32 Rockwell Automation Publication 2080-UM002L-EN-E - November 2021
Chapter 2 About Your Controller
• The effect of voltage sag on other equipment in the system.
If the entire system is powered-up at the same time, a brief sag in the power
source voltage typically will not affect any equipment.
Loss of Power Source
The optional Micro800 AC power supply is designed to withstand brief power
losses without affecting the operation of the system. The time the system is
operational during power loss is called program scan hold-up time after loss of
power. The duration of the power supply hold-up time depends on power
consumption of controller system, but is typically between 10 milliseconds and
3 seconds.
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 sp
ecified 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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