Stahl - Catalog - STAHL - #34

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2/3 2 Automation 02.07.2008 Safety Barriers Series 9001, 9002, 9004 Application Safety barriers are used as economical interfaces without galvanic isolation between intrinsically safe and non-intrinsically safe circuits. They protect circuits (i. e. cable and apparatus) in hazardous locations. Safety barriers are so-called associated apparatus: Since they also contain non-intrinsically circuits they must either be installed in the safe area or if certified in Zone 2 / Division 2. The combination with an further type of explosion protection (e.g. flame proof enclosure) enables the installation in Zone 1. 09911E02 Function Safety barriers are used to limit the power supply into an intrinsically circuit in such a way that neither sparks nor thermic effects (hot surfaces) can cause an ignition. A safety barrier thus contains three essential elements: • Zener diodes for limiting the voltage • Resistor or components for limiting the current • Fuse for the protection of zener diodes 09912E02 R. STAHL safety barriers Series 9001, 9002 and 9004 also contain a protective circuit with an exchangeable fuse externally accessible, protecting the internally encapsulated non-accessible fues of the safety barrier. The protective circuit prevents both fuses tripping at the same time. In order to cover the complete spectrum of instrumentation applications a few types of safety barriers include function blocks like e.g. electronic current limitations, amplifier, etc. Potential Equalisation / Grounding Differences in potential can delete the intrinsically safety and thus make explosion protection ineffective, since safety barriers have no galvanic isolation between input and output. All (national) standards for the installation of intrinsically safe circuits thus require: • the existance of a potential equalisation or grounding system as well as • the connection of safety barriers to this potential equalisation R. STAHL safety barriers can alternatively be connected directly via the electrically conducting snap-on mechanism or by means of the ¿ / PA-terminal to the potential equalisation. Ex i 9001 / 9002 / 9004 Hazardous area max. 250 V Ex i Encapsulation / PA / PA