Stahl - Catalog - STAHL - #37

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2/6 2 Automation 02.07.2008 Safety Barriers Series 9001, 9002, 9004 Addition possibilities Example: I = current addition U = voltage addition When interconnecting two safety barriers for alternating potential I + U results, thus a current addition as well as a voltage addition is to be taken into consideration. The EN 60079-11, table A.1 contains the permissible value pairs / combinations of permissible maximum safe values for: • Voltage Uo • Current Io • External capacitance Co The following procedure is to be applied: 1. Test, if the value combination Uo and Io determined is permitted Example 1: Values 28 V / 100 mA are permitted, since the current Io can be up to 120 mA at 28 V for explosion group IIC Example 2: Values 24 V / 210 mA are permitted only for IIB 2. Determination of capacitance Co from voltage Uo Example: Uo = 27 V. For IIB the result is Co = 705 nF It is not allowed to apply the ignition diagrams acc. to EN 60079-11 for the assersment of the intrinsic safety in case that safety barriers with electronic current limitations need to be interconnected. A suitable procedure is described in the EN 60079-25. Interconnection of Safety Barriers Polarity - + ~ - I U I and U + U I I and U ~ I and U I and U I and U