Ξ June 10th, 2009 | → Comments Off on How to set up a UHF reader and obtain high read rates. | ∇ General RFID Questions, UHF Ultra High Frequency |
There are some misconceptions on RFID FHSS UHF (Radio Frequency Identification, Frequency Hopping Spread Spectrum, Ultra High Frequency) technology – Out of the box and the reader is working perfectly is something that just doesn’t happen.
There are no specific settings that will work for any environment – each implementation is different – even if the implementation is exactly the same as the last one if it is in a different physical location there will be differences in the read zone – hence most Gen 2 readers provide a number of different channels (for the frequency hopping) and the capabilities to tune the read zone to your unique requirements.
You need to set up the reader with the antennas and then just determine the read zone. Since readers come with either an integrated antenna or up to 4 antenna ports, the best method is to use just one antenna first to obtain a single read zone. Once the reader is operational and reading tags you then need to determine the actual size of the read zone. Then you can change the settings on the reader to build a bigger or smaller read zone that is optimized for the application requirements.
Since a read zone is 3 dimensional you need to determine the area – length, width, height, that gives you the highest read rate – known as the 3 dBi beam width – first. For more information on the 3dBi beam width refer to our antenna tutorial at http://www.skyrfid.com/RFID_Antenna_Tutorial
To calculate the read zone use one tag only and use the same tag each time. Keep the tag horizontal for the best read rate – turning the tag vertically will usually drop the read distance by 3 dBi or 50%! Hold the tag away from your body – arms outstretched – to minimize the impact of your body on the read zone. We humans absorb the RF wave so if you hold the tag close to your body you reduce the read distance by more than 3 dBi! If you are setting up a read zone for cardboard, metal or other materials, try to use exact samples of the material. A 0.5 meter (1.5 foot) or longer wooden pole will really eliminate your presence in the read zone if you attach the tag to the material that you have already attached to a wooden pole. Move slowly around to each outer limit of width and height where the tag still reads correctly and on a predictable basis. Then move away from the reader slowly to determine the length of the read zone. Make sure that you try to point the tag towards the antenna to get the best read rate and then parallel to the reader to get the fringe of the zone. (The RFID wave comes out from the reader like an expanding funnel so the strength of the wave decreases dramatically with the distance.)
Once you have determined the overall read zone you can then adjust the settings (Frequency and Output Power) one at a time and check the results – the read zone may move forwards, backwards, grow larger or smaller or a bit of each.
To determine the longest read distance in a non scientific way stand in front of the reader – 3 – 5 meters away and walk backwards with the tag attached to the pole to see when the reads stop. That gives you distance – do the same thing for width and height to determine the area.
Walking in front of the reader is not scientific as you actually change the read zone – going backwards reduces that impact but it is still there. If you walk forwards again you will actually distort the read zone. It takes about 20 – 30 seconds to disperse the distortion.
After you have obtained the longest read distance and have an idea of the read zone area with the 3 dBi beam width then you can set up the reader so that the read zone hits the tag in the center of the overall read zone and then gives you the best constant read rate for that environment.
With multiple antennas there are a variety of ways to enhance the existing read zone or create new read zones.
For more informaton contact the Experts at SkyRFID – +1 647 476 3265 or +1 519 489 2557