Choosing RFID For Industrial Applications; Part 2


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In part one of this blog series, I provided an introduction to the 3 most common frequencies/systems used in industrial RFID. In this post, I will provide more details specifically about LF or Low Frequency based RFID.

Low Frequency

Image 1, Low frequency Balluff tag samples

LF RFID systems, as they have become known, generally operate between 70 kHz to approximately 500 kHz. These systems can vary greatly in cost depending on how proprietary they are. LF systems are typically station based. This means the tags (see image 1) have data read and/or written to them at a specific “choke” point in a process, typically by a read/write coil or “head”. These systems are also commonly used as “read only” systems for the purpose of data tracking only.

A read-only RFID system typically uses a preprogrammed individual serial number normally no more than 5 bytes or 40 bits in data capacity. This data is used by a control system to track a transportation device such as a pallet. As the pallet with the tag moves from the beginning to the end of a process, the serial number is then associated with the part it carries during WIP (Work-in-Process), allowing data, generated during the process, to be collected in a central database referenced to the serial number on the tag. When the pallet is returned to the beginning of the process for a new part, the serial number is re-associated with the new part and the tracking process starts over again.

Most read/write versions of LF tags are limited to less then 200 bytes in data capacity, but allow you to write data to and from the tags when required. Many LF tags are EEPROM (Electronically Erasable Programmable Read Only Memory) and are therefore limited to around 100K write sequences, but can handle unlimited read sequences. To conserve memory, many control systems will use binary based values like pass/fail data to maximize the data capacity available on a tag. This also helps to minimize the amount of data requiring transmission, allowing for minimal dwell times at any one read/write station.

Image 2, Inductive coupling example

Most LF systems are based on inductively coupled technology. These systems are also known as passive and typically do not contain a power source like a battery. Instead, inductive coupling (based on Faraday’s Law) powers the tag using energy generated from a coil in the read/write head to induce a voltage in the coil, thus powering it (see image 2).

Data transmission is typically done by changing one characteristic of an alternating field used to power the tag. For example, some manufacturers will use Pulse Coded Modulation to carry the data. This helps make the tags’ data less susceptible to interference from other frequencies or simple magnetic forces.

LF RFID systems can provide greater range performance, as much as 70 to 150 mm on non-alloy surfaces, and as much as 50 mm mounted on or in metal. For example, on a transportation pallet, there is less power degradation when the LF system is mounted on or flush mounted in a metal alloy compared to other system types like HF or High Frequency. But due to the nature of a low transmission frequency, a LF system typically has the longest transmission time for a given block of data compared to HF or UHF systems. For example, to read a block of 4 bytes or 32 bits of data, a read process can take 180 milliseconds or more. To write the same 4 bytes of data can take 300 milliseconds or more. LF systems are typically not used in applications that require moving read/write or “on-the-fly” operation.

In the next blog post of this series, I will continue to define in more detail the next of the three frequency/system types introduced in the first series post moving on to HF or High Frequency.

Click here to learn more about Balluff industrial RFID.
Click hereto read a whitepaper on “Choosing RFID For Industrial Applications”.

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