TEMPERATURE AND HUMIDITY CONTROLLED IN METROLOGY LABS

Walk into a metrology laboratory and you'll notice something right away: regardless of the season, technicians are always wearing a sweater. Why? Because temperature and humidity are kept constant at 20 °C and 50% RH.

To anyone outside the field, this might look like excessive caution. In reality, maintaining a stable environment inside the laboratory is one of the fundamental requirements for obtaining reliable measurements.

The environment becomes an integral part of the measurement itself.


The environment affects the result

Every material reacts differently to temperature changes.

Steel, for example, has a linear expansion coefficient of about 11.5 µm/(m·°C). This means a 1-meter steel bar elongates by roughly 11.5 micrometers for every degree Celsius increase in temperature. That may sound negligible, but in precision metrology, a few micrometers can make the difference between a compliant part and one that is out of tolerance.

The effect is even more pronounced with materials like aluminum, whose expansion coefficient is roughly double (23 µm/(m·°C)). A 500 mm component can vary by more than 10 micrometers with a temperature difference of just 1 °C.

It's not only the workpiece being measured that's affected by temperature — measuring instruments are subject to the same laws of physics.

A caliper calibrated immediately after being transferred from a 30 °C workshop could show small dimensional variations that affect the measurement. The same principle applies, even more strongly, to micrometers, ring gauges, plug gauges, and gauge blocks, where accuracies of just a few microns are required.

For this reason, before any measurement is taken, instruments and components are left to acclimatize — a necessary step to eliminate the effects of thermal shock.


What is acclimatization, and why is it essential?

Whether it's a measuring instrument or a mechanical part, the object is never measured as soon as it arrives in the laboratory. Coming from outside, its temperature is initially very different from that of the measurement environment. Before any inspection begins, it's given the time needed to reach thermal equilibrium with the lab.

Only once temperature and ambient conditions have stabilized can truly representative measurements be taken.


Why is 20 °C the reference temperature in metrology?

In dimensional metrology, 20 °C is the universally adopted reference value.

This reference was set by ISO in 1947 under standard ISO/R 1:1951 (R stood for Recommendation, the name given to standards of that era), which fixed the temperature for "industrial length measurements" at 20 °C. After a series of revisions and harmonization efforts, standard EN ISO 1:2022 confirms 20 °C as the standard reference temperature for geometrical and dimensional measurements.

This makes it possible to compare a measurement taken today in one laboratory with one taken tomorrow in another, with consistent and comparable results.


An invisible detail that guarantees quality

Anyone observing a coordinate measuring machine or a high-precision instrument might assume reliability depends solely on the technology. In reality, data quality emerges from the interplay of many factors: instruments, operators, procedures, and environment.

Temperature, humidity, and acclimatization times aren't mere organizational details — they're essential elements of the metrological process. It's precisely this attention to often-underestimated details that distinguishes a metrology laboratory capable of turning a simple reading into genuinely reliable technical information.