Buffering of Process Messages including Time Stamps with ALARM_7B
The conventional alarm blocks "Alarm_8" and "Alarm_8P" are used to signal status changes of events/alarms to the operator system, together with a time stamp. This time stamp is generated when the alarm block is called.
For the purpose of traceability, the process messages in the automation system shall remain available, even if the connection to the operator system fails. Furthermore, a time stamp indicating the time of occurrence shall be stored and displayed when the event is displayed on the operator system at a later point.
This may be reasonable in configurations like the following ones:
- In hierarchical control topologies with S7-300 controllers
- For signal time stamping in an ET 200 unit
- In telecontrol applications
With the solution described here, the connection between automation system (AS) and operator system (OS) can be continuously monitored. If the connection to the OS is interrupted, the alarm signals including the relevant time stamps of the events will be stored. These time stamps can be generated on the basis of the CPU clock or by an external source.
After restoration of the connection, the buffered alarms will be sent to the OS, together with the time stamp generated when the event occurred.
This solution comprises the alarm block “ALARM_7B”, a documentation describing its function principle and an instruction with an example on how the block is used.
- as of PCS 7 V7.1
- or as of STEP 7 V5.4 SP4, S7-SCL V5.3 SP5 and WinCC 7.0 SP1