User Manual

Alarm management
Effects of BACnet properties on alarm response
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value of [EnAlm] (that is, [EnLm = EnAlm], Limit enable = Enable alarm). This
variable is equivalent to the standard BACnet property Limit_Enable.
Low limit [LoLm]
This parameter (data type Real) defines the low alarm limit. If [PrVal] exceeds
the high limit value [LoLm] for longer than the period defined under
[TiMonDvn], an OFFNORMAL alarm condition prevails, namely: LOW_LIMIT.
This is equivalent to the standard BACnet property Low_Limit.
Message text [MsgTxt]
For Desigo PX, the variables [MsgTxt] or [EvtMsg] contain the message text of
the last event notification associated with TO_OFFNORMAL, TO_FAULT and
TO_NORMAL alarms.
Deviation monitoring period [TiMonDvn]
This refers to a delay before generating the alarm if an alarm condition is
detected without a prior change in switch command (that is, without a set point
change). [TiMonDvn] is not an integrating function, that is, the condition
causing a change in the alarm state must persist without interruption for a
period of time at least equivalent to the duration of [TiMonDvn], before it has
any effect. The BACnet standard only supports a [TiMonDvn] for a monitoring
period and the associated alarm delay. This is equivalent to the standard
BACnet property Time_Delay.
In certain applications, different end-switch monitoring periods are required for
Open and Close commands and for the Idle state.
For this reason, the additional properties [TiMonOff] und [TiMonOn] have been
introduced for the binary input, binary output, binary value and multistate
output objects.
Switch off- [TiMonOff] and switch on monitoring period
[TiMonOn]
Delay time before an alarm is generated when there is a preceding set point
enable command. This is equivalent to proprietary BACnet properties
Time_Delay1 and Time_Delay2.
Delay time before an alarm is generated in the event of a set point switch-off
command.
Application: Control of fire protection dampers (see further below).
The definitions of the set point and the measured value depend on the object
type:
Object type Set point Measured value
Binary Input invers [RefVal] [PrVal]
Binary Output [PrVal] [FbVal]
Binary Value invers [RefVal] [PrVal]
The following example shows the use of the three time periods [TiMonDvn],
[TiMonOn], [TiMonOff]. For another example, see Alarm Example.
It is assumed that a fire damper has two separate feedback mechanisms (end
switches). This means that the damper is commanded via the commands Open
[TiMonOff]
[TiMonOn]
Examples