Learn the basics about how to manage your RFID reader software to show sensor tags in the ID list and retrieve the information from the sensors.
You know that the software RFID reader manufacturers provide won’t allow you to read sensor tags in the solution you are developing. You may even try to run the default software and find out that the RFID sensor tag does not even return the unique ID. ‘What’s going on here?’
Well, as discussed previously, RFID sensors require more power to work. This is due to the tags needing not only the power to switch on the RFID chip and return the ID but also to power up an external device – be it a sensor, an actuator or any other component of your choice.
Making a sensor tag to the tag inventory list
Because of that extra power requirement, RFID sensor tags will need some extra time to switch on – or reply to the reader. The electronics of the sensor will include a capacitor to store energy so that the sensor tag works properly. Before being able to perform any measurement this capacitor needs to be full, which takes time.
Default RFID software programs are likely programed to send very short signals. The shorter the signal, the less the power transmitted, making the solution more efficient. Standard identification tags do not need much energy so the read happens in milliseconds.
However, when dealing with RFID sensor tags, you want more power transmitted so that the capacitor charges faster. The more energy you transmit, the shorter the startup time.
In order to do that, one of the easiest and best working tricks is to send a command multiple times. This is not because you need the information many times but because sending commands will
guarantee you are transmitting energy at the same time. Remember: no signal no power transmitted.
Once the capacitor is charged, measurements can be taken by the sensor and sent back to the reader. The key here is to maintain a balance between data rate and power consumption.
In general, the higher the sampling rate from the sensor, the higher the power consumption. This is due to the sensor requiring power to take each measurement.
Note that the sampling rate is different from the data rate we receive at the RFID reader. We can be sampling at 10 samples per second but receiving only one sample per second at the reader – losing data – or receiving 20 samples per second – oversampling or sending the same data more than once.
The reason for this is that the sampling rate is completely independent from the data rate. Sampling rate is exclusive of the sensor while data rate is exclusive of the RFID system – speed at which reader and tag can communicate.
We will deal with this when talking about reader APIs.
For more information about read range in RFID systems download the ‘The essential guide to developing RFID sensor software‘ free eBook.