24 n SAFETY June 2026 www.drivesncontrols.com When muting reaches its limits Muting is a well-established technique that allows the safety functions on machinery to be bypassed temporarily so that material can be fed through protective devices such as light curtains or laser scanners without interrupting production. But muting has practical limitations, allowing incorrect operation and manipulation. In such cases, alternative security concepts are needed. Various types of muting are used in industrial automation: two- or four-sensor, time-controlled or sequence-controlled. The international standard DIN EN IEC 62046 regulates the requirements for entry and exit stations with muting and stipulates, in particular, that: n muting must be activated via at least two independent bridging signals; and that n muting must offer protection against foreseeable incorrect operation or manipulation. The standard thus defines clear requirements for implementing muting. 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 effective, and manipulation or incorrect operation are more likely. This means an raised risk for operators with potentially dangerous consequences. 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 (see Fig 1). The openings in the mesh structure prevent the muting sensors from generating stable switching signals, making it impossible to mute the safety devices. In practice, the pallet is itself sometimes used as a muting trigger – a procedure that is not permitted. A person could, for example, place an empty pallet in the safety device and thereby disable the protective device deliberately. This safety gap can be closed reliably using smart process gating, in which the bridging function is activated by two independent control signals without external muting sensors. The gating on the safety light curtain is activated by: n a control switching (CS) signal from the system controller as the first (initiating) signal; and n a protective field interruption (PFI) signal, triggered by the transported goods in the light curtain protective field, as a second (verification) signal. The gating function is activated by the correct sequence of the CS signal and protective field violation and is monitored by the light curtain. Shortly before the transported goods enter the protective field, the controlling PLC sends the CS signal to the safety light curtains. The timing must be set so that the distance between the transported goods and the protective field is less than 200mm, preventing a person from passing through immediately before the goods. If the transported goods enter the protective field within four seconds, the light curtain uses its own PFI signal and suppresses a safety shutdown. Gating ends either automatically, immediately after the conveyed material has passed through and the protective field has been cleared, or by resetting the CS signal via the PLC. This method results in a particularly compact design, because no extra muting sensors are needed directly upstream or downstream. Hazard 2: Safety gap due to incompletely loaded pallets If a pallet is only partially loaded, or if the transported objects are significantly narrower than the conveyor system, a gap will occur during muting (Fig 2). A person can enter the danger zone through this gap without the safety function being triggered. Muting can enable uninterrupted material flow in automated systems, but incorrect implementation can create safety gaps that require alternative approaches. In this article, the safety specialist Leuze electronic considers some of them. This multi-beam laser system provides access guarding on conveyors. It limits access to hazardous areas, using muting sensors to allow pallets to pass through unhindered.
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