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February 4, 2020 - Vista, California - Axiom Test Equipment, an electronic test equipment rentals and
sales company headquartered in North County San Diego, has published a blog post
entitled "Finding Faults with TDR Test Instruments." It is about selecting and
using time-domain reflectometers (TDRs). This in-depth blog post goes over how
TDRs work, which types of test equipment can be used to make TDR measurements,
and what performance parameters should be compared when selecting a TDR for your
particular test requirements and test environment.
"Time-domain reflectometers (TDRs)
are easy-to-use test instruments usually associated with finding faults in cables
and antennas. How they work is simple: send a pulse with fast rise time into a cable
under test and measure reflected signals that take place where the characteristic
impedance (usually 50 Ω) deviates from the nominal value, usually because of
a break or disturbance in the line. This approach to finding a fault can also be
applied to fiber-optic cables using an optical pulse. Comparisons of the transmitted
and reflected signals can provide information about the length of the line, the
loss of the line, and the locations of discontinuities and breaks in the line. TDRs
have been compared to radar systems, which transmit pulses and measure reflections
from illuminated targets.
TDRs find changes in impedance through a transmission line, cable, or antenna
by analyzing changes in voltage with time due to reflections. This contrasts with
frequency-domain reflectometers (FDRs), which typically send swept-frequency signals
into a transmission line and study how the signals are affected due to reflections
at impedance junctions. TDRs can make measurements such as distance-to-fault tests
with access to only one port, such as a cable connector. FDR-based measurements
find faults using scattering parameters (S-parameters) to measure forward and reflected
voltages, but they require access to at least two (input and output) ports of a
cable under test.
TDR measurements can be made with a pulse
or step generator, an oscilloscope, and test software running on a computer, but
it is typically more convenient to perform TDR measurements on a single instrument
devoted to the task. Such dedicated TDRs are available in rack-mountable benchtop
style or as portable, battery-powered units perfect for in-field testing. They are
available for measurements on metal cables and optical cables and, with built-in
computer power and memory, can be set up automatically for measurements on metal
cables with specific impedances and dielectric types or optical cables at different
wavelengths. When armed with suitable performance levels, a TDR can handle a wide
range of applications, from finding faults in runs of coaxial cable to isolating
impedance mismatches in printed circuit boards (PCBs).
What performance parameters should be compared when considering a TDR? The most
fundamental consideration is the type of system or component to be tested, since
TDRs are available for testing metal cables and transmission lines, as metal TDRs
(MTDRs), as well as for optical cables, as optical TDRs (OTDRs). Each type is designed
for a specific test environment—MTDRs for a characteristic impedance, such as 50
or 75 Ω, and OTDRs for a wavelength. Adapters are often available for an MTDR, for
example, to equip an instrument set up for testing 50-Ω devices to make measurements
at 75 Ω, as in cable-television (CATV) systems..."
If you would like help selecting any type of test equipment for your project,
contact Axiom Test Equipment's sales department at
call 760-806-6600, or browse Axiom Test Equipment's inventory online at
About Axiom Test Equipment
Get Exactly What You Need. Rent - Buy
- Repair - Trade-In
Established in 2005, Axiom Test Equipment strives to continually improve itself
and offer the best value for its customers. We offer our customers several practical,
efficient and cost effective solutions for their business or projects' test equipment
needs. Whether you need to
buy test equipment, repair test equipment, sell or trade equipment, we are committed
to providing superior customer service and high quality electronic test equipment.
At Axiom Test Equipment we provide several services. We
test and measurement equipment. We also sell test equipment. If you have a piece
of malfunctioning or broken test equipment we also have an in-house repair lab.
For anyone seeking a way to offload their surplus or obsolete equipment, we offer
a trade-in program or we can buy the equipment from you.
We stock a comprehensive inventory of equipment and can use our extensive network
to find you those hard to get items. We believe in getting equipment to you quickly
and at a competitive price.
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