The core of any RF-ID system is the ‘Tag’ or ‘Transponder’ which can be attached to or embedded within objects.
A RF-ID reader sends out a radio frequency wave to the ‘Tag’ and the ‘Tag’ broadcasts back its stored data to the reader. The system works basically as two seperate antennas, one on the ‘Tag’ and the other on the reader.
The data collected from the ‘Tag’ can either be sent directly to a host computer through standard interfaces, or it can be stored in a portable reader and later uploaded to the computer for data processing.
The automatic reading and direct use of the ‘Tag’ data is often called ‘automatic data capture’ and with a RF-ID tag system, which works just as effectively in environments with excessive dirt, dust, moisture and poor visability, you can be assured that it overcomes the limitations of other automatic identification approaches.
How the Low Frequency Tag system works
When the transponder, which is battery free, is to be read, the reader sends out a 134.2KHz power pulse to the antenna lasting approximately 50ms. The magnetic field generated is ‘collected’ by the antenna in the transponder that is tuned to the same frequency. This received AC energy is rectified and stored on a small capacitor within the transponder. When the power pulse has finished the transponder immediately transmits back its data, using the energy stored within its capacitor as its power source.
In total 128 bits are transmitted (including error detection information) over a period of 20ms. This data is picked up by the receiving antenna and decoded by the reader unit. Once all the data has been transmitted the storage capacitor is discharged resetting the transponder to make it ready for the next read cycle. The period between transmission pulses is known as the ‘sync time’ and lasts between 20ms and 50ms depending on the system setup.