Electromagnetic flowmeter measurement principle is Faraday's law of electromagnetic induction to measure the volume flow of conductive liquid and slurry in the enclosed pipe, including acid, alkali, salt and other corrosive liquids. Electromagnetic flowmeter in the cooling water measurement of the steel industry, most of the false alarms are erased by the electrode bubbles to form a brief induction signal is zero, which is a cavitation phenomenon, which we call the bubble noise. Here to talk about the bubble noise problems and solutions.
First of all, the installation should meet the requirements of the electromagnetic flowmeter upstream straight pipe length requirements, regulate the installation of the instrument, choose a place far away from the heat source, the rational use of the pipe flow rate, the choice of high-quality PFA fluoroplastic lining and high purity alumina industrial ceramic conduit. These measures will help prevent or reduce the occurrence of vortices and gas separation. In other words, to improve the sensor manufacturing process, to improve the use of instrument environmental conditions and installation conditions, the use of upstream instrumentation to install exhaust valve and other measures, it is possible to avoid the problem.
Secondly, setting the electromagnetic flowmeter damping time and function reasonably can also solve the false alarm of the bubble noise measurement. The choice of damping time is based on the pulse width of the bubble noise in the flow signal. Damping time should generally be bubble noise pulse width of 3 to 5 times. If the bubble noise pulse width is 10s, damping time should be taken 30 ~ 50s. The specific choice should be based on the required control accuracy, 3 times the pulse width control error of 5%, 5 times the pulse width control accuracy higher than 1%.
Increasing the instrument damping time can effectively solve the impact of this impulsive bubble noise, but also brings the disadvantage of being unresponsive. That is, when the actual flow fluctuates, the meter responds slowly. This is undoubtedly a challenge for cooling water systems that require tight control. In order to solve this problem, the intelligent electromagnetic flowmeter can use software logic to judge that coarse error processing method. In the event of such a failure, by adjusting the flow of insensitive time and amplitude limits of these two conditions to determine the flow is changing, or the bubble erased electrode. If it is not the bubble erased electrode noise, CPU normal sampling, computing and digital filtering; if it is determined that the bubble noise is generated, cut off the measured value to maintain the previous flow measurement. In this way, the damping time during normal flow measurement is still 3 ~ 6s. Only when there is a bubble noise, the length of the pulse width will be insensitive longer, the system control time will be longer.
When we reasonably choose the rate-of-change limits and the insensitive time values ​​of the electromagnetic flow rate converter with coarse error suppression function, the converter can not only suppress false alarms caused by bubble noise, but also keep the response speed of the meter in normal operation Set the damping time value.
Electromagnetic flowmeter bubble noise research, the bubble should be on the electromagnetic flow sensor electrode simulation test, but so far there is no such condition. Therefore, we only use the electromagnetic flow signal generator signal switching, bubble noise simulation. Appropriately select the damping time and smart electromagnetic flowmeter bubble noise processing method, the observed flowmeter display and output signal changes, to determine the effect of dealing with bubble noise is obvious. Switch the switch of the standard signal source of the intelligent electromagnetic flowmeter to quickly set the flow rate and zero point, and keep the signal zero as needed to simulate the occurrence and existence of bubble noise. Change the instrument damping time and set different rate of change limits and insensitive time values, test instrument output changes. The results show that large damping time and intelligent bubble noise processing can achieve large changes in the output does not occur, the latter is more conducive to measuring the reaction rate during normal measurement increased.
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