EMC Control in Main Frame Computing Systems

With today's ever increasing demand for faster, larger, and more reliable computing systems, the main frame computer -is much more commonplace than any other time in history. The mainframe computer as described in this paper is one that requires more than 60 cubic feet of floor space and above. The speeds of today's mainframe ( 7 2 0 MIPS) are consistently increasing the demands on impedance control, cable shielding, and compartment shielding. The days of 100 MHz bandwidths are over and the problem areas we are now dealing with are in the areas of 200 500 MHz. The theories and procedures followed for small systems (home computers) are not always going to work on some of the larger systems. The typical radiated bandwidth of a small computing system has dropped off significantly after 100 MHz while the mainframe's radiated bandwidth has just started to fall off. The mainframe looked at as_a~radiation source is much more concentrated, that is, it has much more radiated power available per unit/volume, typical input power to the mainframe computer is in the area of 6 1 2 KVA. If not controlled, the interference potential is staggering. The typical mainframe installation is another area of concern, visiting a typical computer site at a company which uses mainframe usually finds one in a virtual maze of computing systems and their associated peripheral equipment. it is not difficult to find these types of installations either. Typically, they have one floor full of mainframe computers with the floors above and below dedicated to the associated support equipment. We are talking about acres of potential RFI sources to any nearby susceptor. Now that the system has been defined, the EMCad analysis can begin. EMCad stands for Electromagnetic Compatibility Analysis and Design. It was developed by Chris Kendall of CK Consultants, Inc. and Franz Gisin of Rolm Corp. This software predicts the conducted and radiated emissions of any given system along with the susceptibility characteristics, including crosstalk analysis. Frame by frame each signal's contribution to the radiated and conducted profile of the system can be calculated. These levels are then plotted and the maximum emission envelope will be shown, From this emission envelope the required shielding and filtering can be calculated. Typical Mainframe Configuration