704-5010-130 Datasheet, PDF (21/36 Pages) Magnetrol International, Inc. – GuidedWave Radar Level Transmitter

3.2.2 Time Domain Reflectometry (TDR)
TDR uses pulses of electromagnetic (EM) energy to mea-
sure distances or levels. When a pulse reaches a dielectric
discontinuity (created by media surface), part of the energy
is reflected. The greater the dielectric difference, the
greater the amplitude (strength) of the reflection.
Although TDR is relatively new to the industrial level
measurement industry, it has been used in the telephone,
computer, and power transmission industries for years. In
these industries, it is used to successfully find wire or cable
breaks and shorts. An EM pulse is sent through the wire
traveling unimpeded until it finds a line break or short. A
reflection is then returned from the break and a timing
circuit pinpoints the location.
In the Horizon transmitter, a waveguide with a character-
istic impedance in air is used as a probe. When part of the
probe is immersed in a material other than air, there is
lower impedance due to the increase in the dielectric.
When the EM pulse is sent down the probe and meets the
dielectric discontinuity, a reflection is generated.
3.2.3 Equivalent Time Sampling (ETS)
ETS is used to measure the high speed, low power EM
energy. ETS is a critical key in the application of TDR to
vessel level measurement technology. The high speed EM
energy (1000 ft/µs) is difficult to measure over short
distances and at the resolution required in the process
industry. ETS captures the EM signals in real time
(nanoseconds) and reconstructs them in equivalent time
(milliseconds), which is much easier to measure with
today’s technology.
ETS is accomplished by scanning the waveguide to collect
thousands of samples. Approximately 8 scans are taken per
second.
3.3 Troubleshooting
The Horizon transmitter is designed and engineered for
trouble-free operation over a wide range of operating
conditions. Common transmitter problems are discussed
in terms of their symptoms and recommended corrective
actions. Information on how to handle material buildup
on the probe is also provided in this section.
WARNING! Explosion hazard. Do not connect or disconnect equip-
ment unless power has been switched off or the area is
known to be non-hazardous.
57-603 Horizon Guided Wave Radar Transmitter
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