Scanning Technology
Scanning Physics and Terminology
Yes, it's a science. Put simply, a scanning device simply emits
a bright light and reads what is reflected back to it. The black
lines of a barcode reflect less light, and more light is reflected
by the white spaces. The "decoder" then figures out that it is a
barcode, what symbology it is (more on "symbology" later), and what
information is in that barcode.
Aggressive: the relative ability of the scanner to read a barcode
on the first attempt.
Depth of Field: the distance from the front of the scanner to the
barcode.
Mil: The width of the narrowest bar in a barcode, measured in 1/1000ths
of an inch. The width of the narrowest bar of a 15 mil barcode is
15/1000ths of an inch. This is also sometimes referred to as the
"X dimension." With respect to scanners, the overall height or width
of a barcode is not necessarily important, but the "mil" is vitally
important.
Scanning Methods
Wand:
Perhaps the least expensive way to scan a barcode, the wand is a
pen-like device that must be in contact with the barcode. It also
must be held at a certain angle, and be passed over the barcode
at a consistent speed (neither too fast nor too slow). Wands present
a variety of challenges that make them most useful when price is
the most important factor.
CCD:
A CCD is a scanning "gun" that floods the barcode with light, then
reads what's reflected back to it. It's more expensive than the
wand, but is also more efficient and easy to use. It can only read
barcodes from a close distance (less than 6" in most cases) and
can only read barcodes that are no wider than the scanner itself.
However, CCD's have the reputation of being highly reliable. They're
great for light-to-medium retail and out-of-doors applications where
sunlight makes it difficult for the scanner to"see" what is being
scanned.
Laser:
Though laser scanners are more expensive than wands and CCDs, they
are the most versatile (see "Laser Scan Engines" below) and aggressive
tools for scanning barcodes. A laser beam is emitted from the scanner
that either reads left-to-right and right-to-left, or vice versa.
Imager:
It is not possible for a wand, CCD, or laser scanner to read a matrix
code (see "2D Symbologies" below). Enter the imager. These devices
can not only read matrix codes, but also1D and other 2D Symbologies.
And imagers can be used in the creation of ID cards that require
a picture of the person.
Laser Scan Engines
It's not possible for one scanner to be all things to every customer.
Because of this, there are scanners that are designed to be used
in very specific applications. Before you purchase for a scanner,
you should first know something about the symbology of the barcode
and the mil of that barcode (if applicable).
Standard
If there were a scanner that attempts to be all things to everybody,
this would be it. It would likely read 1D barcodes that are between
5 and 20 mils.
High Density
High density scanners are used for reading small, dense barcodes,
such as those typically found on jewelry tags. This type of scanner
might, for example, read down to a 2-mil barcode and up to a 7-mil
barcode.
High Visibility
Remember that a scanner reads what is reflected back to it. However,
if the scanner were being used in a very bright environment, the
light that would normally be reflected back would be "washed out"
by the ambient light, such as sunlight. So a high visibility scanner
has a brighter beam of light to overcome this problem.
Long Range
In a warehouse environment, it is sometimes necessary to read a
barcode from a long way away - such as 40 feet! Long Range scanners
will typically have an "aiming beam," which is a bright dot to assist
the user in locating the specific barcode that the user wishes to
scan. To be able to read a barcode from 40 feet away, the barcode
should be very large and printed on material (called "retroreflective")
that can reflect, rather than absorb, a lot of light.
Omni-directional
All of the above scanners require the barcode to be turned in a
specific direction because they only emit a single line. An Omni-directional
scanner emits a pattern of several lines. Think about a visit to
the grocery store. Can you imagine how slow it would be if the cashier
had to make sure that every barcode was turned in a specific direction?
Where Omni-directional scanners are being used, the user can have
a bottle standing up, or lying on its side, or at an angle as the
bottle is presented to the scanner. It doesn't matter which way
the barcode is positioned.
2D Scanners
These are not to be confused with Imagers. 2D laser scanners "raster,"
which means they scan left to right, right to left, and up and down.
Typically, they will only read PDF417 and 1D Symbologies. These
scanners also are generally more expensive than conventional 1D
scanners.
1D Barcode Symbologies
1D - one dimensional
These are symbologies that only include vertical lines and spaces.
There are more symbologies than are listed here, but these are some
of the most common.
UPC
UPC is a 12-digit symbology that is used in retail applications.
UPC-A
UPC-A is what you normally would see, for example, on a box of cereal.
This numeric-only barcode is basically broken up into 3 parts. The
first character is what is referred to as the System Digit and is
a way of identifying the industry to which the product might be
associated. The next 5 digits identify the manufacturer. The manufacturer
must acquire this number from the Uniform Code Council. The next
5 digits are the manufacturer's way of identifying the product.
The last digit, known as the "check digit," is the result of a mathematical
calculation using the previous 11 digits.
UPC-E
UPC-E, a compressed version of an UPC-A, would be typically seen
on a can of soda or pack of gum, where there is not much available
space. UPC-E will not have a system digit, and the zeros from the
UPC-A will be "suppressed." Therefore, UPC-E can be expanded back
into a valid UPC-A code.
Supplementals: Two or five-digit supplementals are commonly found
on periodicals or publications. A supplemental is a small barcode
that is to the right of the UPC-A or -E barcode.
EAN
The European Article Numbering system is a European version of UPC.
Country codes are used to allow the use of one barcode both internationally
and domestically. For example, 00, 02, 03, 04, 05, 06, 07, and 09
are assigned to USA and Canada, while 40 - 43 are all used for Germany.
EAN-13
EAN-13 is basically an UPC-A with a leading digit, which is usually
representative of a country code. Two and five digit supplementals
are supported.
EAN-8
This is a smaller version of the EAN-13. It also has a two-digit
country code, followed by data and a check digit.
ISBN (International Standard Book Number):
Also called "Bookland," this symbology is used on books and other
publications. Though it is part of the EAN family, there are no
country codes used. The ISBN number is simply preceded by "978"
or "979." The 5-digit supplemental is simply the price preceded
by a "5".
Code 39
A Code 39 barcode will always begin and end with the pattern of
"narrow-narrow-wide-wide-narrow" bars. Code 39 is probably the most
popular symbology other than UPC. It can encode numbers, uppercase
letters, and a dash. The "full ASCII" version of Code 39 will additionally
encode $, ?, +, and %.
Code 128
Code 128 is a unique symbology, which includes "subsets" for encoding
different characters. Subset "A" will encode uppercase alphanumeric
characters, subset "B" will encode lowercase alphanumeric characters,
and subset "C" will only encode numbers. A nice feature of this
symbology is that it is possible to have all 3 subsets in a single
barcode. By combining all 3 subsets, you could actually produce
a barcode that is "Code128."
Code 93
Code 93 is an enhanced version of Code 39. Basically, Code 93 will
encode every character on a keyboard, including uppercase and lowercase
letters, numbers, and other symbols.
Interleaved 2 of 5
"I 2 of 5" is a numeric only symbology that must contain an even
number of digits. It is actually possible to get a partial, but
valid scan of an I 2 of 5 barcode because the barcode is in pairs.
The odd position digits are encoded in the bars and the even position
digits are encoded in the spaces. Be sure to program your scanner
or decoder for the exact number of characters in your I 2 of 5 barcode.
Standard 2 of 5
The difference between Standard and Interleaved 2 of 5 is that with
Standard, the data is only in the bars and not the spaces.
Codabar
Here, the barcode must begin and end with an A, B, C, D, E, N, T,
or *, which cannot be used anywhere else within the barcode. Codabar,
commonly used in libraries, blood banks, and by overnight delivery
services, can only encode numbers and the following characters:
$, :, /, ., and +.
2D Symbologies
2D - two dimensional
It is sometimes not possible to put all the required data into the
limited amount of available space using a 1D barcode. For example,
several states have begun putting 2D barcodes on the back of driver's
licenses. Encoded into this barcode is all of the data that is printed
on the license. 2D barcodes are also being used for tracking printed
circuit boards in computer equipment.
Stacked codes
Stacked codes are made up of bars and spaces that are stacked on
top of each other.
PDF417
PDF417, which was designed by Symbol Technologies, has a maximum
capacity of 1,850 text characters, 2,710 digits, or a total of 1,108
bytes. PDF417 has several levels of "error checking" which allow
a scanner to decode the barcode even when it has been damaged. The
more error checking that is built into the barcode, the larger it
becomes.
Code 16K
Developed by Laserlight Systems, Code 16K can encode a maximum of
77 text characters or 154 digits and can contain between 2 and 16
rows. The structure of the barcode is based on Code 128.
Code 49
Code 49, developed by Intermec Technologies Corp., was the first
stacked barcode symbology. A cross between UPC and Code 39, Code
49 has the ability to pack 170 alphanumeric characters within one
square inch.
Matrix codes
Matrix codes almost look as if they have no form within a square.
Matrix codes are able to encode even more information in a smaller
space than a stacked code.
MaxiCode
United Parcel Service originally developed MaxiCode. Easily identified
by its bull's eye in the middle of the barcode, MaxiCode is capable
of containing about 100 characters in a one-inch square symbol.
It also has error checking capabilities, as it is still possible
to get a good read even though 25% of the barcode is destroyed or
missing.
DataMatrix
DataMatrix is an extremely efficient symbology developed by CiMatrix.
DataMatrix is most commonly used on printed circuit boards, as it
can store up to 50 characters in a square symbol that is only 2mm
or 3mm in size. It can also be as large as 14". The Aztec code,
developed by Welch Allyn, Inc., has a maximum capacity of 3,067
letters or 3,832 numbers, or a total of 1,914 bytes of data. Like
the MaxiCode, it also has a bull's eye, but its bull's eye is square.
Decoded vs. Undecoded
A scanning solution generally involves 4 components: the scanner,
the barcode decoder, the host communications, and the host.
"Decoded" scanners have the decoder and host communications abilities
built in to them, making it possible to connect the scanner directly
to a PC, for example.
"Undecoded" scanners must be connected to a device which is capable
of decoding the scanned barcode. Many times, an undecoded scanner
will be connected to a "decoder" or "wedge," but they might also
be connected to a Portable Data Terminal.
A "decoder" or "wedge" is basically a box that serves two functions:
decoding the barcode and transmitting that data to the defined host.
The barcode decoder inside this box is often capable of manipulating
the data as well as decoding the barcode. For example, a decoder
can add a character before the barcode or after the barcode, or
even delete data.
This leaves the other side of the equation: communications. For
a scanner to provide the user with what he expects, the scanner
or decoder box must be programmed to communicate with the device
to which it is connected. Just because the physical connection is
correct does not mean that the decoder will know how to communicate
with that device.
For assistance in choosing the best Scanner for your business needs
contact T&W Enterprises
Technical Support.
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