Rob Lewis, managing director of Fortress Interlocks, considers the options available to prevent fault masking in safety monitoring systems. The much-discussed phenomenon of fault masking (unintended resetting) when connecting multiple volt-free contacts in series in safety-monitoring systems is now covered in EN ISO 14119 and an associated technical report. In simple terms, if gate switches are wired in series, then it is still possible to reset a safety circuit, even after a short circuit has occurred on one part of the circuit, because one of the other gate switches can still open both circuits, allowing the fault to be cleared from a safety relay or PLC. The effect is so pronounced that for a system with more than one frequently opened guard, the level of diagnostic coverage (DC) falls to zero, resulting in the performance level being reduced to a maximum of PL c.
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机译：Fortress Interlocks的常务董事Rob Lewis考虑了可用于防止安全监视系统中的故障掩盖的选项。现在，EN ISO 14119和相关技术报告涵盖了在安全监控系统中串联连接多个无电压触点时引起广泛讨论的故障屏蔽（意外重置）现象。简而言之，如果栅极开关串联连接，则即使在电路的一部分发生短路之后，仍然可以重置安全电路，因为其他栅极开关之一仍可以断开两个电路，允许从安全继电器或PLC中清除故障。效果如此显着，以至于对于一个具有多个经常打开的防护装置的系统，诊断覆盖率（DC）降至零，从而导致性能水平降低至PL c的最大值。
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