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
The reader/gateway configurations play a critical role in determining whether a setting is causing the reader to read stray tags. 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/202756208-How-do-I-send-you-my-reader-config-and-settings- for acquiring the reader/gateway configuration and settings.
In situations where the stray tags are being read on one reader but not by another, we suggest comparing the configurations of the two readers to find the differences that could be causing the Stray Tag reads.
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.
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.
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.
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
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