What is Calibration?

07 June 2023 · 3 min read

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What is Calibration?

Laser Trackers naturally see an erosion in their performance over time. Wear and tear from regular use, plus a host of environmental factors, can create slippage in accuracy. Fortunately, there are many ways to test your Laser Tracker to determine whether it is fit for service.

The most common term that is used for Laser Tracker testing is Calibration. Tracker OEMs and many Metrology Service Providers (MSP) offer Laser Tracker Calibration. But Calibration is actually a very specific term, relating to a set of validation tests and performance corrections. Many of the checks done by Tracker operators and MSPs fit into different categories like Compensation, Verification, and Certification, and each process is important to maintaining Tracker performance. So, what is Calibration? How does it differ from the other methods? And how do you know when your Tracker is actually being calibrated or needs to be? Let’s take a look.

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Calibration is the most comprehensive way to guarantee Laser Tracker performance. Traditionally, full calibration can only be performed by the OEM because they have proprietary knowledge of the internal mechanisms, firmware, software, and calibration values of the Tracker. This is important because Calibration, as defined by the International Vocabulary of Metrology (VIM), is a two-step process.

The first step is to “establish a relation between the quantity values with measurement uncertainties provided by measurement standards,” which simply means that the Tracker’s current performance is evaluated against some kind of reference standard (usually a laser rail and interferometer). ISO 17025, NIST.IR.8016, and ASME B89.4.19 all establish reference standards against which Trackers can be compared.

These standards (along with published OEM specifications) can be used for Verification and Certification of Laser Tracker performance. This process alone only evaluates the current performance of the tracker, and for Certification and Verification, provides the Tracker with a pass/fail certificate. It cannot, however, correct any errors that are found in Tracker performance.

Correction happens in the second defined step of Calibration. The second step “uses this information to establish a relation for obtaining a measurement result from an indication,” which means that Calibration uses the information gathered in step one to identify where Tracker errors are occurring and make the necessary corrections or repairs to return the Tracker to optimal performance.

This second step is unique to Calibration and is the only way to use the data gathered in Step 1 to improve tracker performance. The VIM includes notes to specify this, saying that Calibration should not be confused with small Compensation efforts (like 1 or 4-point QVC) or Verification, and that the first step alone is often perceived as Calibration.

To visualize the differences between Verification, Certification, and Calibration in a different way, let’s compare them to how we examine and correct our vision. Often people are unaware that vision problems are developing, because our brains compensate for subtle changes in visual processing. But that doesn’t correct the long-term errors, and they eventually need to come in for an eye exam. Tests like the eye chart and phoropter, for example, serve as the Verification and Certification stages of this exam. They evaluate your vision performance against a standard and help identify where issues are taking place. Lastly, corrective lenses or LASIK surgery Calibrate vision to correct errors at the source. And much like a Laser Tracker, people who wear glasses need to return to the Optometrist regularly to have their prescription Calibrated as vision performance changes. In short, Calibration is the two-step process of evaluating Tracker performance against a reference standard and, most importantly, using that information to make improvements to the Tracker’s performance. Verification and Certification tests only perform the first part of this evaluation without

correcting error sources. Compensations can temporarily offset Tracker error without identifying the source of the issue.

If your service provider is only performing the evaluation measurement, then your Tracker is not receiving full calibration, which usually needs to be performed by the OEM. Full calibration is recommended yearly for all Laser Trackers, and we discuss the reasons why in our 7 Reasons to Calibrate Your Laser Tracker Today video.

The team of experienced metrologists at API Services are available for Laser Tracker Certifications of all brands both on site and at our service centers across North America and Globally. And All API Trackers can receive full calibrations to B89 Standard at our calibration labs. Visit services.apimetrology.com to learn more.

– Radar

Radar (Radio Detection and Ranging) emits microwave pulses and measures the time for echoes to return. Because radio waves have long wavelengths, radar devices can detect objects at great distances and through fog, rain or dust. They are widely used in aviation, weather monitoring and speed‑enforcement. Radar systems provide a long range but lower spatial resolution compared with LiDAR . This lower resolution arises from the larger wavelength and beam divergence; as a result radar cannot pinpoint features smaller than several centimetres.

(source:wevolver.com)

– LiDAR

LiDAR (Light Detection and Ranging) uses pulsed laser light to measure distance. Because it operates at optical wavelengths, LiDAR can produce very high‑resolution 3D point clouds. It is the backbone of autonomous vehicles and aerial mapping. LiDAR systems generally have a shorter to medium range but offer high spatial resolution, enabling detailed 3D mapping

LiDAR’s ability to capture millions of points quickly makes it ideal for applications such as autonomous driving and surveying. For manufacturing metrology, LiDAR is useful for creating digital twins of large objects or structures. However, typical LiDAR accuracy (millimetre to sub‑millimetre) is not sufficient for tight‑tolerance inspections that require micron‑level precision. Therefore, LiDAR still falls short for high‑precision metrology in aerospace and automotive manufacturing.

– Laser Radar

Laser radar is often used to describe high‑precision laser time‑of‑flight systems. It uses a narrow, focused laser beam and measures not only the time of flight but also the angles of the incoming beam to compute precise coordinates. Laser radar systems can achieve micron‑level precision but typically operate over shorter ranges and at slower scanning speeds compared with LiDAR. Laser radar system steers a focused beam, reading the return signal directly from the object without a retroreflector, and is engineered to provide precise, industrial measurements with tolerances of thousandths or even tenths of thousandths of an inch. However, the speed of data collection is sacrificed for resolution—laser radar scans smaller areas more slowly to achieve high accuracy

(source:eastcoastmetrology.com)

– LADAR (Dynamic 9D LADAR by API)

LADAR (Laser Detection And Ranging) is sometimes used interchangeably with LiDAR, but API’s Dynamic 9D LADAR is a novel system that blends interferometry with laser scanning. LADAR is an interferometry‑based non‑contact measurement system that provides fast and accurate data acquisition. It overcomes several limitations of conventional measurement methods by delivering micron‑level resolution and eliminating issues such as limited accuracy, slow data acquisition speeds and sensitivity to surface reflectivity. LADAR technology uses fast data acquisition to deliver rapid, real‑time data collection, significantly reducing measurement and analysis time compared with traditional methods. It also functions effectively in noisy production environments and at various incident angles. The technology delivers rapid, real‑time data collection, making it suitable for in‑line production measurements where conventional laser radar is too slow.

To learn more about how LADAR can preform in line inspection, click here.

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