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,
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