RFID gets the message
RFID is a method of contactless identification with a portable database on a coded tag read without requiring direct line of sight.
Main RFID Selection Criteria
Source: Control Engineering with input from Siemens Energy & Automation
R adio Frequency Identification (RFID) has been in use for more than 15 years. Industrial automation applications include automobile manufacturing, electronic component or appliance assembly, and machine tool tracking.
"RF" is a method of contactless identification without requiring direct line of sight. The "ID" comes in the form of a portable database on a coded tag that can store manufacturing process data or identification numbers. Barcode technology, for example, requires line of sight as well as some direction orientation.
The "tag" in an RFID system has a memory that can be read-only, write-once-read-many (WORM), read-or-write, or a combination of all three. The tag can store information about the item to which it is attached. It may store information about processes that must be performed. With read/write capability, process data can also be written to the tag.
Two tag types
Tags are available in a variety of memory types and data capacities. Permanent, read-only memory generally has a serial number programmed during the manufacture of the tag. It has unlimited life. Random access memory (RAM) requires a battery to maintain its data. Data capacity of RAM varies from 2K bytes up to 32K bytes or more. Many electronically erasable programmable read only memory (EEPROM) tags have specifications for limited write cycles of about 100,000, although the can often be written reliably to more than 500,000 cycles. Read cycles are unlimited. Data capacity of EEPROM memory varies from a few hundred bytes to several hundred, and the data itself has a life of 10 years or more.
Recently developed Ferroelectrical Random Access Memory (FRAM) is gaining popularity among factory automation applications. Without a battery, FRAM has the virtually unlimited write cycles of RAM.
RFID has two basic tag types. Active tags use a battery for power to transfer data to and from the reader. These tags are generally RAM memories. Active tag advantages include longer transmission distances between the tag and the reader. Disadvantages include battery maintenance.
Passive tags use the RF field of the reader for power. These tags can have any of the four memory types. Advantages of passive tags include longer service life since no battery is required for data transmission. In the case of RAM memory, batteries are used only for data storage. Batteries in passive tags, depending on the amount of data transferred and number of times, can last for many years. One disadvantage is slower overall tag read or write times, as there is a startup time when the tag enters the RF field of the reader.
Position reader head
Reader heads-the other end of the RFID equation-come in a wide variety of shapes and sizes. Distances between tags and readers vary from a few millimeters to several meters. The frequency of the data transmission and the size of the reader and tag determine the distance. Frequencies used in most RFID applications vary from 125KHz to 2.45GHz. Higher frequencies, in the MHz and GHz range, enable longer transmission distances. Readers and tags are normally sized proportionally to one another. In general, a smaller tag will require a proportionally smaller reader and will have a shorter read distance between the two. Reader sizes vary from a 10-mm diameter cylindrical barrel type to units built like metal detectors that you could walk through.
RFID use is growing. It is a reliable and proven technology and will continue grow as manufacturers look for more methods to reduce manufacturing costs.
Ed Rogin, product manager, intelligent sensing,
Siemens Energy & Automation, email@example.com
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