Influencing Factors of Mass Flow Meter Measurement Environment

Factors affecting the measurement environment of the mass flowmeter: 1. The influence of fluid pressure First consider that the fluid pressure should not exceed the specified working pressure, and secondly consider the degree of influence of static pressure changes. Pressure changes affect the degree of tube tension and the extent of the Budden effect, as well as the original zero offset that disrupts the asymmetry of the tube. Although the instrument constant variation and zero drift are very small, the influence on the high-precision instrument cannot be ignored when the difference between the pressure used and the calibration is very large. Small-diameter instruments have a large wall thickness and pipe-diameter ratio, and the influence is small; large-diameter instruments have a large wall thickness and pipe-diameter ratio. 2. Fluid density affects the fluid density change to change the quality of the flow measurement system, thereby changing the balance of the flow sensor, resulting in zero point offset. If you measure a specific liquid, as long as you adjust it to zero under the condition of the actual liquid density, the density will not change much during use, so there is generally no problem. However, when measuring several liquids with large density differences on a pipe, it will bring additional errors of zero point changes. 4. The content of heterogeneous phases in the two-phase fluid affects the measurement. Manufacturers often say that the percentage of free gas contained in the volume ratio has little effect on the measurement. When measuring liquids with small, well-distributed gas bubbles, such as ice cream and similar emulsions, the effect may be relative. Some models have no obvious effect when the air bubbles are 1%, some models have an error of 1%~2%, and one of the double-pipe straight pipes is as high as 10%~15%; when the air bubbles are 10%, the error generally increases to 15%~ 20%, individual models up to 80%. In addition, differences in fluid pressure, flow velocity, viscosity, and gas-liquid mixing methods have different effects. When measuring liquids containing a small amount of solids, all types of CMF have high reliability. When the solid content is large or the solid has strong abrasiveness or soft solid (such as vegetable pieces in food soup), the single-tube straight-tube type or the series-connected double-tube type should be selected. Because if the parallel double-pipe type is used, foreign matter or wear may adhere to the shunt, which may change the flow of the two shunts and cause errors; more serious cases such as blockage of one way may not be found immediately. 5. Affected by environmental vibration CMF can work in a vibrating environment, but it needs to be isolated from vibration, such as connecting with a vibrating tube with a flexible tube and using a vibration-isolated support frame. But it should be prevented that the vibration frequency is the same as the working frequency or harmonic frequency of CMF. Multiple instruments of the same model are installed in series or relatively close to parallel, especially on the same support platform, the operating frequency vibration of each CMF will affect each other, causing abnormal vibration, and in severe cases, the instrument will not work. When ordering, it can be specially proposed to the manufacturer to stagger the working frequency of the two series CMFs. 6. Influence of pipeline stress If the center of the pipeline connected to the flow sensor is misaligned (or not parallel) or the temperature of the pipeline changes, the pipeline stress will form pressure, tension, or shear force to act on the alignment between the CMF measuring tubes, causing the detection probe to fail. Asymmetry, resulting in zero shifts. After the CMF is installed, it needs to be zeroed to eliminate or reduce this effect. If the tubing is severely misaligned, zero adjustment may not be possible. If the temperature of the pipeline deviates from the installation temperature, the thermal expansion (or contraction) force generated by the pipeline will also act on the flow sensor. Some CMF designs have a heavy flow divider at the inlet and outlet of the measuring tube, which can reduce the influence of pipeline stress on the measuring tube. Straight measuring tube CMF is particularly susceptible to the influence of thermal expansion force, and thermal expansion isolation fittings can be installed in the pipeline if necessary.

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