Metrology has come a long way since its humble beginnings in the ancient world, a time where measurement standards were based on body measures such as fingers, palms and hands… the flood level of the Nile in approximately 3000 B.C. was given as six cubits and one palm.
But man truly is the measure of all things. Luckily, today we have more precise instruments to measure dimensions, while our palms have been freed to carry much more reliable hand tools. Back then, it is said that the standard measure of length was the body of a country’s literal ‘ruler’. Today we have the benefit of traceable calibrations linking back to a known standard (or a different kind of pyramid).
Fast forward 5000 years and it goes without saying that the worlds of the manufacturing, aerospace and automotive industries go hand-in-hand with high precision. Dimensional equipment such as micrometers, calipers, and gauges play an instrumental part in manufacturing high quality products and to perform their job to the highest standards these devices require maximum precision.
With items requiring such a high degree of accuracy it’s no surprise the calibration process itself needs to maintain strict standards. In a process where even the tiniest change in environmental conditions can affect the results of a calibration, the dimensional calibration process really is fascinating (although maybe we’re slightly biased).
Read on to find out how the dimensional equipment calibration process works and why it’s important to calibrate your dimensional equipment on a regular basis.
The Goldilocks of calibration conditions
Dimensional equipment calibrations are usually carried out by dedicated laboratories equipped with highly-skilled technicians using documented procedures, and conducted using a range of state-of-the-art testing tools.
Part of the ISO 17025 standard used by accredited laboratories ensures that key environmental conditions (such as ambient temperature and humidity) are controlled in calibration labs.
Consider temperature as one of those key factors. Labs need to ensure they maintain a consistent temperature – not only of the equipment or parts to be calibrated – but also that of the measuring equipment and the temperature of the calibration environment itself. The Goldilocks principle is very much a cornerstone of dimensional calibration. The temperature has to be ‘just right’.
The main reason for this? Metal can expand or shrink due to the temperatures it’s exposed to. A small difference in temperature can make all the difference to dimensional tools, especially when working with such small increments of measurement.
To ensure the environment is consistent, measurements are taken in a 20°C temperature-controlled room or by making temperature corrections if the measurements are taken at a different temperature.
But ensuring that the temperature of dimensional equipment is kept consistent during calibration is not a simple process. It involves a number of additional steps; including strict temperature control within the lab, wearing gloves to prevent heat transferring from the hands to the item, and allowing the item to acclimatise to the temperature within the lab before calibration.
Gauge blocks are the master dimensional standard used in most calibration laboratories. These are sets of individual blocks where two opposing faces have been precisely ground flat and parallel so that the faces are an exact distance apart, giving a length accuracy of as low as a few micro-inches. They are calibrated to be accurate at 20 °C and kept at this temperature when taking measurements of dimensional tools to mitigate the effects of thermal expansion.
Quality control and safety
It’s also important to remember that calibrating your dimensional equipment isn’t a one-off. You should be using calibrations to monitor the capability of your dimensional equipment over time to ensure it’s performing at its optimal best.
Regular calibration ensures that dimensional equipment retains its capability and traceability. Take dimensional gauges, they are often used on a daily basis across many industries and their results are depended upon to ensure quality and safety, however if the gauge was dropped and damaged then it could easily provide the wrong results. In the automotive industry, for instance, which relies on the accuracy of manufacturing parts, quality is vital. Regular gauge calibration is important to ensure control points are correct and to establish the foundation of the vehicle.
In the aerospace engineering field, micrometers are one of the most fundamental measuring tools. They have the ability to take accurate readings to extremely small measurements with a standard accuracy up to the one thousandth of an inch, to check the width of extremely small parts – which has a huge bearing on safety.
Interested in learning more?
Our team of metrology calibration specialists are experienced in of calibrating your micrometers, calipers, gauge blocks and many more types of dimensional measuring equipment. They can also answer any questions you have around dimensional equipment calibrations.
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