Actions
There is another approach while applying actions. At first, actions (activity types) performed by the system are defined. After that, chart is created. Here action order and interconnection are defined. Every action is associated with one or several steps. It is possible that action can be launched at one step and stopped at another. It is also possible that started action shall be stopped independently of any step. For example, having started action, elevator should go to at least next floor and let off passengers, even if command to stop was issued. Actions are shown on SFC-chart in shape of rectangles placed to the right of step and connected to it graphically. The important thing here is that the same action can be used in different steps. For example, Cooling & Drying steps employ air-cooling action. Actions do not belong to the certain step, they are independent SFC-component program elements.
Action identifiers should be unique within component limits. They should not be the same as the step and transition identifiers.
Action Qualifiers
Type | Description |
N - non-stored action | The action is executed in every work cycle while the step is active. |
P - impulse | The action is executed for the first time during activation, for the second time after activation. |
P0 - impulse (falling edge) | The action is executed once during deactivation. |
P1 - impulse (rising edge) | The action is executed once during activation. |
S - stored | The action is activated and remains active till reset. The action is executed in every cycle even if the step is not active. |
R - reset | The action is deactivated. |
L - time limited | The action is activated together with step and remains active for the predefined time, but not longer than step. |
SL - stored and time limited | The action is activated together with step and remains active for the predefined time, independent of step activity. Action can be deactivated in advance from another step with R classifier. |
D - delayed | The action is activated in preset time after step activation and remains active till the step is active. If step is active less than preset time, action will not be activated. |
DS - delayed stored | The action is activated in preset time after step activation and remains active till reset. If step is active less than preset time, action will not be activated. During parallel reset execution in the process of time-taking (in another step with R classifier), action will not be activated. |
SD - stored delayed | The action is activated in preset time after step activation even if step is not active. But if reset is executed in the process of activation delay counting (in another step with R classifier), action will not be activated. Activated action remains active till reset. |
L, D, SD, DS, and SL qualifiers require time constant specifying in TIME format. For example: T#10s.
Was this page helpful?