Hangzhou Yankong Technology Co., Ltd
Common problems and solutions of electromagnetic flowmeter and orifice flowmeter
Release time：
2023-01-12 17:06
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The application of electromagnetic flowmeter has always been very extensive. Because it is specially designed for water metering business in water supply enterprises, it has the ability of waterproof, anti-corrosion, anti-interference, and anti-lightning.
1. The problem of sensor grounding The flow signal detected by the sensor electrode of the electromagnetic flowmeter is at the millivolt level, and it is based on the potential of the fluid in the sensor, so external interference has a great influence on it. Therefore, good grounding is largely It determines the measurement accuracy of the flowmeter. As the measured fluid itself is an electrical conductor, other irrelevant electromagnetic interference must be excluded. The potential signal detected by the electrodes is not disturbed by external parasitic potential. There should be a good separate grounding wire for the sensor, and the grounding resistance is less than 10Ω. If there is an insulating layer or long and short metal pipes in the pipeline connected to the sensor, grounding rings should be installed on both sides of the sensor. the
2. Effect of electrode lining attachments When measuring fluids with attached sediments, the electrode surface will be polluted and often cause zero point changes, so attention must be paid. Quantitative analysis of the relationship between zero point change and electrode contamination is difficult, but it can be said that the smaller the diameter of the electrode, the less affected it will be. During use, attention should be paid to cleaning the electrode to prevent adhesion. The error Δε generated when deposits are attached to the lining, if the attached thickness is the same, can be obtained by the formula: Δε=1-2/[1+(Kω/Kf)+(1- Kω/Kf )×(1-2t /D)2] calculation, where Kω and Kf are the conductivity of the deposit and the measurement fluid respectively, the thickness of the deposit is t, and the diameter is D. If in the formula, Kω and Kf are equal, there is no error. When the conductivity of the deposit is low, the above formula is also valid, but it is limited because it will increase the output impedance of the electrode. For example, the insulating sediment immersed in the fluid is This situation. On the contrary, if metal powder is attached, the induced potential will be short-circuited due to the high-conductivity adhesion layer, which will cause the electrode output to be low, resulting in a negative deviation. When measuring fluids with sedimentation deposits, in addition to choosing linings that are difficult to adhere to sedimentation such as glass or polytetrachloroethylene, the flow rate should also be increased. If the fluid contains air bubbles uniformly, the volume flow rate including the air bubbles is measured, and the measured flow value is not stable, and errors are introduced. To sum up, when choosing a flowmeter, especially a large-diameter electromagnetic flowmeter, the maintenance of the electrodes and lining of the sensor should be considered in the future. For example, choose the scraper electrode or replaceable electrode of Shanghai Guanghua Almate Instrument Co., Ltd., or preset a cleaning hole at an appropriate position upstream or downstream of the sensor, so as to clean the sensor in the future.
3. The length of the signal transmission cable The shorter the connecting cable between the sensor (ie electrode) and the converter, the better. However, some sites are limited by the location of the installation environment, and the distance between the converter and the sensor is relatively long. At this time, the maximum length of the connecting cable must be considered. The maximum length of the connecting cable between the sensor and the converter is determined by the distributed capacitance of the cable and the conductivity of the measured fluid. In actual use, when the conductivity of the measured fluid is within a certain range, the maximum length of the cable between the electrode and the converter is determined. When the cable length exceeds the maximum length, the loading effect caused by the distributed capacitance of the cable becomes a problem.
In order to prevent this from happening, a double-core, two-layer shielded cable is used, and the converter provides a low-impedance voltage source so that the inner shield and the core wire get the same voltage to form a shield, even if there is distributed capacitance between the core wire and the shield. But the core wire and the shielding are at the same potential, so there will be no electricity flowing between them, and there will be no loading effect of the cable, so the maximum length of the signal cable can be extended. In addition, special signal transmission cables can be used to extend the maximum length between the converter and the sensor.
flow meter,electromagnetic
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