Allen-Bradley micrologix 1500, Руководство пользователя

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Publication 1764-UM001A-US-P
2-6 Installing Your Controller
Loss of Power Source
The 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 the type and state of the I/O, but is typically
between 10 milliseconds and 3 seconds. When the duration of power loss reaches
this limit, the power supply signals the processor that it can no longer provide
adequate dc power to the system. 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.
NOTE
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.