Researches On The Dry Calibration Of Large Electromagnetic Flowmeters Based On Unit Element

In the current field of flow measurement,reliability and accuracy are very demanding, electro-magnetic flowmeter is considered to be one of the most reliable and accurate instrument. The application of electromagnetic flowmeter especially large diameter are increasingly being used,such as the reservoir water, the source of water into the water plant, water supply factory, sewage treatment and effluent disposal areas,it can be used as water supply billing and metering instrumentation. With the development of urbanization and the increase in water consumption,the demand of large diameter flowmeter increasing quickly,Electromagnetic flowmeter have significantly advantages compared to the traditional flowmeter. At present electromagnetic flowmeters are basically using the actual flow calibration. But the need for calibration of electromagnetic flowmeters adds considerably to the cost of these instruments especially in the larger sizes(about $3million for 1000mm in diameter). The problem of calibration equipment obstructs the development of large diameter flowmeters. Study of an inexpensive and effective calibration method has become one of the most important task in the field of flowmeter.This paper is based on the relationship between unit element and weighting function, raised and discussed a technique for calibration of large electromagnetic flowmeters which avoids the need for a calibration flow rig, which is called dry calibration of large electromagnetic flowmeters based on unit element. Then we discussed the transfer of calibrate standard and method of accuracy analysis. The task and achievement of this thesis is as follow:I. Based on basic principles of electromagnetic flowmeter and its weight function, the paper in-depth studied of the electromagnetic flowmeter calibration of sensors and converters,also studied of the fundamental mode of the complete and its parameter fundamental relation, find out the coefficient composition characteristics of sensor and the basic reasons leading to inconsistent coefficient, given the basic relational model of sensors coefficient and converters coefficient in calibration and set.II. On the basis of the principles and characteristics of currently existing dry calibration methods,according to unit element and weighting function of electromagnetic flowmeter, and take the weighting function of the unit element in large-diameter sensor as basic data of dry calibration, the paper raised a dry calibration method based on unit element and discussed its basic framework.III. According to the basic formula of induced electromotive force,established the calculation and analysis method of the calibration reference,by the introduction of the velocity distribution and zero point,we get the integrated calculating method of dry calibration, and given the implementation steps of unit element dry calibration method. Also the paper studied several factors which may have impact on the accuracy in dry calibration, such as the actual velocity, aperture and step size of unit element, velocity measurement accuracy, the spatial relationships of magnetic fields and weighting function, positioning accuracy, the inclination and height offset of unit element electrodes and diameter deviation of electromagnetic flowmeter.IV. This thesis researched and designed of the dry calibration equipment including small flow supply equipment, positioning system, data acquisition and processing system, and unit element. Recently we concrete realized the dry calibration equipment and given the operation method of dry calibration equipment, then analyzed and compared the effectiveness of the new dry calibration equipment.V. Conducted a confirmatory experimental research work for the new dry calibration method. This thesis discussed the baseline transfer method and the calibration data acquisition method of reference sensor. By implemented the dry calibration experiment under the given conditions and steps, we get the dry calibration experimental data and stability test data of dry calibration equipment, verified the feasibility of the new dry calibration method and equipment.