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How to understand the accuracy and repeatability of flow meters/flow sensors? The accuracy and repeatability of flow meters (flow sensors) are the core indicators for evaluating their performance, directly affecting the reliability of measurement results. Below is an analysis of the definition, importance, interrelationships, and precautions in practical applications:
1. Accuracy Definition: Accuracy refers to the degree to which a measured value is close to the true value, reflecting the size of the system error. In flow meters, it is manifested as the deviation between the output value and the calibration curve, usually expressed as a percentage (such as ± 1%). Example: If the accuracy of the flowmeter label is ± 1% FS (full range), the error is ± 1 mL/min when the range is 100 mL/min; If the flow rate is 50 mL/min, the error is still ± 1 mL/min (i.e. 2% FS). If marked as ± 1% Rd (reading), the error is ± 1% of the actual value (i.e. ± 1 mL/min and ± 0.5 mL/min) regardless of whether the flow rate is 100 mL/min or 50 mL/min. Key point: Difference between FS and Rd: Full Scale (FS): Error is expressed as a percentage of the range, and relative error increases at low flow rates. Suitable for mechanical or low-end instruments. Reading (Rd): The error is expressed as a percentage of the actual measured value and remains constant. Suitable for digital instruments or high-end devices. Selection criteria: For high-precision requirements (such as drug mixing), priority should be given to flow meters labeled with Rd. FS annotation devices can be selected for scenarios with limited budget and high tolerance for low traffic errors. Influencing factors: Calibration conditions (temperature, pressure, medium characteristic
Definition of Repeatability: Repeatability refers to the consistency of multiple measurement results under the same conditions (such as environment, flow rate, medium), reflecting the size of random errors, also expressed as ± percentage.
. Example: If the repeatability of the flowmeter is ± 0.5%, and the flow rate is repeatedly measured at 100 mL/min under the same conditions, the result should always be within the range of 99.5~100.5 mL/min. Key point: Relationship with accuracy: Reproducibility is the foundation of accuracy: High accuracy requires high repeatability as a prerequisite. If the device has poor repeatability (such as ± 5%), even if the labeling accuracy is ± 1%, the actual data is still unreliable. Independence and complementarity: When the device has high repeatability but low accuracy, although the data is concentrated, it deviates from the true value; On the contrary, the data is scattered but may be close to the true value. Important scenario: Long term monitoring or automated control (such as industrial processes) requires high repeatability to ensure stability. Experimental research, such as fluid mechanics, requires both high accuracy and high repeatability. Influencing factors: mechanical wear, stability of electronic components, fluid pulsation. Installation methods (such as pipeline vibration, straight pipe section, and hall length).III. Relationship between Accuracy and Repeatability Accuracy (precision): A comprehensive indicator of accuracy and repeatability, reflecting the sum of systematic error and random error.
. High accuracy: The data is both close to the true value (high accur
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