Errors in orifice flow meter and solutions

Abstract: The information on the error of the orifice flowmeter and the solution is provided by the excellent flowmeter and flowmeter manufacturers and quotation manufacturers. The reasons for the error of the orifice flowmeter in the measurement: The standard orifice is a differential pressure generating device for measuring flow, and it can measure the flow of various fluids in the pipeline with various differential pressure gauges or differential pressure transmitters. Orifice flowmeter throttling device includes annular chamber orifice, nozzle, etc. . For more flowmeter manufacturers to select models and price quotations, you are welcome to inquire. The following are the details of the orifice flowmeter errors and solutions. The reasons for the error of the orifice flowmeter in the measurement: The standard orifice is a differential pressure generating device for measuring flow, and it can measure the flow of various fluids in the pipeline with various differential pressure gauges or differential pressure transmitters. Orifice flowmeter throttling device includes annular chamber orifice, nozzle, etc. The orifice flowmeter throttling device is used together with the differential pressure transmitter to measure the flow of liquid, steam and gas. The orifice flowmeter is widely used in petroleum, chemical, metallurgy, electric power, light industry and other departments. Due to the wide application range and large number of orifice flowmeters, customers often respond that after a period of use, orifice flowmeters often do not match the actual flow. With a large amount of data, it is concluded that there are several major reasons for the error. 1. Since the orifice plate has been used for a long time, especially when the measured medium is mixed with impurities such as solid particles, or is chemically corroded, the geometry and size of the orifice plate will change. If the entrance edge of the orifice plate is sharp The pressure becomes dull due to the impact or corrosion of the medium, so that the pressure difference ΔP generated when the same amount of fluid passes through is reduced, resulting in a low display value. In serious cases, the orifice plate needs to be replaced. 2. Maybe because of the long time, the zero point of the transmitter will drift. If it is negative drift, the output current of the transmitter is less than the standard 4MA, and the flow rate is low. If it is positive drift, the output current of the transmitter is greater than the standard 4MA. , the flow rate is high. If the range setting is large, the flow rate will be displayed on the low side; if the range setting is small, the flow rate will be displayed on the high side. 3. The gas flow meter shows that it is too small. It is checked that the orifice plate is installed backwards. In fact, the sharp side of the orifice plate should be the inlet end facing the fluid flow direction, and the bell-shaped side is the outlet end. Pay attention to the direction. In addition, during installation, the center of the orifice opening and the center line of the pipeline are not concentric, which will also cause measurement errors. Extended reading: Mingyu automatic control flowmeter 4. In actual use, the surface of the orifice plate may be covered with a layer of dirt, or due to the deposition of impurities in the front and rear corners of the orifice plate for a long time, or due to strong corrosion, the pipeline will be damaged. The gradient of the flow cross-sectional area, as well as the leakage and blockage of the pressure guiding catheter, will cause measurement errors. Because the gas used by some manufacturers is dirty (including tar), the pressure-taking ring chambers before and after the orifice plate are blocked, there is no pressure difference at the pressure-taking port, and the flow meter has no flow display. After dismantling, clean the two ring chambers and replace the pressure guiding pipe , the flow meter shows normal. The following will introduce the main measures to solve the measurement accuracy of the orifice flowmeter: 1. The orifice flowmeter is calibrated one by one. As we all know, standard orifice plates can be used directly as long as they are designed and manufactured with reference to relevant standards and do not require real flow calibration. Because the outflow coefficient can be calculated directly by the software, the computer calculation is ideal after all, and it is still different from the on-site environment. Therefore, in order to ensure the measurement accuracy, it is recommended to perform real flow calibration for each flowmeter, and the calibrated outflow The coefficients are compared with the calculation results, and the difference is calculated and corrected. 2. Reynolds number correction, there is a definite relationship between the flow coefficient of the orifice flowmeter and the Reynolds number. When the mass flow changes, the Reynolds number changes proportionally, thus causing the flow coefficient to change. 3. The influence of temperature on the orifice flowmeter and its correction. The change of fluid temperature causes the change of density, which leads to the change of the relationship between differential pressure and flow rate. The correction of temperature change is to use a temperature instrument to measure the on-site temperature and then input it into the secondary instrument to correct the error caused by the temperature change. 4. Swellability correction. When the orifice flowmeter measures the flow of steam and gas, the expansion of the fluid must be corrected. For the specific correction coefficient, please refer to the design manual of the throttling device. 5. Calculation of steam mass flow, when the orifice flowmeter measures steam, the flow value is first obtained from the differential pressure signal, and then the density is obtained from the steam temperature and pressure values ​​to calculate the steam flow quality. The above is the whole content of this article. You are welcome to inquire about the flowmeter selection and quotation of our factory. 'Orifice flow meter produces errors and solutions'

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