User guide

SC105 9-Pin to RS-232-DCE Interface
6
For transmission, the RAD modem uses a cable made of two pairs of twisted
wires with a shield. Data rates up to 9600 bps are possible. The low voltage
transmission levels minimize cross talk between adjacent lines within the same
cable. Data are transmitted and received at a balanced impedance, providing
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 km Miles km miles km
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
5.1 RAD Modem - Two Way
4-WIRE UNCONDITIONED
TELEPHONE LINE
OR
TWO TWISTED PAIRS
SRM
9 TO 25 PIN
ADAPTOR
SC105 DATALOGGERPC SRM
Figure 3. Two Way Communication
When using Campbell Scientific’s datalogger support software to communicate
through the SC105/RAD modem, “Set-up” 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.
5.2 RAD Modem Wiring and Grounding
Figure 4 shows a typical set-up of the RAD modems. Installation is as follows:
1. Set the DCE/DTE switch on the back of the RAD modem connected to the
SC105 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.
2. 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 22
Tel: [phone]
http://www.anixter.com
3. Wiring connections are made as shown in Figure 4. Note wires labelled A
and B are one twisted pair of the cable. Wires labelled C and D are the
other twisted pair.
4. 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 4. The transient
protection shown may be purchased from Campbell Scientific, Inc. (p.n.
#5563 shown in Figure 4, p.n. #6536 includes a plastic case, p.n. #6361