Muriel, See answers below. Scott Lacey
-----Original Message----- From: owner-emc-p...@ieee.org [mailto:owner-emc-p...@ieee.org]On Behalf Of Muriel Bittencourt de Liz Sent: Thursday, August 03, 2000 5:46 PM To: Lista de EMC da IEEE Subject: doubt on conducted emissions Hello Group, I have some doubts concerning conducted emissions: 1. I'll make a hypothetical case: Let's say I have 2 electronic equipment (they can be switched mode power supplies). Equipment A requires 100W. Equipment B requires 3W. Let's say that my readings of conducted emissions, collected in a receiver, are: [EMI of equipment A at f=200kHz]=90 dBuV [EMI of equipment B at f=200kHz]=90 dBuV Making some calculations, I evaluate the interference voltage relative to 90dBuV ==> EMI in volts= 31.6mV Here begin my questions: # This 31.6mV is a voltage that propagates on the mains wires. I understand that the purpose of the EMC regulations (in the frequency range of 150kHz-30MHz) is to prevent that this voltage interfere with a radio receiver equipment or other electronic equipment. How long this voltage propagates in the mains wires (until which distance it is significant)?? A: Anything on the same branch circuit might be affected. The wire may also act as an antenna and radiate the interference. It may also couple to other circuits that run near it. # Is there any difference between the 90dBuV that equipment A (100W) generates to the 90dBuV that equipment B (3W) generates (Qualitative and quantitative)?? A: No. Both are 90 dB relative to 1 uV. The interference, in this case 200 kHz, is mostly a result of circuit layout inefficiencies. The voltage rise time (dv/dt) of the switching element is what generates the interference. Regardless of power ratings, most switch-mode supplies operate at a nominal primary voltage of either 150Vdc (110-120Vac in), or 300Vdc (230-240Vac in or 110-120Vac doubler). # This 31.6mV has a perturbing effect to the equipment A?? And to equipment B?? A: This interference may have a perturbing effect to any equipment that is sensitive at that frequency or one of its harmonics. # Concluding: This voltage is perturbing only for radio receivers?? Is this the goal of the regulations imposed by the agencies (CISPR, FCC, etc.)??? A: This voltage may also affect sensitive analog instruments (causes shifts of reading), may cause false clocking of digital circuits, and so forth. The agencies attempt to address this issue in two ways. First, they set limits for conducted and radiated emissions. Second, they (EC, etc.) require RF immunity testing so that a piece of equipment will not be adversely affected. Thanks in advance for the answers Regards Muriel Bittencourt de Liz Group for Conception and Analysis of Electromagnetic Devices GRUCAD/EEL/UFSC Florianópolis, SC Brazil ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson: pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson: pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org
