Why is Calibration Of Portable Arms So Important?

Published by CMMXYZ on February 7, 2020

Understanding why I should have my FARO or Absolute ROMER portable arm calibrated.

Articulated arm coordinate measuring machines (portable CMMs/portable measuring arms as they are also called) like other measurement devices require regular calibration or verificationPortable arms are subject to more rigorous usage than regular CMMs therefore, they require more frequent scrutiny. If a portable CMM is used with care and to manufacturers recommendations it will maintain accuracies extremely well over the long term.

Calibration and Verification what is the difference?

Calibration  ( 1or 2 step process ) is based on the process of comparison with a reference or standard in order to give set corrections and/or uncertainties of the instrument being calibrated. In step 2 the results of the portable arm calibration process may then be used in the adjustment of the instrument to within the manufacturer’s specifications if required.

In the 2-step CMM calibration process step 1 is calibration. Step 2 is adjustment, usually performed at the manufacturer’s site.

The International Vocabulary of Metrology – Basic and general concepts and associated terms (VIM 3rd edition) section 2.39 (6.11) defines calibration as an:

“operation that, under specified conditions, in a first step, establishes a relation between the quantity values with measurement uncertainties provided by measurement standards and corresponding indications with associated measurement uncertainties and, in a second step, uses this information to establish a relation for obtaining a measurement result from an indication

 NOTE 1 A calibration may be expressed by a statement, calibration function, calibration diagram, calibration curve, or calibration table. In some cases, it may consist of an additive or multiplicative correction of the indication with associated measurement uncertainty.

NOTE 2 Calibration should not be confused with adjustment of a measuring system, often mistakenly called “self-calibration”, nor with verification of calibration

NOTE 3 Often, the first step alone in the above definition is perceived as being calibration”


This is the process of checking against a standard or reference to confirm that an instrument fits the broad and specific specs provided by its manufacturer. Verification uses the same tests that are employed for calibration, only in a condensed format.

Verification is a much quicker process than calibration enabling the equipment to be  returned to service faster usually lasting 1 -2 days. It simply informs the user that the equipment is ether performing to the manufactures spec or not.  If the equipment is not, the question to be asked is “ is the error reported still within the user’s acceptance?” Often it is, therefore the user can choose to continue using this piece of equipment.   If it is not within the users acceptance  in most cases the equipment will have to be shipped back to the factory so the necessary adjustments and or repairs can be made.  This is a lengthy process that can often takes 3 to 4 weeks or more

Standards for Calibration and Verification on portable arms.

The 2 national standards that are currently in use(as of the publishing of this article) are: B89.4.22-2004 (R2019) Methods for Performance Evaluation of Articulated Arm Coordinate Measuring Machines and IS0 10360-12:2016 Geometrical product specifications (GPS) – Acceptance and reverification tests for coordinate measuring systems (CMS) – Part 12: Articulated arm coordinate measurement machines (CMM) It is advisable to choose the standard that the OEM had originally used to specify the arms accuracy, in this way a simple comparison to the portable CMMs dimensional condition can be easily ascertained.

How to select a portable arm calibration / verification provider?

By choosing IS0/IEC 17025 accredited lab the customer is assured of reliable results and that the service provider is regularly audited and held to the highest procedural and technical standards.

A further conformance to look for is the ISO 9001 Quality Management System. This assures the calibrators registration to this body guarantees the customer that they are dealing with an organization that is serious about its organizational and quality capabilities.

Here at CMMXYZ we calibrate and verify portable arms.  You can learn more about our company and experience.

What to choose for my portable arm: Calibration or Verification?

 2-step Calibration should be chosen

  1. If your portable Arm has been dropped or otherwise visibly mistreated.
  2. If your arm is noticeably out of tolerance
  3. If time without the Portable arm is not a problem.

1-step Calibration should be chosen

  1. A full calibration is required, but no adjustment.
  2. If your portable arm is of recent vintage and in good condition.
  3. If cost is an issue.
  4. You cannot wait 4 weeks for a factory calibration

Verification should be chosen

  1. If the portable arm is in good condition and used properly.
  2. If the portable CMM is old and parts are not available.
  3. You require the portable arm back immediately.
  4. The measurement results provided by the portable CMM have been consistent.
  5. Your financial budget is a factor (verification generally cost 70% less than calibration)

As a service many independent service providers can arrange to send your portable arm back to the manufacturer if the results are outside of your acceptance zone or if the equipment has been damaged.  If you are looking for a service provider for your portable CMM or just have questions feel free to contact us for more information.

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