13
MEASUREMENT OF THE DISTANCE
Measurement of the distance must be made after setting of VF or selecting of a cable from the
List.
Measurement of distance is always carried out between two cursors. For measurement of
the distance from the cable beginning to heterogeneity it is necessary to make a zero cursor
become an active. Above the zero cursor there should be a label. If there is no label, press
[
ОК
] - and label will appear above the zero cursor. Establish the cursor on the beginning of
a measuring pulse by the
◄►
keys. Then pressing the [
ОК
] key switch to the measuring
cursor and establish it on the beginning of the re
fl
ected pulse. Cursors should be established
on the pulse beginning, instead of on a maximum (top) of a pulse. For more exact positioning
of the cursors it is recommended to use the zoom.
LOCALIZATION OF PAIR MISBALANCING BY TDR
This method allows locating the place of symmetry failure of the cable pair. For this purpose
in the TDR measurements you should to use the measuring scheme of asymmetry attenuation
LBal. You can detect a balance failure and noise security failure. Disbalance of the cable pair
is lead to the loss of noise security. What fact can cause a symmetry breaking of the cable
pair? The protection elements and defective cross connections; defective splices and splitter;
insulation defects, split location Defective connections can cause an ohmic asymmetry of the
cable pair
Ra
. Insulation defects are accompany with the resistance decreasing with respect to
ground or neighbors wires
LQ
R
.
Measuring of the misbalancing cable pair location
For TDR with the symmetrical input and output.
The measuring pulse generator output is connected to the twisted pair with local defect. The
waves distributed along the symmetrical cable pair and have a small in
fl
uence to cable shield
and to another cable pair. The in
fl
uence is determined from
LBal
(Longitudinal balance).
For typical network the value of
LBal
does not exceed the level of -40 dB. On this value the
in
fl
uence (caused by own heterogeneity of the cable) is decreased and allow to increase the
limit value of detected defect in two orders by comparison with the similar way.
