Ensure Readability of 2D Bar Codes

Written by: Microscan Systems, Inc.

2D bar codes and symbols, such as Data Matrix, are used on thousands of diverse items for accurate identification, protecting product integrity, providing critical maintenance information, and even keeping production processes flowing efficiently. Ensuring their readability is critical, especially for open source manufacturers that use Data Matrix symbols which must be read elsewhere in the supply chain.

It is important to note that a successful read on one imager does not necessarily signify a quality code. Only a Data Matrix Verifier can measure the quality of the printed or directly marked code against parameters defined by symbol verification standards.

Common questions about Data Matrix verification include:

Q. Why can’t I just use an imager to check readability? A. Imager technology and performance varies widely and symbols must often be decoded by multiple brands within the supply chain. Your imager’s ability to read your symbol does not ensure that it can be read by a different imager.

Q. How will verifying symbol quality affect my bottom line?
A. Ensuring your symbols can be decoded each and every time can reduce costs associated with returned products; increase the efficiency of your manufacturing process; allow preventative care of the symbol marking equipment; and eliminate fines levied in some industries by noncompliance with symbol quality standards.

Q. Do I need to verify if the encoded data is for internal use only?
A. While verification within a “closed-loop” system is not as critical, ensuring the readability of symbols is an easy way to prevent time-consuming and potentially costly problems within your company.

Q. What are the standards for Data Matrix verification?
A. The two most common standards are ISO/IEC 15415 and AS9132A.

The ISO/IEC 15415 standard specifies the methodologies for measuring, evaluating, and grading 2D symbol characteristics in order to indicate the quality of the mark. In addition, the standard identifies possible causes for symbol degradation. See below for complete parameters.

The AS9132A standard specifies uniform quality and technical requirements for Data Matrix direct part marking symbols on metal substrates. Direct part marking methods addressed in the AS9132A standard include: dot peen, laser etch, and electrochemical etch. Manufacturers of aerospace components are directly affected by the AS9132A standard.

Q. How do I choose a verifier?
A. Certified verifiers are highly desirable. The lighting and optics of the verifier must be factory calibrated to gain ISO/IEC 15426-2 certification, which guarantees accurate and consistent verification results from one verifier to another. Currently the only Data Matrix verifier to achieve ISO/IEC 15426-2 certification is Microscan’s Quadrus® Verifier.

Q. How does the Quadrus® Verifier work?
A. Present a part or label to the center the symbol in the Field of View. The image is captured and the verifier evaluates the symbol based on the selected standard. A symbol quality report with graded results is immediately displayed.

ISO/IEC 15415 Verification Parameters

Symbol Contrast
Difference in reflectance between the light and dark regions of the symbol.

Fixed Pattern Damage
Refers to quiet zone, finder pattern, and clock pattern damage. Missing elements or distortions to these patterns can severely inhibit readability.

Axial Non-Uniformity
Amount of deviation along the symbol’s major axes.

Grid Non-Uniformity
Refers to the cell deviation from the theoretical or “ideal” grid intersections to those that are determined by the reference decode algorithm.

Modulation
Measures the ability to discriminate between light and dark elements.

Unused Error Correction Capacity
Amount of error correcting capability remaining after applying the error correcting algorithms to reconstruct a damaged or poorly modulated symbol.

Would you like to learn more about 2D bar codes and Data Matrix verification? Call 425-226-5700 or visit www.microscan.com to request the full version of our Data Matrix Verification white paper and a Bar Codes 101 CD.