Rockwell Automation 1772-LV,D17726.6.1 A and I MNL MINI-PLC-2/15 PROCESSO - Manual (Page 22)

Assembly and Installation
Chapter 3
3Ć2
EXCESSIVE HEAT
For most applications, normal convection cooling keeps Controller components
within the 0
0 to 60 0 C ambient operating range. Thus, the proper spacing of
components within the enclosure is usually sufficient for heat dissipation.
There are however, some applications where a substantial amount of heat is
generated by equipment either inside or outside the enclosure. In these cases,
blower fans may be placed inside the enclosure to assist air circulation and to
reduce “hot spots” near the Controller.
CAUTION: Do not bring outside air into the enclosure; it may
introduce harmful contaminants or dirt.
ELECTRICAL NOISE
When the Mini-PLC-2/15 Controller is operating in a “noise-polluted”
industrial environment, special consideration should be given to possible
electrical noise interference. potential noise generators include inductive loads
such as relays, solenoids, motors and motor starters when they are operated by
“hard contacts,” such as pushbuttons and selector switches. in the case of
reversing motor starters, hard contacts are wired to make each starter
electrically as well as mechanically interlocked. In this case, suppression is
needed at the device because of the hard contacts in the circuit with the load.
Suppression for noise generators may be necessary when these types of loads
are connected as output devices of when connected along the same AC line
which brings in power to the Mini-PLC-2/15 Controller.
A suggested electrical noise suppression unit for small AC devices (i.e, relays,
solenoids, and starters up to NEMA Size 1) is shown in Figure 3.1. For larger
contractors of NEMA Size 2 and above, a parallel varistor for transient voltage
limitation is needed in addition to the RC network shown in Figure 3.2 and
Figure 3.3. DC relays are suppressed by freewheeling diodes as shown in
Figure 3.4.