Products > Test Equipment
HP 3457A DMM reads 0.550 Ohm over value
Kleinstein:
The correct connection is B. Both A and C measure the resistance between the 2 inner contacts and thus not a proper 4 wire short.
bdunham7:
--- Quote from: Swake on February 06, 2023, 09:37:03 pm ---Sure test leads are not ideal. But these do not explain half an Ohm.
--- End quote ---
Probably not, but it's not out of the question. Anyway, a shorting link or short bare copper wire of decent size should answer the question. Give it time to settle.
Swake:
Allow me to disagree about position B.
The 'resistance' should be put between the 2-wire leads. De idea is to have those leads as close as possible to the 'resistance'. The 2 additional sense leads should be connected as close as possible to those leads.
Ideally all 4 leads have the same length. In this specific case as there are not really leads the 'resistance' is to be put vertically in the middle of the 4 posts and connected left and right, but since it is a single piece of rigid wire I can't see how to do this.
bdunham7:
--- Quote from: Swake on February 06, 2023, 09:57:38 pm ---Allow me to disagree about position B.
--- End quote ---
Nope, no disagreement allowed! :)
The point of a 4-wire short is not to measure its resistance, but to trick the meter into seeing absolute zero resistance, or as close to it as possible. The way the expensive OEM shorts work is sort of the opposite of your diagram 'D'--they directly connect the two source terminals with one conductor and the two sense terminals with another and then connect those two conductors together with a third, typically smaller, conductor right in the middle. So 'D' turned 90 degrees.
Your diagram 'B' will work well enough, but due to some specifics as to how these meters work, I would have the connecting loop part at the bottom rather than the top. In practice that probably makes very little difference.
Swake:
Ok, so I made the short as described in the calibration manual of the 3458A with 2.5mm² freshly stripped bent wire.
The DMM was kept switched on but untouched for the last 12 hours or so. Also waited 2 hours for the copper wire to come 'at temperature' before taking the measurements.
2-Wire mode reads 0.44432 Ohm
4-Wire mode reads 0.00022 Ohm
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version