GRAFCET diagrams (Sequential Function Charts) are representations of sequential controls for which the specification language GRAFCET (GRAphe Fonctionnel de Commande Etapes/Transitions) according to DIN EN 60848 has been used.
The approach for creating GRAFCET diagrams is similar to the approach for functional diagrams. The representation of such a sequential control can be realized on an existing or new page. It is not necessary to store a form.
Example:The following figure shows the schematic layout of a GRAFCET diagram.
| A |
GRAFCET table |
||
|
Variable |
DT |
Function text |
|
|
Zv |
-P1 |
Pump |
|
| B |
Zu |
1-1A1 |
Cylinders |
The table of variables is displayed in the area A. The heading and table header are created by means of a macro. A single table row B with the property texts (variable, DT, etc.) is inserted via the functional placing from within the device navigator. The structure and interpretation of the GRAFCET diagram are displayed in the area C. The GRAFCET elements steps, actions, and transitions can be inserted via the GRAFCET menu.
GRAFCET elements
The essential elements of a GRAFCET diagram are steps, related actions and transitions. In all types of sequences, steps and transitions must alternate constantly. Please see the DIN EN 60848 standard for information on the correct layout and meaning of the individual elements of a GRAFCET diagram.
Steps
A step identifies the state of a part of the sequence. Steps must have a designation to be identifiable. The recommended representation of a step in the diagram is a square.
Actions
A step can be allocated one or several actions. An action defines what is to be done to a variable. Actions are generally represented by rectangles.
The variables can be combined in a variable table transparently. Via the additional placing of device tags in this variable table, a connection to the EPLAN devices is established.
Transitions
A transition marks the transfer from one step to the next. In the diagram, a transition is mostly represented by a line perpendicular to the connection between the two steps.
A transition may contain a name; it must be placed on the left and must be inside brackets. The transition condition is placed to the right of the transition.
Tables of variables
Tables that list the variables used in the diagram can be inserted in GRAFCET diagrams. Usually, the devices projected in EPLAN are placed only textually (i.e., as property texts) in the variable table of the GRAFCET diagram. This means that the Functional placing with symbol graphic project setting must be deactivated.
The table header is created by means of a macro. A single table row with the property texts of a function (displayed DT, function text, etc.) can be inserted from the device navigator via the Place functional > With symbol graphic popup menu items. The property arrangement of the texts is defined by the special symbol stored in the project settings.
See also