Sunday, April 17, 2011

Standardized Safety Function Blocks of PLCopen

Currently, the PLCopen workgroup has specified 19 safe function blocks regarding their inputs/outputs, state engine, error recognition and error handling. These blocks include important safety functions such as Emergency Stop, Safety Door, Mode Selector and Two-Hand Control. Based on the PLCopen specification, providers of safe automation systems can implement and certificate these blocks considerably easier. The exemplary mentioned blocks are already today part of the safe programming system SAFEPROG which has been successfully certified within the scope of the Phoenix Contact Interbus Safety Platform.

The correct use of safe function blocks according to the PLCopen is simplified for the PLC programmer by the manufacturer-embracing functionality. This also includes the low need for training and the easier transferring of programmed safety functions to different PLC system. A further advantage is the low effort arising for the commissioning staff when validating the PLC program, as parts of the safety logic are based on already certified software modules. KW-Software will be one of the first companies starting the implementation of the PLCopen safe function blocks. In 2005, 10 safe software blocks are expected to be provided by KWSoftware within a library in the programming system SAFEPROG.

Clear separation of safe and non-safe functions
To avoid a possible mistaking of safe and non-safe data types (variables), the data type SAFEBOOL was defined in the PLCopen specification. The data type SAFEBOOL can only be used in combination with safety-relevant software blocks. Corresponding plausibility checks – as they are implemented in SAFEPROG – should be performed by the programming system. To meet the programming guide lines described in the PLCopen specification, the graphic editor in the engineering software should support the safety-relevant programming by means of suitable measures. This can be done by displaying the different function block types with different colors, by marking non-safe data types (variables) - as shown in figure 3 - as well as by further plausibility checks in the graphic editor.

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