Sequential function chart

The sequential function chart (SFC, English: Sequential Function Chart SFC) is one of five in the EN 61131-3 standard programming languages ​​and is used for programming a programmable logic controller in the form of a Petri net. Under Siemens STEP 7, the SFC as S7-GRAPH is known.

Operation

A sequence control system is a chain of control steps, which are connected to each other by forwarding conditions (transitions). Right on the step icons, commands, also called actions involved. When you reach a control step with an attached action, an output is set, for example, or a program jump performed. The transitions, which are located between the control steps are associated with input bits, such as limit switches, limit switches. The first control step usually has no separate action, as this is also considered as initialization. This means that the program will start at the first operating cycle of the initialized step. Each control step is connected by a transition to the next control step.

Benefits

Especially for error analysis, the control flow is well suited because the current control step and the transition conditions at any time be visualized.

Disadvantages

For machine an output- oriented programming is advantageous. In a network, both the power-on and the switch-off conditions are treated. The step sequence splits what complicates troubleshooting.

Dissemination

The flow control is widely used, especially for large systems. Despite standardization does not offer any PLC manufacturers the SFC as programming software.

• Programmable logic controller