Banner EZ-SCREEN­ Safety Light Curtain Systems - Manual (Page 37)

P/N 133487
35
Banner Engineering Corp. • Minneapolis, U.S.A.
www.bannerengineering.com • Tel: 763.544.3164
Overview
35
Banner Engineering Corp. • Minneapolis, U.S.A.
www.bannerengineering.com • Tel: 763.544.3164
EZ-SCREEN
Instruction Manual
Installation and Alignment
3.5.1 OSSD Output Connections
Both the Output Signal Switching Device (OSSD) outputs must
be connected to the machine control so that the machine’s
safety-related control system interrupts the circuit or power to
the Machine Primary Control Element(s) (MPCE), resulting in a
non-hazardous condition.
Final Switching Devices (FSDs) typically accomplish this when
the OSSDs go to an OFF state. See Figure 3-21.
Refer to the output specifications in Section 2.7 and the warning
at left before making OSSD output connections and interfacing
the EZ-SCREEN System to the machine.
3.5.2 FSD Interfacing Connections
FSDs (Final Switching Devices) can take many forms, though
the most common are forced-guided, mechanically linked relays
or an interface module. The mechanical linkage between the
contacts allows the device to be monitored by the External
Device Monitoring circuit for certain failures.
Depending on the application, the use of FSDs can facilitate
controlling voltage and current that differs from the OSSD
outputs of the EZ-SCREEN. FSDs can also be used to control
an additional number of hazards by creating multiple safety stop
circuits.
Safety Stop Circuits
A safety stop allows for an orderly cessation of motion for
safeguarding purposes, which results in a stop of motion
and removal of power from the MPCEs (assuming this does
not create additional hazards). A safety stop circuit typically
comprises a minimum of two normally open (N.O.) contacts from
forced-guided, mechanically linked relays, which are monitored
(through External Device Monitoring) to detect certain failures
in order to prevent the loss of the safety function. Such a
circuit can be described as a “safe switching point.” Typically,
safety stop circuits are either single-channel, which is a series
connection of at least two N.O. contacts; or dual-channel, which
is a separate connection of two N.O. contacts. In either method,
the safety function relies on the use of redundant contacts to
control a single hazard (if one contact fails ON, the second
contact will arrest the hazard and prevent the next cycle from
occurring). See Figure 3-21.
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 single-channel or dual-
channel control. (See Figure 3-23.)
Dual-Channel Control
Dual-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, dual-channel control with EDM monitoring should
be used in any installation where the FSDs are located remotely
from the MPCEs.
Single-Channel Control
Single-channel control 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, single-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 dual-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.