid flow state, does not cause pressure loss, and is easy to install.
(2) It can measure the flow of highly corrosive and non-conductive media.
(3) The ultrasonic liquid flow meter has a wide measurement range, with diameters ranging from 2cm to 5m.
(4) It can measure the flow of various liquids and wastewater.
(5) The measurement of volumetric flow is not affected by the temperature, pressure, viscosity, or density of the fluid. It is available in both fixed and portable versions.
(1) The temperature measurement range is limited, typically only measuring fluids below 200°C.
(2) Susceptible to interference from bubbles, scaling, pumps, and other ultrasonic noise sources, affecting measurement accuracy.
(3) Requires strict straight pipe sections: 20D upstream and 5D downstream; otherwise, dispersion increases and measurement accuracy decreases.
(4) Uncertainty in installation can cause significant measurement errors.
(5) Scaling in the measurement pipeline can severely affect measurement accuracy, leading to significant errors or even failure to display flow.
(6) Lower reliability and accuracy levels (generally around 1.5-2.5 levels) with poor repeatability. The ultrasonic flow meter determines flow by measuring the fluid velocity and multiplying it by the pipe's cross-sectional area. However, it cannot directly measure the internal diameter and pipe roundness, only estimating the cross-sectional area based on the outer diameter and wall thickness, which introduces uncertainties exceeding 1%, limiting accuracy.
(7) Short service life (typically, accuracy can only be maintained for two years).
The ultrasonic liquid flow meter accuracy is almost unaffected by the temperature, pressure, viscosity, or density of the measured fluid. It can also be made into a non-contact and portable measurement instrument, making it suitable for measuring highly corrosive, non-conductive, radioactive, and flammable/explosive media that other types of instruments struggle to measure.
Electromagnetic flow meters cannot measure liquids with very low conductivity, such as petroleum products and organic solvents. Due to liner material limitations, general electromagnetic flow meters cannot measure high-temperature liquids. Electromagnetic flow meters determine volumetric flow based on the velocity of conductive liquids. However, for liquid media, mass flow should be measured, considering fluid density variations with temperature. If the converter does not account for fluid density, only providing volumetric flow at normal temperature, the measurement is inaccurate.
The ultrasonic liquid flow meter determines volumetric flow by measuring fluid velocity. However, for liquid media, mass flow should be measured. The instrument calculates mass flow by multiplying volumetric flow by a preset density, but as fluid temperature changes, density changes. Presetting a fixed density cannot ensure mass flow accuracy. To obtain true mass flow, both fluid velocity and density must be measured.
Ultrasonic and electromagnetic flow meters use different measurement methods. Ultrasonic liquid flow meter use sound waves with frequencies ranging from 20KHz to 100KHz, whereas electromagnetic meters use 2.4GHz electromagnetic waves. Ultrasonic measurement is more restrictive and easily affected by iron-based objects. Additionally, lower frequencies result in higher attenuation, limiting the measurement range and making it suitable mainly for large-diameter pipelines and open channel flow measurement. Electromagnetic meters, with higher frequencies and lower attenuation, can measure large ranges, especially in storage tanks. However, dielectric constant considerations must be noted, as low dielectric media may not be measurable or may have a limited measurement range.
Ultrasonic liquid flow meter are suitable for large circular and rectangular pipelines and are not limited by pipe diameter. Their cost is generally independent of pipe size, making them ideal for large pipelines where real-flow calibration is impractical. They allow non-contact measurement, and clamp-on transducers can be installed externally without stopping flow or cutting pipes. This unique advantage makes them suitable for mobile measurement applications and pipeline flow assessment, as they do not cause pressure loss.
Electromagnetic flow meters are more complex to install and require stricter conditions. The transmitter and converter must be matched and cannot be mixed with different models. Installation requires selecting a site free from vibration and strong magnetic fields. The transmitter must have good contact with the pipeline and be properly grounded. It must also be at the same potential as the measured fluid. Air pockets in the measuring tube must be eliminated to avoid measurement errors. Electromagnetic meters require conductive liquids and are typically installed by cutting the pipeline. However, they offer high accuracy under suitable conditions. Disassembly is challenging, requiring process shutdowns for calibration, which must be done every six months for 0.5% accuracy.
Ultrasonic and electromagnetic flow meters each have advantages in different environments. For low-cost applications with lower accuracy requirements, ultrasonic liquid flow meter are preferable. When installation and maintenance budgets are sufficient and high accuracy is required, electromagnetic meters should be chosen. Measurement personnel should carefully assess interference sources in the working environment and take effective anti-interference measures accordingly.
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