LDG-DN200 electromagnetic flowmeter calibration and comparison methods

In order to ensure the accuracy of the flow value or flow measurement value of the LDG-DN200 electromagnetic flowmeter, the electromagnetic flowmeter must be calibrated. Calibration is sometimes called calibration or verification. In fact, calibration includes two aspects: ① transmit the value to the instrument and determine the position of the flow scale mark (or determine the signal output by the flow scale); ② adjust the output of the instrument to the standard value (reference value) Compare to determine the accuracy of the instrument and determine its error value. In the past, the flow instrument industry used to calibrate the flow value transmission properties using flow "calibration", which was commonly called "calibration" in the hydrology and water industry. The user's calibration process to determine the accuracy properties of the instrument was called flow "checking". These names are now becoming consistent and "calibration" is used instead. The state-authorized flow laboratory is also named "Flow Calibration Laboratory". There are two methods for flow calibration of LDG-DN200 electromagnetic flowmeter: direct measurement method and indirect measurement method.

The direct measurement method, also known as the real flow calibration method, uses the actual fluid to flow through the instrument to be calibrated, and then uses other standard devices (standard flow meters or flow standard measuring instruments) to measure the flow rate of the fluid flowing through it, and compare it with the flow rate of the instrument to be calibrated. The flow value is compared. This method is called wet calibration. The flow value obtained by the real flow calibration method is both reliable and accurate. It is currently used by many flow meters (such as electromagnetic flowmeter, positive displacement flowmeter, turbine flowmeter, Coriolis mass flowmeter), and is used as a basis for establishing standard flow rates. method. Before the electromagnetic flowmeter leaves the factory, the manufacturer uses the real flow calibration method to complete the flow value transfer process on the flow calibration standard device (sometimes referred to as the flow standard device or flow calibration device). The user unit must also conduct real flow calibration on the flow calibration standard device for the instruments after regular verification and maintenance.

The flow calibration standard device is established in accordance with relevant standards and verification regulations, and is recognized by a specialized agency authorized by the state. A device that can transmit flow values ​​is a calibration equipment that provides flow values. Values ​​are traceable to national metrological reference quantities of mass, time and temperature. Dry calibration is an indirect calibration method. It measures the structural dimensions such as the flow area of ​​the electromagnetic flow sensor and the magnetic flux density B, calculates the flow value, and obtains the corresponding degree. Dry calibration was a calibration method developed in the 1970s to solve the problem of the inability to achieve real flow calibration of large-diameter electromagnetic flowmeters. It was once included in the Japanese Industrial Standard JIS Z8764-1975 "Method of measuring flow rate using electromagnetic flowmeter". Due to its relatively low density, it is rarely used now. The content of dry calibration in the Japanese Industrial Standard JIS Z 8764 "Electromagnetic Flowmeter" revised in 1986 is no longer part of the main text, but has been moved to the explanation part (equivalent to the appendix and preparation instructions of our country's standards). On-site "flow comparison" refers to the electromagnetic flowmeter on-site and other“Reference flow" for comparison. For example, the measurement value of a temporarily installed ultrasonic flow machine, the measured liquid volume in the inflow pipe system, etc. can be used as the "reference flow". "Flow comparison" is only an auxiliary Conduct a sexual inspection to evaluate the electromagnetic flowmeter measurement value, general error range, and determine whether the instrument is normal or faulty.