Impinj IoT Device Interface API - Example Inventory Configurations

This document describes the configuration and usage of example inventory JSON configurations, utilized by the Impinj IoT device interface, for three common RAIN RFID use cases.

For additional information, please refer to to this article on the Impinj Support Portal: What Reader Mode, Session, and Search Mode should I use for my application?

The examples configurations can be downloaded here: example_inventory_configs.zip

Usage

The referenced example inventory JSON configurations can be utilized directly with Impinj RAIN RFID readers that support the Impinj IoT device interface. These examples are intended to be good starting points for tuning an application, but most applications will require fine-tuning of the relevant parameters to optimize the RAIN RFID system for maximum performance.

It is recommended that these example JSON configurations are simply referenced or copied and then modified to fit the particular application. Please see the following sections for specific recommendations on tuning for a particular use case.

In any use case it is recommended to:

  • Provide appropriate names for each antenna utilized to help identify the source of each tag read in the reader event stream more easily.
  • Tune transmit power to minimize the number of reported stray tags, and minimize reader interference in dense reader environments.

Smart Shelf

Tagged items are placed on several "smart" shelves, and those shelves are constantly monitored by a RAIN RFID system to detect when an item is removed from a shelf. There is usually then some application logic to act on a detected removal.

An example of this may be a retail display with products on these smart shelves. When a customer removes an item from its shelf, a nearby visual display shows the customer details about the item.

Parameter Tuning for Smart Shelf

  • RAIN RFID Parameters
    • RF Mode: 1 (Hybrid)
    • Hybrid mode inventories tags quickly but with relatively low sensitivity. This is ideal for an application that is reading a low number of tags that can be read easily. The higher read speed of this mode allows the application logic to quickly detect that an item has been moved.
    • Search Mode: Dual Target B to A Select
      • 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. This is good when all tags in the field of view can be read consistently, and ensures that all tags are read while allowing them to be inventoried again quickly.
    • Session: 2 or 3 (High Persistence)
      • Choosing a session with a high persistence time in combination with the Dual-Target B to A Select search mode allows the reader to more directly control the tag state and responses. Choosing session 0 or 1 in this use case would likely result in less consistent results.
  • Variable Parameters
    • Transmit Power: The transmit power should be reduced so that only the items of interest are being read consistently. Having a very high transmit power will introduce stray tag reads from other areas that can potentially increase the latency of the system in detecting when an item is removed from a shelf.
    • Estimated Tag Population: The estimated tag population should be tuned per antenna to reflect the number of items to be monitored by that antenna. A lower number of items is better for detection latency, and having more items per shelf will increase the detection latency.

Portal

Bulk containers carrying several or many tagged items pass through a door or portal that is flanked by RAIN RFID antennas. As these containers pass through the door/portal, the goal is usually to read as many of those tags as possible for shipping and logistics confirmations.

Parameter Tuning for Portal

  • RAIN RFID Parameters
    • RF Mode: 4 (Max Miller, for ETSI use mode 5)
      • The Max Miller mode offers a blend of sensitivity and speed which is required for this use case. There is often a reasonably large tag population in each container and a limited amount of time to read the tags as the container is carried through the portal. The larger tag population also usually comes with some amount of difficulty in reading tags as items in close proximity can cause significant interference or detuning.
    • Search Mode: Single Target
      • Using a Single Target search mode will ensure that tags that have already been inventoried will remain silent, which is important for reading as many unique tags as possible.
    • Session: 2 or 3 (High Persistence)
      • Choosing a session with a high persistence time in combination with a single target search mode ensures that the inventoried (read) tags will remain quiet for as long as the container is within the field of view of the portal antennas.
      • NOTE: If tuning a portal or door where other readers are in close proximity, it is possible that a session 2 will be inventoried by another reader and remain "inventoried" when passing through the portal. This would cause the portal reader to miss the tag. To avoid this situation, it may be appropriate to use Session 1 (medium-short persistence) in dense reader environments. Another possible strategy to avoid missing tags this way is to use Session 2 on one reader and Session 3 on the nearby reader.
  • Variable Parameters
    • Transmit Power: The transmit power should be reduced so that the portal can reliably read the tags of interest without reporting stray tags (or a low acceptable number of strays).
    • Estimated Tag Population: The estimated tag population should reflect the estimated average number of items within the expected containers. This number may need to be tuned for optimal performance, but it is generally better to under-estimate the tag population than to over-estimate, as the reader Q algorithm is more efficient at adjusting upwards than downwards.

Conveyor

Tagged items are carried along a conveyor system, and particular checkpoints along the conveyor are monitored by a RAIN RFID system to confirm transfer of the item through those checkpoints.

Parameter Tuning for Conveyor

  • RAIN RFID Parameters
    • RF Mode: 4 (Max Miller, for ETSI use mode 5)
      • On conveyors, there are often only 1 or a few tagged items that need to be read at a time, but the items may move through the read zone quickly, and the tag or item orientation may make the tag harder to read. Therefore, monitoring a checkpoint of a conveyor system requires a balance of both speed and sensitivity, which is offered by the Max Miller mode.
    • Search Mode: Dual-Target B to A Select
      • The Dual-Target B to A Select search mode allows the reader to inventory all of the tags in the field of view of the checkpoint antenna quickly, and if an item becomes stuck in the field, it will be easily detected by showing continual reads. The Dual-Target mode also allows subsequent antennas to read the tags regardless of the previous state of the tag. In this use case it is recommended to also use the reportingIntervalSeconds property to reduce the number of duplicate tag reports for a given checkpoint.
    • Session: 2 or 3 (High Persistence)
      • Because Dual-Target search mode allows the tag to be read in either session state, a high-persistence session is ideal to reduce inconsistency.
  • Variable Parameters
    • Transmit Power: The transmit power should be reduced so that the checkpoint antenna can read tags reliably in the most difficult expected tag/item orientation but minimize the number of stray tags reported.
    • Estimated Tag Population: 2 The estimated tag population should be set very low for most conveyor applications that expect there to be only 1 or a few tagged items at a time. It is more efficient for the reader Q algorithm to adjust upward than to adjust downward.
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