Flow means the amount of fluid flowing through a given section within a unit time. If it is represented with the volume of size, that can be volume flow. The average flow is an average value of flow in the measuring time. Calibrating apparatus of large—bore flow meter include some auxiliary facilities such as fluid source、pressure accumulator、pipe system、timer、volumetric standard and commutator. The operational principle: to install the tested flow meter on the apparatus, and then start fluid cycle system to make the fluid go through the tested flow meter and standard flow meter. To operating the tested flow meter
and standard flow meter at the same time and to compare the flow value of output from these two flow meter, further assuring the accuracy of measuring and repeatability.
Based on using different standard measuring tools, calibration method can be divided as volumetric method、mass method and master meter calibration method. Volumetric method is to apply standard container to measure the discharge of liquid volume in the measuring vessel over a period of time. The quality method is to calculate the flow by using a balance to weigh the quality of fluid in the container for a period of time. The standard scale uses standard apparatus which is on the basis of the standard flow meter to make a fluid pass through the standard flow meter and the tested flow meter continuously at the same time intervals. Compared with their flow value of output, the metering performance of tested flow meter can be sure.
Calibration method contains static volume method and variable water method( dynamic volume method). Static volume method is to separate the water tower and volumetric standard to make constant indenter and static reading. Variable water method is to separate water tower and volumetric standard to make indenter become smaller and then read in a dynamic state. The backward of calibration is that the equipment is too large. The volume of the volumetric standard will increase as the caliber of flow meter and the verification time increase. Master meter calibration overcomes the backward mentioned above. Under the same flow circumstances, Master meter calibration should be used the container that has small volume, and the verification time can be longer. As for the checklist with the low-resolution ratio, to add the verification time is an efficient approach to decrease the gauging error. The general gauging apparatus take advantage of standard scale to verify. To an instrument with high requirements, it is better to take standard master meter calibration and mass method to verify in order to ensure the accuracy of measuring.