ISO IEC 29133:2010 pdf – lnformation technology —Automaticidentification and data capture techniques – Quality test specification for rewritable hybrid media data carriers.
6.4 Process control methods
6.4.1 Process control considerations ISOIIEC 15416 process control
ISO1IEC 15416 has an Informative annex addressing process control requirements. The procedures defined in that annex are not appropriate for Rewritable Media, because they apply to a situation where successive symbols are being produced using a substrate that is reasonably consistent between impressions (i.e they form a homogeneous set). The ISO!IEC 15416 process control methods are designed to monitor and control drift in a homogeneous set. In contrast, the process used to erase and rewrite Rewritable Media can have successive media components that might have been recycled many or few times in a completely random mix (i.e. they form a heterogeneous set), In addition, Rewritable Media is affected not only by the number of erase and re-write cycles but also unexpected damage and the usage conditions, etc.
A more appropnate process control methodology for Rewntable Media is defined in Heterogeneity
The nature of Rowritablo Media is that it will deteriorate over time based on a complex set of causes. A basic cause is the number of rewrite cycles, but deterioration can be accelerated due to adverse environmental conditions to which the media is exposed when in use as a data carnei’ during the application cycle (e.g. if it Is exposed to higher than average heat). Because batches of Rewritable Media that are being processed for rewriting are likely to be heterogeneous with each item of Rewritable Media presenting a different state of quality, it is difficult to predict the presence of items that might no longer be suitable for rewriting. Sample size considerations
Whereas with a homogenous set it is possible to apply sophisticated tests to a small sample, for Rewritabie Hybrid Media it is more appropriate to apply simple tests on a larger sample or on all items. The following sub- clauses identify a range of tests of increasing sophistication. Therefore, the extent that they can be applied will range from the possibility of testing a small sample size to a full inspection.
6.4.2 Reflectance test
A simple test that can be applied is a reflectance test of the background colour of the substrate.
A basic test should be applied to each item of Rewritable Media as it is presented to the erase and rewrite cycle, based on the reflectance of the substrate (R,,.j. The application should set the threshold relative to the reflectance of new media. The default threshold is a decrease of 10% for the reflectance of the substrate (R..,.) (e.g. for new media with Rmax equal to 0,83 the reflectance test threshold is  0,75 for each rewnte cycle).
Any item of Rewritable Media that fails this reflectance test should be subjected to the requirements defined in ISOIIEC 15416 andlor ISO/IEC 15415.
6.4.3 Symbol contrast test
A better assessment of the suitability of Rewntable Media for re-use can be achieved by incorporating a Symbol Contrast calculation based on the highest and lowest reflectance value of any scan line through the Rewr,table Media. This test could be applied to an item of Rewritable Media prior to erasure. If the calculated
Symbol Contrast is below that defined for the application, the item of Rewritable Media should be subjected to the requirements defined in ISO/JEC 15416 andlor ISO1IEC 15415
Instead of measuring the Symbol Contrast on a random selection of graphical images (some of which might. or might not, be bar codes) an alternative procedure can be considered. If the application standard provides sufficient label area, a set of special marks can be printed on each rewrite of the cycle.