Stahl - Catalog - STAHL - #35

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2/4 2 Automation 02.07.2008 Safety Barriers Series 9001, 9002, 9004 Selection Criteria - Function and Safety Selection of safety barriers is generally carried out in two steps: • Functional consideration • Safety consideration 1. Functional consideration Safety barriers are first selected according to their electrical requirements. It is therefore necessary to know the electrical data of the connected apparatus. Further selection criteria: • Polarity of the voltage at the safety barrier UN (+, -, ~) in reference to ¿/PA • Voltage UN • Max. permissible voltage drop across the barrier, caused by the line resistance RL and / or a constant voltage drop ãU • Type of signal to be transmitted; voltage signals can only be transmitted via barriers with purely resistive line resistance; this limitation does not apply to current signals. 09934E02 It is furthermore to be examined, if the circuit may be grounded or if an earth-free („floating“) circuit is required due to electrical or measurement reasons. An earth-free („floating“) circuit can usually be established by using a dual-channel safety barrier or interconnecting two single-channel safety barriers. 09935E02 09936E02 Grounded circuit Floating circuit For many standard application in instrumentation special safety barriers are available, which are designed optimally for the respective application according to the criteria mentioned above. 1 Ex i 3 4 2 PA / 1 Ex i 3 4 2 PA / PA /