Banner SC22-3E Safety Controller with Ethernet - Manual (Page 43)

WARNING: . . . Safety Output Lead Resistance
In order to ensure proper operation, the resistance in the Safety Output wires should not exceed 10 ohms. A higher
resistance than 10 ohms may mask a short between the dual-channel Safety Outputs and could create an unsafe condition
that may lead to serious bodily injury or death.
4.7.3 FSD Interfacing Connections
Final switching devices (FSDs) can take many forms, though the most common are forced-guided (mechanically linked) relays or Inter-
facing Modules. The mechanical linkage between the contacts allows the device to be monitored by the external device monitoring circuit
for certain failures.
Dependent on the application, the use of FSDs can facilitate controlling voltage and current that differs from the OSSD outputs of the
Controller. FSDs can also be used to control an additional number of hazards by creating multiple safety stop circuits.
Safety (Protective) Stop Circuits
A safety stop allows for an orderly cessation of motion or hazardous situation 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 of a
minimum of two normally open contacts from forced-guided (mechanically linked) relays, which are monitored to detect certain failures
such that the loss of the safety function does not occur (i.e. external device monitoring). Such a circuit can be described as a “safe
switching point.”
Typically, safety stop circuits are a series connection of at least two N.O. contacts coming from two separate, positive-guided relays,
each of them controlled by one separate Safety Output of the Controller. The safety function relies on the use of redundant contacts to
control a single hazard, so that if one contact fails ON, the second contact will arrest the hazard and prevent the next cycle from occur-
ring.
Interfacing safety stop circuits must be wired so that the safety function can not be suspended, overridden, or defeated, unless accom-
plished in a manner at the same or greater degree of safety as the machine’s safety-related control system that includes the Controller.
The normally open outputs from an interfacing module are a series connection of redundant contacts that form safety stop circuits and
can be used in either single-channel or dual-channel control methods. (See wiring diagrams.)
Dual-Channel Control. Dual-channel (or two-channel) control has 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 action of one of the FSD outputs. The result could lead to the loss of redundancy or a complete loss
of safety if not detected and corrected.
The possibility of a wiring failure 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. Thus, 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 (or 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 (e.g., a short-circuit to a secondary source of energy or voltage).
Thus, this method of interfacing should only be used in installations where FSD safety stop circuits and the MPCEs are physically located
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 two-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.
• Routing interconnecting control wires with low voltage or neutral that can not result in energizing the hazard.
• Locating all elements (modules, switches, devices under control, etc.) within the same control panel, adjacent to each other, and
directly connected with short wires.
SC22-3/-3E Safety Controller Instruction Manual
P/N 133487 rev. C www.bannerengineering.com - tel: 763-544-3164 43