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Maintenance of electromagnetic flowmeters must learn to use scientific methods

With the continuous advancement of human science and technology, the design and manufacture of electromagnetic flowmeters and the stability and stability of measurement have also developed rapidly. Now the electromagnetic flowmeters we see at industrial production sites are not only beautiful in appearance, but also in measuring components. The products are not in the same breath, and with the integration of large-capacity and high-speed computing chips, the measured data is quite reliable. In order to help the users have a correct understanding of the electromagnetic flowmeter, it can be targeted when selecting the electromagnetic flowmeter, and the correct selection of the instrument can be combined with the actual application, the working principle of the electromagnetic flowmeter, and the actual selection The position and installation give corresponding precautions, and at the same time, combined with the actual troubleshooting examples, the relevant maintenance procedures are introduced. It can be said that the electromagnetic flowmeter plays an important role in industrial flow monitoring. The technicians should continuously learn and upgrade relevant skills to provide better service and application promotion services for the electromagnetic flowmeter. Applications such as installation and selection, maintenance and troubleshooting are described.
First, the working principle of electromagnetic flowmeter
When the conductor performs the cutting magnetic line motion in the magnetic field, the corresponding induced electromotive force is generated at both ends, that is, Faraday's law of electromagnetic induction. In addition, when the conductive liquid flows in a tube (not magnetic) perpendicular to the magnetic field, a proportional induced electromotive force is generated perpendicular to the flow direction, according to the right hand rule,
E=kBDV
Where E is the induced electromotive force, V; k is a constant; B is the magnetic induction, T; D is the inner diameter of the tube, m.
According to the composition of the electromagnetic flowmeter, it can be divided into two parts: the transmitter and the flow sensor. The coil is respectively provided with a coil on the upper line of the tube. After being energized, a magnetic field is generated through the inside of the tube; and at the contact between the liquid and the wall of the tube, there is an electrode device capable of transmitting the generated induced electromotive force to the transducer portion, and the induced current is caused by Transformers to provide.
Second, the scientific application of electromagnetic flowmeter
Type selection
(1) Selection according to flow rate, flow rate and caliber
When the flow reaches the full stroke, the flow rate of the liquid can be selected from a wide range and can range from 1 to 12 m/s. Generally, the upper limit of the flow rate cannot be greater than 5 m/s, and the lower limit of the flow rate is set to 1 m/s. When the electromagnetic flowmeter is used as an abrasion resistant fluid such as slurry or sand, the flow rate is often controlled to be 2 to 3 m/s or less, which is prescribed for the purpose of reducing wear of the electrode and the liner.
Generally, electromagnetic flowmeter products range from 10mm to 3000mm. In practical engineering applications, there are many uses for small-caliber electromagnetic flowmeters.
(2) Selecting according to the conductivity of the fluid to be tested
In practical industrial applications, the electromagnetic flowmeter is designed for the conductivity of the measured liquid, and its valve threshold is set in the range of (5 × 10-6) to 10-4 s / cm according to the relevant regulations, and the threshold is due to electromagnetic The type of flow meter varies.
(3) Selecting according to the mixture contained in the fluid to be tested
When the zinc is smelted by the wet method, the slurry often contains more large particles, and when these large particles are rubbed on the surface of the electrode, the signal stability of the fluid is disturbed. If the electromagnetic flowmeter with a diameter of 80mm is used for the comparison test of the slurry flow rate and the clean water, then under normal circumstances, the electromagnetic flowmeter will show a numerical change within 7% to 10%, and the instrument error of the magnetic flux induction coil is also provided. Approximate within ±2%.
2. Selection and installation
(1) Precautions for selection
The general electromagnetic flowmeter has the protection level of IP65. Pay attention to the following points when installing the location:
, as far as possible to avoid direct sunlight; second, to ensure that away from the water source, to avoid direct leaching of rain; third, the ambient temperature is guaranteed to be in the range of minus 25 to 10 ~ 50 ° C; fourth, with large transformers, motors Isolation of equipment that will cause large electromagnetic field interference; Fifth, anti-vibration, avoiding the selection of places with large vibrations, which is important for large integrated electromagnetic flowmeters; sixth, with corrosive high-concentration gases Separate.
(2) Precautions during the installation process
a. Installation direction: to ensure that the upstream of the electromagnetic flowmeter is about 10D distance, and the downstream air is about 5D straight pipe section. It should be ensured that the sensor of the electromagnetic flowmeter can be moved horizontally, tilted and vertically without being blocked. When measuring the solid-liquid two-phase fluid, the horizontal position will increase the wear of the lower part of the liner, so the vertical position is placed as Suit it to flow from bottom to top.
b. Install the negative pipe pressure: avoid shrinkage after the fluid is cooled as much as possible on the sensor and the downstream valve, because the shrinkage will make the pressure inside the pipe become negative.
c. Grounding: Under normal circumstances, the sensor of the electromagnetic flowmeter should be grounded separately, and the grounding resistance is 100Ω. If the electrolyte leakage affects the normal measurement, the electromagnetic flow sensor should be isolated from the connected electrical equipment. .
d. Bypass pipe: It should be installed in accordance with the principle of facilitating the cleaning of the electromagnetic flowmeter sensor.

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