Campbell Scientific MD9 Coax Multidrop Interface User Manual
Page 6
MD9 Multidrop Interface
2
The MD9 at the computer is connected to one or more other MD9s with coax
cable terminated with BNC connectors. Refer to Appendix A for cable
specifications and source references.
The MD9 at the datalogger is connected via an SC12 cable (supplied with the
MD9) and is powered from the datalogger SERIAL I/O port.
Each MD9 includes a BNC "T" connector to allow for coax in/ coax out. "T"
connectors on MD9s at the beginning (computer) and end (last datalogger) of
the network must be terminated with 75 ohm Coax Terminators in order to
prevent signal reflection from one end of the cable to the other. Place
terminators on the ends of the main cable only. Any branch cables from the
main cable to an MD9 should be less than 10 feet in length. No terminator is
used on the T connector at the MD9 on a branch. (Figure 2-1).
There are two ground terminals located between the Serial I/O
and Coax Connectors on the MD9. When installing the MD9, a
16AWG or heavier wire should be connected from earth ground
to one of these terminals.
FIGURE 1-1. MD9 Multidrop Interface
NOTE