Using RF Technologies for Real Time Control
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Using RF Technologies for Real Time Control
Article Introduction
Rfid (radio frequency identification) is a technology that incorporates the use of electromagnetic or electrostatic coupling in the radio frequency (rf) portion of the electromagnetic spectrum to uniquely identify an object, animal, or person

Article Description
RFID is coming into increasing use in industry as an alternative to the bar code. The advantage of RFID is that it does not require direct contact or line-of-sight scanning. An RFID system consists of three components: an antenna and transceiver (often combined into one reader) and a transponder (the tag). The antenna uses radio frequency waves to transmit a signal that activates the transponder. When activated, the tag transmits data back to the antenna. The data is used to notify a programmable logic controller that an action should occur. The action could be as simple as raising an access gate or as complicated as interfacing with a database to carry out a monetary transaction. Low-frequency RFID systems (30 KHz to 500 KHz) have short transmission ranges (generally less than six feet). High-frequency RFID systems (850 MHz to 950 MHz and 2.4 GHz to 2.5 GHz) offer longer transmission ranges (more than 90 feet). In general, higher the frequency, the more expensive is the system.

It wasnt so long ago that when someone referred to "a radio frequency system" in the plant or warehouse, there was little question that the technology was radio frequency data communications (RFDC). But recently, things have gotten a bit more complicated. And just as there are different kinds of snow to the Eskimos, there are different kinds of radio frequency based technologies for operating managers.Beyond RFDC, there are two other technologies. One is radio frequency identification (RFID) and the other is a real-time locator system (RTLS).

Each is a stand-alone system that uses radio frequency to communicate information about inventory from the plant or warehouse floor to an information system. This provides real-time control of materials from individual items to full pallet loads. All three significantly enhance operating efficiencies by identifying the location of those materials and making the information available for real-time decision-making. Despite their similarities, the intended uses of the three are as different as the hardware that makes them work. RFDC communicates collected data. RFID identifies inventory and its characteristics. An RTLS locates inventory as it moves about the plant or warehouse floor. As a result, each is suitable for distinct data capture and data communication applications, and has unique benefits.

Both RFDC and RFID have been commercial realities for more than a decade. But it is only in the past 4 or 5 years that RFID costs have come down sufficiently to make it a practical reality for industrial use. RTLS, on the other hand, was generally unheard of until 3 years ago when the technology was commercialised. The bottom line is these three technologies can greatly simplify your operations by ensuring that the right data is available in the right place at the right time. Here are the basics of each to help you find the right fit for your facility.

Radio frequency data communications
The chief intention of an RFDC system is the two-way communication of data between any location on the shop or warehouse floor and a host computer. The resulting immediate availability of data allows control systems such as warehouse management software to direct activities in real-time. Hand-held, vehicle-mounted, and fixed-position terminals on the floor receive data either from manual keyboard entry or from automatic data capture (ADC) devices such as bar code scanners and voice systems. This information is then sent by radio frequency to an access point that feeds the information to the host over a wire. The movement of information from one point to the other typically takes less than a second. An RFDC system also feeds information back to workers regardless of where they are on the floor, even hundreds of feet away. This eliminates the need to return to a central information point to receive additional instructions, maximizing worker mobility and productivity.

Depending on your specific needs, there are different radio frequencies used to communicate information. For applications that can accept a relatively slow transfer of information, the frequency used is between 450 and 470 MHz. This is known as narrow band RFDC. With steadily increasing demand for large volumes of data, narrow band is the least often specified today. It is, however, used with some of the latest wireless bar code scanners. For higher data rates, there are other frequency ranges. They are 902-928 MHz, 2.4 GHz, and 5.6 GHz. All are known as spread spectrum frequencies because they spread data across a wider frequency spectrum than narrow band.

Radio frequency data communications (RFDC)
Hand-held and vehicle-mounted RFDC terminals collect data using a bar code scanner, magnetic stripe reader, or even a portable RFID reader. Radio frequency then transmits data to a wired local area network (LAN) linked to a host.
Follow-up information follows the path in reverse.
Receiving operations - Inventory put away - Order picking - Shipping

- Maximum mobility of workers
- Real-time inventory status updates
- Lower costs
- Higher productivity

Radio frequency identification
RFID, on the other hand, is a more versatile system because it both collects and communicates information about inventory. And unlike RFDC, RFID does not typically use portable terminals, making it more fixed in position on the shop or warehouse floor. Typically, data is stored in small tags, which act as portable databases when attached to a unit of inventory. Unlike standard bar codes that can store only a few bits of data, an RFID tag can store several thousand. This allows the tag to both identify the unit of inventory and carry additional information about it. When the tag passes within a short range (a few inches) of a reader, the information on the tag is transmitted by radio frequency. In some advanced systems tags can be read on items travelling along conveyors at speeds up to500 ft/min. The reader, in turn, passes it on to a computer that displays the data. This information can then be used at that station or another one on a network. Beyond characteristics of the item, the tag could carry all of the manufacturing instructions for work-in-process. When the work is completed, new information can then be written back to the tag, adding to the portable database which could remain with the manufactured item for its life. Such read/write capabilities make RFID a complementary technology to other forms of automatic data capture such as bar codes. In fact, paper-thin RFID tags are being sealed between two sides of a bar code label and used as luggage tags in tests across Europe. Other applications for RFID include access control.

Radio frequency identification (RFID)
An RFID tag (also called a transponder) is programmed with information about a unit of inventory. When the tag passes within close range of a reader, the information on the tag is read and displayed on a terminal. A remote host computer is not needed. New information can be written to the tag too.
- Inventory identification
- Lot tracking
- Portable manufacturing data file
- Finished product maintenance history

- Local access to inventory database
- Highly accurate data
- Increases speed of data call up/capture
- Reduces operating costs

Real time locator systems
While similar to RFID in technology, an RTLS only cares about one type of information-the location of a unit of inventory or asset. An RTLS encodes an identifying number on a tag similar to those used with RFID. The tag includes a small battery that allows it to emit a radio frequency signal announcing its presence at pre-set intervals. Readers mounted on the ceiling then pick up the signal. Although the signal is sent at the same general frequency, 2.4 GHz, as many spread spectrum RFDC systems, there is said to be no interference between the two. To determine the tags location, a single reader needs to sense the signal with one suppliers system. The other suppliers system requires three readers to pick up the signal before it can triangulate the tags position. The former generally requires more readers than the latter. Both systems determine the tags location to within a few feet. A host computer can store all location updates, creating a log. Although commercialised 3 years ago, both suppliers are reporting initial success stories in industrial and health care applications with RTLS used to track the progress of inventory to the assembly line.

Real-time locator systems (RTLS)
Battery-powered RFID tags emit a signal to cell controllers mounted up to 200 ft distant. When controllers pick up the signal, they determine within a few feet the position of the tag and the inventory unit attached to it.
Posted : 10/21/2005

Using RF Technologies for Real Time Control