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ZigBee coordinators that properly implement safe state functionality will send regular ‘stop revert’
commands to all connected meters whenever they are communicating successfully with the ESCo,
and will send regular ‘start revert’ commands during ESCo communications outages.
Safe State Manual Override
In normal operation, the state of the relay can be set remotely by the ESCo or manually using the
front panel button on the device. When communications are interrupted – due either to a loss of
ESCo communications from the ESBox, or a loss of ZigBee communications between the meter and
the ESBox – the safe state mechanism can guarantee that the switch state will revert to a pre-
defined safe state. However, the designated safe state may not always be the state desired by the
consumer, meaning that there must be a mechanism to manually override the switch state during
times when the normal ESCo controls are not available.
Safe State Manual Override enables consumers to manually set the switch state of their device
during communications outages. When the switch state is manually set
following the start of a safe
state reversion countdown
, the switch will ignore safe state reversion triggers until manual override
is disabled by receipt of a ‘stop revert’ message from the ZigBee coordinator. Since ‘stop revert’
messages will only be received by the device if the ZigBee network is working
and
the ESBox is able
to communicate with the ESCo, the device will be under the control of the ESCo meaning that
manual control can be cancelled.
Safe State Reversion Reports
The safe state mechanism includes a
report
capability to enable the ESCo to determine if a switch
state transition occurred autonomously.
If safe state reversion reporting is enabled, bit 1 of the
Switch State attribute will be set to 1 if a reversion to safe state was the cause of the most recent
switch state transition.
Safe state reporting example: The Switch Safe State attribute is set to 3, and the relay is currently
OFF (Switch State = 0). The SS9005 loses contact with the ZigBee network, causing the switch state
to revert to the selected safe state (ON). The Switch State attribute (attribute 0) will be set to 3,
indicating that the switch is on (bit 0 ==1) and a reversion has occurred (bit 1 = 1).
The reversion to safe state report bit in the Switch State attribute will be cleared the next time the
switch state is changed, either remotely or using the front panel button on the SS9005.
Effect of Factory Reset on Safe State Settings
Performing a factory reset on the device will reset the ‘Switch Safe State’ attribute to 4 (disabled),
and the ‘Switch Safe State Reversion Delay’ attribute to zero.
