Thermal Barcode Printers: A look at Printhead and DPI Requirements

by ScanSource Technical Services on September 15, 2010 · 0 comments

in Barcode Printing,POS,RFID,ScanSource POS & Barcode,Technical Education Portal,Technology,Wireless

In real simple terms a Thermal Printhead is made up of a series of perfectly square heating elements over a ceramic substrate. These heating elements are usually referred to as dots. The number of these dots per inch (dpi) indicate the resolution of the printhead. The standard DPIs are 203, 305, 406, 609. The higher the DPI the smaller each dot, hence a higher resolution. Matching the DPI to the application is almost as important as selecting the correct media. The next few slides detail when each DPI would be used. Outside of North America it is common to see the printhead referred to in Dots Per Millimeter.

  • 203 dpi – 8 dot
  • 305 dpi – 12 dot
  • 406 dpi – 16 dot
  • 609 dpi – 24 dot

203 dpi – 8 dot

One reason the DPI is so important is it dictates the size of the barcodes that can be printed. For most general barcoding and labeling purposes a 203 dpi printer is adequate. Each dot in a 203 DPI – 8 dot printhead is 5 mils wide. Each mil is .001 of an inch. This means the dot is .005 inches wide. Since you cannot turn on half a dot (it is all or nothing) the smallest barcode that can be generated is 5 mils. The size of the barcode then goes up in increment of 5. So a 203 dpi – 8 dot printer can generate barcodes of 5 mils, 10 mils, 15 mils, etc. For most general applications a 5 mil barcode is small enough. Most standard scanners usually have a minimum read spec of about 5 mils anyway. As you can see from the illustration below some basic graphics are printable with 203 DPI – 8 dot.

305 dpi – 12 dot

305 dpi – 12 dot printer have dots that are 3.3 mils wide. This allows for printing of barcodes of close to 3 mils. Since most high density scanners have a minimum read spec of 3 mils, 300 dpi – 12 dot printers are adequate for most customers high density barcode printing needs. 305 dpi – 12 dot also allows for more detailed graphics and smaller font sizes. It also allows for a range of barcode sizes that are not available using 203 – 8 dot, printheads, 3 mil, 6 mil, 9 mil, etc. It is important to keep in mind that if a customer’s barcode spec is very specific, which some compliant barcode specs can be, that a specific DPI printer may be required. For example if the customer has to product a 5 mil barcode, with no variation at all, they will have to go with a 203 – 8 dot printhead. A 300 DPI – 12 dot printhead just cannot produce a 5 mil barcode. Thankfully most customers do not have to be quite so specific. Most customers would have a hard time telling the difference between a 5 mil barcode printed with a 203 dpi – 8dot printer and a 6.6 mil barcode generated with a 305dpi – 12dot printer.

406/609 dpi – 16/24 dot

406 DPI – 16 dot and 609 DPI – 24 dot, are used for applications where extreme resolutions are needed. Often the need is for very detailed graphics or fonts. They both also offer a greater range of barcode mil sizes as well, useful if a specific size is required. They also allow for extremely small 2d barcodes.

Determining your DPI

DPI/MM and “X” Dimension

  • How does this relate to a bar code?
  • Remember the “X” Dimension?
  • How would I print a 10 mil bar code?
  • What about a 5 mil bar code?
  • 12 mil?
  • 50 mil?
  • Mil Spec 1182 or 100% UPC?
  • Graphics?
  • Highest quality graphics or photos?

As we have seen the Dots Per Inch directly effects the size barcodes that can be generated. It also effects the quality of the graphics and fonts. Take a second and think about which DPI you would recommend for each application.

Printhead Widths

In addition to different resolutions, printheads (and the printers that contain them) come in different widths. This allows you to chose the width that is closest to the actual label size you are printing. By far the most popular width in label printers is 4 inches. There are other options which would be used for narrow or wide labels. The sizes listed here are just examples. With a print width of 5.04 inches, the Zebra 140XiIII+ for example, will fall between these sizes and the Sato M10e has a printhead that is 10.5 inches wide. It is important to remember there is a max label width and a max print width listed on printer spec sheets. Max label width indicates the actual width of the label and liner that can fit in the printer. Max print width indicates the actual width of the heating elements. For example the Datamax I-4210 has a max media width of 4.65 but a max print width of 4.10 inch. Using media wider than 4.1 inches will simply result in white space on the edges.

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