Cutler-Hammer D320 PLC, User Manual

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Chapter 4: Installation and Wiring
25
Power-Up Sequence
In a properly designed control system, the default Off state of the system is the safe state, in which no
machinery is operating. Before the PLC is powered-up, line power and control power are applied to the
system. Once the system is powered up in the safe/default state, the PLC is powered up and begins
system control. As necessary, the control system should be modified to ensure the proper delayed
startup to prevent problems on power-up.
For example: 1) Run the PLC after turning on the power
2) Use an external or internal timer to delay the operation of the PLC.
Momentary Power Failure and Voltage Drop
Momentary Power Failure
The D320 PLC will ride through momentary power failures of 10 msec or less. The PLC will stop and
turn off its outputs if a momentary power failure greater than 20 msec occurs. For momentary power
failures between 10 msec and 20 msec, the PLC's operation depends on circumstances at that time, and
is not defined. The control system should be designed specifically to ensure safe operation for these
potential power-loss conditions.
Voltage Drop (Brownouts)
The PLC will stop and turn off its outputs if the PLC 's power supply voltage drops below the
allowable fluctuating voltage range (see specifications for power supply units).
CAUTION:
Steps should be taken to prevent damage to the PLC system through fluctuating
voltages, brownouts, blackouts, shorts, ground faults, or other power supply
failures. For example, you may need to apply an isolation transformer before the
incoming PLC power supply and/or I/O control wiring.
System Installation Guidelines
Environmental Usage Conditions
Avoid the Following Environments:
•
Ambient temperature outside the range of 0 to 55
°
C (32 to 131
°
F).
•
Humidity levels outside the range of 30% to 85%.
• Abrupt temperature variations which lead to the formation of dew.
•
Presence of corrosive or flammable gases.
•
Presence of dense dust, salt, and iron concentrations.
•
Presence of corrosive solutions such as benzene, thinner, alcohol, ammonia and caustic soda.