Campbell Scientific MD9 Coax Multidrop Interface - Manual (Page 8)

MD9 Multidrop Interface
4
TABLE 4-1. ID Settings for MD9 Connected to Computer
Software Used ID
Dos PC208 (GraphTerm, Telcom, and PC208E) 1 - 254
Windows PC208W (Tcom) 255
An MD9 with the ID set to 255 can be used with the DOS PC208
by adding a pound sign (#) to the end of the base MD9 dialing
path in the PC208 station file. This is useful if PC208 and
PC208W must be used on the same MD9 network.
Address 255 is also used when the MD9 is connected to a
telephone modem (Section 6).
MD9s are shipped with the Baud Rate Selection Jumpers set at 9600 Baud.
Other baud rates may be selected when necessary. All MD9s in a system must
be set at the SAME baud rate.
9600 Baud 1200 Baud 300 Baud
A-B Short A-B Open A-B Short
C-D Short C-D Short C-D Open
FIGURE 4-1. ID Switch and Baud Rate Selection Jumpers
5. Maximum Number of Dataloggers and Coax
Length
The maximum coax run that can operate reliably is dependent on the signal loss
due to the type of wire selected and the load placed on the system by each MD9
and coax terminator. The total signal loss in an MD9 system cannot be greater
than 50 db.
Each MD9 attenuates the signal by 0.2 db. Each 100 ft. of Belden 9100 coax
cable attenuates the signal by 0.6 db. The terminator pair account for a 6 db
loss. A quick calculation shows that a network of 34 dataloggers on 5,000 feet
of coax is a workable system.
NOTE
NOTE