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How to solve the description of bubble noise of electromagnetic flowmeter

The principle of electromagnetic flowmeter measurement is Faraday's law of electromagnetic induction to measure the volumetric flow of conductive liquids and slurries in closed pipes, including highly corrosive liquids such as acids, alkalis, and salts. Most of the false alarms in the measurement of cooling water in the steel industry are caused by bubbles rubbing through the electrodes, and the induced signal for a short period of time is zero. This is a cavitation phenomenon, which we call bubble noise. The following describes 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 impact 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 study of bubble noise of electromagnetic flowmeter should be carried out by using a bubble to simulate the electrode of the electromagnetic flow sensor, but this condition has not yet existed. Therefore, we only use the switching of the electromagnetic flow signal generator signal to simulate the bubble noise. Appropriately selecting the damping time and the method of intelligent electromagnetic flowmeter to deal with bubble noise faults, the effect of observing the display and output signal changes of the flowmeter and judging the treatment of bubble noise is obvious. Switch the switch of the standard signal source of the intelligent electromagnetic flowmeter, quickly set the flow rate and zero point, and keep the signal zero time as needed to simulate the occurrence and existence of bubble noise. Change the meter damping time and set different rate of change limits and insensitive time values to test the change in meter output. The results show that the increase of damping time and intelligent bubble noise processing can achieve no large changes in output, the latter is more conducive to the improvement of measurement reaction speed during normal measurement.

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