Banner AG4 Series Safety Laser Scanner
Final switching devices (FSDs) typically accomplish this when the OSSDs go to an OFF state. See Figure 3-19. Refer to
the output specifications in Section 2.2 and the warnings below before making OSSD output connections and interfacing
the Scanner to the machine.
3.7.2 FSD Interfacing Connections
Final switching devices (FSDs) can take many forms, although 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 Scanner. FSDs can also be used to control an additional number of hazards, by creating multiple safety
stop circuits.
Safety Stop (Protective Stop) Circuits
A safety stop allows for an orderly cessation of motion for safeguarding purposes, which results in the stopping 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 (via 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 3-19.
The interfacing of the safety stop circuits must be accomplished so that the safety function cannot 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 Scanner.
The normally open safety outputs from a safety 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 3-20.)
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 increases, as the length or the routing of the interconnecting wires increases, or if the FSD safety stop circuits
WARNING . . . INTERFACING OF BOTH OSSDS
Both of the 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) (e.g., 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 Scanner OSSD output parameters and machine input parameters must be considered when interfacing
the Scanner solid-state 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 could result in
serious bodily injury or death.
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