Glossary
Glossary–41502C MTDR User Manual
means that each division is 0.5 rho (500 millirho). A pulse set to be four
divisions high would make each division 0.25 rho (250 millirho).
Noise
Any unwanted electrical energy that interferes with a signal or measurement.
Most noise is random with respect to the signals sent by the TDR to make a
measurement and will appear on the waveform, constantly constantly
moving up and down on the display. The NOISE FILTER control sets how
many waveforms will be averaged together to make the waveform displayed.
Noisy waveforms appear to fluctuate around the real signal. Because it is
random, noise will sometimes add to the real signal and sometimes subtract
energy from the real signal. By adding several noisy waveforms together, the
noise can be “averaged” out of the signal because the average amount of
noise adding to the signal will be nearly the same as the average amount of
noise subtracting from the signal. More waveforms in an average are more
likely to approach the real signal (although it takes longer to acquire and add
together more waveforms).
Open Circuit
In a cable, a broken conductor will not allow electrical energy to flow
through it. These circuits are also called broken circuits. The circuit is open
to the air (which looks like a very high impedance).
Precision
The statistical spread or variation in a value repeatedly measured, generated,
or displayed under constant conditions. Also called repeatability.
Reactance
A conductor’s opposition to the flow of AC electrical energy through it. All
conductors have some reactance. Reactance is made up of capacitance and
inductance. Capacitance is the ability of conductors separated by thin layers
if insulation (dielectric) to store energy between them. Inductance is the
ability of a conductor to produce induced voltage when the electrical current
through it varies. All conductors have some capacitance and inductance, so
all conductors have some reactance, which means they all have impedance.
Reflectometer
An instrument that uses reflections to make measurements. Our reflectome-
ters use electrical energy that is reflected back from points along a cable.
Resistance
A conductor’s opposition to the flow of DC electrical energy through it. All
conductors have a certain amount of resistance. Resistance is the low (or
zero) frequency part of impedance.
Resolution
For a given parameter, the smallest increment or change in value that can be
measured, generated, or displayed.