Q-Value and Session Value

In multi-tag inventory parameters, the settings for the Q-value and Session value affect tag inventory speed and count accuracy. While the default Q-value is displayed as 4, the system internally employs a dynamic Q that adjusts automatically based on the number of detected tags; a fixed Q-value can also be configured.

The Session value controls a tag's "readability status" and "state retention duration" via the session layer (S0/S1/S2/S3/AUTO), thereby addressing the issue of duplicate reads.

The Q-value (Query Parameter) is an algorithmic parameter used by the reader to adjust the probability of tag response; it directly impacts reading efficiency and anti-collision performance in multi-tag scenarios. When tag density is high, the Q-value should be increased to widen the response window and reduce collisions; conversely, when tag density is low, the Q-value should be lowered to shorten response time and increase speed.

As a reader identifies tags, they alternate between two states:

State A: Readable by the reader

State B: Temporarily dormant; does not respond to commands

The Session defines the persistence and transition rules for tag states (A/B). Each tag possesses four independent session layers, with each layer containing both A and B states (defaulting to A); the reader can toggle the state (A↔B) using the Select command or ACK response. Characteristics vary significantly across session layers:

①　S0: The tag's state reverts to A immediately after leaving the RF field; suitable for single-tag scenarios.

②　S1: After entering State B, the tag automatically reverts to A within 500ms to 5s (depending on the chip model); suitable for high-frequency inventory in dynamic environments.

③　S2/S3: The tag remains in State B for at least 2 seconds after leaving the RF field, during which it does not respond to queries; this reduces duplicate reads and is suitable for dense tag environments.

④　Auto1/2/3: Alternates between S2 and S3 for queries; suitable for inventory in fixed, enclosed tag environments.

The Q-value regulates tag response density, while the Session value controls the tag's dormancy cycle to minimize redundant scanning.