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Bar Codes

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Authored by: Niels Wartenberg and Susan Snyder; Microscan Systems Inc.

Many labs will invest an extensive amount of time and capital on automated instruments to improve efficiency and increase productivity. What is often overlooked is the bar code that supports the automation process. An understanding of what a bar code is, how it functions, and how it brings advantages to laboratory applications will provide the foundation needed to leverage bar code technology effectively for achieving the objectives of the automation application while obtaining the highest data integrity possible.

The traditional bar code can best be described as a series of parallel bars and spaces, commonly referred to as elements. The bars, the dark elements of the bar code, absorb light. The white spaces reflect light. Predetermined width or height patterns defined by the symbology are used to encode the data in the symbol. A light source, typically the laser diode of a bar code scanner, is used to extract the data from the bar code. As the light moves across the bars and spaces of the bar code, the light is reflected back to a photo diode, which measures the light levels reflected by the bars and spaces. The data are then decoded by the scanner and output. Because only the widths or the heights of the bars and spaces are important in decoding the symbol, single-row bar codes are considered one-dimensional codes.

Two-dimensional codes can be grouped into two different categories: stacked linear codes and matrix codes. Stacked codes are rows of width-modulated bar codes stacked directly on top of each other. Each row is the same length and resembles a single-line bar code. Matrix codes are a two-dimensional pattern of data cells in the shape of a square, circle, or polygon. Unlike linear and stacked bar codes, matrix codes must be read with an image-based reader. They cannot be decoded by a laser scanner.[1] Bar codes can either be width-modulated or height-modulated. Height-modulated bar codes are almost exclusively used in the document and mailprocessing industry. Width-modulated, or traditional linear bar codes, are the most common type of bar code and are the focus of this tutorial (Figure 1).

Figure 1: Bar code symbologies can be divided into two distinctly different groups: width-modulated and height-modulated bar codes.

There are numerous considerations that one should review before selecting a bar code. The following links lead to more detail on each.

Bar codes are a key piece in the laboratory automation puzzle. While the number of different factors initially may appear large, the implementation of tracking with bar codes can, and has been, successfully implemented.

Key steps to success include:

  1. Identifying objectives and requirements of the completed solution.
  2. Assessing future needs.
  3. Having good communication of requirements to all vendors to minimize unforeseen surprises once the solution is implemented.

The authors would like to thank James R. Gross, Laboratory Market Manager at Brady(R), Milwaukee, WI, for providing information on the various printing methods and label media available to laboratories. They would also like to thank Matt Allen, Product Marketing Manager at Microscan Systems, for his helpful discussions during the development of this tutorial and for reviewing the manuscript.

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