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MUTING IN PRACTICE
WHEN SAFETY BECOMES A VULNERABILITY Dr Albrecht von Pfeil, Director Safety Solutions, Leuze electronic
Designed to allow objects to
UNCONSCIOUS RISKS
pass through safety barriers
Various types of muting are used in industrial automation: whether they be 2-sensor, 4-sensor, time-controlled or sequence-controlled. The IEC 62046 international standard1 regulates the requirements for entry and exit stations with muting and stipulates in particular that: • muting must be activated via at least two independent bridging signals • muting must offer protection against foreseeable incorrect operation or manipulation. The standard thus defines clear requirements for the implementation of muting applications. In practice, however, it is not always fully complied with — either because the specific application requirements are not fully known and may therefore differ from real-life conditions, or because risky compromises are deliberately made to achieve high process stability. As a result, safety functions become less
in factories, muting can also introduce new safety risks if not implemented correctly.
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uting allows the safety function on machines or systems to be temporarily bypassed so that material can be fed in or out through protective devices such as light curtains or laser scanners without interrupting the production process. However, in doing so, personnel safety must be guaranteed at all times. Muting applications often reach their limits in practice, however, allowing incorrect operation and manipulation. In such cases, alternative security concepts are required.
effective, and manipulation or incorrect operation are more likely. For operators, this means an unconsciously increased liability risk and potentially serious consequences for employee safety.
HAZARD 1: SAFETY GAP DUE TO PALLET MUTING In automated systems, meshed containers or other objects that are difficult for muting sensors to detect are often fed onto or discharged from pallets (Figure 1). The openings in the mesh structure prevent the muting sensors from generating a stable switching signal, making it impossible to mute the safety device. In practice, the pallet itself is sometimes used as a muting trigger (Figure 2) — a procedure that is not permitted, since a person could, for example, simply place an empty pallet in the safety device and deliberately disable the protective device.
This issue is sponsored by — Moore Industries — www.miinet.com