Rockwell Automation 2080-LC50 Micro830 and Micro850 Programmable Controllers User Manual - Manual (Page 30)

16 Rockwell Automation Publication 2080-UM002F-EN-E - December 2013
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.
Master Control Relay A hard-wired master control relay (MCR) provides a reliable means for
emergency machine shutdown. Since the master control relay allows the
placement of several emergency-stop switches in different locations, its
installation is important from a safety standpoint. Overtravel limit switches or
mushroom-head push buttons are wired in series so that when any of them opens,
the master control relay is de-energized. This removes power to input and output
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.