User Manual

Alarm management
Effects of BACnet properties on alarm response
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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]
[TiMonOff]
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.
[TiMonOn]
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]
Examples
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 and Close. The first end switch, the Open switch
delivers the signals Fully open or Not fully open. The second end switch, the Closed switch delivers the
signals Fully closed or Not fully closed. The following is an example of how to connect the BO (binary
output for commanding and integrating the Open switch) and BI (the binary output for the closed switch):