User Manual

SAFETY
Safety handbook page - 38 -
PNSPO
7.4 Muting application
The muting function is a temporary automatic suspension of a safety function(s) by
safety-related parts of the control system, as described on the EN954-1 (Safety-related
parts of control system).
Muting application is very often used in combination with safety photoelectric sensors
(ESPE, like safety light curtains). The general requirements for this kind of device are
listed below, basing on the EN61496-1:
-
When the muting function is activated the safety outputs are in the ON state, also
when the ESPE is activated.
- The muting function is active when a predefined sequence of at least two signals
reaches the muting control unit. The signals shall be generated from two or more
muting sensors (e.g. photoelectric sensors, limit switches or proximity sensors)
located near the ESPE device and activated with the object passage.
- At least one indicator shall illuminate when the ESPE is in muted condition. The
indicator should be visible from any position near the dangerous zone.
- Any fault condition in the muting inputs or in the indicator or a wrong signals
sequence is revealed and the muted condition is prevented.
More specific requirements are included in type C norms (see below).
The muting function is essential in an automatic cycle of a plant where a crossing of the
light barrier is requested from machine tools or other objects (e.g. pallets) without
stopping of the plant.
A typical application is the palletiser / depalletiser machine. The pallet must go through
the light barrier monitored zone freely while the access of a person must stop the plant
immediately.
Application example for palletiser
A: Main ESPE device
B: Pallet movement direction
C: Pallet conveyor
D: Danger zone
G: Fixed guards
M1, M2: Muting beam sensors
It’s necessary to realize a system that is able to discriminate between:
- authorized objects to go trough the light barrier freely and
- non authorized objects (e.g. person).