28 Rockwell Automation Publication 2080-UM002K-EN-E - March 2019
Chapter 2 About Your Controller
Input States on Power Down
The power supply hold-up time as described above is generally longer than the
turn-on and turn-off times of the inputs. Because of this, the input state change
from “On” to “Off ” that occurs when power is removed may be recorded by the
processor before the power supply shuts down the system. Understanding this
concept is important. The user program should be written to take this effect
into account.
Other Types of Line Conditions
Occasionally the power source to the system can be temporarily interrupted. It is
also possible that the voltage level may drop substantially below the normal line
voltage range for a period of time. Both of these conditions are considered to be a
loss of power for the system.
Preventing Excessive Heat
For most applications, normal convective cooling keeps the controller within the
specified operating range. Ensure that the specified temperature range is
maintained. Proper spacing of components within an enclosure is usually
sufficient for heat dissipation.
In some applications, a substantial amount of heat is produced by other
equipment inside or outside the enclosure. In this case, place blower fans inside
the enclosure to assist in air circulation and to reduce “hot spots” near the
controller.
Additional cooling provisions might be necessary when high ambient
temperatures are encountered.
Do not bring in unfiltered outside air. Place the controller in an enclosure
to protect it from a corrosive atmosphere. Harmful contaminants or dirt
could cause improper operation or damage to components. In extreme
cases, you may need to use air conditioning to protect against heat build-
up within the enclosure.
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