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# Electromagnetic flowmeter mass time method calibration device and series calibration diagram

by：Sure     2021-08-04
The mass-time method This method is similar to the volume-time method, except that the standard container is replaced by an accurate weighing instrument, as shown in Figure 8-4. Due to the high accuracy of the weighing instrument (generally 10-5), the calibration accuracy of the mass-time method is higher than that of the volume-time method, which can be between 0.02% and 0.05%. Figure 8-4 Schematic diagram of mass-time method flow calibration device 1-Positive pressure vessel mass-time method This method is similar to the volume-time method, and only an accurate weighing instrument is used instead of the standard container, as shown in Figure 8-4. Due to the high accuracy of the weighing instrument (generally 10-5), the calibration accuracy of the mass-time method is higher than that of the volume-time method, which can be between 0.02% and 0.05%. Figure 8-4 Schematic diagram of mass-time method flow calibration device 1-positive pressure vessel; 2-valve; 3-inspected flow meter; 4-commutator; 5-lower pool; 6-pump; 7-electromagnetic flow of standard weighing instrument The meter measures volume flow. When calibrating the weight-time method with water on the device, the influence of density changes and the problem of buoyancy correction should be considered. The flow rate can be calculated by the following formula: W——weight of water weighed by the weighing instrument, kg; —density of water, kg/l; t——measurement time (time for water to flow into the weighing apparatus), s; —air buoyancy correction Coefficient: where-density of air, kg/m3;-density of water, kg/m3;-density of weight material, kg/m3. Table 8-1 The density temperature of water at different temperatures/(℃)56789101112 density/(kg/l)0.999960.999940.999900.999850.999780.999700.999600.99950 temperature/(℃)1314151617181920 density/(kg/l)0.999380.999240.999100. 998940.998770.998590.998400.99820 Temperature/(°C) 2122232425262728 Density/(kg/l) 0.997990.997770.997540.997290.997040.996780.996510.99623 Temperature/(°C) 293031323334 Density/(kg/l) 0.995940.995650.995340.995020.994700.99437 This type of device It is the most accurate device. Because the liquid is weighed when it is still, the pipeline system has no mechanical connection and is not affected by the flow of power. High-precision weighing equipment can be used, such as a standard weighing instrument with an accuracy of 0.01% to 0.005%. The accuracy of the device is generally 0.05% to 0.1%, up to 0.02%. 3. Standard table comparison method The equipment of the above two calibration methods is more complicated, and the investment is relatively large, and not every unit has conditional settings. It is simpler and more convenient to adopt the standard table comparison method. In this method, a standard flow meter with a higher accuracy is connected in series with the calibrated flow meter, and the fluid flows through the two at the same time, and the displayed values u200bu200bof the two are compared to determine the error of the meter to be tested to achieve the purpose of calibration. This method is the least expensive and simple to operate. It is also made into mobile vehicle-mounted standard meter calibration equipment. In recent years, this method has been valued and recognized by all walks of life in China. The State Bureau of Technical Supervision has produced the corresponding 'Verification Regulations' and promulgated JJG643-94 'Verification Regulations for Flow Standard Devices of Standard Meter Method'. The accuracy of the device should not be less than 1/2 of the accuracy of the meter being checked. The front and rear straight pipe sections of the standard meter are generally not less than the length of the straight pipe section of the same type of ordinary meter. The front and rear straight pipe sections of the meter to be calibrated should meet the requirements of the specification of the meter. The volume of the connecting pipe section between the standard meter and the meter to be calibrated should be as small as possible under the condition of meeting the requirements of straight pipe sections. The flow regulating valve should generally be installed on the downstream side of the meter, and the regulating performance should be stable. Figure 8-5 shows the calibration diagram of a common standard flowmeter (usually a turbine flowmeter or an electromagnetic flowmeter) in series with the flowmeter to be calibrated. Figure 8-5 Series calibration Figure 1-Stop valve; 2-Calibrated flow meter; 3-Flow regulator; 4-Standard flow meter, 5-Flow control valve Calibrated flow meter 2 is installed upstream of the standard flow meter 4, A flow regulator 3 is installed in the middle. After the flow regulating valve 5 is installed in the rear straight pipe section 10DN of the standard flow meter 4, the flow regulating valve 5 adjusts the flow of the fluid to the required value. If the standard flowmeter does not use the turbine flowmeter but uses the electromagnetic flowmeter to calibrate the electromagnetic flowmeter, there is no need to install the flow regulator 3. The length of the straight pipe before the calibrated flowmeter and between the two flowmeters can be shortened to 10DN
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