According to a major RFID Reader and tag manufacturer there are 128
ways to configure reader-to-tag and tag-to-reader communications. Many readers come some pre-set settings for 4 or 5 of the "best" or "better"
combinations.
Here are some that I look out for when setting up a reader configuration:
- RSSI: check the farthest distance a tag can be from the antenna,
gets its RSSI value and then set the reader to filter out any tags with a
lower RSSI value
- DRM: unless there are more readers using more than the 50 available
channels (915MHz is really 902-928) with channel hopping across 50
channels, use Single Reader Mode or Multi Reader Mode if available
- Note: If using Single Reader Mode (not all readers provide
Multi-Reader mode settings), then it becomes an interesting equation of
how to avoid tag collisions and avoid missing tag reads due to some
persistent values
- Auto-Start: With auto-start, readers are setup to read either
periodically, immediately or based on some input trigger. If using
periodic reads, set the periodic reads small enough that some one
walking by an antenna with an rfid-tagged asset will be in front of the
antenna long enough for a read to take place. I like to use 250ms for
directional portals if not using continuous or immediate reads.
- Singulation and Dual Targets: With Class 1 Gen 2 standards, tags can
be in either state A or state B. Sort of like putting your
hand down after a roll-call and then leaving it down if the analogy
makes sense. So unless I know the last roll call and its results, its
best to choose "dual-target" to ensure all tags are read. Dual target makes sure all tags in both states are read.
- Channels: In the case of multi-reader environment, since there are
50 available channels to choose from, why start all the readers at
channel 1? The possibilities of channel hopping become higher and I like to setup each reader to start on a different channel.
- Sessions: Sessions are useful in multi-reader environment in
that if 3 or 4 readers are working in a multi-reader environment then
each reader can be set to interact with tags in a different session. One
things I only recently understood was that Sessions greater that 1 (i.e
Session 2 or 3), leave their tags in state B indefinitely. So,
definitely, use dual target if you require all tags to be read and are
using more than one session.
- Note: This brings up a value to set for tag persistence.
Persistence sets how long a tag will be state B or "hands down in the
roll call analogy" before it switches back to state A. If using sessions
greater than 1, then setting this value may not have the expected
effect
- Picture a cone in front of the antenna: its useful to ne'er forget
that an antenna creates a cone which defines its read circumference and
area. These days we can fine tune antennas to read from a couple of
inches in front of the antenna to a couple of metres away (or farther).
Granted periodic stray reads occur and the antenna footprint is never a nice,even oval or circle and dead spots or null are a reality.. however, we can work with these limitations by
imagining a read area shaped like a cone in front of the antenna and ensuring tags within this area are always read.
I moved my post on some of the params that I find useful when setting up RFID readers and antenna to get better reads into its own page under RFID on this blog.
