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How to effectively solve the noise flow of electromagnetic flowmeter

How to effectively solve the noise bubbles of electromagnetic flowmeter? Electromagnetic flowmeters are often seen in many places. Most of the false alarms in the measurement of cooling water in the steel industry are caused by bubbles rubbing through the electrodes, forming a short-time induction signal of zero. This is a cavitation phenomenon, which we call bubble noise. Let me introduce the avoidance and solution of the bubble noise problem.

Firstly, it should meet the requirements of the length of the straight pipe section upstream of the electromagnetic flowmeter from the installation, standardize the installation of the instrument, choose the installation place away from the heat source, use the pipeline flow rate reasonably, and select the PFA fluoroplastic lining with high finish and the high-purity alumina industrial ceramic conduit. These measures will help prevent or reduce the occurrence of vortices and gas separation. That is to say, improving the sensor manufacturing process, improving the environmental conditions and installation conditions of the instrument, and adopting measures such as installing an exhaust valve upstream of the instrument may prevent problems from occurring.

Secondly, reasonable setting of the electromagnetic flowmeter damping time and function can also solve the false alarm of bubble noise measurement. The choice of damping time is based on the pulse width of the bubble noise in the flow signal. Generally, the damping time should be 3 to 5 times the pulse width of the bubble noise. If the bubble noise pulse width is 10s, the damping time should be 30~50s. The specific selection should be based on the required control accuracy, 3 times the pulse width control error is 5%, and the 5 times pulse width control accuracy is higher than 1%.

Increasing the meter damping time can effectively solve the influence of this pulse-type bubble noise, and also brings the disadvantage of slow response, that is, when the real flow fluctuates, the meter reacts slowly. This is undoubtedly a problem for cooling water systems that require sensitive control. In order to solve this problem, the intelligent electromagnetic flowmeter can use software logic to judge the method of coarse error processing. In the event of such a fault, it is judged whether the flow is changed by adjusting the insensitive time of the flow and the range of the change, or whether the bubble is wiped over the electrode. If it is not the noise of the bubble rubbing the electrode, the CPU performs normal sampling, calculation and digital filtering; if it is determined that bubble noise is generated, the measured value is cut off and the previous flow measurement value is maintained. Thus, the damping time during normal flow measurement is still 3~6s. Only when there is bubble noise, the length of the pulse width is lengthened according to the length of the pulse width setting, and the system control time is also lengthened.

When we reasonably choose the rate-of-change limit value and the insensitive time value of the electromagnetic flow converter with coarse error suppression function, the converter can not only suppress false alarms caused by bubble noise, but also maintain the response speed of the instrument during normal operation. Set the damping time value.

The above is how to effectively solve the noise bubble method of electromagnetic flowmeter, I hope to help all the friends who use electromagnetic flowmeter!

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