Currently, electromagnetic flow meters are the most commonly used method for measuring wastewater discharge in cities and industries. Electromagnetic flow meters offer high accuracy and long service life, making them the preferred choice in the environmental metering industry. Proper selection of the electromagnetic flow meter is crucial for its optimal performance, taking into account factors such as the chemical properties of the fluid medium, pipe diameter, flow range, lining material, electrode material, and output signal.
I. Measurable fluid media
Based on the principle of electromagnetic flow meters, we know that they can be used with conductive liquids; any liquid with a conductivity greater than 5 μ/cm can be used with an electromagnetic flow meter. However, electromagnetic flow meters are limited to measuring only liquids and cannot measure gases, steam, etc.
II. Choice between integrated or split type
Electromagnetic flow meters come in integrated and split types. Integrated flow meters are generally used in favorable environments, where the sensor and converter are integrated. Split flow meters, on the other hand, have separate sensors and converters, and are typically used in situations where data readings are not suitable. Examples include high ambient temperatures, significant pipeline vibration, corrosive environments, and flow meters installed at high altitudes. In such cases, a split flow meter with a 10m cable connected to the converter is used to ensure the converter operates in a suitable environment.
III. Sensor Aperture Selection
Generally, for ease of installation, reducers should be avoided. However, this is contingent on the applicable flow velocity within the flowmeter tube being within the range of 0.3 m/s to 10 m/s. This selection is often applicable to newly designed projects, where the current operating conditions and future full-load operation of the equipment must be considered when choosing the flow velocity. However, sometimes the sensor diameter may differ from the diameter of the connected process piping. For example:
(1) The flow velocity in the pipeline is low and the process flow rate is relatively stable. In order to meet the requirements of the instrument for the flow range, the flow velocity is locally increased at the flow meter. The sensor diameter is selected to be smaller than the process pipeline diameter, and reducers are installed before and after the sensor.
(2) For large-diameter electromagnetic flow meters, the larger the diameter, the higher the price. For situations where the flow velocity in the pipeline is low and the process parameters are stable, a flow meter with a smaller diameter can be selected. This not only allows the flow meter to operate in a better working condition, but also reduces investment costs.
IV. Selection of electrode materials: 316L electrode, tantalum electrode, HC electrode, platinum electrode, etc.
V. Selection of Grounding Ring Material
The grounding ring material can be the same as the electrode material, and generally, a material with the same corrosion resistance as the pipe material can be selected.
VI. Selection of Lining Materials
Depending on the medium, the following materials can be selected: PO material, rubber material, polytetrafluoroethylene material, polyurethane material, and ceramic lining.
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