TDR200-Based Time-Domain Reflectometry System
10
FIGURE 7-1. TDR System Components
7.1.1 Data Logger
Campbell Scientific CR6-series, CR800-series, CR1000X, CR1000, and
CR3000 data loggers are used in a TDR system to automatically control the
TDR200, SDM8X50 multiplexers, and telemetry for obtaining measurement
results remotely. Refer to Section
(p. 14)
, for more
information.
7.1.2 TDR200
The TDR200 contains the pulse generator for the signal applied to a TDR
sensor. It also digitizes the reflection and applies numerical algorithms for
measuring volumetric water content or electrical conductivity. The TDR200
communicates with the data logger using SDM protocol or with a computer
using
PC-TDR
and serial communications.
7.1.3 SDM8X50
The SDM8X50 is a 50 ohm, eight-to-one, coaxial multiplexer designed to
minimize signal attenuation. All SDM8X50 channels have equal transmission
line lengths. Spark gaps protect against voltage surge damage. Hermetically
sealed, non-latching electromechanical relays are activated to connect the
TDR200 to different multiplexer channels. After a 30 second timeout, the
relays unlatch providing additional surge protection. Relays used on the ground
and signal lines fully isolate each sensor during measurements.
