Label Sensing: The Difference Between Gap, Line & None

After our very popular blog post, "Difference between Direct Thermal and Thermal Transfer", I thought it would only be fair to explain the difference in the sensing options too.

What are they?

The different sensing options are all optical. They can either detect a gap, a hole or a black line that is printed for the sole purpose of sensing. These are used to tell the printer where the start and finish of each label is. If these are not set correctly they can cause your printer to either error or print incorrectly.


Let's start with the most common option in professional printing; the gap option. A huge selection of rectangular, opaque, die cut labels (labels that are pre cut to size) have a gap of ~3mm between them. The printer will have an optical sensor that will shine an invisible light through both the label and the backing paper. It will be calibrated* to detect the difference between a label and the gap between each label. If there is an inconsistency it will know something isn't right and will give an error; such as if there's no gap when there should be then there is a possible paper jam or overlapping labels. If there is a gap when there shouldn't be then there's a label missing or you've come to the end of the roll. Some examples of printers that use a gap sensor would include but not limited to: any Labelstation, any Dymo LabelWriter and most Zebra printers.


Another common sensing option is the line or also known as black line. This is commonly found on labels and tags that either have no gaps between them (for example continuous media with perforations), clear die cut labels, round or other shaped die cut labels. This is usually a solid black line between 3mm and 5mm deep that spans the whole width of the media but can also be used for detecting small holes instead. A sensor detects the lines so it knows where the start and finish of each label is. Unlike the gap sensor that shines through the media, the line sensor looks for a reflection. It will be calibrated* for the two different intensities of reflection of what is a black mark and what isn't. Similar to the gap sensor, if it fails to detect a black mark when it probably should, or one when it shouldn't, or one that appears to be too big/often, it'll give an error to correspond with it. Some examples of printers that use a black line sensor would include but not limited to: any Labelstation, any Brother QL and Zebra GK printers.


Also know as continuous. This one is real simple. A continuous media that has no gaps or perforations and is just one long straight run. Usually a sensor will still be looking to see when you run out but otherwise it doesn't function to the size of the labels. The length of the label can be variable and entirely your choice. Some examples of printers that can print on continuous media would include but not limited to: any Labelstation, any Brother label printer, Dymo Rhinos and LabelManagers and Zebra printers. * It's recommended to calibrate after each new roll of media is installed as different batches can give different readings.

Label sensing examples

Front Back
These are clear labels. It would be impossible for the printer to know where the start and finish of each label is without the black line on the back of the backing paper.

If you have any further questions about label sensing and advice on printers and labels please do not hesitate to contact us.