What Is Traceability in Metrology?

The world of metrology is all about accuracy and reliability. When a measuring instrument has both, you can confidently ensure that your products are consistent and compliant with QA and safety specifications.

To determine a measuring instrument’s accuracy, you need to establish traceability. If you can trace the source or the reference in calibrating your instrument back to a widely-known and trusted source, you can be confident in your measurements’ accuracy. 

But what is traceability in metrology? We’ll provide some answers and insights into metrology below.

Metrology: A Quick Refresher

Metrology is the science of measurement. It establishes common measuring standards or “units” that can be used across the board to describe a physical characteristic. 

Metrology has broad applications, including manufacturing, transportation, healthcare, and consumer goods production. In manufacturing, metrologists ensure that production equipment and the finished products have accurate, reliable, and consistent measurements.

Why is metrology important? One minor measurement flaw can cause major product defects – and, in the case of automobiles, for example, compromise user safety. As such, metrology is vital for quality assurance, quality control, consumer safety, and customer satisfaction. 

Here’s where traceability comes into play.

What Is Traceability in Metrology and Why Is It Important?

Traceability is the ability to trace a measurement to a recognized, well-defined reference point or standard (usually an internationally recognized measurement system). Suppose you’re measuring the length of an object using a caliper. Thanks to traceability, you know that the inches and centimeters in your caliper measure the same as the inches and centimeters in other people’s calipers.   

However, traceability in metrology is a bit more complex. Essentially, if a measuring tool can be traced back to a reliable, internationally recognized standard as its source, that’s traceability.

Here’s a practical example of how traceability works in metrology:

  1. Suppose a facility uses calipers to measure parts. To ensure their calipers are all accurate, they calibrate them in-house using a caliper checker. 
  2. Like most measuring tools, however, the caliper checker will eventually fall out of calibration because of frequent use. When this happens, the facility sends its caliper checker to a trusted local calibration lab to be calibrated. 
  3. The local calibration lab uses a set of gauge blocks to calibrate the caliper checker. To ensure their gauge blocks are accurate, the lab sends them to a higher-level, primary calibration laboratory for assessment. 
  4. The high-level lab will have two sets of gauge blocks: the working masters and the NIST-calibrated masters. 

The NIST-calibrated masters are, as the name suggests, sent to The National Institute of Standards and Technology. NIST is a US agency that uses sophisticated tools and technology to set standards for internationally recognized measurement units. Only well-funded high-level labs send equipment to NIST for calibration (because they can afford the cost and lengthy turnaround time of having one of the country’s most trusted agencies calibrate their devices). 

The lab calibrates its working masters against the NIST-calibrated masters to achieve top-level accuracy (afterward, the latter are safely stored to preserve their integrity for many years). The lab’s metrologists then use the working masters for their daily tasks – including calibrating the gauge blocks sent by the local lab.

  1. At NIST, technicians calibrate the high-level lab’s masters using the agency’s own set of gauge blocks. These, in turn, are calibrated using another set of masters. NIST develops masters using high-tech laser systems that calculate the truest, most accurate units of measurement.  

The traceability in this example goes like this: 

NIST masters > NIST working gauge blocks > high-level laboratory masters > high-level laboratory working masters > local laboratory gauge blocks > a factory’s caliper checker > caliper > the parts being measured on the production floor. 

Why is traceability important? 

Traceability is vital in metrology because it gives us a strong foundation and confidence in our measurements. Being able to trace measurements back to national and international standards ensures their accuracy and reliability. It also guarantees consistency of measurements over time and across locations, which is crucial for quality control and compliance. 

The Pillars of Metrological Traceability

These factors or pillars must be present to establish true traceability and verify the accuracy of a measuring tool:

  1. International measurement standards – Institutions entrusted with studying and developing the rules of measurement, like NIST, establish international standards that are universally accepted. Having such standards ensures consistency and that measurements are comparable globally.
  2. A reliable reference point – There must be a gold standard for measurement, which will become the basis for accuracy for all measuring tools. Meter Bar 27 is an example. It is the physical prototype measuring the official “one meter” that the International Bureau of Weights and Measures (BIPM) at Sèvres sent to the United States. Of course, physical prototypes of pure measurements are no longer used today, but we have established standards for determining a unit of measure. These standards specify the reference points that accredited calibration laboratories must uphold.
  3. Calibration and comparison – Once you’ve identified a reference point, your measuring instruments must be calibrated and compared against them for accuracy. For example, if you have a ruler, you match it against a known accurate ruler to see if its centimeters, millimeters, and inches are perfectly aligned. Calibration and comparison are crucial in metrological traceability because they ensure that your instruments match the reference point. This is how you establish their accuracy and reliability.  
  4. Chain of comparisons – This pillar is based on the fact that we can’t all access a pure reference point like Meter Bar 27. So, to establish traceability, the first instrument (or the masters, in the example involving calipers above) must be in line with the trusted reference, and all succeeding instruments in the chain must be in perfect match with the ones before them. If you can trace an instrument’s calibration chain back to the source, you can be confident in its accuracy.

Achieve Accuracy and Consistency with Metrological Traceability

Metrological traceability impacts all aspects of life, from the quality of the meals you order in a restaurant to the integrity of the office building where you work. Learning what is traceability in metrology and understanding its pillars allows for a deeper understanding and appreciation of the importance of accuracy and consistency in measurements. 

If accuracy and consistency are vital in your business, we can help establish traceability in your operations with our customized metrology services and solutions. 

ATT Metrology is the only Airbus-approved US metrology company certified to inspect tooling and production parts for Airbus facilities. We are also one of the few Boeing-certified metrology companies in the world, further attesting our credibility and commitment to providing superior metrology solutions to our customers.

Contact ATT Metrology Solutions and talk to our specialists today.