Banner EZ-SCREEN­ Safety Light Curtain Systems - Manual (Page 34)

page 34
Banner Engineering Corp. • Minneapolis, MN U.S.A.
www.bannerengineering.com • Tel: 763.544.3164
Installation and Alignment
EZ-SCREEN Grid
Instruction Manual
The interfacing of the Safety Stop Circuits must be accomplished so that the
safety function can not be suspended, overridden, or defeated, unless
accomplished in a manner at the same or greater degree of safety as the
machine’s safety related control system that includes the EZ-SCREEN.
The normally open safety outputs from an interface module provide a series
connection of redundant contacts that form safety stop circuits for use in either
1-channel or 2-channel control. (See Figures 3-17 and 3-18.)
2-Channel (Dual-Channel) Control
Two-channel control provides the ability to electrically extend the safe switching
point beyond the FSD contacts. With proper monitoring (i.e. EDM), this method
of interfacing is capable of detecting certain failures in the control wiring between
the safety stop circuit and the MPCEs. These failures include a short-circuit of
one channel to a secondary source of energy or voltage, or the loss of the
switching ability of one of the FSD outputs. Such failures could lead to the loss of
redundancy — or to a complete loss of safety, if not detected and corrected.
The possibility of a failure to the wiring increases as the physical distance
between the FSD safety stop circuits and the MPCEs increase, as the length or
the routing of the interconnecting wires increases, or if the FSD safety stop
circuits and the MPCEs are located in different enclosures. For this reason,
2-channel control with EDM monitoring should be used in any installation where
the FSDs are located remotely from the MPCEs.
1-Channel (Single-Channel) Control
One-channel control, as mentioned, uses a series connection of FSD contacts to
form a safe switching point. After this point in the machine’s safety-related
control system, failures can occur that would result in the loss of the safety
function (such as a short-circuit to a secondary source of energy or voltage).
For this reason, 1-channel control interfacing should be used only in installations
where FSD safety stop circuits and the MPCEs are mounted within the same
control panel, adjacent to each other, and are directly connected to each other; or
where the possibility of such a failure can be excluded. If this can not be
achieved, then 2-channel control should be used.
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 can cause short-circuits at that
point.)
• Using positive-opening or direct-drive components, installed and mounted in a
positive mode.