I attach my responses at the end of Mr. Lacey's, in CAPS. I disagree with Mr. Lacey on some details.
---------- >From: "Scott Lacey" <[email protected]> >To: "Muriel Bittencourt de Liz" <[email protected]> >Cc: <[email protected]> >Subject: RE: doubt on conducted emissions >Date: Thu, Aug 3, 2000, 6:49 PM > > > Muriel, > See answers below. > > Scott Lacey > > -----Original Message----- > From: [email protected] [mailto:[email protected]]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. ANSWER FROM KJJ: IT IS HIGHLY UNLIKELY THAT ANYTHING OTHER THAN A TUNED RADIO RECEIVER COULD BE SUSCEPTIBLE TO 31.6 mV SUPERIMPOSED ON OVER 200 VAC. I SAY 200 VAC, BECAUSE IN THE USA WHERE WE HAVE 120 VAC POWER, WE HAVE NO CE LIMITS BELOW 450 kHz SINCE WE DO NOT HAVE LW RADIO BROADCAST SERVICE. I SAY THAT YOU WOULD HAVE TO INTENTIONALLY DESIGN EQUIPMENT TO SENSE 31.6 mV SUPERIMPOSED ON THE AC LINE. I WOULD NOT WORRY ABOUT COUPLING EITHER, AT 200 kHz, COUPLING IS INEFFICIENT, AND ANYTHING SENSOTIVE TO MILLIVOLT POTENTIALS SHOULD BE SHIELDED ANYWAY. > > # 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). KJJ: AGREE. > > # 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. KJJ: AS ABOVE, 31.6 mV ONLY AFFECTS A TUNED RADIO RECEIVER. ANY OTHER NON-ANTENNA CONNECTED ELECTRONICS WOULD BE TOTALLY IMMUNE TO SUCH A DISTURBANCE. > > # 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. KJJ: IF A POWER SUPPLY PROVIDED ONLY 40 dB OF ISOLATION AT 200 kHz (note that it provides 80 dB or better at the power frequency) THEN YOU WOULD HAVE 316 uV ON THE Vcc INPUT TO ICs. THE ICs THEMSELVES PROVIDE REJECTION OF NOISE AT Vcc INPUTS. THERE WILL BE NO PROBLEM FOR SENSITIVE ANALOG INSTRUMENTS, AND ESPECIALLY NO PROBLEM FOR DIGITAL CIRCUITS. IN THE USA, THERE EXISTS A REPORT FROM THE NOW DEFUNCT COMPUTER AND BUSINESS EQUIPMENT MANUFACTURERS ASSOCIATION EMC GROUP WHICH EXPLAINS HOW THE CE/RE LIMITS WERE DERIVED (BY CBEMA). THERE IS NO MENTION OF ANY OTHER VICTIM BESIDES BROADCAST RECEIVERS, RADIO AND TV. > > Thanks in advance for the answers KJJ: YOU ARE WELCOME. > > 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: > [email protected] > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Jim Bacher: [email protected] > Michael Garretson: [email protected] > > For policy questions, send mail to: > Richard Nute: [email protected] > > > > ------------------------------------------- > This message is from the IEEE EMC Society Product Safety > Technical Committee emc-pstc discussion list. > > To cancel your subscription, send mail to: > [email protected] > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Jim Bacher: [email protected] > Michael Garretson: [email protected] > > For policy questions, send mail to: > Richard Nute: [email protected] > > ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: [email protected] Michael Garretson: [email protected] For policy questions, send mail to: Richard Nute: [email protected]
