Strategies for handling unwanted tag reads

Overview

A common use case in RFID involves reading tagged items at specific "read zones".  RFID equipment such as a reader with connected antennas or gateway (such as xArray, xSpan or xPortal) is installed at each read zone and tuned to provide coverage for that specific area (e.g. dock door).  When tagged items are detected by the reader or gateway at this location, these read events are used as evidence to conduct business transactions such as shipment or receipt of those items.  A common question related to this scenario is how to deal with stray or unwanted tag reads.  These unwanted reads may come from tagged items staged near a read zone or passing by the read zone but not intending to be read.  This article covers various techniques and strategies for dealing with these unwanted tag reads.

 

Use the Latest Software Releases

Please ensure you're working with our latest releases of firmware, software (e.g. ItemTest), and development libraries.  Bug fixes and enhancements are only applied to our latest releases.

Upgrade the Reader Firmware

Please start by upgrading to the latest firmware version on all readers and gateways.  You can get this firmware from the Impinj Partner you purchased your hardware from.  If you are an Impinj Partner, please login to the support portal and download the latest version.

Upgrade the Software

Please upgrade to the latest versions of ItemTest, Speedway Connect, and/or ItemSense.

Upgrade the Development Libraries

Please upgrade to the latest versions of the SDK, LTK, or ETK libraries.

Capture Reader Configurations

Compare Configurations

Application Changes

If none of the above items work, try making application-based changes to help figure out what is going on. 

Test with a different application

Please try another application if the current application is reading stray tags.  Our ItemTest software (https://support.impinj.com/hc/en-us/articles/208589707-Impinj-ItemTest-Software) is a great tool for doing just that.  Alternatively, you can try one of our Octane SDK examples or Speedway Connect. 

Test with different application settings

Try adding filters, changing Reader modes, and/or testing different Transmit Power and Receive Sensitivities. 

Filters

If an EPC tagging strategy is being used, you can setup a filter to either include those tags you want to see or exclude those tags you do not want to see. 

Reader Modes

A less sensitive reader mode such as Max Miller or Dense Reader M4 may help to mitigate stray reads. 

Reader Transmit Power and Receive Sensitivity

Reader transmit power may be too high and receive sensitivity may be too low.  To help determine the right settings, perform a Margin Test. 

Perform a Margin Test

A margin test will perform a power sweep and tell you what minimum amount of transmit power is needed in order to read a stray tag.  Make sure to run multiple tests.  Here is an article with more details for how to conduct the Margin Test: https://support.impinj.com/hc/en-us/articles/202756388-Performing-a-Margin-Test-using-Impinj-ItemTest-software. 

Use other information 

Collect data such as tag read counts, RSSI, and/or other other low level metrics to create an algorithm to determine which tag reads are meaningful.  For example, a tag with a low read count may indicate a stray when compared against other tags with higher read counts. 

Environmental/System Changes

Here are some other suggestions to try. 

Physically isolate the read zone

Here are some ways to isolate the reader/gateway portals:

1) Create a portal/tunnel that is designed to only read tags that are inside

2) Enforce a keep out zone around the portal

3) Use RF-blocking foam or other material

     • http://www.eccosorb.com/products-overview.htm 

Consider tag usage 

Tag sensitivity continues to increase with new generations of Monza products.  Additionally, the size and mounting location can affect how well a tag is able to be read.  Having a mixed population of tags (both chip and inlay size) can make it difficult to tune a portal.  If possible, select tags with the same Monza chip (e.g. all Monza 6) as well as same inlay size. 

Capture Reader/Gateway Logs

It is possible there is an error in the log files that explains why something is not working.  Additionally, you will need to provide Impinj support (should they need to get involved) this information.  Please follow the instructions at: https://support.impinj.com/hc/en-us/articles/202756238-How-do-I-capture-logging-events-from-my-reader- to collect the reader/gateway logs. 

Increase the logging level

Additional information provided by logs may help identify problems the reader may be experiencing.

How to do it