Automatic data capturethe term automatic data capture (ADC), also known as automatic identification and data capture(AIDC), refers to the technology that provides direct entry of data into a computer or other microprocessor controlled system without using a keyboard. this can be used in data collection in warehousing as material handling and staking.

The drawbacks of manual data capture is

error occur in both data collection and keyboard entry of the data when accomplished manually. time factor when manual methods are used, there is a time delay between when the activities

and event occur and when the data on status are entered into the computer labor cost the full time attention of human workers is required in manual data collection and

entry, with the associated labor cost.

nearly all of the automatic identification technologies consists of three principle components

encoded data:-a code is a set of symbols or signals representing alphanumeric characters. machine reader or scanner:- reads and converts encoded data into electrical analog signals decoder:-the components transform the electrical signals into digital data and finally back into

the original alphanumeric characters.

ADC technologies can be divided into the following categories:-

optical most of these technologies are high contrast graphical symbols that can be interpreted by an optical scanner.

magnetic which encodes data magnetically , similar to recording tape. electromagnetic the important group is radio frequency identification (RFID). smart card this term refers to small plastic cards embedded with microchips capable of

containing large amount of information. touch techniques such as touch screens and button memory biometric these technologies are utilized to identify humans or to interpret vocal commands of

humans.

though ADC is an error free system some form of errors do come into picture , so the industry has identified two parameters to measure the errors

first read rate (FRR) this is the probability of successful reading by the scanner in its initial attempt

substitution error rate (SER) this is the probability or frequency with which the scanner incorrectly reads the encoded character as some other character .

Bar codes are of two basic types:

Linear Encoded data are read using a linear sweep of the scanner. Two-dimensional Encoded data must be read in both directions.

A. Two forms of linear bar codes: Width-modulated Symbol consists of bars and spaces of varying width. Most widely used (e.g.,

Universal Product Code) Height-modulated Symbol consists of bars and spaces of varying height. Used only by U.S. Postal

Service for ZIP code identification

(a) Width-modulated bar code, exemplified here by the Universal Product Code (UPC), and (b) height-modulated bar code, exemplified by Post net, used by the U.S. Postal Service.

Difficulties with the "Morse" bar codes:

only the dark bars are used, thus increasing the length of the coded symbol, and

the number of bars making up the alphanumeric characters differs, making decoding more difficult

B. Two-Dimensional Bar Codes

a. Stacked bar codes

i. Consists of multiple rows of conventional bar codes stacked on top of each other

b. Matrix symbologies

i. Consists of 2-D patterns of data cells that are usually square and are colored dark or white

ii. Advantage over stacked bar codes is capability to contain more data.

2-D Stacked Bar Code (PDF417)

2-D Matrix Bar Code (Data Matrix)

Radio Frequency IdentificationRF is widely used to augment bar code identification by providing the communication link between remote bar code reader and some central terminal. generally known as RFDC in radio frequency identification an identification tags containing electronically coded data is attached to the subject item and communicates these data by RF to a reader as the item passes . the reader decodes and validates the RF signal prior to transmitting the associated data to a collection compute system.

it is generally different than the wireless television transmission in a way that the communication is in two direction rather than in one direction. the identification tag is transponder, which is a device capable of emitting a signal of its own when it receives a signal from external source. signal power is substantially lower in identification application , and communication distance from few mm to several meters. which can be increased by the use of battery powered tags, capable of transmitting the ID over greater distances.

identification tags are usually read only devices that contain up to 20 characters of data representing the item identification and other information to be communicated. advanced in technology have provided with much higher data storage capacity and the ability to change the data a in the tag

advantages of RFID includes

identification does not depend on physical contact or direct line of sight observation by the reader

much more data can be contained in the identification tag than with the most ADC technologies

data in the read write tags can be altered for historical purposes or reuses of the tag

MACHINE VISION the principle application of machine vision currently is for automated inspection tasks. for ADC applications, machine visions system are required to read 2-D matrix symbols, such as data matrix . and they can also be used for stacked barcodes. application of machine vision also include other types of automatic identification problems and these applications may grow in numbers as the technology advances , for example machine vision systems are capable of distinguishing between a limited variety of products moving down a conveyor so that the product can be sorted . the recognition tasks is accomplished without requiring that a special identification code be placed on the product . the recognition by the machine vision is based on the inherent geometric feature of the object.