Specifications

Appendix F
Publication 1747-6.2
Calculating Heat Dissipation
for the SLC 500 Control
System
This appendix will assist you in calculating the heat dissipation of
your SLC 500 Controller. It consists of the following:
• definition of key terms
• table and graphs
• example heat dissipation calculation
• heat dissipation worksheet (page F–8)
To select an enclosure, see page 2–15.
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.
Total watts — the watts per point plus the minumum watts (with all
points energized).
There are two ways to determine the module heat dissipation. You
can use the Total Watts value from the table on page F–2 or you can
calculate the value.
Total Watts — maximum amount of heat the module generates with
field power present (with all points energized). Use this especially if
you are not sure how many points will be energized at any time.
Calculated Watts — if you want to determine the amount of heat
generated by the points energized on your module, use the formula
below. Then use these values for calculating the power supply
loading for each chassis — this is done using the worksheet.
Module Heat Dissipation =
(number of points energized x watts per point) + minimum watts
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 F–7. This worksheet shows
you how to calculate the heat dissipation for the example SLC
control system on page F–6. Once you feel comfortable with the
layout of the worksheet, go to the worksheet on page F–8 and fill it
out for your control system.
Definition of Key Terms
Module Heat Dissipation:
Total Watts Vs. Calculated
Watts