Flow Sensor Performance Comparison
Application on Flexible Tubes Tested in Realistic Environment
Althea, one of the leading North American contract manufacturers specializing in cGMP manufacturing, analytical development, aseptic filling, and protein delivery technologies, was looking to evaluate flow systems for multiple applications throughout their facilities. One of the main goals was to replace scales for volume measurement by flow sensors. For that reason, three competing flow sensor set-ups were tested for their measuring performance and suitability for the customers’ specific application needs.
Accuracy & Precision
Accuracy and precision are often confused, especially when someone asks how accurate SONOTEC sensors actually are.
Accuracy describes the error between the real and the measured value. It is an indication about how close you can get to the correct value. Reversely, precision describes the random spread of measured values around the average measured values. It finally defines how consistent you can get the results. The standard deviation (STDEV) of a measuring sequence stands for a measure of precision.
Precision is by far the most critical determinant for any measuring device and the basis for an accurate measurement. A precise flow sensor can be calibrated to become an accurate one; the reverse case is not possible. Resolution indicates the smallest detectable change in flow that a sensor can measure.
Flow Sensor Comparison on Flexible Tubes
Sensor Set-Up & Test Arrangement
Test set-ups A / B / C / D / E / F represent a 60 minutes run each, while the sensors have been re-clamped from test to test as visualized in the chart. Set-up Z, however, was the only 180 minutes run performed.
Minimization of Systemic Measurement Errors
The sensor set-up was chosen to minimize systemic measurement errors while comparing the sensors to each other. All test conditions were kept as stable as possible by using the same sensor and application set-up in steady ambient conditions such as temperature and air pressure. All sensors have been calibrated to the applied test setup to finally refer to the pump output at 3.5 litres per minute.
Measuring Results
Interpretation of the Results
Summarizing all six 60 minutes runs and the 180 minutes run, the average standard deviation of the SONOFLOW CO.55 V2.0 sensor of 0.0406 litres per minute indicates the highest precision of all three tested sensors. This number, however, represents an average precision of 1.16 % of the SONOTEC device, compared to 4.04 % (Sensor X) and 4.82 % (Sensor Y).
The SONOFLOW CO.55 V2.0 stands out for high precision and best accuracy
As the precision specifies the repeatability of the sensor describing how consistent results could be reached; accuracy in turn, defines the error between the real and the measured value. Accuracy, indeed, is finally an issue of a high precision and an optimum calibration of the sensor.
With reaching the best values of the standard deviation during each run, the SONOFLOW CO.55 V2.0 shows the best precision of all competing sensor set-ups. This outstanding performance makes sure to also reach consistently high accuracies, ranking the SONOFLOW CO.55 V2.0 top in five of seven of the simulations realized. This, however, could be even topped by an improved calibration to the test environment.
The high resolution of the SONOFLOW CO.55 V2.0 is therefore also one of the key reasons reaching these exceptional results.
More Information about Ultrasonic Flow Meters
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