The steady operation of vortex flow meter is related to the quality of vortex flow meter, selection/installation/parameter setting of vortex flowmeter, field interference and many other factors. This paper analyzes the application problems of vortex flowmeter from the shallow to the deep through six fault phenomena, which is worth careful reading and collection by instrument technicians.

Six common faults in vortex flowmeters

Phenomenon 1: The vortex flowmeter shows stable value and clear trend, but the error is obvious.

Analysis: Setting and configuration error in DCS.

The square root operation is the most common error (the square root operation is only for the differential pressure flowmeter, the vortex flowmeter flow total calculation does not need to open the square), and the common temperature and pressure conversion formula, the density query formula error, and the correction error can be corrected.

Phenomenon 2: when starting up, the vortex flowmeter shows a value of zero. When the process is normal, the measurement is normal.However, in normal production, the flow rate is slightly small and then returns to zero. When the flow rate is large, the measurement is normal

Analysis: the lower limit of the flowmeter is higher than the small flow rate when starting, the problem is: the diameter of the flowmeter is too large, or the lower limit of the flowmeter itself is too high.

The lower limit can be reduced by increasing the sensitivity, but there is likely to be no flow and an indication. The reason is that: under high sensitivity, the interference is mistakenly identified as vortex flowmeter signal, so products with smaller diameter should be replaced to enhance the flow signal, which may lead to three problems.Therefore, it is better to replace products with lower measurement limits.

Phenomenon 3: When the flow rate is large, the vortex flowmeter error is serious, and even the body/sensor breakage occurs.

Analysis: The stability of the vortex street tends to deteriorate with the increase of the flow velocity. If it cannot be effectively suppressed, the number of vortices will be generated, that is, the phenomenon of “leakage wave”. After the common flow exceeds the upper limit, the flow rate increases. The smaller the value of the "reverse" phenomenon, the more common error, the greater risk is the body break in the sensor / vortex.

Here, the risk of fracture of the vortex generator and the vortex street sensor must be removed first, and the larger diameter specification must be replaced, but the phenomenon is easy to occur. Therefore, replacing a product with a higher measurement limit is a better solution.

Phenomenon 4: no flow, vortex flowmeter has indication value; after adjustment, zero point is stable, but there is flow, and there is no indication

Analysis: When there is no flow, the vortex flowmeter outputs an interference signal. By reducing the sensitivity and discarding the interference, the flowmeter can be reset to zero. However, if the intensity of the interference signal is higher than the maximum flow of the vortex signal, it means: discarding the interference. At the same time, the flow signal is completely discarded and the flow meter is not available.

Phenomenon 5: abnormal fluctuation of indication value, large error of vortex flowmeter

Analysis: Insufficient straight pipe section, excessive installation eccentricity, large-size foreign object hanging/attaching, gas-liquid coexistence and other conditions that damage the Karman vortex street, the flow meter will misunderstand the turbulent flow and the whirlpool as the vortex signal.

Phenomenon 6: The flow changes, while the vortex flowmeter shows the value is basically the same, or the change is chaotic, it can not reflect the flow change trend

Analysis: The vibration interference and electromagnetic interference signal intensity exceeds the vortex signal intensity at the maximum flow rate. The flowmeter outputs the interference signal frequency, which has nothing to do with the vortex frequency. Therefore, it is independent of the flow rate, the envelope contains flow information, and the other is interference.