Omron NX1P2 Series Hardware User Manual page 153

Order of Powering On and Off the Controller and Controlled Sys-
tem
Outputs from Units, such as DC Output Units, may malfunction momentarily when the Unit power sup-
ply is turned ON. This may cause problems in the system if the Unit power supply is turned ON after
the I/O power supply (i.e. controlled system's power supply) is turned ON. To prevent possible mal-
functions, configure an external circuit that prevents the power supply to the controlled system from
turning ON before the power supply to the Controller itself.
Also, the external circuit must be configured so that the Unit power supply turns OFF only after the
power supply to the controlled system has turned OFF.
Precautions for Safe Use
It takes approximately 20 seconds to enter RUN mode after the power supply is turned ON.
During that time, digital outputs on the CPU Rack will be OFF. The slave outputs behave ac-
cording to the setting values. Use the system-defined variables and the NX Unit device varia-
bles in the user program to confirm that I/O data communications are established before at-
tempting control operations. External communications are also not performed during startup.
Order of Powering Off the Controller and Controlled System
If you turn OFF the Unit power supply before turning OFF the I/O power supply, which is supplied to
the control system, the output terminals on the DC Output Unit or other Units may malfunction and the
control system may be temporarily unable to perform normal output operation. In order to prevent such
errors, the external circuits should be configured to turn OFF the Unit power supply after the power
supply to the control system is turned OFF.
Failure of the Built-in Output or Output Section of the Output Unit
It is possible for an output to remain ON due to a malfunction in the internal circuit of the built-in output
or output section of the Output Unit, such as a relay or transistor malfunction. Be sure to add any cir-
cuits necessary outside of the Controller to ensure the safety of the system in the event that an output
section fails to go OFF.
Interlock Circuits
When the Controller controls an operation such as the clockwise and counterclockwise operation of a
motor, provide an external interlock such as the one shown in the following example to prevent both
the forward and reverse outputs from turning ON at the same time if required by the application.
Example:
ON_MC1
Controller
ON_MC2
NX-series NX1P2 CPU Unit Hardware User's Manual (W578)
Interlock circuit
MC2
MC1
Motor clockwise
MC1
Motor counterclockwise
MC2
5 Installation and Wiring
5
5-9