How RFID EPC Codes Work

How RFID EPC Codes Work

Posted in:

Asset Numbering

When using electronic asset numbering, RFID technology identifies assets to enable operations of all sorts to improve their ROI. Financial returns are routinely, if subtly, felt in major infrastructures such as power and utility systems, oil pipeline networks, electrical grids, agricultural enterprises and transportation networks where rugged and portable RFID is often used in the field. But, asset numbering is equally apparent in enterprises like medicine, manufacturing and retail trade where business is transacted, more or less, under one roof-not to mention its use in transit.

In all of these situations, the ability to track service equipment, tools and product through the use of numbered tags, readers and software is a boon in reducing the cost of inventory. But, ultimately, because of tag/asset numbering, returns also accrue through better management efficiency in WIP, maintenance, worker safety, and compliance certification.

The Method

Usually, asset tags are encoded in their chip (ic) memory with a specially formatted digital number string called an EPC code and, then, attached to an asset. In the encoded form within the chip and, sometimes, in printed number form on the face of the tag, the string represents the manufacturer of the asset, the asset group to which it belongs, and the specific asset. (To standardize ID systems, this universal electronic ID numbering system is facilitated for non-profit use by EPCglobalinc, an organization setup to achieve worldwide adoption of the code).

When the tag is activated by programmed radio waves transmitted from the reader (interrogator), the tag transmits its stored information back to the reader, again, by radio waves and, ultimately converts through an electronic system to identify the asset for human use and a host of purposes.

Applications include the ability to analyze inventory, track assets, initiate actions in WIP and more. Nevertheless, using EPC as an identification system is not an RFID mandate, but when assets from all over the world are acquired and placed in the supply chain or a production chain, its benefits through standardization can easily be seen, especially when compatibility is a concern.

Tag Numbering Examples

To show the usefulness of the tag number string, imagine a distribution center manager using an RFID system who wants to know if a particular palette of toy trucks has been placed in transit. The controller (the manager, in this case) uses an RFID reader to activate a tag which sends back its identification information to inform the controller that the palette is still present in the warehouse. The manager realizes that the trucks need to be moved.

In another example, according to an article by Claire Swedberg in RFID Journal, oil pipelines can be embedded with RFID tag coupled with sensors to measure pipeline walls using ultrasonic waves: crude oil is especially caustic. Along the line, pipeline personnel attach many tags to the pipe walls. The tag sensors measure the walls and detect a small 0.1 millimeter (0.004 inch) change at a specific place in the pipe.

The measurement is stored in the tag’s chip memory and that information along with the tag number bearing the measurement’s location (also in the chip) is transmitted by tag antenna to the next tag down the line and so on, eventually making a mesh-like scan of the line culminating in wall data sent to a reader and computer software.  Analyzing the data, an inspector is alerted, possibly by a software generated alarm, to an eventual pipe failure at the particular spot on the line. Crews are sent to repair the pipe before a rupture occurs.

When, at a RFID equipped warehouse fire, firefighters take extra precautions because they know at particular location a small group of burning products is emitting toxic gas, numbered RFID tags play a part in safety.

When milk laden pallets are confiscated because the milk has been tainted with e-coli and toddlers miss milk breaks at pre-school, numbered RFID tags prevent illness.

To uninformed eyes, the number, seems inconsequential, but, really, it isn’t.

The Construct

RFID tags can be engineered to identify items really, really well using lot or batch numbers, stock numbers, production dates, and other particulars. Strings often end with discrete serial numbers; after reads, an RFID electronic system discriminates among tag strings within the range of the RFID reader: while the reader reads them all simultaneously, the system parses them out to be recognized separately, even to the last encrypted number in the string.

As indicated earlier, depending on client need, RFID tags can be designed in a number of ways. Usually, for encryption purposes, the 24-digit hexadecimal number string, the EPC, is used to represent the internal binary workings of the integrated circuit.

The String

Why 24 hexadecimal digits?

One blogger on Electrical Engineering suggests that the number  “ will allow for us to keep making RFID tags without ever repeating an identifier if we don't want to. . . .We will never run out, or at least never in the amount of time that RFiD is still a relevant technology.” The string (EPC code) represents the almost unfathomable number of  bit possibilities in the tag’s chip memory: the multitude enables the asset to be uniquely numbered and uniquely identified.

So why are hexadecimal numbers are used?

Humans have a hard time grasping the large number of digits in a binary number system with the base of two.  Yet, this is the number that really represents the internal workings of a RFID computer chip. The state (electrical impulse: on or off) of those binary bits is the identification of the asset and, thereby, also storage of the identification. So, to represent the internal workings, engineers use strings of Hex numbers, a 16-base alphanumeric number system, that is shorter than binary. (Facility in the use of converting numbers from one base to another helps in understanding this concept since three bases are at work here: tens (decimal), twos (binary)  and sixteen (hexadecimal).)

To number assets and aid in information retrieval, the string is divided into four segments representing bits of memory, 96 bits in all.

  • The first two numbers in the string represent 8 bits of memory to identify the EPC format being used.
  • The next seven numbers represent 28 bits of memory that identify  global manufacturers, approximately 268 million are possible.
  • Following are six numbers that represent 24 bits of memory that identify product, approximately 16 million products are possible per manufacturer.
  • Finally, the last nine numbers represent 36 bits of memory that identify specific items, approximately 68 billion unique items are possible per products.

The first nine numbers are assigned to the tag by EPCglobal specifying the data format of the EPC through familiarity with EPC Tag Data Standards and providing encodings for numbering schemes within an EPC. The last fifteen numbers are assigned by an EPC manager. It is within the last group of numbers that the RFID tag client might have input into the number since an asset’s serial number resides there.

In a typical number string, the last 36 bits of memory leave room for various item attributes. Longer strings can be added to the length of the number but such an addition will influence the size of the tag and raise other concerns, including cost. Being discerning about how much information really needs to be represented in the string, many tag purchasers will opt for the shorter typical string to save money.

Granted, companies have been using serial numbers without connection to RFID for decades. They serve some of the same purposes as mentioned above. So what’s the big deal? Wide scope global identification, for sure, rather than company wide identification. But more than that. The immediacy RFID tags provide is a big deal. Knowledge is available, without actually seeing an asset, in real time. Change can be dealt with immediately if needed. When lights go out in a thunderstorm, service technicians can know immediately which pole to climb for reconnection by looking at their cell phone screens. And again, delivery trucks can be pulled before they reach a school with tainted milk.

RFID asset numbering, also, enables more accurate analysis, foresight and planning. Because of advanced accurate inventory assessment, before leaving for the site, a plumbing contractor will definitely have the wrench to close a gushing pipe later in the day.

RFID converters along with their inlay suppliers provide these uniquely numbered tags for your assets. Many make available “copy only”, “serialized/unserialized”, and “bar code with human readable numbers” RFID tags.

If “techie” is what you are not, these providers will help you work your way through the technicalities of asset numbering without even mentioning hex numbers. But, with RFID tagging, your assets and your financial well being will be more secure with the knowledge they help you procure.