Specifications

2–23 Selecting Your Hardware Components
Publication 1747-6.2
The recommendations given previously provide favorable operating
conditions for most controller installations. Your application may
involve one or more of the following adverse conditions. Additional
measures can be taken to minimize the effect of these conditions.
Class I, Division 2 Applications
Important: When installing peripheral devices (for example, push
buttons, lamps) into a hazardous environment, ensure
that they are Class I, Division 2 certified, or determined
to be safe for the environment.
Excessive Line Voltage Variations
The best solution for excessive line voltage variation is to correct
any feeder problems in your distribution system. Where this does
not solve the line variation problem, or in certain critical
applications, use a constant voltage transformer. If you require a
constant voltage transformer, connect it to the power supply and all
input devices connected to the SLC 500 controller.
Connect output devices on the same power line, but their connection
along the power line is normally made before the constant voltage
transformer. A constant voltage transformer must have a sufficient
power rating for its load.
Excessive Noise
When you operate the SLC 500 controller in a “noise polluted”
industrial environment, special consideration should be given to
possible electrical interference.
The following reduces the effect of electrical interference:
• SLC 500 controller design features
• proper mounting of controller within an enclosure
• proper equipment grounding
• proper routing of wiring
• proper suppression added to noise generating devices
Potential noise generators include inductive loads, such as relays,
solenoids, and motor starters when operated by “hard contacts” like
push buttons or selector switches. Suppression may be necessary
when such loads are connected as output devices or when connected
to the same supply line that powers the controller.
Lack of surge suppression on inductive loads may contribute to
processor faults and sporadic operation, RAM can be corrupted (lost)
and I/O modules may appear to be faulty or reset themselves.
For extremely noisy environments, use a memory module and
program it for auto loading on processor fault or power cycle for
quick recovery.
S
pecial
C
onsiderations