Time-Based vs Modern Condition-Based Calibration Metrology

Traditional Time-Based vs. Modern Condition-Based Calibration in Metrology

In a May 2024 webinar to celebrate World Metrology Day, experts from TÜV SÜD and academia discussed the merits of condition-based calibration in comparison with traditional time-based calibration.

Read my summary of the discussion below or watch the full panel discussion of this and other thought-provoking questions in the webinar recording (Question 2: Timestamp 20:00)

The time-based calibration of measuring instruments, based on the SI Units traceability pyramid, international standards and National Measurement Institutes has served the science of metrology exceptionally well for decades, even centuries.

Advances in instrument diagnostic capabilities and data sciences such as machine learning are seeing a push towards the use of Condition-Based Calibration (CBC) to (primarily) reduce operating costs. Does the panel think that there is a danger in moving too far from the established and proven time-based, traceable calibration methodology? And if so, what are the dangers and how can they be addressed?

The Case for the Sievert Approach

We were pleased to have Professor Manus Henry, Professor of Flow Measurement at Coventry University and the University of Oxford, and Chair of the National Measurement System's Flow Programme Expert Group (PEG), on the panel. Manus took the lead explaining the concept of self-validating sensors, or Sievert sensors. This innovative approach was developed in the 1990s by Manus and his Professor, David Clarke and resulted in British standard BS7986.

"The key idea is to integrate diagnostics and metrology, so that instead of a device generating some device-specific error code, a Sievert sensor is required to generate online and dynamic uncertainty estimates," Manus explained.

This approach offers several advantages:

1. Real-time quality assessment: Systems can evaluate measurement quality on-the-fly, without interpreting device-specific error codes.
2. Preserved traceability: Vendors map detected conditions to corresponding increased uncertainties, which can be externally verified in National Measurement Institute (NMI) labs.
3. Reduced calibration frequency: Instruments may be calibrated less often, but the calibration procedure becomes more sophisticated to verify diagnostic performance.

The Primacy of Metrology Labs

Manus emphasised the importance of maintaining the authority of National Measurement Institute (NMI) labs and the primacy of traceability. The Sievert scheme achieves this by:

• Allowing vendors to innovate and patent device-specific diagnostics
• Tying these innovations into the existing metrology scheme through dynamic online uncertainty estimates

This approach prevents the risk of losing the established metrology framework amidst a sea of vendor-specific diagnostics, which could lead to excessive time between calibrations under market pressures.

Challenges In CBM

While the concept of CBM is promising, Dr Chris Mills, Senior Consultant at TÜV SÜD, raised some valid concerns. He recalled how diagnostics was a key topic when he started his flow measurement career over 16 years ago but there hasn’t been much uptake. Despite the availability of diagnostics, many people still prefer the traditional, time-based maintenance (TBM) method.

Chris highlighted several challenges:

• Comfort with established methods: Many professionals are reluctant to change from calendar-based calibration approaches.
• Knowledge gap: Implementing diagnostics requires new skills and understanding.
• Vendor-specific terminology: The lack of standardisation makes it difficult for users to navigate different systems.

Diagnostics serve two purposes: maintenance reduction and issue detection. However, calendar-based calibrations remain important for several reasons:

• Familiarity and comfort for customers
• Confidence in regular checks
• Risk management

While diagnostic-based approaches may extend calibration intervals, they pose potential risks. For example, if an issue is discovered after an extended period, it's unclear when the meter shifted, potentially leading to significant financial risks.

Chris believes that in the near future, a combination of both approaches is likely to be most effective. In my opinion, Chris's perspective holds merit. When dealing with financial risks that involve millions of pounds, it's understandable that many individuals seek the security and assurance that comes from a verifiable calibration process. It's challenging to place complete trust in diagnostic data, especially when the stakes are so high. You could potentially face substantial financial losses or legal repercussions. The desire for a traceable calibration situation stems from the need to mitigate these risks and establish a solid foundation for decision-making in high-stakes financial scenarios.

Real-World Applications

TÜV SÜD expert in hydrogen fluid flow measurement, Dr Piotr Traczykowski, brought practical insights into the discussion by sharing his experience with hydrogen refuelling stations. He noted that many operators are not even aware that they need to check the zero of their flow meters, let alone send them for calibration. This lack of awareness and maintenance is a significant risk that needs to be addressed.

The shift from time-based to condition-based calibration is not without its challenges and risks. While modern technologies offer promising solutions, the need for traceability, certification, and standardisation remains crucial. The panellists agreed that a balanced approach, integrating both traditional and modern methods, would be the most effective way forward.

Watch the full panel discussion of this question in the webinar recording (Timestamp 20:00)

PANELLISTS

Professor Manus Henry, Professor of Flow Measurement at Coventry University and the University of Oxford.

Professor Henry is also chair of the National Measurement System’s Flow Programme Expert Group.

Dr Chris Mills, Senior Consultant, TÜV SÜD

Chris is an expert in Coriolis meters and active in many flow measurement technical committees and the development of several ISO metering standards.

Dr Gabriele Chinello, Head of CCUS, TÜV SÜD

Gabriele is also a technical advisor on CCUS metering to the UK Department of Energy Security and Net Zero (DESNZ) as well as participating in various ISO and BSI committees.

Dr Piotr Traczykowski, Clean Fuels Consultant TÜV SÜD

Piotr is heavily involved in hydrogen metrology and accurate measurements of hydrogen dispensed by hydrogen refuelling stations.

MODERATOR

Colin Lightbody, Principal Consultant, TÜV SÜD

Colin spent many years working across the world as a Metering Consultant for an energy services company. He has contributed to the development of several ISO metering standards for Coriolis and ultrasonic flow metering and has been awarded a patent for a flow meter verification technique.

Read Colin's other blog posts answering some of the questions we addressed during this webinar about The Evolution of Metrology in the Energy Transition and The Future of Traditional Flow Measurement Technologies in a Digital World.

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