User manual

Chapter 3 – Installation and Wiring
3–10 LT Series User Manual
3.2.5 Installation Cautions
A problem in the external power supply or an LT unit failure can lead to operation
failures.
Since these types of failures can affect the entire system, as a preventive measure,
be sure to set up a protection circuit (such as an Emergency Stop, Protection
Network, Interlock, or System Design Circuit) in areas where potential failures
may occur.
Examples of protection circuits that ensure the system’s reliability include the
following:
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 Failsafe Electrical Circuits
When designing failsafe circuits, be aware of possible malfunctions resulting from
differences in the startup times of the control device connected to LT output unit
(especially the DC power supply), the LT unit’s system, and the program. When
using a remote I/O, create a logic program to check the terminal status.
For example, connect an electrical voltage relay coil to the LT output unit power
supply circuit and to any connected control devices’ power circuit, then connect
their contacts to the LT input unit. Design the circuit so that it checks for an ON
signal from the electrical voltage relay using a logic program, then executes the
ladder program of the control device connected to the LT output unit.
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 Input Voltage
The power supply must be DC 24V (between DC 20.4V and DC 28.8V).