Muting is used to temporarily disable the safety function of a light curtain during automatic loading or unloading of a machine. At this critical moment, it is necessary to distinguish between material and people. This is usually done by monitoring the sequence of intervention and the timing of two muting inputs. But sometimes irregularities in the movement of the material make this impossible. For these cases, SH4 offers the possibility to replace the time monitoring with a sequence monitoring of 4 independent muting inputs, thus improving the protection against manipulation and bypassing of the safety function.