POTS Testing and Fault Location
The POTS Toolbox
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4-17
CPE Correction
If a bad Ground connection, open sheath, or far-end CPE termination is
present, the tester will measure a 3T Capacitance Ratio that is much lower than
normal. As a result, the 990 will display
Open Ground or CPE on the results
screen and will also provide a
CPE Correction softkey C. If a bad ground
connection or open sheath is not suspected, press the CPE Correction softkey.
The unit will then display corrected distances, subtracting CPE effects.
Adjusted Opens Test
A cable manufacturer’s data can vary by as much as 7% among cables.
Therefore, for greater accuracy, it is strongly recommended that you first
perform an Opens test on a known good pair in the cable. This data can then be
saved as a Custom Cable Type for further use on faulted pairs in the same
cable. Alternatively, if the length of a good pair is known by another more
accurate means, you can enter that length and store the data as a Custom Cable
Type. This is called an Adjusted Opens measurement.
Figure 4-8 shows the results from a balanced pair being used to create a
Custom Cable Type for future usage on other pairs in the same cable
To run an Adjusted Opens test, do the following:
1. Run an Opens Test on a good, balanced pair in the cable.
2. Press A(
Adjusted Opens).
A screen like the one in Figure 4-8 is displayed:
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