Rockwell Automation 1761-HHP-B30 MicroLogix 1000 with Hand-Held Programmer (HHP) - Manual (Page 27)

Chapter 1
Installing Your Controller
1–11
Power Supply Inrush
The MicroLogix power supply does not require or need a high inrush current.
However, if the power source can supply a high inrush current, the
MicroLogix power supply will accept it. There is a high level of inrush
current when a large capacitor on the input of the MicroLogix is charged up
quickly.
If the power source cannot supply high inrush current, the only effect is that
the MicroLogix input capacitor charges up more slowly. The following
considerations determine whether the power source needs to supply a high
inrush current:
•
power-up sequence of devices in system
•
power source sag if it cannot source inrush current
•
the effect of the voltage sag on other equipment
If the power source cannot provide high inrush current when the entire
system in an application is powered, the MicroLogix powers-up more slowly.
If part of an application’s system is already powered and operating when the
MicroLogix is powered, the source voltage may sag while the MicroLogix
input capacitor is charging. A power source voltage sag can affect other
equipment connected to the same power source. For example, a voltage sag
may reset a computer connected to the same power source.
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 20 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.
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.
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.