The following method may be used in determining total I/O rack heat dissipation such as is the case when calculating what size air conditioning is required for a cabinet. Except for discrete I/O, it is not necessary to look up or determine individual module heat dissipations and then add them up. Since all the modules are being powered by the rack power supply, whatever power it is putting out is being converted to heat regardless of how many or what kind of modules are contained in the rack. All that is required is to use the maximum input power to whatever power supply is being used and then multiply by 3.413 to give the worst case heat dissipation in BTU's. Other cards such as discrete inputs and outputs will also dissipate some power from their user side connections that will vary depending on operating voltage and loading. Their user side power should be obtained from either calculations (p=ie) or their individual specifications and this figure can be added into the worst case power supply one. Just remember the equation (BTU's = power in watts * 3.413).
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