Campbell Scientific TDR100 Time Domain Reflectometry Systems - Manual (Page 18)

TDR100
5.3 TDR100
The TDR100 contains the pulse generator for the signal applied to a TDR
probe. The TDR100 also digitizes the reflection and applies numerical
algorithms for measuring volumetric water content or electrical conductivity.
The TDR100 communicates with the datalogger using SDM protocol or with a
computer using PCTDR and serial communications.
5.4 SDMX50
The SDMX50 is a 50 ohm, eight-to-one, coaxial multiplexer. The same
multiplexer circuit is packaged as the SDMX50, the SDMX50LP or the
SDMX50SP. The SDMX50 is designed to minimize signal attenuation and all
channels have equal transmission line lengths. Spark gaps provide protection
from voltage surge damage. Figure 5-2 describes typical signal attenuation
from the common to one output channel for frequency range important for
TDR measurements.
100 1
.
10
3
1.4
1.2
1
0.8
0.6
0.4
0.2
0
Frequency (MHz)
SDMX50 attenuation (dBm
)
FIGURE 5-2. SDMX50 signal attenuation.
Each of the eight ports can be connected to a probe or another multiplexer (see
Figure 5-1).
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