Normally, a maximum of one alarm on an object in the system can be active at a time. If an alarm situation arises on an object where an alarm has already been triggered, the latest alarm will be ignored by the system.
However, for digital and analog objects it is possible to have up to 32 simultaneous alarms. In this case, the object must be defined with an object template and its alarm bit must be set to Single Bits.
If the Single Bits option is not used, the alarms are read from the PLC in several successive scans. In other words, there can only be several, unfinished alarms on the same object in the Alarm List if Single Bits are used.
The individual alarm bits can be placed freely. However there can only be one acknowledge bit to the PC, independent of whether the alarm bit is Single Bits or not.
Alarms not defined as Single Bits are moved from the Alarm List to the Alarm Log when a new alarm occurs. However, the acknowledge entry is left empty so that it is apparent from the log that the alarm has not been acknowledged.