Method for measuring pulsating flow by electromagnetic flowmeter Posted by : admin / Posted on : Apr 15， 2020

Pulsating flow is common in industrial pipe flow. It may be generated by rotary or reciprocating prime movers, compressors, blowers, and pumps. Rotating machinery with wings can also generate small pulsations at the blade passing frequency. Some volumetric flowmeters can also generate pulsations. Resonance caused by vibration, oscillation of pipeline operation and control system, flow separation caused by valve "hunting", pipeline fittings, valves or rotating machinery are also possible sources of flow artery movement.
There are three methods to measure the pulsating flow rate: 1. Use a flowmeter with a fast response; 2. Attenuate the pulsation to a sufficiently small amplitude with an appropriate method, and then measure it with a common flowmeter; The measured flow value is corrected for errors. In some systems, the latter two methods need to be combined to achieve the measurement. This is because the amplitude of the pulsation is large, which is beyond the applicable range of the estimation formula. If only the damping method is used, the attenuated pulsation amplitude fails to enter the stable flow range. .
When the electromagnetic flowmeter selects a higher excitation frequency, it can respond quickly to the pulsating flow, so it can measure the pulsating flow. It is commonly used to measure the outlet flow of reciprocating pumps and diaphragm pumps. The electromagnetic flowmeter used for pulsating flow measurement usually needs to be specially designed in the following three aspects, and be properly debugged when it is put into operation.
(1) The excitation frequency is adjustable in order to obtain an excitation frequency suitable for the pulsation frequency. Too high and too low are disadvantageous.
(2) The analog signal processing part of the electromagnetic flowmeter should prevent it from entering a saturated state when the peak of pulsation comes. The pulsating peak value of the pulsating flow is sometimes surprisingly high. If the peak value occurs, the flow signal input channel of the electromagnetic flowmeter enters a saturated state, just as the peak value is eliminated, which will inevitably cause the instrument to indicate a low value.
(3) In order to read the average value, the display part should be smoothed. Because the measuring part of the electromagnetic flowmeter can quickly respond to the change of the pulsating flow rate and truly reflect the actual flow rate, but if the display part also displays the actual flow value faithfully, it will inevitably cause the display value to jump greatly up and down, which is difficult to read, so the display should be taken The average value over time. The implementation method is usually to insert an inertial link. After selecting an appropriate time constant, the instrument can display stably. But if the time constant is chosen too large, when the average flow rate changes, the display part responds sluggishly, giving the observer an illusion.