Fail-Safe Circuits - Omron CS1D DUPLEX SYSTEM - 10-2009 Operation Manual

Fail-safe Circuits

5-1

Fail-safe Circuits

Order of Supplying Power
Managing PLC Errors
Managing Output Malfunctions
Emergency Stop Circuit
150
Be sure to set up safety circuits outside of the PLC to prevent dangerous con-
ditions in the event of errors in the PLC or external power supply.
If the PLC's power supply is turned ON after the controlled system's power
supply, outputs in Units such as DC Output Units may malfunction momen-
tarily. To prevent any malfunction, add an external circuit that prevents the
power supply to the controlled system from going ON before the power supply
to the PLC itself.
With a Single CPU System or a Duplex CPU System in Simplex Mode, PLC
operation will stop and all outputs from Output Units will be turned OFF when
any of the following errors occurs.
• Operation of the Power Supply Unit's overcurrent protection circuit
• A CPU error (watchdog timer error) or CPU on standby
• Any of the following fatal errors: Memory error, I/O bus error, duplicate
number error, fatal Inner Board error, too many I/O points error, I/O setting
error, program error, cycle time overrun error, or FALS(007) error
With a Duplex CPU System in Duplex Mode, PLC operation will stop and all
outputs from Output Units will be turned OFF when any of the following errors
occurs in the active CPU Unit.
• CPU on standby
• Any of the following fatal errors: I/O bus error, duplicate number error, too
many I/O points error, or I/O setting error.
Be sure to add any circuits necessary outside of the PLC to ensure the safety
of the system in the event of an error that stops PLC operation.
Note When a fatal error occurs, all outputs from Output Units will be turned OFF
even if the IOM Hold Bit has been turned ON to protect the contents of I/O
memory. (When the IOM Hold Bit is ON, the outputs will retain their previous
status after the PLC has been switched from RUN/MONITOR mode to PRO-
GRAM mode.)
It is possible for an output to remain ON due to a malfunction in the internal
circuitry of the Output Unit, such as a relay or transistor malfunction. Be sure
to add any circuits necessary outside of the PLC to ensure the safety of the
system in the event that an output fails to go OFF.
The following emergency stop circuit controls the power supply to the con-
trolled system so that power is supplied to the controlled system only when
the PLC is operating and the RUN output is ON.
An external relay (CR1) is connected to the RUN output from the Power Sup-
ply Unit as shown in the following diagram.
Section 5-1