Programmable Safety Controller SCR P
44
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6.7.1 Safety Relay Outputs
The SCR P has isolated redundant relay outputs that can be used to control/switch a wide range of power characteristics
(see
on p. 12). Unlike a solid-state Safety Output, within an output module an individual safety relay
output (Mx:ROx) functions as a group and cannot be split.
The Safety Relay Outputs are controlled and monitored by the SCR P without requiring additional wiring.
For circuits requiring the highest levels of safety and reliability, when used in pairs (two N.O.), either Safety Output must be
capable of stopping the motion of the guarded machine in an emergency. When used individually (a single N.O. output),
fault exclusion must ensure that failures cannot occur that would result in the loss of the safety function, for example, a
short-circuit to another safety output or a secondary source of energy or voltage. For more information, see
Single-channel
Control
Safety (Protective) Stop Circuits
Whenever possible, incorporating External Device Monitoring (EDM) and/or Adjustable Valve Monitoring (AVM) is highly
recommended to monitor devices under control (FSDs and MPCEs) for unsafe failures. See
on p. 44 for more information.
Output Connections
—The Safety Relay Outputs must be connected to the machine control such 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. When used, Final Switching Devices (FSDs) typically accomplish this when the safety outputs go to
the Off state.
The Safety Relay Outputs can be used as the Final Switching Device (FSD) and can be interfaced in either a Dual-Channel
or Single-Channel safety (protective) stop circuit (see
on p. 46). Refer to
on p. 12 before making connections and interfacing the Safety Controller to the machine.
The level of the safety circuit integrity must be determined by risk assessment; this level is dependent on the configuration,
proper installation of external circuitry, and the type and installation of the devices under control (FSDs and MPCEs). The
safety relay outputs are suitable for Category 4 PL e / SIL 3. See
on p. 45 for hookup examples.
Important:
The user is responsible for supplying overcurrent protection for all relay outputs.
Overvoltage Category II and III Installations (EN 50178 and IEC 60664-1)
The SCR P is rated for Overvoltage Category III when voltages of 1 V to 150 V ac/dc are applied to the output relay contacts.
They are rated for Overvoltage Category II when voltages of 151 V to 250 V ac/dc are applied to the output relay contacts and
no additional precautions are taken to attenuate possible overvoltage situations in the supply voltage. The SCR P can be
used in an Overvoltage Category III environment (with voltages of 151 V to 250 V ac/dc) if care is taken either to reduce the
level of electrical disturbances seen by the SCR P to Overvoltage Category II levels by installing surge suppressor devices
(for example, arc suppressors), or to install extra external insulation in order to isolate both the SCR P and the user from the
higher voltage levels of a Category III environment.
For Overvoltage Category III installations with applied voltages from 151 V to 250 V ac/dc applied to the output
contact(s):
the SCR P may be used under the conditions of a higher overvoltage category where appropriate overvoltage
reduction is provided. Appropriate methods include:
• An overvoltage protective device
• A transformer with isolated windings
• A distribution system with multiple branch circuits (capable of diverting energy of surges)
• A capacitance capable of absorbing energy of surges
• A resistance or similar damping device capable of dissipating the energy of surges
When switching inductive ac loads, it is good practice to protect the SCR P-2 outputs by installing appropriately-sized arc
suppressors. However, if arc suppressors are used, they must be installed across the load being switched (for example,
across the coils of external safety relays), and never across the SCR P-2 output contacts (see WARNING, Arc
Suppressors).
6.7.2 EDM and FSD Hookup
External Device Monitoring (EDM)
The Safety Controller’s safety outputs can control external relays, contactors, or other devices that have a set of normally
closed (N.C.), force-guided (mechanically linked) contacts that can be used for monitoring the state of the machine power
contacts. The monitoring contacts are normally closed (N.C.) when the device is turned Off. This capability allows the Safety
Controller to detect if the devices under load are responding to the safety output, or if the N.O. contacts are possibly
welded closed or stuck On.
The EDM function provides a method to monitor these types of faults and to ensure the functional integrity of a dual-
