1. Length of straight pipe section: meets basic requirements and flexibly responds to space limitations
Core requirements:
Electromagnetic FlowmeterIt is necessary to ensure uniform distribution of fluid velocity, usually requiring a straight pipe section of the first 10DN (pipe diameter) and the last 5DN. If there is insufficient space, the following measures can be taken:
Tilt installation: When the flowmeter is installed downstream of the elbow or valve, tilt the electrode axis at a 45 ° angle to the axis of the obstruction to avoid velocity sensitive areas and reduce errors caused by velocity asymmetry.
Installing a flow regulator: Installing a bundle type, AMCA grid type, or Zanker rectifier upstream of the flow meter can shorten the demand for straight pipe sections to the first 2DN and optimize the flow field distribution.
Flow coefficient correction: By on-site calibration, the flow coefficient is determined based on the actual length of the pipe fittings and straight pipe sections, eliminating the influence of installation conditions on accuracy.
Case: Due to space limitations, a sewage treatment plant was unable to meet the requirements of the first 10DN straight pipe section. By installing a Zanker rectifier and calibrating the flow coefficient, the measurement error was reduced from 5% to 1.2%.
2. Avoid electromagnetic interference sources: dual protection of physical shielding and grounding
Interference source:
The electromagnetic fields generated by large motors, transformers, frequency converters, and other equipment can interfere with flow meter signals, leading to measurement fluctuations.
Solution:
Physical shielding: Install a metal shielding cover (such as copper or aluminum material) around the flowmeter to isolate external magnetic field interference.
Reliable grounding:
The flowmeter casing, shielded cable, measuring body, and two end pipelines need to be separately grounded with a grounding resistance of ≤ 10 Ω.
Avoid connecting to electrical or public grounding grids to prevent interference caused by ground potential differences.
Anti interference model: Priority should be given to flow meters designed with special circuits (such as low-frequency rectangular wave excitation) to enhance their ability to resist electromagnetic interference.
Case: The electromagnetic flowmeter in a chemical plant fluctuated by ± 8% due to not being separately grounded; After installing a shielding cover and optimizing grounding, the fluctuation was reduced to ± 0.5%.
3. Full tube operation: prevent interference from bubbles and sediments
Key risks:
Non full tube state can lead to poor electrode contact, and the deposition of bubbles or solid particles can alter the flow field distribution, causing measurement errors.
Installation points:
Vertical installation: The fluid flows from bottom to top, ensuring that the pipeline is always filled with liquid and avoiding the accumulation of bubbles.
Horizontal installation: Keep the electrode axis horizontal to avoid sediment covering the electrode or bubbles gathering at the top of the pipeline.
Siphon design: If the pipeline is not fully filled or empty, install the flow meter on the U-shaped siphon and use the liquid level difference to ensure full pipe.
Case: After installing a flow meter horizontally in a sewage treatment plant, the measurement was interrupted due to sediment covering the electrode; After switching to vertical installation and regular cleaning, the operational stability was improved by 90%.
4. Avoid vibration and high temperature environments: ensure equipment lifespan
Environmental requirements:
Vibration source: Keep away from vibration equipment such as pumps and compressors, or fix the pipeline with shock-absorbing brackets to prevent sensor loosening or signal distortion caused by vibration.
Temperature and humidity: Installation environment temperature ≤ 60 ℃, relative humidity ≤ 95%, avoid direct sunlight or rainwater erosion, and prevent electronic components from aging.
Case: Due to long-term exposure to high temperatures, the lifespan of a flowmeter in a steel plant has been shortened to one year; After migrating to a cool place, the lifespan is extended to over 5 years.
5. Independent wiring of signal lines: reduce interference from power cables
Wiring specifications:
Separation of signal lines and power cables: Avoid parallel laying with high-voltage cables and frequency converter output lines, with a recommended spacing of ≥ 30cm.
Shielded cable usage: Use twisted pair shielded cables to transmit signals, with one end of the shielding layer grounded to prevent electromagnetic induction interference.
Software filtering: Enable digital filtering algorithms (such as moving average filtering) in the flowmeter settings to further eliminate noise signals.
Case: A power plant experienced a fluctuation of ± 15% in the output of a flow meter due to the laying of signal lines and power cables in the same conduit; After switching to independent wiring and enabling software filtering, the fluctuation decreased to ± 1%.