Multimeter Tests
126 MAX-635G
Resistance
Resistance
The Resistance test, also known as shorts, allows you to measure the
resistance values in ohms, of the wire pair under test. Use this test to
identify shorts and grounds when the far end is open, comparing the ohms
reading of each lead combination. You want high-ohm values between the
leads when measuring to an open, the higher the better. But if a reading is
very low, such as 200 k
Ω T-G/A-E, we know there is a ground fault present.
It is also valuable to apply a short across T/A-R/B at the far end, and then
measure the round trip loop resistance, in which case you will see that low
values with the far-end short are applied ( 2500
Ω, depending on loop
length and condition). It is even more valuable to run the resistance
balance test when the far end is shorted above, as the test will calculate
the resistance in ohms of each side/leg of the pair, so you may see the
difference, in effect the balance. Significant differences indicate one-sided
faults or series resistance and/or high resistive partial opens. Typical values
for POTS circuits are 1 to 3.5 M
Ω across each lead combination, whereas
pairs for broadband DSL should be at least 5 M
Ω; and for higher speed
broadband circuits, > 20 M
Ω is recommended.
Resistance values are valuable when the far end is shorted and grounded
(all leads). We can get an accurate ohms value for each lead/leg
independent of the other and compare them (resistance balance), looking
for a different ohms value on one side versus the other, indicating series or
one-sided faults/imbalances sometimes also called partial dirty or high
resistive opens. These can be difficult to locate, as they are not clearly a
ground fault, but RFL would be the primary way to locate a one-sided
series fault. In some cases, a TDR may reflect off of such a fault but then
again, may not. Try TDR first, but be prepared to try RFL if you really need
this pair in service for a high-speed broadband.
To select either TDR or RFL tests:
1. Press
to return to the Copper Main menu.
2. Highlight TDR or RFL and press
to launch the test.
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