The quality testing standards of ultrasonic flowmeters mainly include the following aspects: Performance indicators: Measurement accuracy: Different application scenarios and accuracy levels of ultrasonic flowmeters have corresponding accuracy requirements. For example, in some common industrial applications, the accuracy may be between ±1% and ±2%; For more demanding measurement applications, the accuracy may need to reach ±0.5% or even higher. In the detection, through the comparison test with the standard flow device, calculate the error between the measured value and the standard value, and judge whether it meets the accuracy requirements. Repeatability: reflects the consistency of the results when the flowmeter measures the same flow rate multiple times under the same conditions. The repeatability error should usually be within a certain allowable range, such as not exceeding ±0.2% of the measured value, etc., the specific value depends on the specifications and application requirements of the flow meter. Linearity: The degree of linear relationship between the output signal of the flowmeter and the flow rate. Ideally, the output of the flowmeter should have a strict linear relationship with the flow rate, but in practice there will be a certain deviation. The detection of linearity is usually determined by measuring at different flow points and then analyzing the deviation of the measured value from the theoretical linear relationship. Range ratio: The ratio of the maximum flow rate to the minimum flow rate that the flowmeter can accurately measure. The larger the range ratio, the wider the application range of the flowmeter. In general, the range ratio of ultrasonic flowmeters should meet the needs of practical applications, and the common range ratio is 10:1 to 100:1 or even higher. Signal quality: Signal strength: The ultrasonic signal received by the sensor should be strong enough to ensure the accuracy and stability of the measurement. When detecting, the signal strength value can be viewed through the display interface of the flowmeter or the relevant detection equipment, and the signal strength is generally required to be above a certain threshold, such as the Q value (signal quality index) greater than or equal to 85. Signal stability: During the measurement process, the ultrasonic signal should be stable, and there should be no large fluctuations or intermittent interruptions. The stability of the signal is evaluated by observing the change of the signal over a long period of continuous measurement. Temperature and pressure compensation performance: If the flow meter has a temperature and pressure compensation function, the effectiveness of the function needs to be tested. Under different temperature and pressure conditions, the flow meter should be able to accurately compensate the measurement results, so that the output flow value is closer to the actual flow rate. For example, in an environment with large temperature changes, the temperature compensation error of the flowmeter should be within the specified range. Electrical performance: Power supply adaptability: The flow meter should be able to work normally within the specified power supply voltage and frequency range. For example, for an AC powered flowmeter, when the power supply voltage fluctuates ±10% and the frequency fluctuates ±5%, the flowmeter should be able to operate normally and the measurement results should not be significantly affected. Insulation resistance: The insulation resistance between the electrical part of the flow meter and the housing should meet the safety requirements, and the insulation resistance is usually required to be greater than a certain value, such as 100MΩ, to ensure safety during use. Anti-interference ability: The flow meter should have a certain anti-electromagnetic interference, radio frequency interference and other capabilities. In the presence of external interference sources, the measurement results of the flowmeter should not be significantly affected. The measurement accuracy and stability of the flowmeter can be checked by testing in a simulated interference environment. Mechanical structure and installation requirements: Appearance inspection: the shell of the flow meter should have no obvious scratches, deformation, cracks and other defects, the surface coating should be uniform and firm, and the identification and nameplate should be clear and readable. Sensor installation: The installation position of the sensor should meet the design requirements, the connection with the pipeline should be firm and sealed, and the installation Angle and direction of the sensor should be correct to ensure the normal transmission of ultrasonic signals. For example, when installing a sensor on a horizontal pipe, ensure that the sensor is perpendicular to the pipe axis; When installing on a vertical pipe, the appropriate installation position should be selected according to the flow direction of the fluid. Protection level: If the flow meter is used in harsh environments, such as humidity, dust, corrosive gas and other environments, its protection level should meet the requirements, and can effectively prevent the damage of the external environment to the flow meter. Calibration conditions: flow standard device: The flow standard device used to detect the ultrasonic flowmeter should have a valid verification certificate, and the uncertainty of the measurement results should not be greater than 1/3 of the maximum allowable error value of the flowmeter to be detected. Flow standard devices can be different types of devices such as mass method, volume method or standard table method. Fluid for verification: The fluid used for verification should be a single-phase gas or liquid, filled with the test pipeline, and the flow should be free of vortices, visible particles, fibers and other substances. For the liquid flowmeter, the liquid should be higher than its saturated vapor pressure, and the temperature, pressure and other parameters should meet the specified requirements; For the gas flowmeter, the pressure, temperature, and composition of the gas should also meet the corresponding conditions. Environmental conditions: The temperature, humidity and atmospheric pressure of the verification environment should be within the specified range to ensure the accuracy of the test results. For example, the ambient temperature is generally 5 ° C to 45 ° C, the humidity is 35% to 95% RH, and the atmospheric pressure is 86kPa to 106kPa.
Post time: Nov-03-2024