Coriolis mass flowmeter is a flow measurement technology with the highest measurement accuracy at present, and it will not be affected by changes in the temperature, pressure, and viscosity of the measured medium during the measurement process, and it does not require the requirements of front and rear straight pipe sections during installation. Therefore, it has become the measurement technology favored by users. The Siemens mass flowmeter has a unique double-tube series measurement structure (see Figure 2). The Coriolis mass flowmeter is currently a flow measurement technology with the highest measurement accuracy, and it will not be affected by the measured medium temperature during the measurement process. , The influence of pressure, viscosity changes, and the installation does not require the requirements of the front and rear straight pipe sections, so it has become the measurement technology favored by users. The Siemens mass flowmeter has a unique dual-tube series measurement structure (see Figure 2), with a measurement accuracy of up to 0.1%, and has excellent measurement effects for small flow rates and low flow rates, so it stands out in the fierce competition. Figure 2 The double-tube series structure is aimed at users producing products that are mostly used for medical treatment, so ISO2852 stainless steel casing sanitary connection is used. (See Figure 3) Figure 3 ISO2852 Sanitary Connection Automation Expert Meeting 2007 Kunming 2.3. After problems and solutions were put into use, users reported that the measurement accuracy was poor. From the many years of application experience of the Siemens Instrument Department, we know that the successful use of mass flow meters can only be obtained after correct installation and zero adjustment. Therefore, we have analyzed the problems reported by users may be caused by incorrect installation or failure to carry out accurate zero calibration. caused. The user has done 6 tests before and after. From the field measurement data, the measurement error is as high as 2-4%, which is much higher than the 0.1% in the parameter. Times Mass2100 totalizer reading [kg] METTLER TOLEDO weighing reading [kg] Absolute error [kg] Accuracy 1 20.5 -21.4 -0.9 4.21% 2 21 -21.4 -0.4 1.87% 3 22.7 -23.2 -0.5 2.16 %4 22 -22.6 -0.6 2.65%5 24.67 -25.4 -0.73 2.87% After-sales service engineers inspected on-site and communicated with users, and found that there were two reasons for this result: 3.1 Di15 caliber mass flowmeter was not disassembled and transported Bolts for fixing. On both sides of the MASS2100 Di6 and Di15 sensors, in order to ensure that the measuring pipe will not be damaged due to violent bumps or collisions during transportation, a long bolt is extended from both sides of the sensor to support the measuring pipe to make it Will not shake during transportation. However, in actual use, the user did not remove the long bolts and replaced them with the short bolts that came with the package. Therefore, in use, the vibration of the measuring pipeline is subjected to the frictional resistance of the long bolts, which causes abnormal operation. (See Figure 4) Figure 4 Replacement of transportation fixing bolts After finding this problem, the after-sales service engineer immediately replaced the short bolts. 3.2 The user did not perform zero point adjustment. According to the working principle and vibration model of the Coriolis mass flowmeter, when the fluid velocity in the pipeline is zero, the vibration phases of the pickup electrodes A and B located at the two symmetrical vibration excitation electrodes should be exactly the same. In other words, the detected time difference should be zero, but due to the vibration source near the installation location, when we think that the flow rate in the flow meter is zero, in fact the time difference detected by the pickup electrodes A and B is not zero, and there is a slight Therefore, before normal use, we need to calibrate the flowmeter to identify this small time difference so as to eliminate it in normal use. And if the zero point adjustment is not performed, when measuring large flow rates, the zero point deviation may not have a significant impact on the accuracy, and as the flow rate decreases, the impact on the accuracy becomes more and more obvious. Fig. 5 The book room uses the Di15 caliber used by the on-site user for measurement, and the maximum flow rate is 5600kg/h, while the flow rate used by the user for comparison is less than 30kg, which means that the flow rate is at a very low level, so the zero point deviation causes measurement errors Exceeding standards. The after-sales service engineer then instructs the user to re-calibrate the zero point on the spot. Steps: 1) Turn on the pump to allow the fluid to flow through the mass flow meter fully and remove the original pipeline air. Keep it for at least 5 minutes, so that the temperature of the measuring pipe is basically the same as that of the fluid; 2) Stop the pump. And immediately close the valve before the flowmeter; 3) Close the valve after the flowmeter; 4) Enter the instrument menu to perform zero calibration. (Use the default time of 30s) Steps 2 and 3 must ensure that the front and rear valves of the flowmeter are closed tightly, and that the fluid in the flowmeter has a pressure of at least 0.5bar. After recalibrating the zero point, the comparison test results are as follows: Times Mass2100 totalizer reading [kg] METTLER TOLEDO weighing reading [kg] absolute error
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