Rockwell Automation 1747-L40 SLC 500 Fixed Hardware Style - Manual (Page 138)

D
Appendix
D–1
Calculating Heat Dissipation for the SLC 500
Control System
This appendix will assist you in calculating the heat dissipation of your SLC
500 control system. It consists of the following:
•
definition of key terms
•
table and graphs
•
example heat dissipation calculation
•
heat dissipation worksheet (page D–5 )
To select an enclosure for your SLC 500 control system, refer to chapter 1.
The following terms are used throughout this appendix. Familiarize yourself
with them before proceeding further into the appendix.
Watts per point — maximum heat dissipation that can occur in each field
wiring point when energized.
Minimum watts — amount of heat dissipation that can occur when there is
no field power present.
Maximum watts — maximum amount of heat that the module generates
with field power present.
There are two ways that you can calculate heat dissipation.
Calculated Watts — if you want to determine the amount of heat generated
by the points energized on your module, use the formula below for
calculating the heat dissipation of each module. Then use these values for
calculating the heat dissipation of your control system, which is done using
the worksheet.
(number of points energized x watts per point) + minimum watts = heat dissipation of module or controller
Maximum Watts — maximum amount of heat that the module generates
with field power present. Use maximum watts especially if you are not sure
how many points on a module will be energized at any time.
Once you have determined which way you will calculate the heat dissipation
of your modules, see the Example Worksheet for Calculating Heat
Dissipation on page
D–4 . This worksheet shows you how to calculate the
heat dissipation for the example SLC control system also on page D–4 .
Once you feel comfortable with the layout of the worksheet, go to the
worksheet on page
D–5 and fill it out for your control system.
Definition of Key Terms
Module Heat Dissipation:
Calculated Watts vs. Maximum
Watts