Flowmeter selection principle - Solutions - Huaqiang Electronic Network

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The selection of the flowmeter refers to the safety, accuracy and economy of the measurement according to the actual requirements of the supply of the instrument product according to the production requirements, and the method and measuring instrument of the flow sampling device are determined according to the nature and flow of the fluid to be tested. Type and specifications.
The flow measurement is safe and reliable. Firstly, the measurement method is reliable, that is, the sampling device does not cause mechanical strength or electrical circuit failure during operation, and the accident occurs. Second, the measurement instrument does not affect the safety of the production system under normal production or failure conditions. . For example, for the measurement of the normal temperature and normal pressure flow, non-standard speed measuring devices such as a cantilever beam double horn tube or a plug-in flow meter, and a target type, a turbine flow meter, etc. having low structural strength are generally preferred. Explosion-proof instruments should be used for fuel-fired power plants and where flammable gases are available.
On the basis of ensuring the safe operation of the instrument, we strive to improve the accuracy and energy saving of the instrument. To this end, not only must the display instrument that meets the accuracy requirements be selected, but also a reasonable measurement method should be selected according to the characteristics of the measured medium. The main steam flow measurement of power plants, due to its importance to the safety and economy of power plants, generally adopts a mature standard throttling capacity with differential pressure flowmeter. The chemical water treated sewage and fuel are dirty flow and low Reynolds respectively. The number of viscous flows does not apply to standard throttles. For the dirty flow, a non-standard throttle such as a circular orifice plate is used with a differential pressure gauge or an ultrasonic flowmeter, and the viscous flow can be respectively a volumetric type, a target flowmeter, and the like. The water volume of the turbine, the circulating water volume of the condenser and the regenerative steam of the regenerative unit are all flow measurement parameters of large diameter (above 400mm). Due to the difficulty in processing and large pressure loss, standard throttling devices are generally not used. According to the special characteristics of the tested media and the measurement accuracy requirements, the plug-in flowmeter, the speed measuring component with the differential pressure gauge, the ultrasonic flowmeter, or the non-loss method such as the marking method and the simulation method are respectively used to measure the flow rate.
In order to ensure the service life and accuracy of the flowmeter, we must pay attention to the anti-vibration requirements of the instrument when selecting the type. Choose wet and humid instruments in hot and humid areas. Correct selection of the instrument's specifications is also an important part of ensuring the service life and accuracy of the instrument. Special attention should be paid to the choice of static pressure and temperature resistance. The static pressure of the meter is the degree of pressure resistance. It should be slightly larger than the working pressure of the measured medium, generally 1.25 times to ensure no leakage or accident. The choice of the range of the range is mainly the choice of the upper limit of the meter scale. The selection is small, easy to overload, damage the instrument; the selection is large, which hinders the accuracy of the measurement. Generally selected as 1.2 to 1.3 times the maximum flow value in actual operation.
Contact instruments that are installed on production pipelines for long-term operation should also consider the energy loss caused by flow measurement components. Under normal circumstances, multiple measuring elements with large pressure loss, such as throttling elements, should not be used in the same production pipeline.