Duty Cycle: What is it and How is it Used?
Introduction
Duty Cycle is term that is associated with RFID readers and describes a property that dictates the amount of time a reader is transmitting.
Duty Cycle can be best described as the proportion of time an RFID reader is transmitting a signal with respect to an on/off cycle time. A “low duty cycle” is when a reader is setup to transmit for short bursts rather than continuous transmission. Typically, the total cycle time for any reader transmission is approximately 1 second; therefore, a “low duty cycle” could consist of 200 ms of “on” time and 800 ms of “off” time. Because most readers are capable of reading several hundred tags per second, the user may hardly notice that the reader is not continuously reading if the RFID tags are in the read zone for at least one second.
The main advantages of using a low duty cycle are:
1. Lower Power Consumption: An RFID reader can use approximately 12 Watts of DC power when transmitting at full RF levels. The DC supply must be able to supply of a constant source of power in order for the reader to function. However, when the power source is a battery, using a low duty cycle will allow the battery to drain less over time compared to continuous reading.
2. Less Heat is Generated: Excess power is dissipated as heat. This is especially true when, on average, 12 Watts of DC power is being used to produce 1W of RF power. The extra 11-10 Watts is therefore dissipated as heat causing the temperature of the reader to rise for a long period of time. A low duty cycle generates less heat over time because the reader operates for a shorter amount of time.
3. Reduction in Reader Collision: Reader collision can occur when multiple readers in the same vicinity are communicating with the same batch of RFID tags. Using a low duty cycle will allow the readers to transmit for a shorter amount of time; therefore, the chances of readers interfering with each other and transmitting at the same time is reduced.
While there are several advantages to using a low duty cycle, there are many applications where it isn’t a great fit. As always, thorough testing is necessary to determine the best settings for your RFID system.
Conclusion
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Special thanks to Dan Ratner, Senior Technical Engineer at ThingMagic, a JADAK brand, for his insight.
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