Campbell Scientific UT20 and UT30 Tower-based Weather Stations - Manual (Page 39)

UT20 and UT30 Tower-based Weather Stations
8.3.4 SRM-5A Rad Modem and SC932A Interface
Rad Modems enable communication between the datalogger and computer
over 4-wire unconditioned telephone line, or cable with two twisted pairs of
wires.
The maximum distance between modems is determined by baud rate and wire
gauge. At 9600 baud the approximate range is 5.0 miles using 19 gauge wire,
4.0 miles using 26 gauge wire.
Installation requirements depend on the type of cable that is used, and how it is
installed (direct burial, conduit, etc.). In general, follow state and local
electrical codes.
A recommended rodent-proof burial cable is PN F-02P22BPN, available from
ANIXTER. Call ANIXTER at (708) 677-2600 for the name of a local
distributor.
8.3.4.1 SRM-5A at the Datalogger
1. Plug the SRM-5A into the SC932A. Position the notched tabs in the
mounting bracket over the two screws in the SRM-5A (refer to FIGURE
8-11). Thread the SRM-5A screws through the bracket and into the
SC932A.
2. Attach the SRM-5A and SC932A mounting bracket to the enclosure
backplate using the two screws and nylon inserts provided (FIGURE
8-10).
3. Connect the SC932A to the datalogger’s I/O port with an SC12 cable.
4. Mount the pn 6361 Surge Protector to the enclosure backplate using the
hardware provided. Connect the ground wire to the enclosure ground lug
(FIGURE 8-12).
5. Cut a 12 inch long piece of two twisted pair cable and connect it to the
SRM-5A as shown in FIGURE 8-12. Fasten the cable to the strain relief
tab with a cable tie.
6. Route the cable previously attached to the SRM-5A, and the two twisted
pair cable (from the other SRM-5A) to the 6361. Connect the cables as
shown in FIGURE 8-12. Strain relief the cables to the side of the
enclosure using cable ties and tabs.
8.3.4.2 SRM-5A at the Computer
1. Mount the 6361 (or pn 5563) to a flat surface (close to the computer) using
two screws. Ground the center terminal to an earth (or building) ground
using a 12 AWG or larger diameter wire.
2. Cut a piece of two twisted pair cable long enough to reach from the 6361
to the computer. Connect the cable to the SRM-5A as shown in FIGURE
8-11. Fasten the cable to the strain relief tab with a cable tie. Connect the
SRM-5A to the computer’s serial port.
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