Rockwell Automation 1763 MicroLogix 1100 Programmable Controllers User Manual - Manual (Page 27)

Publication 1763-UM001D-EN-P - March 2011
Installing Your Controller 25
This is referred to as a power supply shutdown. The processor then performs
an orderly shutdown of the 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.
TIP
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.