What is the AD filter

The AD filter is designed to minimise the effect of false alarms.

It is an advanced adaptive filter designed to work on any scenario.

It uses several mechanisms:

• • Discard reads from tags that continuously generate reads.

  • Discard selected reads from tags that periodically generate reads.

  • Fade away the sounder volume when the same tag is read continuously, down to the point it is turned soundless.

  • Persist state across reboots. This helps whenever the EAS system is shut down daily.

How the AD filter works

The state machine for the filter work as follows.

AD filter configuration

The filter configuration aims to be as simple as possible

Description of filter settings

Time filter

Enable/Disable AD filter

Calibration (silent) time (m)

Upon device operation, it is possible to enable a silent time period.

The silent period enables a transient period, where false alarms may be generated, however soundless and therefore reducing customer dissatisfaction. 

re-enable period (h)

This setting controls the minimum time period without reads for a filtered tag to be alarmed again.

A tag in the BLOCKED state will only move back to ALARMED state if there are no reads in the a time period larger than re-enable period (h)

This is the T2 in the diagram

Persist state across reboots

Enable/disable the state persisting mechanism.

This should be enabled in case the EAS system is rebooted daily.

Alarm sounder time (s)

Time period where an alarm will trigger the sounder.

Alarm light time (s)

Time period where an alarm will trigger the light.

Sound fade away

Enable/disable the sounder fade away mechanism.

When enabled, a tag generating an alarm will start with the louder possible sound and will decrease the volume during the Alarm sounder time (s) period.

This feature reduces the dissatisfaction of customers, as the loud sound is a source of stress.

The sound decreases as an exponential decay following the formula f(t)=fadeAwayFactor/(t^fadeAwayPower)

• • t expresses time since the first tag read

  • fadeAwayFactor is a constant factor

  • fadeAwayPower is the time power

How the sound decreases can be fine controlled with the advanced configuration.

Advanced conf

JSON configuration to control AD filter parameters:

adPreBlockTimeMin: this is the T1 time in the diagram. Defaults to 5 minutes

fadeAwayMaxVolume: initial volume when an alarm starts. Defaults to 10

fadeAwayMinVolume: end volume if an alarm. Defaults to 1

fadeAwayFactor: the factor of the volume formula. Defaults to 70

fadeAwayPower: power factor of the volume formula. Defaults to 1.5

An example of such configuration is:

{"fadeAwayMaxVolume":8,"fadeAwayMinVolume":2,"fadeAwayFactor":70,"fadeAwayPower":1.5,"adPreBlockTimeMin":5}

How can I detect which tags were filtered?

When there is a false alarm, the event is filtered and it is not sent to the TCP port 3177. However, you can check which tags were filtered by using this URL:

http://<device-ip>:3161/devices/<device-id>/readMode/ADFilterTags

Remember to change the device IP and device ID.