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Electromagnetic Flowmeter Selection and Installation - Focus on Microfluidic Control Technology

Reasonable selection and precise equipment electromagnetic flowmeter are very important for ensuring measurement accuracy and extending the life of the surface. The following is a brief introduction of the principle of electromagnetic flowmeter selection, equipment conditions and application of precautions.
(A) Selection principle of electromagnetic flowmeter
The selection of the electromagnetic flowmeter is mainly the precise selection of the transmitter, and the converter only needs to be matched with it.
1. The choice of caliber and range
Transmitter diameter is generally the same diameter as the pipe system. Assuming that the pipeline system is to be planned, the caliber can be selected based on the flow planning and flow rate. For the electromagnetic flowmeter, the flow rate is suitable for 2-4m/s. In exceptional circumstances, such as liquids with solid particles, taking into account the situation of the wear, the optional common flow rate ≤ 3m / s, for the easy handling of the fluid. Optional flow rate ≥ 2m/s. After the flow rate is judged, the transmitter caliber can be determined according to qv=D2.
The range of the transmitter can be selected according to two principles: First, the surface full-scale is greater than the expected maximum flow value; Second, the normal flow is greater than 50% of the surface full-scale to ensure a certain measurement accuracy.
2. Lining material and electrode tree selection
The lining material and electrode material of the transmitter must be accurately selected according to the physical and chemical properties of the medium, otherwise the surface will be damaged quickly due to the corrosion of the fabric and the electrode, and the leakage of the highly corrosive medium will cause the event. Therefore, it is necessary to carefully select the electrode and cloth material according to the specific measurement medium in the production process.
The choice of temperature and pressure
Electromagnetic flow meters can measure fluid pressure and temperature with certain limits. When selected, it is necessary to use pressure lower than the working pressure of the flowmeter. Now, the working pressure specifications for domestically produced electromagnetic flowmeters are:
Less than 900 mm diameter, working pressure 1MPa;
More than 1000mm diameter, working pressure is 0.6MPa.
Less than 50mm diameter, working pressure is 1.6MPa; If there is extra pressure on the transmitter pressure, you can discuss with the manufacturer. Some manufacturers have been able to produce electromagnetic flow transmitters with a withstand voltage of 32 MPa.
The working temperature of the electromagnetic flowmeter depends on the fabric material used, generally 5-70°C. If you do special treatment, you can go beyond the above-mentioned plans, such as wear-resistant and corrosion-resistant electromagnetic flowmeter produced by Guangzhou Instrument Control Factory. The transmitter allows the temperature of the measured medium to be -40 to 130 °C.
Electromagnetic Flowmeter
(B) Electromagnetic flowmeter equipment
To ensure the measurement accuracy of the electromagnetic flowmeter, accurate equipment is very important.
1 transmitter should be equipment in the indoor monotonically ventilated place. Avoid the equipment in the local environment temperature is too high, should not be subject to severe vibration, try to avoid equipment with a strong magnetic field, such as large motors, transformers and so on. Avoid equipment in the presence of corrosive gases. The equipment address is easy to repair. This is the environmental condition that guarantees the normal operation of the transmitter.
2 Both ends of the transmitter should be equipped with valves and bypass.
3 In order to ensure that the measuring tube of the transmitter is filled with the measured medium, the changer is preferably vertical and flows from bottom to top. Especially for liquid-solid two-phase flow, vertical equipment is necessary. If the site only allows horizontal equipment, it is necessary to ensure that both electrodes are at the same level
4 In order to avoid annoying signals, the signal between transmitter and converter must be transmitted with shielded wires. It is not allowed to place the signal cable and the power cable in parallel in the same cable duct. The signal cable length must not exceed 30 m in general.
5 The millivolt communication 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 position the transmitter and the fluid to maintain equal potential, in order to ensure a stable measurement, the transmitter housing and the metal tube should have outstanding grounding at both ends, and the converter housing should also be grounded. The grounding resistance cannot be greater than 10, and cannot be shared with the grounding wire of other electrical equipment. Assuming excellent contact between the transmitter housing and the metal pipe is not guaranteed, use metal wires to connect them. And then reliable grounding.
6 In order to avoid the impact of flow rate relative measurement, the flow control valve should be set under the transmitter. For a small-diameter transmitter, since the distance from the center of the electrode to the inlet of the flowmeter is equivalent to several times the length of the diameter D, the upstream straight tube may not be used as a rule. However, for larger diameter flowmeters, generally there should be more than 5D straight sections in the upper stream, and the lower section generally does not make straight sections.
7 converter equipment address should avoid AC, DC strong magnetic field and vibration, ambient temperature is -20 to 50 °C, does not contain corrosive gases, relative humidity is not more than 80%.

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