Thanks for the URL link. Our understanding/knowledge of the measurement principle appears to be the same. I just needed a sanity check as I was sharing the concept with a peer. In the heat of battle I over looked to consult google. Thanks, Victor, -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Glidden, Kevin Sent: Wednesday, June 23, 2010 10:50 AM To: [log in to unmask] Subject: Re: [TN] Resistance measurement Nice simple description here: http://www.allaboutcircuits.com/vol_1/chpt_8/9.html -----Original Message----- From: Woolley, Mark D. (Mark) [mailto:[log in to unmask]] Sent: Wednesday, June 23, 2010 10:04 AM To: [log in to unmask] Subject: Re: [TN] Resistance measurement 4-wire is used as Robert Konder stated in low resistance mesaurements. If the system is nulled correctly the 4-wire measurements are usually slightly higher than DMM measurements, because the 2-wire DMM measurements also measures the resistance in the wires. In a 4-wire test, neglible current travels through the "sense" wires and there is no voltage drop across them. The "sense wires are usually buffered with a 10 Mohm series resistance (or higher in specialized meters) to prevent current flow in them. The DMMs used today normally use less than 1mA to make a resistance measurement rather than impressing a voltage on the3 resistance and measuring the current as the old analog meters did. However, it is important to realize that when measuring low resistances quantization errors during the conversion become very important, if the meter is not designed for low resistance measurements. Remember the accuracy of a DMM is always some percentage of full scale plus or minus one digit. So a reading of 0.32 ohms is not any different than a reading of 0.33 ohms, or 0.31 ohms on a 3 Ohm full scale reading. mark Mark Woolley |PTRL Laboratory | Avaya | 1300 West 120th Ave | Westminster, CO 80234 USA | -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Victor Hernandez Sent: Wednesday, June 23, 2010 6:52 AM To: [log in to unmask] Subject: [TN] Resistance measurement Fellow TechNetters: What is the difference between a 4 point measurement system and conventional DMM measurement? Should the readings be identical or within a tolerance? Depending on scale settings and tolerance of instrument. Measurement conducted on DIMM net on a populated board. Victor, ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. 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For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________ --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 -----------------------------------------------------