Two things to note when using vortex flowmeters

Thread Content

Every device has its own specific usage guidelines, and vortex flowmeters are no exception. Today, I’ll tell you about two key points that should be taken into account when using vortex flowmeters. Determine the minimum flow rate and select an appropriate diameter. First, the upper and lower limits of flow rate as well as the normal flow rate specified for the process are analyzed; the flow rate in kg/m3 is converted into the flow velocity under operating conditions (in m/s). Within the normal measurement range of the vortex flow meter, the Reynolds number Red lies between 2×104 and 7×106. Within this range, the accuracy of flow measurement can reach the level specified by the technical specifications; exceeding this range will result in significant measurement errors. Vortex flow meters can measure upper flow velocities; generally, this is 60 m/s for gases, 70 m/s for steam, and 7 m/s for liquids. The characteristic of vortex flowmeters is that they are sensitive to low flow rates but not to high ones; therefore, it is crucial to determine the lower flow limit for vortex flowmeters. Under normal circumstances, the diameter of the instrument selected should ensure that the flow velocity of gas is not less than 7 m/s, and the flow velocity of liquid is not less than 0.7 m/s. If the flow rate does not meet this requirement, intermittent reduction or expansion should be appropriately employed to minimize pipe losses. When selecting the caliber, it is also necessary to avoid situations where the frequency generated by normal flow rates is around 50 Hz, as power-frequency interference entering the instrument is not easy to detect and can lead to measurement errors. Dynamic compensation must also be carried out. Since a vortex flow meter can only measure the volume of fluid under the prevailing conditions in the pipeline, changes in parameters such as flow rate, pressure, and temperature cause the density to change, while the volume under those prevailing conditions remains constant. As a result, the frequency generated by the vortex flow meter does not change; hence, the same frequency can correspond to different flow rates under standard conditions. Therefore, when measuring gases and superheated steam, pressure and temperature compensation must be applied; when measuring saturated steam, pressure compensation is required, while for measuring liquids, temperature compensation is necessary. A vortex flow meter consists of a sensor and a display instrument. Generally, the accompanying display instruments come equipped with various compensation functions that users can adjust as needed. A vortex flow meter consists of a sensor, a counting and display unit, and a pre-amplifier. Its counting and display unit can count the signals output by the converter, thereby enabling functions such as recording, storing, calculating, and setting flow rates. Also known as its secondary instrument, it is composed of a single-chip microcomputer system. In addition, it can also be used to control the liquid crystal display to show information such as the measured instantaneous flow rate and total flow rate. However, some Yokogawa vortex flowmeters are capable of communicating data with remote computers, featuring communication interfaces that are used for dynamic monitoring.