Vop Variations; Maximum Length; Frequently Asked Questions - Fluke Networks TS100 Mode D'emploi

TS100 Cable Fault Finder
Users Guide

VOP Variations

This characteristic speed of the signal for a particular
cable is not normally a tightly controlled part of the
cable manufacturing process and can vary widely from
one manufacturer to another as well as from one box
of cable to the next. As with all TDR-based cable
measurement tools, the TS100 measures TIME within
specified tolerances, but the displayed LENGTH is the
result of the calculation with the user-selected VOP and
is only as accurate as that selected VOP.
For most uses, a length reading with an incorrectly set
VOP is sufficiently accurate to locate the fault in the
cable. After all, an installed cable is hardly ever run in a
straight line. It can be stapled along the 2x4, laid
diagonally in the ceiling, and coiled behind the
junction box, all of which is not visible.
Also, common sense should prevail. For example, if the
tester reports an open at 80 feet (25 meters), and you
can see a junction box at about 70 feet (20 meters),
your first step should be to check at the junction box.
However, for some uses such as measuring the
remaining cable in a box, it is important to set the VOP
correctly in order to achieve the accuracy desired.
Depending on the cable construction (shielded,
twisted, etc.), insulating material (foam, air, fiber, etc.),
and conductors tested (wire-to-wire, wire-to-shield),
coiling the cable on a spool or in a box may alter its
VOP.
Additionally, other conductors in close proximity to the
conductors being tested can affect the VOP. For
example, a solitary 12 gauge THHN in a metal conduit
has a VOP of 82, while that same wire in a smaller
conduit filled with other wires has a VOP of 72.
The actual VOP of any particular cable is
dependent on the conductor spacing and the
material between the conductors and could
vary by as much as ±5 feet (±2 meters) from the
value listed in Table 2.
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Note
To set the VOP for more accurate length
measurements, see "Velocity of Propagation" on page
6. See Table 2 and Table 3 for the VOP values for many
cable types and conditions.

Maximum Length

The maximum length of cable that can correctly be
measured by the TS100 is determined by several
factors. The most significant is the signal loss of the
cable itself. When the signal loss in a particular cable is
large enough, the tester cannot "hear" the TDR echo
and cannot determine the length of that cable. In this
situation, the tester displays "Err" on the display. The
amount of signal loss in a cable is determined by the
characteristics of that cable and its length. The
maximum length shown in Table 2 is the length above
which the tester is not expected to be able to make a
valid measurement. For lengths above those stated in
Table 2, the tester's accuracy is not specified.

Frequently Asked Questions

Q: How do I calibrate or perform a self test on the
tester?
A: There are no adjustments inside the tester, and the
internal coating protects the critical components from
moisture and contaminants. There is nothing to
calibrate. A self test is performed by the tester every
time you turn it on. Since there is no loss of any settings
when the tester is off, there is no penalty to just
turning it off and on if you wish to perform a self test.
The tester displays 8.8.8.8. during the self test.
Q: Does it matter which clip lead I connect to which
wire in the cable under test?