WARNING: Interfacing of Both OSSDs
Both OSSD (Output Signal Switching Device) outputs must be connected to the machine control so that the
machine’s safety-related control system interrupts the circuit to the machine primary control element(s),
resulting
in a non-hazardous
condition.
Never wire an intermediate device(s) (for example, PLC, PES, or PC) that can fail in such a manner that there is the
loss of the safety stop command, OR in such a manner that the safety
function
can be suspended, overridden, or
defeated, unless accomplished with the same or greater degree of safety.
WARNING: OSSD Interfacing
To ensure proper
operation,
the Banner device output parameters and machine input parameters must be
considered when interfacing the Banner device OSSD outputs to machine inputs. Machine control circuitry must
be designed so that the maximum load resistance value is not exceeded and that the maximum
specified
OSSD
Off-state
voltage does not result in an On
condition.
Failure to properly interface the OSSD Outputs to the guarded machine may result in serious bodily injury or
death.
4.4.2 FSD Interfacing
Connections
FSDs (Final Switching Devices) takes many forms. The most common are forced-guided, mechanically linked relays, or interface
modules. 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 Type 2. FSDs can also be used to control an
additional
number of hazards by
creating
multiple
safety stop circuits.
Protective
Stop (Safety Stop) Circuits
A
protective
stop (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
protective
stop circuit typically comprises a
minimum of two normally open 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,
protective
stop circuits are either single-channel, which is a series
connection
of at least two normally open
contacts; or dual-channel, which is a separate
connection
of two normally open 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 arrests the hazards and prevents
the next cycle from occurring.
The interfacing of the
protective
stop circuits must be accomplished so that the safety
function
cannot be suspended, overridden, or
defeated, unless accomplished in a manner of the same or greater degree of safety as the machine’s safety related control system that
includes the EZ-SCREEN Type 2.
The normally open safety outputs from an interface module provide a series
connection
of redundant contacts that form
protective
stop circuits for use in either single-channel or dual-channel control.
Dual-Channel Control
Dual-channel control provides the ability to electrically extend the safe switching point beyond the FSD contacts. With proper
monitoring, 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 a loss of the switching
ability of one of the FSD outputs. Such failures may lead to a 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 increases,
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 a 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 cannot 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.
EZ-SCREEN
®
Type 2 Light Screen
30
www.bannerengineering.com - Tel: 763.544.3164
