Hi Ed, Yes, I agree. The way you suggested is an ideal method to get Ambient noise in the Conducted emission test. Please allow me to make two more points about impedance vs. frequency:
(1) It is inconvenient in practice to find "a resistive load sized to draw the same amount of power." We have to make the equivalent load first, connect it to a power cord, and then plug the power cord into EUT port of the LISN. If we consider the equivalent load should be not only at 60 Hz, also "equivalent" on 150 KHz - 30 MHz to the EUT, it would become much more troublesome. As a matter of fact, the frequency range of 150 KHz - 30 MHz is of our interest. (2) From the standpoint of spectrum analyzer, does it make lot of difference between using open circuit and equivalent load on EUT port of the LISN to detect the Ambient noise on 150 KHz - 30 MHz? Please correct me. Best Regards, Barry Ma ------------- Original Text From: <[email protected]>, on 10/7/98 9:34 AM: ------------------------ From: Bailin Ma <[email protected]> Subject: RE: Grounding of screen room Date: Tue, 6 Oct 98 14:35:43 PDT To: [email protected], TREG <[email protected]> Cc: Mekonen Buzuayene <[email protected]> > Hi Lauren, > > It is my understanding that properly grounding the screen room is important > in Conducted emission test and have little effect on Radiated emission > test. The way you described is a very good and simple method for evaluating > the shielding effectiveness (SE) of the screen room. The SE, however, is > not critical in Conducted emission test. > > A simple way, similar to what you described, to evaluate the background > noise of Conducted emission test is turning off the power of DUT when you > get ready to run the test to see if you can 'hear' anything on the > spectrum analyzer. > > Please correct me. Pardon, Barry, but I think I will. You should measure the Ambient conducted emission level by loading the LISN's with a resistive load sized to draw the same amount of power as your typical test specimen. This loads the external power source (some sites may be using their own generator or electronic power converter), allows the shielded enclosure powerline filter to work into a load impedance more normal than an open circuit, and validates the performance of the powerline filter and the LISN's (cheap or damaged filter inductors will degrade or even create noise). Regards, Ed -------------------------- Ed Price [email protected] Electromagnetic Compatibility Lab Cubic Defense Systems San Diego, CA. USA 619-505-2780 List-Post: [email protected] Date: 10/07/1998 Time: 08:34:44 -------------------------- o --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators).
