How do you measure a flow meter? What methods do you usually use?
Indirect verification is also called verification. It measures the geometry of each part of the flowmeter, determines the physical quantity related to the flow rate, and checks the flow of the flowmeter, the conditions of use and whether the operation is carried out according to the rules. In the natural gas flow measurement, flow measurement device and Venturi nozzle can be used for assay of cadre. In general, the method is convenient and simple, less investment in equipment verification. However, due to the characteristics of flowmeter is not only related to the geometric characteristics of the instrument, but also related with the pipeline characteristics, fluid properties, flow velocity distribution and other factors, so it can be said that even if the geometric similarity, similar to the two power meter, its value is also difficult to guarantee exactly the same. Therefore, the scope of calibration is limited, accuracy is also not very high, most of flowmeter is generally used direct verification method to pick up the set. The direct verification method is divided into two methods: on-line verification (real flow setting method) and off-line verification.
The off-line calibration method of flowmeter is usually carried out on the flow standard device in laboratory. In the off-line calibration of flowmeter in flow standard device and the working medium flow meter in the test is often the working medium is different from the flowmeter, the verification of the working pressure and temperature is different from the actual working pressure and temperature meter. For the gas flow standard device, air or gas is selected as the test medium. The verification method of offline, must find the physical and chemical properties to medium and medium test measured different are shown to affect the value caused by the meter, we must find out the conditions and conditions of use due to pick up the inconsistency of flowmeter are shown to affect the results, and the effect of modified. Otherwise, it is difficult to obtain satisfactory flowmeter verification results.
The online test requirement of the flowmeter work in the practical working conditions, by using the standard device will have been authorized by the state, has determined the standard flowmeter colonel. The level of accuracy (or flow standard device) on circuit connected to the meter, with the method for the calibration of flowmeter tested medium so this method to reliably determine the working performance of the flowmeter, can obtain higher accuracy. Due to the standard flow meter (flow standard device) affect the transport and installation difficulties, not only the high cost of online approval approved, and sometimes simply can not be achieved, so the use of online verification method in China's natural gas measurement in a few occasions.
