User Manual

Alarm management
Alarm response of the function blocks
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9.4 Alarm response of the function blocks
Alarm Collection
The default value of [EnEvt] for the Alarm Collection object is FALSE, that is, [EvtSta] transitions are not
notified.
An OFFNORMAL alarm is generated when:
● The following applies to one or more alarm collection members:
[EvtSta] <> NORMAL and applies simultaneously for all these members: [StaFlg].Fault = false.
A FAULT alarm is generated when:
● The following applies to one or more alarm collection members:
[StaFlg].Fault = true and therefore is set [Rlb] = UNRELIABLE_MEMBERS.
Analog Input, Analog Value, Analog Output
The Analog Input, Analog Value and Analog Output function blocks all have an identical alarm handling
procedure.
The analog output function block also has a feedback value [FbVal]; however, this is not used for alarm
monitoring. High and low alarm limits (variables [HiLm] and [LoLm]) are set for the OFFNORMAL alarms of
analog objects. An OFFNORMAL alarm occurs either when the high alarm limit is exceeded, or when the
current value falls below the low alarm limit. OFFNORMAL alarms are thus subdivided into two
subcategories: HIGH_LIMIT and LOW_LIMIT. In addition, the variable [Nz] can be used to define a
switching hysteresis for [HiLm] and [LoLm] to prevent over-frequent switching of alarms around the alarm
limit.
Alarm response
An OFFNORMAL alarm is generated:
● [PrVal] has either remained above the high alarm limit specified by the [HiLm] variable for a period of
time longer than the period specified in [TiMonDvn]
● or [PrVal] has remained below the low alarm limit specified by the [LoLm] for a period of time longer
than the period specified in [TiMonDvn]
An existing OFFNORMAL (HIGH_LIMIT) alarm will disappear when [PrVal] has remained below the value
([HiLm] + [Nz]) for longer than the time specified in the variable [TiMonDvn].
An existing OFFNORMAL (LOW_LIMIT) alarm will disappear when [PrVal] has remained below the value
([HiLm] + [Nz]) for longer than the time specified in the variable [TiMonDvn].
● A FAULT alarm is generated as soon as the [Rlb] property of the function block assumes any value
other than NO_FAULT_DETECTED. In particular, this is the case when [Rlb] changes from a value not
equal to NO_FAULT_DETECTED to another value not equal to NO_FAULT_DETECTED.
● A FAULT alarm will disappear as soon as the [Rlb] property of the function block changes from a value
not equal to NO_FAULT_DETECTED back to the value NO_FAULT_DETECTED.
BACnet Device Info Object
OFFNORMAL alarms
All the alarm-generating objects described so far model specific types of individual data points (physical or
virtual). The BACnet device object by contrast, models the properties of an automation station as a
complete entity. Alarm-relevant faults which cannot be allocated to a data point can be generated in an
automation station (see the examples further below). This is why the BACnet device object includes an