A peripheral port termination for EMI tests

While conducting EMI tests on equipment containing output ports, it is required that the output ports are loaded at the time of carrying out the tests. For EMI tests on PCs the peripheral ports require to be loaded with the appropriate peripheral. The printer port of the PC requires to be loaded with a printer. Since the Centronics port has been standardized for PCs equipped with a parallel port for a printer, it is necessary to load this port with a Centronics printer. When a printer is connected to the port during the conduct of the EMI test, it is difficult to differentiate the EMI generated by the PC, from that generated by the printer. Consequently it is not possible to quantify the EMI generated by the PC without recourse to software routines. It therefore becomes necessary to terminate the ports without additional EMI being generated. This paper describes the design of a termination for the Centronics port which will reduce the possibility of improper interpretation of the measurements obtained through EMI tests on PCs. This technique also helps to obtain repeatable results while testing PCs for EMI.