Your Barcode Doesn’t Scan: Why?
UPC with 29 Bars
When your barcode doesn’t scan, it is like falling off an emotional cliff. With no information other than the deafening silence of no “beep”, how do you determine what’s wrong?
The obvious answer is to use a verifier. Usually—but not always—when a scanner cannot decode a barcode, a verifier can. This is because a verifier has a special decode algorithm that makes it possible to read even a very poor quality barcode. This is because verifiers, like scanners, cannot produce a diagnostic report without decoding the symbol; the whole point of a verifier is to test and grade a barcode—even a very poor quality barcode. So the unique ability to read very bad barcodes is engineered into a verifier’s capabilities.
Defect in bars and pattern background
But of course everything has its limitations, AKA tolerances. What do you do when you simply cannot read the barcode? Here are some strategies that can help you figure out what’s wrong with a dead barcode.
- Count the bars. This is not practical with some symbologies, but with UPC it’s easy. Version A or full size UPC should have 30 bars, 29 spaces. If a bar is missing, it won’t decode, no matter what you do. Obviously this only works for 1D barcodes.
- Looking closely at the bars, even if you cannot realistically count them. See if there are some bars that look much smaller than the other bars. If you find some, look directly above and below them on the label. If that pattern can be seen there too, there could be a non-working print head pixel. Looking above and below the barcode for this telltale clue is important, since the damage to the barcode might also occur at a bar edge and not down the center of a bar.
- Look for similar damage in a 2D symbol. Capable as they are to correct errors, 2D symbols are not infallible. Once all the error correction is used, they fail to decode and the verifier cannot help you figure out what’s wrong.
- Is there a laminate over the barcode? If you can test the barcode before the laminate is applied, this can be helpful in isolating the laminate as problematic.
- Is there a pattern in the background behind the barcode? A scanner or verifier cannot distinguish those extra dark areas as not being part of the encoded pattern of bars or 2D elements. The damaging pattern can be regular, such as a halftone screen, or it can be random, such as text or graphics in the background: a watermark or something printed on the reverse side of the substrate.
Violated right quiet zone
- Violated quiet zones can cause a 1D or a 2D barcode to fail to decode. Some scanners and verifiers are less sensitive to this than others, but if you happen to have one that is, examine the symbol closely to determine whether there are infringing text or graphics, or if the symbol is placed too close to the edge of the label or the corner of the package.
Technology is such a reliable and powerful tool, we often forget that our eyes and a low power magnifier can help considerably in solving vexing problems with barcodes.
John helps companies resolve current barcode problems and avoid future barcode problems to stabilize and secure their supply chain and strengthen their trading partner relationships.
