Notes on Configuration
S7-GRAPH for S7 300/400 Programming Sequential Control Systems
14-8
C79000-G7076-C526-01
14.2
Points to Note about Programming Sequencers
Initialization
The sequencer is initialized using the INIT_SQ parameter. If this changes to "1", all
steps marked as initial steps are activated. All other steps are deactivated.
After turning on the controller, the sequencer is in the same mode as it was when
the controller was turned off, in other words if the controller was in the SW_AUTO
mode before it was turned off, it will be in this mode when it is turned on again. If
you want to avoid this, the sequencer must be set to the required mode (for
example SW_MAN) explicitly when it is turned on, for example using the
initialization signal.
If the status of the process (system or machine) does not correspond to the initial
state of the sequencer, you can deal with this in two ways:
•
The process is, for example, changed to the initial state by a command. If you
want to change the process to the initial state, it is usually advisable to create a
separate sequencer for this purpose.
•
The sequencer can be synchronized with the process state using the
synchronize function.
Which method you use depends on the type of process.
Interlocks
In S7-Graph, interlocks can be defined for each step. All actions that are executed
depending on a condition are only activated when the interlock conditions are
satisfied.
If the interlock conditions are not satisfied when the step is active, an error
message is sent to the console (for example operator panel). The error is cleared
when the interlock conditions are satisfied.
Supervisions
In S7-Graph, monitoring conditions can be defined in the form of supervisions for
each step. The most common supervision condition is the execution time of the
actions. If the supervision condition is satisfied, in other words an error has
occurred, an error message is sent to the console (for example operator panel).
Such errors are acknowledged via the ACK_EF parameter.
Depending on the compilation settings (menu command Options > Block
Settings) of the created S7-Graph FB, acknowledgment may be required.
•
Compilation options "Acknowledge Errors" checked:
The error is only cleared when the supervision is no longer satisfied and an
acknowledgment signal is sent.