1 rad modem - two way, 2 rad modem wiring and grounding – Campbell Scientific SC932A 9-Pin to 9-Pin RS-232 Interface User Manual

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SC932A 9-Pin to RS-232-DCE Interface

excellent immunity to circuit noise. Table 1 gives the data rate possible for
several gage cables across several distances.

TABLE 1. Approximate Range, miles and km

Data Rate

19 Gauge (0.9 mm)

24 Gauge (0.5 mm)

26 Gauge (0.4 mm)

bps

miles

9,600

6.2

10.0

2.8

4.5

2.0

3.3

1,200

7.6

12.2

3.4

5.5

2.5

4.0

4.1 RAD Modem - Two Way

4-WIRE UNCONDITIONED

TELEPHONE LINE

TWO TWISTED PAIRS

SRM

9 TO 25 PIN

ADAPTOR

SC932A

DATALOGGER

SRM

FIGURE 2. Two Way Communication

When using Campbell Scientific’s datalogger support software to communicate
through the SC932/RAD modem, “Setup” the link as a direct connect between
the datalogger and the desired COM port. Start two way communication using
the “Connect” button on the Tool bar and the “Connect” button in the
“Connect” window.

4.2 RAD Modem Wiring and Grounding

Figure 3 shows a typical setup of the RAD modems. Installation is as follows:

Set the DCE/DTE switch on the back of the RAD modem connected to the
SC932A to DCE. For a RAD modem connected to a PC, set the
DCE/DTE switch to DCE. For a RAD modem connected to a serial
printer, set the DCE/DTE switch to DTE.

Select a cable with two or more twisted pairs. A recommended direct
burial rodent resistant cable is listed below. They also sell several gopher
resistant cables for even greater protection.

Company

Part Number

AWG.

Anixter

F-02P22BPN

Tel: 847-677-2600
http://www.anixter.com

Wiring connections are made as shown in Figure 3. Note wires labeled A
and B are one twisted pair of the cable. Wires labeled C and D are the
other twisted pair.

Transients induced on the communication line may damage any
electronics connected at either end of the line. To decrease the chances
for damage, spark gaps should be installed as shown in Figure 3. The
transient protection shown may be purchased from Campbell Scientific,
Inc. (p.n. 5563 shown in Figure 3, p.n. 6536 includes a plastic case, p.n.