Ultrasonic flow meters have many advantages such as high measurement accuracy, low maintenance and maintenance costs, and self-diagnosis functions. Multi-channel ultrasonic flowmeters are more and more widely used in the field of natural gas measurement.
There are many factors that affect the uncertainty of the steam flow measurement results of the ultrasonic flow meter, such as the roughness of the inner wall of the upstream straight pipe section of the flowmeter, gas composition, the length of the upstream straight pipe section, fluid flow state upstream of the flowmeter, noise interference, and airflow pulsation. The most common for operators is that noise in the pipeline can interfere with the operation of the ultrasonic flowmeter, which in turn affects the performance of the meter. The typical place where this noise Z is generated is where there is a pressure drop, such as a flow control valve.
The impact of noise on clamp on ultrasonic flow meters and measures to eliminate or reduce the impact of noise. At the beginning of the project, if the engineering designers can recognize these influencing factors and take corresponding measures, the project cost can be greatly reduced, but once all the equipment is installed, and the problems are found and measures are taken, it will generally cost a lot of money. cost. Therefore, it is very necessary to understand these measures to reduce the impact of noise, which can guide the user to apply the ultrasonic flowmeter correctly.
Noise is generated during the operation of process units, such as high-velocity gas passing through pipes, fittings, protruding temperature sensors, regulating valves, etc. . The study found that the biggest noise is the large pressure drop regulating valve. If this noise is not dealt with, it will interfere with the signal detection system of the flowmeter and cause transmission detection errors. The size and nature of the noise generated by the control valve are related to the design of the control valve. In order to achieve the characteristics of "low noise", some control valves deliberately increase the noise frequency, but the high frequency reaches the operating frequency range of the ultrasonic slurry density meter, which seriously affects the normal operation of the ultrasonic flowmeter. Although the control valve can reduce the noise signal by means such as cage design, the characteristics of the control valve also determine that any valve with throttling characteristics is a potential source of ultrasonic noise. Studies have shown that the energy loss of the valve body is proportional to the pressure drop through the valve body and the actual flow rate, and the noise increases with the increase of the energy loss through the valve body.
Once the noise is generated, it will propagate upstream and downstream of the regulating valve, so just installing the ultrasonic flow meter before the regulating valve does not guarantee that the flowmeter will not be disturbed by the noise of the regulating valve. The experimental results show that when the control valve is installed downstream of the flow meter, the noise interference of the sensor near the control valve is 2-4 times larger than that of the sensor far from the control valve.