What are test parameters and how do they enable a comprehensive evaluation of code quality?
Quality assurance through targeted evaluation: measurement parameters for 1D and 2D Codes
Test parameters are crucial criteria used in the quality control and verification of barcodes (1D) and two-dimensional codes (2D) such as QR codes or Data Matrix codes. These test criteria help to ensure the readability, accuracy and reliability of the codes and enable a comprehensive assessment of code quality. They also help to identify and rectify potential code recognition problems at an early stage. The specific marking with (1D) or (2D) indicates for which type of code the respective parameter is relevant, whereas parameters without this marking apply to both code types.
What test criteria and measurement parameters are there?
Code measurement with code verification devices and verification by database comparison
Various quality parameters are taken into account when assessing code quality. Let's start with the basic properties that are decisive for the functionality and readability of a code.
Code properties, layout, data content
- Code type or code symbology: e.g. EAN-8, EAN-13 or Code 128, DataMatrix ECC200 or GS1 DataMatrix codes (inspection possible via code type selection, manually or with the help of an article database).
Quality agreement checklist: Standard or specification of the code and code variant have to be defined. - Code content: is the decoded sequence of digits or combination of numbers and letters (proprietary) (inspection possible using the code analysis function, manually or with the help of an article database).
Quality agreement checklist: Clear specification of how the code content is structured. - Data structure: is the code content that is structured based on standards. E.g. according to ANSI MH10.8.2, GS1, HIBC, HIBCC (inspection by built-in structure analysis, extended optional ScanLink function or manually, configuration may be required).
Quality agreement checklist: which structure type, which article number system, which data elements (article, batch, weight, etc.), fixed or variable number of data elements. - Code size - module size: depending on the code specification. Checking with the verification system is possible (module size, Z-module, matrix cell size) (optional parameters / traditional evaluation) or manually (note scanner resolution and reading range).
Quality agreement checklist: Module size range based on an industry specification (ODETTE, HIBC, EDIICE, GS1, ISBT, securPharm ...) or proprietary matching the printing system resolutions and scanner properties - (2D) Matrix size - 2D Codes only: the matrix size, together with the module size, has to match the scanner properties. Rectangular 2D Code (Data Matrix) have a different width than height.
Checklist: Quality agreement: the matrix size may have to be limited to exclude symbols that are too large (see also code height and width as well as module size and data content). - Code width: Depending on the specification, the code width is limited to a maximum trade show. The width results from the encoded data and the module size (note the reading field width of the scanners at the smallest reading distance) (inspection manually or by code width display).
Quality agreement checklist: width depending on an industry specification (ODETTE, HIBC, EDFICE, GS1, ISBT, securPharm ...) or proprietary to match the scanner properties. - Code height: for barcodes, this is important for reading regardless of the rotational position and for very fast conveyor belts (more reading opportunities with a higher code height). The height and width of square matrix codes are identical. There are also very rectangular matrix codes. (Scanner field of view at all reading distances
Quality agreement checklist: Height depending on an industry specification (ODETTE, HIBC, EDFICE, GS1, ISBT, securPharm ...) or proprietary to match the scanner properties. The requirements for the code position (rotation angle) have to be taken into account. Reading tests with a scanner may be necessary. - Code position: a very important criterion with regard to the design of packaging or in fully automated processes (pallets, packages, production). (Inspection is only possible manually).
Quality agreement checklist: position defined by an industry specification (ODETTE, HIBC, EDFICE, GS1, ISBT, securPharm ...) or proprietary matching the scanner field of view and characteristics of the product or shipping unit. - (1D) Ratio: some barcode types consist of 2 bar widths. The ratio between narrow and wide bars is the ratio. The range from 1:2 to 1:3 is typical.
Quality agreement checklist: Only for Code 39, Interleaved 2of5, Codabar, either according to standard or restricted range. - (1D) Check digit: optional for some barcode types. Mandatory for other barcode types. Otherwise specified by the code type or the data structure used.
Quality agreement checklist: Only for barcode types that allow optional check digits. In data fields, this is part of the data structure check (data fields in 2D Codes can also contain check digits (examples: PPN, GTIN). - (2D) Specification of error correction (2D Code, only if different error corrections are provided (Data Matrix no as fixed, Aztec scalable, QR code 4 different, PDF417 9 different) (unevaluated).
Quality agreement checklist: Error correction level and type have to be defined (e.g. Reed Solomon or CRC, some should no longer be used (e.g. ECC000 to ECC140 for Data Matrix). - (2D) Number of code words (2D Codes , informative, results from the matrix size).
- (1D) Decoding (EN: Decode) (barcode): includes the bright field or quiet zone check, the check of the check digits, code length check (only if applicable), the element and edge determination and an error message if the reference decoding (EN: Reference Decode Algorithm) no longer works. (Inspections with the verification system are possible).
- (2D) Decoding (EN: Decode) (MatrixCode): the reference decoding (EN: Reference Decode Algorithm) is verified as well as the correct code construction. Some errors result in the symbol no longer being recognized. Other errors such as incorrect padding sequences and length specifications or incorrectly set shift characters lead to devaluation. Certain code words are not permitted in some coding variants and this leads to devaluation.
- (2D) FPD (Fixed Pattern Damage): In 2D code measurements, the quiet zones (EN: quiet zone) and finder patterns (EN: finder pattern) are verified, among other things. These individual criteria are summarized and evaluated in the FPD (Fixed Pattern Damage) parameter.
- (2D) UEC: Unused Error Correction For 2D Code measurements, the use of error correction is also evaluated. (UEC - Unused Error Correction)
- (2D) Damage to format information: this parameter is only used for QR codes. It provides information about the error correction level and data masking.
- (2D, stacked, cross row (EN: cross row)) Code word yield
- (2D, stacked, cross row) Code word Print quality
Reflections and contrasts
- Symbol contrast: maximum difference between reflections in gaps, quiet zones and bars (2D + barcode, calculated from Rmax and Rmin) (EN: Symbol Contrast)
- Rmax: maximum reflection in the entire symbol (not evaluated, is included in symbol contrast) (EN: highest or maximum reflectance).
- Rmin: minimum reflection in the entire symbol (not evaluated, is included in symbol contrast)
- (1D) Rmin/Rmax: evaluates the bar blackening with low requirements (barcode only)
- (1D) Minimum edge contrast or minimum adjacency contrast: (ECmin), lowest contrast in the entire barcode (measured on one bar (Rb)/ pair of gaps (Rs)) (EN: Minimum Edge Contrast)
- (1D) Rs: lowest reflection of a gap (EN: space) (not evaluated for ECmin calculation)
- (1D) Rb: highest reflection of a bar (EN: bar) (not evaluated for ECmin calculation)
- Modulation: Uniformity of the reflections separately for the light and dark module areas in the code and quiet zone (2D Code and barcode, note details)
- (2D) MOD: Modulation of a single code word within a code. The results are included in the modulation and reflection range parameters.
- (2D) Reflectance Mar gin: Modulation with the following difference - If code words are handled by error correction then the MOD value for this code word is degree 0 (2D only). In a future version, Reflectance Margin and Modulation are expected to be combined.
- (2D) Contrast uniformity: (Contrast uniformity, only for 2D Codes). This is the code word with the worst MOD value (% specification) (not evaluated, required for calibration)
- (1D) De fects: Evaluates dark spots (EN: Spots) in the gaps and light spots (EN: Voids) in the bars in relation to the symbol contrast.
- (1D) Optional - PCS (ECmin): Print Contrast Signal (evaluates the bar blackening very strictly) based on the reflectance values Rs and Rb
- (1D) Optional -PCS (SC): Print Contrast Signal (evaluates bar blackening with medium requirements) based on the reflectance values Rmax and Rmin
- (2D, DPM) Cell contrast (CC): relative contrast evaluation of the overall symbol, replaces symbol contrast
- (2D, DPM) Cell modulation: (CM) - modulation evaluation with relative values obtained from the adaptive DPM setting of the exposure; replaces modulation (EN: Modulation) and reflectance margin (EN: Reflectance Margin).
- (2D, DPM) Reflection of the symbol (Rtarget): Indication of how much more exposure is needed (the smaller the value, the stronger) based on the ratio of the achieved DPM contrast to the adjusted contrast of a calibration standard.
Dimensional accuracy and printing precision
- (2D) Axial dist ortion: compression or stretching of a code (EN: Axial Nonuniformity)
- (2D) Grid distortion: offset matrix cells (position) (EN: Grid Nonuniformity)
- (2D) Print growth: increase or loss in width of the matrix cells, determined in the X and Y directions and as an average value from both directions (EN: Print growth).
- (1D) Decodability: Evaluation of the dimensional accuracy of bars, gaps and pairs of bars and gaps that are relevant for decoding (scanner) (based on the decoding rule) (EN: Decodability).
- (1D) Mean value: the average widening (+) or narrowing (-) of all bars of a barcode (specified as deviation) (not evaluated, can be evaluated optionally). Checklist quality agreement) (absolute with tolerance specification or percentage in relation to tolerance)
- (1D) Print growth: (EN: print again, print growth) Percentage average specification of the widening or narrowing of the bars in relation to the module width (not evaluated)
- (1D) Bar: Indication of the two extreme deviations of the line widths (not evaluated, can be evaluated optionally)
- (1D) Gap: Indication of the two extreme deviation of the gap widths (not assessed, can be assessed optionally)
- (1D) E value: Specification of the width deviation of pairs of bars/gaps with 2 extreme values (not assessed, can be assessed optionally)
- (1D) P-value: Specification of the two extreme deviations of the character width (a combination of bars and gaps representing a data character, [code word]) (not evaluated, can be evaluated optionally)
Dimensional accuracy and printing precision Switchable DPM criteria in accordance with SAE AS 9132a or DIN EN 9132
- (2D, D PM) Dot size: the dot size indicates the extent to which a round dot fills a matrix cell (optional SAE AS 9132a, can be evaluated optionally) (EN: Dot size).
- (2D, DPM) Dot ovality: the dot ovality specifies the deformation of a dot (starting from a dot peen point which should be circular) (can be evaluated optionally) (EN: Angle of Distortion).
- (2D, DPM) Point offset: if the center of the written point is offset from the center of the matrix cell, this results in a point offset (can be evaluated optionally)
- (2D, DPM) Axis angle distortion: indicates how far the X and Y axes move away from the ideal 90° angle (can be evaluated optionally)
Measurement criteria as the key to code quality and reading reliability
Comprehensive assessment for optimum performance
The test criteria highlight and evaluate the properties of the measured codes. Efficient and reliable code reading, especially in fast, fully automated reading processes, can only be ensured if all properties or measurement criteria are of sufficient quality or fit the application. The determination of the test method and thus the assessment of the print or marking quality allows a compact and efficient coordination of which print quality is required for the respective application (bilaterally or by an association or user group).
Code measurement with code verification devices
How to verify test parameters?
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