Vortex flowmeter is a new type of flowmeter developed in 1970s. Compared with other flowmeters, it has the following advantages: no movable parts in the instrument, simple structure, long service life, etc. But there are also some problems that need to be paid attention to.
1. Minimum Flow Problem
The amplitude of the vortex signal is proportional to the square sum density of the velocity of the medium under test. That is to say, when the detection sensitivity of the vortex flowmeter is constant, the working pressure of the fluid increases, the density increases, and the measured velocity decreases. Conversely, at a certain flow rate, if the working pressure of the fluid increases, the density increases, and the amplitude of the vortex signal increases, the detection sensitivity can be reduced. For atmospheric gas, the lower limit velocity of vortex flowmeter can reach 4-5m/s. For pressurized gases, such as compressed air, the lower limit velocity decreases as the density increases. So when choosing the type, we should consider the actual working flow.
2. Vibration effects
Compressed air is produced by an air compressor or a high-pressure fan. When these equipments are running, they all have varying degrees of vibration. Sometimes the vibration is relatively strong. This kind of vibration will be transmitted through connecting pipes. In the selection and location of vortex flowmeter, this influence factor should be fully considered. In different detection methods, the anti-vibration performance of the instrument is different due to the different detection elements. For the vortex street of the testing element, the vibration resistance can reach 0.5~1G. When determining the installation position of the vortex flowmeter, the power equipment such as air compressor and fan should be kept away as far as possible.
3. Impacts of pulsating flow
Because of the gas output from the fan and compressor, most of them contain a certain component of pulsation. The pulsation frequency and amplitude of the output gas of Roots blower are related to the speed of the waist wheel and the volume of the fixed displacement. Usually, the pulsation frequency is 100-200 HZ, while the frequency of the output gas of reciprocating compressor is low, usually only a few hertz. In addition, some air equipment, if the air hammer, pneumatic tools, etc. will also cause the air flow pulsation, and the frequency and amplitude of this pulsation are random.
