Flow meter selection refers to that according to the production requirements, starting from the actual situation of instrument product supply, comprehensively considering the safety, accuracy and economy of measurement, and determining the mode of flow sampling device and the type and specification of measuring instrument according to the nature and flow situation of the measured fluid.
 & nbsp; 　  The safety and reliability of flow measurement, first of all, the measurement method is reliable, that is, the sampling device in operation will not occur mechanical strength or electrical circuit failure caused by accidents; The second is that the measuring instrument will not affect the safety of the production system in normal production or fault conditions. For example, for the measurement of high-temperature and high-pressure main steam flow in power plant, the primary measuring element installed in the pipeline must be firm to ensure that the mechanism will not be damaged under the erosion of high-speed steam flow. Therefore, the standard throttling device is generally preferred instead of non-standard velocity measuring devices such as cantilever double horn tube or plug-in flowmeter, as well as target type and turbine flowmeter with low structural strength. Explosion proof instruments should be used in oil fired power plants and places with combustible gas.
 & nbsp; 　  On the basis of ensuring the safe operation of the instrument, strive to improve the accuracy and energy saving of the instrument. Therefore, it is necessary not only to select the display instrument that meets the accuracy requirements, but also to select a reasonable measurement method according to the characteristics of the measured medium. The main steam flow measurement of power plant is very important to the safety and economy of power plant. Generally, the mature standard throttling device with differential pressure flowmeter is adopted. The sewage and fuel oil of chemical water treatment belong to dirty flow and low Reynolds number viscous flow respectively, so the standard throttling device is not applicable. For dirty flow, non-standard throttling parts such as round orifice plate with differential pressure gauge or ultrasonic Doppler flowmeter are generally used, while for viscous flow, volumetric, target or wedge flowmeter can be used respectively. The water quantity of water turbine, circulating water quantity of condenser and regenerative steam of regenerative unit are all large diameter pipes（

The standard throttling device is generally not selected for the flow measurement parameters above 400mm due to the difficulties in processing and large pressure loss. According to the characteristics of the measured medium and the requirements of the measurement accuracy, the flow rate is measured by plug-in flow meter, velocity measuring element with differential pressure meter, ultrasonic flow meter, marking method, simulation method and other non loss methods
 
 & nbsp;& nbsp; In order to ensure the service life and accuracy of the flowmeter, attention should be paid to the anti vibration requirements of the instrument. In hot and humid areas, choose hot and humid instruments.
 & nbsp;& nbsp; The correct selection of instrument specifications is also an important part to ensure the service life and accuracy of the instrument. Special attention should be paid to the selection of static pressure and temperature resistance. The static pressure of the instrument is the degree of pressure resistance, which should be slightly greater than the working pressure of the measured medium, generally 1.25 times, to ensure no leakage or accident. The choice of measuring range is mainly the choice of upper limit of instrument scale. If it is too small, it is easy to overload and damage the instrument; The selection is too large, which hinders the accuracy of measurement. Generally, it is 1.2-1.3 times of the maximum flow in actual operation.
 & nbsp;& nbsp; The energy loss caused by the flow measuring element should also be considered for the contact instrument installed on the production pipeline for long-term operation. In general, multiple measuring elements with large pressure loss, such as throttling elements, should not be selected in the same production pipeline.
 & nbsp;& nbsp; In a word, no measurement method or flowmeter can adapt to all kinds of fluid and flow conditions. Different measurement methods and structures require different measurement operations, usage methods and usage conditions. Each type has its own advantages and disadvantages. Therefore, on the basis of a comprehensive comparison of various measuring methods and instrument characteristics, the best type suitable for production, safe, reliable, economical and durable, should be selected