Using barcodes for item identification and data acquisition is critical to the reliable function of automated operations, from ensuring that the correct components are used in the assembly of a smart phone to providing accurate patient data for samples in a laboratory. Poorly-marked or damaged barcodes can have disastrous effects on operational efficiency, product integrity, and corporate reputation - not to mention potential legal implications and serious risks to consumer welfare. In this blog, I'll be discussing quiet zones - the unmarked space every barcode needs around its perimeter to ensure reliable extraction of encoded data and protection against errors and no-reads.
What Exactly Is a Quiet Zone?
The readability of barcodes is determined by how well a barcode reader can decode the data stored in the symbol. Barcode readability is impacted by a number of technical and environmental factors. Although a barcode may have no noticeable visual flaws, subtle inconsistencies in the code, substrate, or even the positioning of the code in relation to the reader may result in no-reads.
The quiet zone is the area that surrounds the barcode or 2D symbol that is free of all text, characters, graphics, marks, and blemishes.
This blank space allows verifiers or readers to " understand" where the barcode begins and ends so the code can be read as intended. This area is also commonly referred to as the no-print zone, as it provides separation from surrounding marks.
Different symbologies have different quiet zone specifications. In 1D or linear barcodes, the quiet zone typically falls to the left and right ends of the barcode. As a general rule, the quiet zone should be a minimum of 10 times the width of the narrowest bar. In 2D symbols, the quiet zone is the space surrounding the entire symbol. Quiet zone requirements for 2D symbols are prescribed by the Association for Automatic Identification and Mobility (AIM), which specifies at least a one-element (or cell) width on each side of the symbol (all four sides). For best results with large 2D codes, it is typically recommended that the quiet zone be 10% of the symbol height or width, whichever is smaller.
A reader may be unable to decode a symbol if text or other markings bleed into the symbol's quiet zone. Quiet zone infringements may also yield inaccurately-decoded data strings if the reader interprets non-symbol elements as part of the symbol. All barcode readers have tolerances for minimum allowable quiet zone size, but not for maximum.
Quiet Zone Violations
A reader may be unable to decode a symbol if text or other markings bleed into the symbol's quiet zone. Quiet zone violations may also yield inaccurately decoded data strings if the reader interprets non-symbol elements as part of the overall symbol.
Some of the most common causes of quiet zone violations - not enough space around the barcode, blemishes in the quiet zone, or text in the quiet zone - have simple solutions. If the space around the barcode has not been designed to allow for an adequately-sized quiet zone, simply increase the size of the area around the code. If there is a blemish or defect in the quiet zone, you should re-print or re-mark the symbol after eliminating potential causes of the defect. If text or artwork falls within the quiet zone, design adjustments must be made to keep the quiet zone clear.
How Can I Fix the Quiet Zones on My Barcodes?
Quiet zone violations are perhaps the most easily-resolved cause of unreadable barcodes. This is because quiet zone violations are often the result of a simple lack of planning for the inclusion of space around a printed or marked symbol. To resolve quiet zone violations, find and eliminate the causes of blemishes around the symbol, double-check that your printing and marking equipment is working as expected, make sure that the marking method you are using is appropriate for the substrate (surface material of your part), and ensure that your product or packaging design accommodates the space requirements for minimum quiet zone. Additional lighting techniques can also be employed during barcode reading in situations where the quiet zone contains noise caused by reflections or shadows on an uneven substrate.
Devote as much space as possible to the quiet zone to reduce the chance of no-reads or decode errors. There is no maximum specification for quiet zone width, so make this area as large as you can within the limits of your application. When the area available to print or mark a barcode is limited by the overall surface area on a part, such as a densely-populated PCB or a tiny electrical component or medical device, quiet zone real estate can be difficult to come by. If quiet zones must be constrained, readers with sophisticated decoding algorithms can often achieve good reads despite minor quiet zone infringements.
Quiet zone violations are only one of the reasons you may be getting no-reads or decode errors for your barcodes. Read our latest white paper on The Most Common Causes of Unreadable Barcodes to find out more about the consequences of low contrast, improper barcode reader positioning, print or mark inconsistency, and barcode damage or distortion.
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