How to detect missing ink or smudges in a barcode quiet zone
The quiet zone is the blank space that must be left on both sides of a barcode. For EAN-13, the left side must have 11 modules and the right side 7 modules; this cannot be changed to 2 millimeters on each side. An extra ink dot in the quiet zone, or bars printed into the quiet zone, are both treated as barcode defects. Clear bars themselves cannot substitute for a qualified quiet zone.
The quiet zone is the blank space that must be left on both sides of a barcode. For EAN-13, leave 11 modules on the left and 7 modules on the right; do not change this to 2 millimeters on each side. If there is an extra ink spot in the quiet zone, or if a bar is printed into the quiet zone, treat it as a barcode defect. Clear bars themselves cannot substitute for a compliant quiet zone.
How Much to Leave
The module width is the width of the narrowest bar, often written as X. The left quiet zone of EAN-13 is 11X, and the right is 7X. If X is 0.33 millimeters, the left side needs about 3.6 millimeters, not 2 millimeters. UPC-A usually has 9X on each side, and Code 128 has 10X on each side. Whichever symbology is written on the job ticket, use that symbology's module count; do not use the millimeter count from the previous job.
If there is an ink spot, a dirt line, or an adjacent graphic encroaching into the quiet zone, the verifier will downgrade the quiet zone item. Even if the bars still look clear to the human eye, the grade may still be below the customer's required C or 1.5.
Stop When You See This
| In the quiet zone | The bars themselves | Action |
|---|---|---|
| Ink spot or dirt line | Regardless of whether they are clear | This section fails |
| Encroached by an adjacent graphic | The bars are complete | Change the layout or registration; do not just wipe off one spot |
| Clean | Bars have breaks | Treat as missing bars; the quiet zone is not the cause |
Do This First This Round
- Confirm the symbology first, then use the module count for the quiet zone; do not use 2 millimeters on a ruler.
- If there is any ink in the quiet zone, do not pass it just because the grade happens to still be C.
- Write the symbology and X into the inspection settings so the camera alarms according to this quiet zone.
