One set DN50mm vortex flow meter, we checked the instruction and found that the liquid flow range is 3~50 m3/h. The result we calibrated on the oil flow standard device is that 10~50 m3/h meets the accuracy requirement. But the accuracy below 10 m3/h is not qualified. How should we evaluate this flow meter?

In the manual of vortex flow meter, the flow range indicated is used for a specific reference medium flow range, such as liquid, generally indicated the room temperature water. For other medium, the available flow range will vary with the viscosity and density of the medium. As the oil flow standard device for diesel oil with greater viscosity and smaller density than water as the calibration medium, the lower limit flow of the flow meter will be increased correspondingly, and the available flow range will be narrowed. Therefore, it is normal for the vortex flow meter to have a small flow performance deterioration in the oil flow calibration device.Therefore, it is not difficult to infer that if LPG (this low viscosity medium) is used to calibrate the vortex flow meter, the opposite result will be better than water.

1.The flow range of vortex flow meter is large, usually is 10:1, but the lower limit of measurement is limited by many factors: Re>10000 is the basic condition for operation of a vortex flow meter. In addition, it is also subject to response signals generated by vortexes.The upper limit of the measurement is the frequency response of the sensor and the frequency limit of the circuit. Therefore, the range of the flow velocity must be calculated and checked during the design, and the flow velocity should be selected according to the flow velocity of the fluid.The environmental conditions of the site are complex. In addition to environmental temperature, humidity, atmosphere and other conditions, electromagnetic interference should also be considered when selecting the model.

2.Vibration is also a strong enemy of this kind of instrument. Therefore, attention should be paid to avoid mechanical vibration in use, especially the transverse vibration of pipeline (vertical to the axis of pipeline and vertical vortexes), which cannot be suppressed and eliminated in the design of flow meter structure.Since the vortex street signal is also sensitive to the influence of the flow field, it is not appropriate to use the straight pipe section length when it can’t guarantee the necessary flow conditions to stabilize the vortex street.Even the capacitance type and ultrasonic type with strong vibration resistance can ensure that the fluid is a fully developed one-way flow, which can’t be ignored.

3.The medium temperature also has a great influence on the performance of vortex flow meter. Such as the pressure stress type vortex flow meter can't use for a long time in the state of 300℃, because of its insulation impedance will by room temperature 10~100MΩ drops to 1~101Ω, and the output signal is smaller, leads to the deterioration of the measured characteristics. In the measurement system, the sensor and the converter should be installed separately, so as not to affect the reliability and service life of the instrument.

The Vortex flow meter is a relatively new type of flow meter, which is still in the development stage and not very mature. If the choice is not suitable, the performance will not play well. Only after reasonable selection, correct installation, but also in the use of the process of serious regular maintenance, continuous accumulation of experience, improve the predictability of the system failure and judgment, the ability to deal with problems, so as to achieve satisfactory results.