BACnet basics
There are 2 types of alarms:
- Intrinsic reporting
- Algorithmic change reporting
Desigo Room Automation uses algorithmic change reporting.
Algorithmic change reporting
The BACnet object is not alarm capable. Alarms and events (notifications) are generated via its own event enrollment object.
The event enrollment object references a value (property) for monitoring from another BACnet object, e.g. analog input, analog value, or in the form of a binary or multistate signal. Details on monitoring are defined using the following event algorithms within the event enrollment object.
Event algorithms | Function |
|---|---|
Change of bitstring / ChangeOfBitstring | Monitoring a bitstring value for a specific state such as InAlarm, fault. |
Change of state/ ChangeOfState | Monitors for a definable status, e.g. program state, system status, load shedding state, silenced, door status, security level, binary value, etc., in other words for the most important information from all objects as defined by BACnet. |
Command failure / CommandFailure | Feedback monitoring: Monitors, via two references, whether a feedback to a switching command occurs within a defined period. |
Floating limit / FloatingLimit | Floating limits: Can monitor, via two references, whether the actual value is located with an adjustable range around the setpoint. |
Out of range / OutOfRange | Monitor Real value for a high/low limit value including delay time and neutral zone. |
Unsigned range | Monitor absolute value for a high/low limit value including delay time and neutral zone. |
You can still define prioritization, alarming (acknowledge and reset) as well as response (alarm or event notification) on the event enrollment object (similar to intrinsic alarms). In other words, all required properties are available on the object and can be edited specific to the application during engineering or commissioning as well as from a BACnet client.
Standard BACnet object
BACnet uses the following properties to display the object state:
Property | State | Description |
|---|---|---|
State indication (status flag) | InAlarm | True process alarm, e.g. high limit is exceeded or low limit breached for an analog input of value object. |
InAlarm, fault | System alarm for no sensor, short circuit, interrupt, etc. | |
Out of service | When the object is placed out of service. | |
Overridden | Local override on an I/O module. | |
Reliability | No error | N/A |