
Glossary
Cable Fault
A defect in a cable or other condition that makes a cable less able to deliver electrical energy than
was designed. Damage to the shield, conductor, or insulation, bad splices, and poorly mated
connectors are frequently encountered cable faults.
Capacitance
See Reactance.
Characteristic Impedance
The ratio of the amplitude of voltage and current in an electrical signal propagating in a cable. In a
coaxial cable, this value (usually written Z
0
) is, in large part, related to the geometrical relationship
of conductor to return path conductor. Cables are usually designed to match the impedance of the
source and load to which they are attached in order to maximize power transfer.
Conductor
A substance that allows electricity to flow through it with minimal resistance. Most conductors are
metals. However, there are many non-metallic conductors, including salt solutions, graphite, and
any element in its plasma state.
dB
dB is the abbreviation for decibel. Decibels are a method of expressing power or voltage ratios as
logarithms. When used for voltage ratios, as in TDR, the formula for decibels is
db
=
20
⋅
log
10
V
i
/
V
l
where V
i
is the voltage of the incident pulse and V
l
is the voltage reflected
back by the load. The dB vertical scale on the CT100 refers to the amount of voltage gain the
instrument applies to the signal before displaying it. For example, when the instrument is
amplifying the voltage by a factor of 100, this indicator would read
vertical scale
=
20
⋅
log
10
100
=
40
dB.
DC
Direct current is unidirectional flow of electrical current. The term DC is also synonymous with
constant; for example, a perfect DC voltage source does not vary from a set value. Batteries are
example of a DC voltage source.
Dielectric
A nonconducting substance or insulator. May also refer to the dielectric strength or relative
permittivity of a medium, which is a measure of the electrical energy stored by a medium when an
electrical potential of a given frequency is applied across it. Also see Insulation.
Digital
Refers to signals in which information is represented by variables that are discrete or
discontinuous both in time and in value. This is in contradistinction to an analog signal, which is
continuous both in time and value.
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Mohr CT100 / CT100HF Operator's Manual