Bar Codes 101
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What is a Bar Code?
Elements of a Bar Code
Bar Code Symbology Types
Bar Code Symbologies
Applications for Bar Codes
Industry Standard
Organizations
Do you have a bar code question?
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What is a Bar Code?
A binary coding system consisting of
varying widths of vertical black lines (called bars) and white spaces that
when read by an optical scanner can be converted into machine language.
Bars and spaces are just one of many "elements" that make up a bar
code.
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Elements of a Bar Code
Almost all bar codes contain the following elements:
Start and Stop Symbologies
At the beginning and end of
some bar code symbols, there are "start" and "stop" characters. These
characters identify the symbology and also enable the scanner to read
the symbol bidirectionally, decoding the data in the correct
order. Bar codes also often include a check digit at the end
that is determined according to an algorithm based upon the preceding characters.
Quiet Zones
In order for
the scanner to recognize the bar code, there must be an 1/4" wide area
next to the start and stop characters that contains no markings. If the space is too short, the bar code symbol will not be read by the scanning device.
Interpretation Line
This is a line of human-readable characters
that is located usually beneath the bar code. An example is shown
in the Code 128.
Bar/Space Patterns
These are the wide and narrow black bars and
whites spaces contained in the bar code.
Inter-Character Gap
In some bar codes, like Code 39 (same as Code 3 of 9), each
character is printed independently of other characters and is not part
of the encoded character and is thus separated by what's called an
inter-character gap.
When exaggerated, you can see the elements for each character and the inter-gap that separates the characters.
Code Density
Code density refers to the
number of data or message characters which can be represented
per unit length of space. Four variables affect code
density: type of code, ratio of wide to narrow elements and the
X dimension.
- Type of Code
UPC bar codes are used in the U.S. and Canada EAN and JAN symbols are used in Europe and Japan respectively. All bar codes have
different structures. Some are able to encode more information per
inch than others. An example is shown in comparing the Interleaved
2of5 bar code with Code 3 of 9. The Interleaved 2of5 can encode more
numeric information than the Code 3 of 9 in the same amount of space.
- Ratio of Wide to Narrow Elements
Ratio is important in deciding on the type of scanning device to
read the code. Changing the code density of a particular bar code
is accomplished by varying the ratio.
- X Dimension
The width of the
narrowest bar or space is referred to as the X dimension, usually
given in mils (thousandths of an inch). The X dimension dictates the
width of all other bars and spaces, and ultimately the length of the
bar code. The greater the X dimension, the more easily a bar code will
scan. The smaller the width of the bar, the
shorter the length of the symbol, the closer the tolerances are and
the more difficult it is to print. The larger the width of the
elements, the more space it takes to print the bar code; therefore,
the lower the bar code density. The thinner the bar and spaces,
the less space is required and the higher the bar code density.
Lower density bar codes are more reliably printed and more
consistently read than higher density bar codes.
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How is a bar code read?When a bar code scanner is passed over
the bar code, the light source from the scanner is absorbed by the dark
bars and not reflected, but it is reflected by the light spaces. A
photocell detector in the scanner receives the reflected light and
converts the light into an electrical signal.
As the wand is passed over the bar code, the scanner creates a low
electrical signal for the spaces (reflected light) and a high electrical
signal for the bars (nothing is reflected); the duration of the electrical
signal determines wide vs. narrow elements. This signal can be "decoded"
by the bar code reader's decoder into the characters that the bar code
represents. The decoded data is then passed to the computer in a
traditional data format.
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Bar Code Symbology Types
Some bar codes are numeric only (such as UPC, Interleaved 2of5, and
EAN). Others have a fixed length (i.e., UPC-A is 12 digits, UPC-E is
6 digits, EAN-13 is 13 digits and EAN-8 is 8 digits). Some bar codes
also have both numbers and alphabetic characters (i.e., Code 128, Code 39
and Code 93). Code 128 enables you to encode all 128
characters.
Bar codes are also grouped into two types of
symbologies: linear or two-dimensional.
Linear Symbologies
A linear
(or one-dimensional or 1D) symbology bar code is made up of one single row of various widths and lengths of predefined black bars and white spaces. Ordinary bar codes are "vertically redundant,", meaning that the same information is repeated vertically. It is in fact a one-dimensional code. The heights of the bars can be truncated without any lose of information. However, the vertical redundancy allows a symbol with printing defects, such as spots or voids, to still be read. The higher the bar heights, the more probability that at least one path along the bar code will be readable.The height of the bars can be truncated without any lose of information. Examples of one-dimensional bar codes are shown below as Codabar, Code 39, and Interleave 2of5.
The most common 1D symbologies are Code 39, pioneered by the defense
and automotive industries; the Universal Product Code (U.P.C.), first
employed by the supermarket industry in 1973; Codabar, used early on by
blood banks, Interleaved 2-of-5 (ITF), Code 128. Another is Code
93.
Two-Dimensional Symbologies
The need for ever increasing amounts of information in
smaller spaces has lead to more compact and higher density symbologies found
in two-dimensional or stacked symbologies. A two-dimensional symbology
is either a "stacked (called matrix)" or
"multi-rowed". Each type allows more information to
be stored in a smaller amount of space.
Initially, two-dimensional symbologies were developed for applications where only a small amount of space was available for an automatic ID symbol. The first application for such symbols was unit-dose packages in the healthcare industry. These packages were small and had little room to place a bar code. The electronics industry also showed an early interest in very high density bar codes, and two-dimensional symbologies since free space on electronics assemblies was scarce.
More recently, the ability to encode a portable database has made two-dimensional symbologies attractive in applications where space is not at a premium. One example is storing name, address, and demographic information on direct mail business reply cards.
For
examples of 2D symbologies, refer to the PDF417 bar code symbology listed below.
Matrix symbologies include
Datamatrix, Maxicode, Dot Code A, Code One, QR Code, and Aztec
Code.
Multi-rowed symbologies include
PDF417, Code 16K, Code 49, Codablock F, MicroPDF417 and
SuperCode.
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Bar Code SymbologiesThe following is a list
of the most popular bar code symbologies in use today:
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 Codabar (also known as USD-4, NW-7, and 2 of 7 code) is used in libraries, blood banks, the overnight package delivery industry, and a variety of other information processing applications.
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Code 39
 (also known as LOGMARS, Code 3 of 9 and the 3 of 9 Code) is an alpha-numeric barcode and is one of the most popular bar codes used in a variety of industries. Each Code 39 character is constructed of five bars and four spaces, for a total of nine elements. Three of these are always wider than the rest. LOGMARS (Logistics Applications of Automated Marking and Reading Symbols) is an application of Code 39 used by the United States Department of Defense.
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Code 16K
 A multi row
symbology, Code 16K offers high information density encoding of the full
(128-character) ASCII set and double density encoding of numeric data
strings
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Code 128
 Code 128 is a very compact and versatile language which allows the encodation of the entire 128 ASCII character set. This symbology is self-checking and is designed with geometric features to improve
scanner read performance.
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Datamatrix
 Data Matrix is a 2-D matrix code designed
for putting a lot of information in a very small space and can store
between one and 500 characters. The symbol is also scalable between a
1-mil square to a 14-inch square. That means that a Data Matrix symbol has
a maximum theoretical density of 500 million characters to the inch! The
practical density will be limited by the resolution of the printing and
reading technology used. Symbols between one-eight inch square to seven
inches square can be read at distances ranging from contact to 36 inches
away. Typical reading rates are 5 symbols per second.
The most popular
applications for Datamatrix is the marking of small items such as
integrated circuits and printed circuit boards. The code is read by
CCD video camera or CCD scanner.
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EAN
 There are two different versions of EAN bar codes, EAN 8 and EAN 13, which can encode 8 and 13 digit numbers. All other countries aside from the United States utilize the EAN bar code for identification on retail goods. The symbol is identical to the UPC-A with one exception, the EAN bar code represents thirteen numeric characters instead of twelve.
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Interleaved 2of5
 Interleaved 2 of 5 is a numeric-only high density symbology that is very compact because information is encoded in both the bars and spaces. Only an even number of numeric data can be encoded within this symbol. This "double density" symbol encodes odd positioned data in the bars, and even positioned data in the spaces. Interleaved 2 of 5 bar codes are used on corrugated boxes, in the shipping industry, and in laboratories.
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MSI Plessey
 was designed in the 1970s by the Plessey Company in England and has been used primarily in libraries and retail applications.
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MaxiCode
 MaxiCode is a two-dimensional
matrix symbology containing a fixed number of dark and light hexagonal
modules. The symbol is specified to be a fixed size. MaxiCode has a bulls
eye finder pattern in the center of the symbol. A two-dimensional device
such as a CCD camera is necessary to scan the symbology. MaxiCode is
designed with two selectable levels of error correction capability. It
supports industry standard escape sequences to define international code
pages and special encodation schemes. MaxiCode is used by the United Parcel Service to encode address
and customer specified data on shipping packages which are scanned on
high-speed conveyors.
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PDF417
 PDF417 is a two-dimensional bar code consists of a stack of vertically aligned rows with a minimum of 3 rows (maximum 90 rows). Each row includes a minimum of 1 symbol character (maximum 30 symbol characters), excluding start, stop and row indicator columns. A PDF417 symbol may contain up to 928 symbol characters or codewords. It is used whenever large amounts of information is required in a small space. The Gettysburg address can be put into a 1" x 1" PDF417 square.
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POSTNET
 (POSTal Numeric Encoding Technique) bar code was developed by the US Post Office to encode zip code information. POSTNET bar codes printed on US mail improve the speed, accuracy and delivery of mail. Some US Post Offices even offer a discount for sending bulk mail when the POSTNET bar code is used.
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The Universal Product Code (UPC) was the first bar code symbology widely adopted. Its birth is usually set at April 3, 1973, when the grocery industry formally established UPC as the standard bar code symbology for product marking. Foreign interest in UPC led to the adoption of the EAN code format, similar to UPC, in December 1976.
There are now five versions of UPC and two versions of EAN. The Japanese Article Numbering (JAN) code has a single version identical to one of the EAN versions with the flag characters set to ``49''.
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UCC/EAN128
 A variation of the Code 128 symbology was designed primarily for product/shipment identification applications. The UCC/EAN-128 specification uses the same code set as Code 128, however a special character (function 1) is used as part of the start code in the symbol. In addition, UCC/EAN-128 symbols utilize standardized application identifiers (AI’s). By 2005 all US retailers will have to be able to scan all EAN/UCC article numbers (8, 12, 13 and 14-digit).
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Applications for Bar Codes
Bar codes are used in any applications where data needs to be automatically identified and captured efficiently and accurately in real-time for purposes of inventory control, asset tracking, product identification, patient information, warehouse picking and packing. Bar codes are used in many industries such as healthcare, packaging, transport, retail, apparel and textiles, automotive, government and defense, and more. Standards for many industries are defined by Industry Standard Organizations. Some of the major organizations obtaining bar codes application, label and product standards are identified in the next section.
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Industry Standard Organizations
The following industry standard organizations are a resource for AIDC application or industry
standards.
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 Industry
volunteers from automotive OEMs, parts suppliers and technology vendors
all work together at AIAG on achieving consensus on common automotive
industry rules for using bar codes, and two dimensional symbols, and other
Automatic Identification technologies in applications such as shipping
labels and parts identification/marking.
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ANSIThe American National Standards Institute facilitates development of American National Standards by establishing consensus among qualified groups.
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EAN International was started in 1974 when manufacturers and
distributors of 12 European countries formed an ad-hoc council. Its brief
was to examine the possibility of developing an uniform and standard
numbering system for Europe, similar to the UPC system already in
operation in the USA. As a result , a UPC compatible system called
"European Article Numbering" was created.
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 The Health Industry Business Communications sets the standards for the health industry.
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 The Japanese Standards Association is responsible for estalishing JAN (Japanese Article Numbering system) bar code standards.
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 The Uniform Code Council administers U.P.C. (Universal Product Code) bar codes for the U.S.
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