TDR SOIL MOISTURE MEASUREMENTS
2
FIGURE 2-1. TDR System Components
2. SYSTEM COMPONENTS
1502B - Tektronix 1502B TDR Cable Tester.
SDM1502 - Communication Interface; this module plugs into the 1502B or 1502C and provides
a Synchronous Device for Measurement (SDM) interface to a CR10 or 21X datalogger.
PS1502B Power Control Module plugs into the battery receptacle of the 1502B; provides for
connection to an external 12 VDC source and allows the datalogger to control power to
the 1502B.
SDMX50 - 50 Ohm Coax Multiplexer - 8 to 1, BNC connectors, enclosure included. This
multiplexer is used to connect additional multiplexers or probes. Balanced probes
attached to this multiplexer require a balun for each probe.
PB30B (-RG8 or -RG58) - 30 cm soil probes; two rods, balanced design, with balun molded in
cable. A BNC connector on the coax cable attaches directly to SDMX50. The -RG8
version uses a low loss coax cable. The -RG58 version uses RG58 coax cable.
COAX TDR - 50 ohm coax cable with BNC connectors for connecting multiplexer.
6549 - 5 conductor cable used for SDM connection between datalogger and multiplexers.
21X or CR10 - The datalogger communicates with the 1502B and multiplexers with the SDM
interface using control ports 1-3 (and single ended channel 1 on the 21X). An additional
control port is used to switch power to the 1502B.
ENC TDR - Enclosure to hold 1502B and datalogger. The ENC TDR includes a transient
suppressor and cabling for connecting the power supply and datalogger. The 1502B
mount allows it to swing out to view screen.
Datalogger Software - Special PROMS for the CR10 or 21X datalogger include Instruction 100
for controlling the 1502B and multiplexers.
6590 - Transient suppressor attaches to cable from 1502B and is required if ENC TDR is
not
purchased.
3. INSTALLATION
The 1502B and datalogger are housed in the
ENC TDR. In most instances power is supplied
from an external 12 volt deep cycle battery
charged by a MSX18R solar panel. Each
SDMX50 multiplexer has its own enclosure.
Coax cable connects the 1502B and the
SDMX50 and SDMX50 to other SDMX50s. In
addition to the coax cable that carries the TDR
signal, the multiplexers must be connected to
the datalogger by a 5 conductor cable which
provides power to the multiplexers and allows
the datalogger to control the multiplexer
switching.
