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May 22, 2023
EZ-SCREEN SLS Safety Light Curtain Instruction Manual
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Methods to exclude the possibility of these failures include, but are not limited to:
Physically separating interconnecting control wires from each other and from secondary sources of power
Routing interconnecting control wires in separate conduit, runs, or channels
Locating all elements (modules, switches, and devices under control) within one control panel, adjacent to each other,
and directly connected with short wires
Properly installing multi-conductor cabling and multiple wires through strain relief fittings. Over-tightening of a strain-
relief device can cause short circuits at that point.
Using positive-opening or direct-drive components, installed and mounted in a positive mode
A machine primary control element (MPCE) is an electrically powered element that directly controls the normal operation of a
machine in such a way that it is the last element (in time) to function when machine operation is to be initiated or arrested
(per IEC 61496-1). Examples include motor contactors, clutch/brakes, valves, and solenoids.
Depending on the level of risk of harm, it may be required to provide redundant MPCEs or other control devices that are ca-
pable of immediately stopping the dangerous machine motion, irrespective of the state of the other. These two channels of
machine control need not be identical (i.e., diverse redundant), but the stop time performance of the machine (Ts, used to cal-
culate the separation distance, see
"Calculating the Safety Distance (Minimum Distance)" on page 22 ) must take into account
the slower of the two channels. Refer to "Generic Wiring Diagrams" on page 47 or consult the machine manufacturer for ad-
ditional information.
To ensure an accumulation of failures does not compromise the redundant control scheme (cause a failure to danger), a
method to verify the normal functioning of MPCEs or other control devices is required. EZ-SCREEN SLS provides a conve-
nient method for this verification: external device monitoring (EDM).
For the EZ-SCREEN SLS external device monitoring to function properly, each device must include a normally closed,
forced-guided (mechanically linked) contact that can accurately reflect the status of the device. This ensures that the normally
open contacts, used for controlling hazardous motion, have a positive relationship with the normally closed monitoring con-
tacts and can detect a failure to danger (for example, contacts that are welded closed or stuck On).
It is strongly recommended that a normally closed, forced-guided monitoring contact of each FSD and MPCE be connected
to the EDM input (see "Generic Wiring Diagrams" on page 47 ). If this is done, proper operation will be verified. Monitoring
FSD and MPCE contacts is one method of maintaining control reliability (OSHA/ANSI) and Category 3 and 4 (ISO 13849-1).
If monitoring contacts are not available or do not meet the design requirement of being forced-guided (mechanically linked), it
is recommended that you:
Replace the devices so that they are capable of being monitored; or
Incorporate the EDM function into the circuit as close to the MPCE as possible (for example, monitor the FSDs); and
Employ the use of well-tried, tested, and robust components, and generally accepted safety principles, including fault
exclusion, into the design and installation to either eliminate, or reduce to an acceptable (minimal) level of risk, the
possibility of undetected faults or failures that can result in the loss of the safety function.
The principle of fault exclusion allows the designer to design out the possibility of various failures and justify it through the risk
assessment process to meet the required level of safety performance, such as the requirements of Category 2, 3, or 4. See
ISO 13849-1/-2 for further information.
WARNING:
External Device Monitoring (EDM)
Creating a hazardous situation could result in serious injury or death.
If the system is configured for “no monitoring,” it is the user’s responsibility to ensure this does not
create a hazardous situation.
EZ-SCREEN provides three possible EDM configurations: 1-channel monitoring, 2-channel monitoring, and no monitoring.
Their functions are described below.
Machine Primary Control Elements (MPCE) and External Device Mon-
itoring (EDM) Input
5.9.3
External Device Monitoring
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