Rockwell Automation 1764-xxxx MICROLOGIX 1500 PROGRAMMABLE CONTROLLERS - Manual (Page 66)

Publication 1764-UM001B-EN-P - April 2002
3-16 Wiring Your Controller
Controller I/O Wiring Minimizing Electrical Noise
Because of the variety of applications and environments where
controllers are installed and operating, it is impossible to ensure that
all environmental noise will be removed by input filters. To help
reduce the effects of environmental noise, install the MicroLogix 1500
system in a properly rated (i.e. NEMA) enclosure. Make sure that the
MicroLogix 1500 system is properly grounded.
A system may malfunction may occur due to a change in the
operating environment after a period of time. We recommend
periodically checking system operation, particularly when new
machinery or other noise sources are installed near the Micrologix
1500 system.
Transistor Output Transient Pulses
The transient energy is dissipated in the load, and the pulse duration
is longer for loads with high impedance. The graph below illustrates
the relation between pulse duration and load current. Power-up
transients will not exceed the times shown in the graph. For most
applications the pulse energy is not sufficient to energize the load.
To reduce the possibility of inadvertent operation of devices
connected to transistor outputs, consider adding an external resistor in
parallel to the load to increase the on-state load current. The duration
of the transient pulse is reduced when the on-state load current is
increased or the load impedance is decreased.
ATTENTION
!
A brief transient current pulse may flow through
transistor outputs if the external supply voltage is
suddenly applied at the V dc and V dc com terminals
(e.g. via the master control relay). It is a fast
rate-of-change of voltage at the terminals that causes
the pulse. This condition is inherent in transistor
outputs and is common to solid state devices. The
transient pulses may occur regardless of whether the
controller is powered or running.