Thread Content
A simple approach is to use a flow meter with higher precision than the flow meter being calibrated, and connect it in series with the latter in the pipeline for calibration. In fact, gas flowmeters cannot be calibrated by themselves. A large set of specialized equipment is required. The standard requirements for calibration are specified in the **Measurement Calibration Specification JJG1037-2008 “Calibration Procedures for Turbine Flow Meters”**. Flow meters can be divided into those for measuring gas flow and those for measuring liquid flow, and the manufacturers of flow calibration devices will provide you with designs for devices suitable for gas flow calibration as well as those for liquid flow calibration. The simple inspection method is also known as the on-site inspection method. This is a method for calibrating flow meters, which involves measuring physical quantities related to flow based on the geometric specifications of various components of the flow meter, as well as checking whether the installation and operation standards of the flow meter are followed in accordance with the technical specifications. In gas flow measurement instruments, devices for accurate flow measurement as well as Venturi nozzles can both be calibrated using the dry calibration method. Generally speaking, the dry school method is convenient and simple, with low investment in testing machinery and equipment. However, since the characteristics of a flow meter are related not only to the geometric properties of the gauge face but also to factors such as pipeline characteristics, fluid dynamics properties, flow patterns, and water flow distribution, it can be said that even for two flow meters with similar geometries and driving forces, it is difficult to ensure that their readings will be exactly identical. Therefore, the application scope of the dry school method is limited, and its precision cannot be very high; for the vast majority of flowmeters, the direct calibration method is generally used for calibration. The immediate calibration method is further divided into two types: free online calibration (real-time flow calibration) and offline download calibration. The free online calibration method involves, under actual operating conditions of the flow meter, connecting a calibrated flow meter (or flow calibration device) that has been calibrated using nationally authorized standard devices and possesses a defined accuracy level, in series with the flow meter’s operational control circuit. The flow meter is then calibrated using the medium being measured; as a result, this method enables accurate determination of the flow meter’s operational characteristics and yields high calibration precision. Due to the difficulties associated with transporting and installing standard flowmeters (flow standard devices), free online calibration not only incurs high costs but also sometimes fails to maintain accuracy; as a result, the method of free online calibration is rarely used in gas meter calibration in China. The offline download calibration method for flowmeters is generally carried out on a flow standard apparatus in the laboratory. In the offline download calibration of flowmeters, the working medium used during calibration by the flow standard device and the flowmeter under test is usually different from the medium under which the flowmeter operates in practice, and the pressure and temperature during calibration are also different from the actual pressure and temperature of the flowmeter. For gas flow rate calibration devices, gas or fuel is generally used as the calibration medium. When using the offline download calibration method, it is essential to identify the effects caused by the differences in the physical and organic chemical properties between the national calibration medium and the testing medium on the readings of the flow meter. It is also necessary to identify the impacts resulting from the inconsistency between the calibration standards and the application standards on the flow meter readings, and to make adjustments to address such impacts. Otherwise, it is impossible to obtain satisfactory flowmeter calibration results.