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Black Mark Sensors

All thermal printers use sensors or optics to determine label or tag length. There are three methods they use to do so:

Black Mark Sensing

Black mark sensing labels have black lines, or bars, printed on their liner or in a specific area on the thermal tag that is used by the printer as a start/stop gap sensor. These lines are a printed black area either between or on each tag or label. The sensor must pass over an area of solid black, with no interference from other black copy to confuse the start/stop points.

Gap Marks

Gap marks are cut-out areas between each label or tag that a printer uses to optically sense the space between them. They can be notches, die-cut or simple cut-out holes. The sensor on the printer must be properly aligned to “see” these cut-out areas. Some printers have center gap readers only, but most mid-range and industrial printers have an adjustable gap sensor.


Continuous labels have no gaps. The gap sensor is turned off, leaving the software to control the start/stop by distance. The printer will simply start printing the first label and print each subsequent label immediately after.

Special Considerations
  • Some labels/tags require more effort during the initial set-up and will always require a specific gap-sensing method.
  • Labels that are circular or multi-sided require an adjustable sensor head that must not be moved.
  • Clear label material requires a black mark sensor bar on the liner
  • A label or tag that has full color bleeding off the top or bottom edges will often trick the censor into reading it as a black mark. These labels will also need printed marks, lines or gaps to help the printer see the exact gap. The printhead sensitivity may also need adjusting.
  • Registration can become difficult when printing small electronic or jewelry labels. Black mark sensors are strongly suggested in these instances.

Remember, while printing black mark sensors will add cost, your printer may not work without them. We at Barcode Factory will be happy to review your application and recommend the most cost-effective method to sense gaps and have a productive tag/label print application.

For more information or to discuss your project, Contact Us or call 888-237-8525.

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