Significant plant maintenance expense is incurred when trying to obtain an accurate flow measurement with good repeatability and long-term stability, particularly when there is no installation location that meets the ‘ideal’ requirements. The use of an on-site flow meter calibration, when combined with the proper flow meter technology, can deliver this desired measurement quality at lower total cost.

Measurement quality is determined by the quality of the total measurement chain. A flow meter may be calibrated in idealized laboratory conditions, but effects from its on-site installation position and signal processing affect the final value reported to the control room. The quality of the whole measurement chain can only be assured on-site when the meter is in operation at its true installation position. In an on-site calibration, the error components caused by different parts of the flow measurement chain are identified and corrected for, allowing correction of the error components where they originate. Years of on-site calibration experience outside minerals processing have shown that by far the largest measurement errors originate not from the flow meters but from other parts of the measurement chain.

This paper presents the most widely applicable on-site calibration method, the radiotracer transit time method, which can account for errors in the measurement chain. The method is widely used in other industries but is not yet widely used in minerals processing. It is flexible in field conditions and provides traceable reference for turbulent flows of clean liquids or slurries. It has been thoroughly tested in over 10,000 accredited on-site calibrations by Indmeas of Finland, with accredited uncertainty as low as 0.5%. Examples are shown.

Maintaining an accurate flow reading over long time periods also requires a stable, reliable flow meter. The array-based non-invasive sonar flow meter is well suited for these challenging applications in minerals processing and solves many long-standing reliability and stability problems. An example is shown for a difficult slurry application.