7. EMI/RFI/HEAT DISSIPATING ENCLOSURE FOR NEMA 12 COMPUTER

A. Problem/Issue

A Multi-National Data Acquisition Products Company were developing a hardened data acquisition computer for a major automaker. The computer needed to be NEMA 12 compliant and at the same time dissipate the heat that was generated by the CPU and other components. This had to be accomplished without the introduction of cooling air into the chassis. A further concern was the total weight of the unit. Using an off-the-shelf extruded heatsink proved to be prohibitively heavy and costly.

B. Analysis

We used thermal modeling software to predict the heat conduction through various chassis sizes using a range of BTU values. The model showed that the CPU/motherboard combination needed to consume less power. Also the motherboard had to chosen so there was access to the CPU using heat pipes. The heatsink had to be re-designed to be lighter and less costly.

C. Solution/Results

They located two other motherboard options and we picked one we could work with. We selected an oversize heat pipe and coupled it to both the CPU and heatsink back plate of the computer using copper hardware and gap pads. We redesigned the heatsink using extruded channels and spot welded it to the back in a pattern that would allow adequate heat conduction and airflow past the cooling fins. Subsequent heat chamber testing showed the new design kept below the component threshold in the range of ambient conditions. The product is in the fourth year of production and is a major contributor to the company's sales volume.