What Reader Mode, Session, and Search Mode should I use for my application?

The purpose of this article is to provide guidance on selecting RFID parameters for common RFID use-cases solved with Impinj Readers such as the Impinj R700 and the Impinj Speedway R420.

Scenario: Inventorying Stationary Tags

For applications where a reader is trying to inventory all tagged items in a specific area zone, and the items are not in motion, e.g. a smart cabinet smart cabinet, use the following settings:

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Reader Mode 1002 - AutoSet Dense Reader Deep Scan automatically cycles through several RF modes to take advantage of varying sensitivity and read-rate settings.  In the modes with high read-rate and low sensitivity it captures the easy-to-read tags, and then cycles through modes with lower read-rate and higher sensitivity to capture responses from the hard-to-read tags. When performing Inventory with the Single Target search mode, tags will only respond once to an Inventory request while they are energized.  Session 2 or 3 have extended persistence so when the reader needs to frequency hop and the tags are de-energized for a period of time they will not reset and present themselves as ready to to be Inventoried again.

Using mode 1002, Session 2 or 3, and Single Target Search Mode will ensure that tags are only Inventoried once, the easiest to read tags are read quickly, and the reader will be able to read the hardest to read tags.

Tuning Options

Using a slower static Reader Mode will be more consistent at the cost of decreased total throughput.  Slower Static modes to try are mode 2 - Dense Reader M4 or mode 3 - Dense Reader M8.

Scenario: Detecting when a Tagged Item is removed from an area

For applications where it is important to know when a tag is removed from a specific location, e.g. tool tracking or a smart shelf, use the following settings:

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Mode 1 - Hybrid inventories tags quickly and has a low sensitivity.  The Dual Target B to A Select search mode Inventories each tag once, then resets all tags in the field of view to be Inventoried again.  Using Session 2 or 3 will have more consistent performance than using Session 0 or 1 due to the longer persistence times in Sessions 2 and 3.

In your application you can determine that an item has been removed from the specified area because the reader will no longer report the tag as present.

Tuning Options

If the tagged items are particularly hard to read, use a more sensitive mode such as mode 2 - Dense Reader M4 or mode 3 - Dense Reader M8.  This will allow the tagged items to be read more consistently but at a lower rate.

Another option for detecting when a tag is not present is to use Single Target and Session 1 search mode.  Tags inventoried with the Single Target search mode with Session 1 automatically present themselves to be inventoried again after a small time delay.  

Scenario: Items moving through a portal

For applications where a single reader is used to determine when items move through an area, such as a dock door or a hallway, use the following settings.

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The Max Miller Reader Mode offers a blend of sensitivity and speed, and using the Single Target Search Mode in Session 2 or 3 will ensure that all tags are Inventoried once and that the reader has time to Inventory harder to read tagged items.

Tuning Options

For applications where tags must be read very quickly try experimenting with reader modes 0 - max throughput, 1- hybrid, and 1003 - Autoset Static Fast.  Mode 0 and 1 are the fastest modes but will not be able to Inventory harder to read tags.  Mode 1003 switches between mode 0 and mode 1 during operation.

For applications where the tagged items are very difficult to read and item accuracy is more important than read speed, try experimenting with modes mode 2 - Dense Reader M4, mode 3 - Dense Reader M8, and mode 1004 - Autoset Static Dense Reader.  Mode 2 and 3 are the slowest and most sensitive modes, mode 1004 switches between mode 2 and 3 during operation.

Additional Considerations

Single Target Session 1

When using Single Target Session 1 with a large tag population and a slower or AutoSet reader mode it is possible to be caught in a loop inventorying the same easy to read tags over and over again.  This is dependent on the number of tags in the field of view, the specific tag IC used in the inlay, and the Reader Mode.

To mitigate this behavior when inventorying large tag populations with Single Target Session 1 use faster modes like modes 0 - Max Throughput, 1 - Hybrid, or 1003 - AutoSet Static Fast.  Another option that will provide similar behavior to Single Target Session 1 with large tag populations is to use the Dual Target B to A Select with Session 2 or 3 with a slower reader mode.

Multiple Reader Environments

When operating in a system with multiple readers Inventorying the same area it is possible for readers to interfere with each other and reduce the total number of tags read by each reader.  In these use cases it is recommended to use Reader Modes designed for Dense Reader operations, 2 - Dense Reader M4, mode 3 - Dense Reader M8, and mode 1004 - Autoset Static Dense Reader.

Additional Reading

To learn more about choosing the reader mode for your application Reader Modes Made Easy provides an overview and comparison of all reader modes.  To learn more about Sessions and Search Modes Understanding EPC Gen2 Search Modes and Sessions describes the differences between each Session and Search Mode and how they are used together to determine when tags are Inventoried.

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