Issue
The StruxureWare Building Operation BACnet digital value is seen as being in alarm
Product Line
EcoStruxure Building Operation
Environment
- BACnet
- Digital Value
- Alarm
Cause
Having created a BACnet Digital Value under the BACnet Interface / Application. When the digital value is "Enabled" (Active Text), the IN ALARM status flag is set. This causes the third party device to show it as being in alarm.
Resolution
From v3.0, EcoStruxure Building Operation is BACnet standard at protocol revision 14 so this is not an issue. The text below was written for earlier versions and is valid for v2.0 and earlier.
It is not possible to disable the evaluation of intrinsic alarming on BACnet points (which updates the status flags and event state properties).
Not updating status flags and event state (according to the alarm-value) was identified by the BACnet Test Lab as a compliance issue with the BACnet standard at protocol revision 6 – the revision SBO implements. The essence of the issue is that we are not allowed to have the intrinsic alarming properties, but not use them – updating the object state according to its configuration.
The feature to disable intrinsic alarming (an alarm disable property) was introduced at a more advanced protocol revision (13), which is not currently not available for SmartStruxure.
A possible workaround for the issue, if the value periodically changes between active and inactive: set the time-delay (which is measured in seconds) to a large value. If the delay is longer than the amount of time the value spends in what would be the alarm state, then evaluation is avoided. A value of 32,000,000 for example delays evaluation for a little more than a year.
NOTE - make sure to set the time delay while status flag in-alarm is false, and event-state is normal, otherwise it would take a year to get out of the alarm state.
