Electromagnetic Flowmeters Installation and selection tips
Author: Source: Date: 2018-05-21 17:16:23
Electromagnetic flowmeter is made according to Faraday's electromagnetic induction law. Electromagnetic flowmeter is used to measure the volume flow of conductive liquid. Electromagnetic flowmeter consists of two parts: electromagnetic flow sensor and converter. Because of its unique advantages, electromagnetic flowmeters have been widely used in the flow measurement of various conductive liquids in industrial processes, such as various corrosive media such as acids, alkalis, and salts.
Selecting the type, specification and installation method of the flowmeter according to the measuring object, measuring medium parameters and working conditions is the most important part of the selection of the electromagnetic flowmeter. For the final use of the unit, the selection points are as follows:
1. Accuracy level and function
According to the measurement requirements and use occasions, select the electromagnetic flowmeter accuracy. For applications such as trade settlement, product handover, and energy metering, the accuracy should be higher (e.g., class 1.0, class 0.5, or higher).
2. Test media flow rate, instrument range and caliber
When measuring general media, the full flow of the electromagnetic flowmeter can be measured in a wide range of media flow rates of 0.5-12m/s. The instrument specification (caliber) is not necessarily the same as that of the process piping. The measurement flow range should be determined within the flow rate range. That is, when the flow rate of the pipeline is too low to meet the requirements of the flow meter, the diameter of the instrument needs to be reduced, thereby increasing the flow rate in the tube and obtaining satisfactory measurement results. Measuring liquid with good conductivity, the maximum flow rate does not exceed 5m/s, and the economic flow rate ranges from 1.5m/s to 3m/s.
3. Electrode material and ground ring material
The electrode's corrosion resistance to the measuring medium determines which electrode material is selected and at the same time it requires no surface effects at the electrical level. In other words, the corrosion resistance of the electrode is an important basis for selecting the material.
Grounding ring material should be the same as the electrode, otherwise it is easy to generate electrochemical polarization potential. Generally, choose 316L or Hastelloy, economic considerations are less expensive to use your precious metals such as rhodium, platinum, etc.
The metal process pipe is in direct contact with the medium. The ground wire is directly connected to the metal pipe or flange, so no grounding ring is required.
Electromagnetic flowmeter installation environment requirements
1. Keep away from equipment with strong electromagnetic fields as much as possible. Such as large motors, large transformers, etc.
2. The installation site should not have strong vibration and the ambient temperature does not change much. Easy to install and maintain places.
3. Selection of installation location: The direction of flow on the sensor and the measured medium flow in the pipeline must be the same.
4. The mounting position must ensure that the measuring tube is always filled with the measured medium.
4. Select where the fluid flow pulse is small, ie keep away from the pump and local resistances (valves, elbows, etc.).
5. When measuring two-phase fluids, choose a place that is not likely to cause phase separation.
6. Should try to avoid installing the earth pressure in the pipe showing negative pressure.
7. In order to clean the electrode and measuring tube without interrupting the flow in the process pipeline, the sensor can be installed in parallel with a cleaning port.
8. Requirement of upstream straight pipe section The sensor requires 5 times the upstream straight pipe section to the sensor caliber. There is no direct pipe section requirement for the downstream of the sensor, and the downstream non-straight pipe section will not affect the measurement accuracy of the flow meter. 9. When the upstream and downstream straight pipe sections have the path When the sensor is inconsistent, install a gradually expanding or reducing tube with a cone angle of less than 150 (preferably 7-80) and then connect it to the pipe.
9. The flow signal generated by the ground sensor is very weak, usually microvolts and millivolts, so preventing the influence of external electrical interference is an important factor in using the flowmeter.
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