On-site calibration of flow sensors acc. to ISO/IEC 17025

Precision for flow sensor data – On-site calibration of flow sensors

Large heat and water meters are often used continuously for decades after their first calibration and installation without any recalibration. On-site calibration of flow sensors is rather limited until today and often-times lackluster in precision. Therefore in most cases, the flow sensors are demounted and  recalibrated on external test benches. The drawbacks of this procedure are an unavoidable interruption of supply and the physical pipe system, with all its implications, which add up to the already high costs of the demounting and recalibration procedure.

Even if the flow sensor is externally recalibrated, the ideal flow conditions in test benches often times differ significantly from the operation conditions of the on-site flow meter installation. These variations range from temperature shifts, different flow conditions or even electromagnetic differences. The resulting measurement error due to stated reasons remains unknown and could generate major impacts – ranging from technical difficulties in control systems to accounting fairness between involved parties. Accurate measurement results allow examining saving potentials in heat grids and more precise calculations of key performance indicators leading to increased energy efficiency.

Accounting reliability – Optical On-site calibration within real operation conditions

The patented measurement technology (co-owner ILA R&D GmbH) is based on the optical measurement principle of Laser Doppler Velocimetry (LDV). With this principle and our measurement technology, local flow velocities are measured across one or multiple pipe diameter paths. By integration of this measured cross section velocity profile you can create a referencing volume flow to test the flow meter against.

The necessary optical access to the flowing fluid is realised by hot-tapping without the need to interrupt pipe operations. The safety of this process is reviewed and certified by TÜV Rheinland. During calibration process, measurement values of the flow sensor are logged with the highest possible temporal resolution.

The measurement error is calculated through a comparison between the calculated LDV volume flow and an time averaged volume flow of the test device on various test points. Based on the on-site specific  measurement uncertainty budget and calibrated measurement-tools, the calibration results are traceable to national measurement standards of the Physikalisch Technische Bundesanstalt PTB (German National Metrology Institute).

Various advantages  - Accredited, traceable, independent and without interruption of supply

• On-site calibration under operational conditions
• No interruption of supply while preparation and calibration procedure
• Traceabillity to national measurement standards of the German National Metrology Institute (PTB) via calibration of the measurement equipment and an on-site specific budget of the measurement uncertainty
• Guaranteed quality and international recognition via accreditation based on DIN EN ISO/IEC 17025 at Deutsche Akkreditierungsstelle (DAkkS)
• Neutral and independent calibration.

Related documents

• Accreditation certificate of the calibration laboratory
• Annex to accreditation certificate
• Flyer for introduction to the technology
• Flyer for more details to the calibration process
• Improving operational efficiency of power plants through on-site calibrations of flow sensors (DHC 2018, Hamburg)
• Publication with a detailed description of the method in Energy Procedia 2018
• Application sheet district heating at VATTENFALL Berlin
• Application sheet for potable water (Brisbane, Australien)

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