TDR200-Based Time-Domain Reflectometry System
12
The ground lug on peripheral SDM8X50 multiplexer enclosures should only be
used if the multiplexer is near enough to conveniently use the same ground
point as the data logger.
7.1.5 SDM Communication
The TDR200, SDM8X50 multiplexers, and data loggers use synchronous
device for measurement (SDM) communication protocol to control
measurements and transfer data. This communication protocol adheres to an
addressing scheme for all communicating devices.
The address selected on the TDR200 must match the SDM address used in the
data logger program. The three multiplexer levels (FIGURE
(p. 10)
) use the following addressing scheme:
•
Level 1 multiplexer—address value equal to the TDR200 address plus 1.
•
Level 2 multiplexers—address value equal to the TDR200 address
plus 2.
•
Level 3 multiplexers—address value equal to the TDR200 address
plus three.
Set the address for SDM8X50 multiplexers using the thumbwheel switch at the
top of the panel.
A 5-conductor cable with shield and drain is shipped with the TDR200 and
ENCTDR100 for connecting the data logger to the TDR200 and the TDR200
to an SDM8X50. If additional cables are needed to connect different levels of
multiplexers, use the CABLE5CBL-L cable. The maximum total length of all
SDM cables should not exceed 500 feet to ensure reliable communication
between SDM devices.
The red and black wires are typically used for 12 VDC and ground. The
remaining three wires connect the control lines (data, clock, enable). On the
CR6-series, CR800-series, CR1000X, and CR1000 data loggers, the ports
labeled
C1
,
C2
, and
C3
are dedicated to data, clock, and enable, respectively
ENCTDR100 with SDM8X50, PS150, TDR200, and CR1000
(p.
). The CR6 can also use universal channels (
U1
,
U2
,
U3
or
U5
,
U6
,
U7
or
U9
,
U10
,
U11
). On the CR3000, the ports are labeled
SDM-C1
,
SDM-C2
, and
SDM-C3
.
7.1.6 ENCTDR100
Many TDR system applications require installation of equipment at field sites.
The ENCTDR100 is a weatherproof enclosure with a mounting plate for a data
logger, power supply, TDR200, SDM8X50, cable strain relief bracket, and
associated cabling. The ENCTDR100 can be mounted on a CM106B tripod for
a free-standing installation.
7.1.6.1 Mounting Equipment in ENCTDR100
The ENCTDR100 is a 16-inch-by-18-inch weathertight enclosure modified for
use with a Campbell Scientific TDR system (FIGURE
). It includes the
following:
•
Enclosure supply kit consisting of desiccant packs, humidity indicator,
cable ties, putty and mounting hardware
•
ENCTDR100 Enclosure Ground Wire Kit
