在出厂之前必须按照检定规程进行检定。 The turbine flowmeter must be verified in accordance with the verification procedures before leaving the factory. That is, the calibration fluid is passed into the flow standard device, and the turbine flowmeter is calibrated one by one. Calibration is sometimes called calibration of the scale. However, after the turbine flowmeter that passed the factory inspection is installed at the site of use, it generally has to pass the practical test of the use link to be truly "qualified". This link is the on-site verification of the accuracy of the meter's indication value during the delivery acceptance. This work is called "verification" because it is different from the test. The term "verification" is defined in GB / T6583-1994 as "recognition through inspection and provision of objective evidence that the specified requirements have been met". Although this is a term in quality management and quality assurance standards, borrowing it to the quality management of measurement systems is basically also applicable. The term "verification" is defined in the national standard as "the procedure for ascertaining or confirming whether a measuring instrument meets statutory requirements, which includes inspection, marking and / or issuing a verification certificate". Obviously, for turbine flowmeters, verification is the work performed on an appliance. After a turbine flowmeter is installed at the site of use, it often needs to be matched with other related meters (such as secondary meters) to form a flow measurement system together with the measured object and run in a specific use environment. Each measuring instrument included in a flow measurement system may be all qualified, but the composition of a flow measurement system may be unqualified because of incorrect selection of instruments, improper range selection, improper matching between instruments, and unreasonable installation. The harsh environment makes the appliance unable to adapt, and the measurement object has too high requirements on the measuring range of the appliance, which will cause the system error to be too large. Therefore, the verification mentioned here is for a measurement system that serves a specific object and runs in a specific environment. A set of flowmeters may not be “qualified” to operate in a particular environment, and another environment may be “qualified”. It may not be "qualified" for this object service, and it may be "qualified" for another object service. Therefore, verification cannot be separated from specific systems, specific phenomena, and specific circumstances. The term "comparison" is defined in the Metrology Dictionary as "comparison of similar benchmarks, standards, or quantities between work-related measuring instruments of the same accuracy level under specified conditions." It seems that it is not entirely appropriate to use the comparison to represent the field verification work, because some field verifications are compared between measurement systems of the same accuracy level, while others are not. But no matter what it is called, this work must be done, and it is very important. During the verification, the supplier may provide a lot of data and reasons to prove that the indication of the measurement system is accurate enough, and the owner unit will perform the acceptance; or the installation and commissioning unit will hand over the work, and the construction unit or the supervision unit appointed by the construction unit will accept the inspection; In the same unit, it may be handed over by the metering equipment department, and the acceptance by the user department.
中装有转子和轴承等以高速转动的可动部分、摩擦部分。 The turbine flowmeter is equipped with a moving part and a friction part that rotate at high speed, such as a rotor and a bearing. Therefore, you should fully understand its structure and processing method, otherwise, it will not exert its characteristics when used. The commonly used material is known as SUS304L low temperature material. If austenitizing can be performed, SUS304 can also be used. Bearing is the most important part of the turbine flowmeter, which determines the characteristics and durability of the turbine flowmeter. If the fluid to be measured is a non-lubricating gas, great care must be taken when selecting a bearing. It has been experimentally proven that the turbine flowmeter used for measuring LNG can use AISI 440C stainless steel ball bearings. When measuring a cryogenic fluid with a turbine flowmeter, the most common failure is the rapid evaporation caused by the pressure loss of the flowmeter. After the rapid evaporation in the flow meter, the turbine will rotate at a speed dozens of times faster than the normal speed. In this way, the bearing will be completely worn out in a short time. The best way to prevent evaporation is to appropriately increase the caliber of the flowmeter. The pressure loss of the turbine flowmeter is proportional to the square of the flow rate. If the measured maximum flow rate can be limited to 1/2 of the meter capacity, the pressure loss can be reduced to the rated 1/4. In general, during intermittent use, if the measured maximum flow rate should be controlled below 70% of the flowmeter range, basically no failure will occur due to the pressure loss of the flowmeter itself. For continuous use, limit the common flow rate to less than 50% of the flowmeter range. This requires the bearing inspection cycle to be more than one year. 的转速不受粘度和密度的影响。 When the fluid is turbulent, the speed of the turbine flowmeter is not affected by viscosity and density. However, when it is laminar, it will be affected. Therefore, where the flow rate is small, there is a certain limit between the density of the measurable fluid and the flow rate. Very low temperature fluids such as liquefied natural gas have an order of magnitude less viscosity than gasoline. Therefore, gasoline calibration can be used to ensure that the value above the range is obtained.