In petrochemical, chemical, electric power, metallurgy, municipal, pharmaceutical and other industries, the technical difficulty and complexity of flow measurement are quite high. Research flow measurement plays an important role in improving product quality, reducing enterprise operating costs, and solving energy conservation and environmental protection. The electromagnetic flowmeter has the advantages of no resistance and no pressure loss, can fully reduce the resistance in the pipeline, meets the requirements of energy saving and consumption reduction, and thus the electromagnetic flowmeter has been widely concerned in the industry. However, although the electromagnetic flowmeter has the above advantages, and is much better in reliability and stability than most other types of flowmeters, in the actual use process, some problems will still occur. Below Huaheng Instrument will list for you. The main points that electromagnetic flowmeters need to pay attention to in engineering applications.
1. The transmitter should be installed at any time to measure the position where the catheter can be filled with liquid to prevent the illusion that the pointer is not at zero due to the absence of liquid in the measuring catheter. It is mounted vertically to reduce errors due to the flow of liquid through the bubbles on the electrodes. If placed horizontally, the two electrodes of the flowmeter must be kept at the same level to prevent it from being insulated by deposits or air at the top of the tube.
2. If necessary, the tube can be emptied, and the built-in empty tube detection line will stop the accumulation and flow signal output.
3. When installing an electromagnetic flowmeter in a fluid flowing in an anode-protected pipeline, the following points should be observed: In order to allow the fluid to be well grounded, the ground ring should be used; when the sensor is connected with the pipeline, there must be insulation between the flanges. Insulation sleeves are also used on the pads and screws.
4. When the electromagnetic flowmeter is installed on the grounded metal pipe, the system potential balance is realized by the grounding terminal on the electromagnetic flowmeter transmitter, that is, the copper core wire with the sectional area of not less than 6mm2 is connected to the grounding terminal; The flowmeter is installed on an ungrounded metal pipe. Both flanges are connected to the pipe flange through a copper core wire with a cross-sectional area of at least 6 mm2, and grounded; connect the transmitter or sensor junction box to the ground terminal. The system potential balance is realized; when the electromagnetic flowmeter is installed on a plastic pipe or a pipe with an insulating lining, the system potential balance is achieved by an additional grounding ring, and the grounding ring is connected to the grounding terminal through a copper core wire having a cross-sectional area of at least 6 mm2.
5. The electromagnetic flow transmitter should be installed in the indoor dry and ventilated place to avoid installation in places where the ambient temperature is too high. It should not be subjected to strong vibration. Try to avoid equipment with strong magnetic field, such as large motor, transformer, etc., to avoid installation. In the case of corrosive gases, the installation site is easy to access, which is the environmental condition to ensure the normal operation of the transmitter.
6. In order to ensure that the measuring tube of the electromagnetic flow transmitter is filled with the measured medium, the transformer is installed vertically, and the flow direction is from bottom to top, especially for the liquid-solid two-phase flow, which must be installed vertically. If the site is only allowed to be installed horizontally, it must be ensured that the two electrodes are at the same level.
7. Both ends of the electromagnetic flow transmitter should be equipped with valves and bypass.
8. The millivolt AC potential measured by the electrodes of the electromagnetic flow transmitter is based on the liquid potential in the transmitter. In order to stabilize the liquid potential and maintain the potential of the transmitter and fluid to ensure stable measurement, the transmitter shell and the metal tube should have good grounding at both ends, and the converter housing should also be grounded. The grounding resistance should not exceed 10 Ohm, cannot be shared with the ground wire of other electrical equipment. If the transmitter housing is not guaranteed to be in good contact with the metal tubing, connect them with metal wires and ground them reliably.
9. In order to avoid interference signals, the signal between the transmitter and the converter must be transmitted by shielded wires. It is not allowed to place the signal cable and the power cable in parallel in the same cable. The length of the signal cable should not exceed 30m.
10, the converter installation site should avoid AC and DC strong magnetic field and vibration, the ambient temperature is -20 ~ 50 ° C, and can not contain corrosive gases, the relative humidity is not more than 80%.
11. In order to ensure the normal operation of the electromagnetic flowmeter and reduce the measurement error, the electromagnetic flowmeter should meet the requirements of a certain straight pipe section before and after. According to JJG 1033-2007 "Electromagnetic Flowmeter Verification Regulations" test standard requirements, usually the front straight pipe section should reach 10D, and the rear straight pipe section should be 5D.
12. Installation location. The electromagnetic flowmeter can be installed vertically and horizontally, but vertical installation is recommended, and the fluid to be measured flows from bottom to top. It can also be installed horizontally, but with the two electrodes on the same level. When installing horizontally, make sure that the measuring catheter is filled with liquid. When the main line is a vertical line, in general, the water flow is required to be bottom-up, and try not to go from top to bottom. The latter is prone to cause large fluctuations in traffic. It is also important to install the full pipe, followed by the distance between the straight pipe. Choose a place that is easy to maintain and convenient for activities. The flowmeter should be installed at the rear of the pump and must never be installed on the suction side: the valve should be installed on the downstream side of the flow.
13. Since the electromagnetic flowmeter measures the weak potential, it is necessary to eliminate all external disturbances to accurately measure, so good grounding is a necessary condition to ensure the stable operation of the electromagnetic flowmeter. Usually grounding is achieved by a grounding ring or a reference electrode in the sensor and a ground connection to the piping system.
14. The installation location of the flowmeter should be away from all magnetic sources (such as high-power motors, transformers, etc.).
15. Like other flowmeters, electromagnetic flowmeters also have a degree of protection. Usually the integrated protection grade is IP65, and the split type is IP68 (for sensors). If the customer has requirements for the installation environment of the instrument, the installation location is underground. Wells or other wet places, customers are advised to use split type. In order to avoid damage to the instrument caused by wrong selection.
16. The electromagnetic flowmeter can measure corrosive liquids, but the customer should correctly provide the properties of other measuring media at the beginning of ordering, so as to avoid errors in the selection of the electrodes during the selection, which leads to the scrapping of the sensor in the later use process, which brings inconvenience to the customer. Economic loss.
17. Although the electromagnetic flowmeter has better reliability, it will not be damaged under normal circumstances. However, due to its principle, the surface of the sensor electrode is always in contact with the liquid. For a long time, the surface of the electrode is relatively susceptible to contamination. Therefore, under normal circumstances, the electromagnetic flowmeter is recommended to be removed by the customer. It is recommended to remove the electrode once a year to one and a half years to ensure the measurement accuracy of the flowmeter. Any instrumentation needs to be “maintained”, and electromagnetic flowmeters are no exception.