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WCS-PG410
Appendix
Cable Length
For the RS-485 data transfer path, a four-wire, shielded, twisted pair data cable must be used.
One core pair is used for the supply voltage, and one pair for the RS-485 data connection. The
maximum length of the cable depends on the capacitance of the data cable—core-core—for
data transfer, and on the cross section of the cables for voltage supply to the read heads. For
data transfer, a small core cross section and thus a small cable capacitance is an advantage,
whereas for the voltage supply, the largest possible cross section is required. The table below
shows the possible cable lengths depending on the cable cross section.
Cable cross
section
2
0.14 mm
2
0.22 mm
2
0.25 mm
2
0.28 mm
2
0.34 mm
2
0.50 mm
1. American Wire Gauge, a system commonly used in North America for the specification of wire diameters in electrical
engineering.
In the calculations, the worst-case scenario was assumed: All read heads are located at the
end of the data cable. In the case of large cable lengths, and when connecting multiple WCS2
read heads with a heater, 6-wire data cables (3 x 2) can be used. These data cables use two
pairs for the voltage supply (doubling the cable cross section), and one pair for the RS-485 data
line. The table below shows the possible cable lengths depending on the cable capacitance
(core-core). The number of connected read heads is of no significance.
Capacitance
(core-core)
60 pF
90 pF
120 pF
Number of read heads without
heater
1
AWG
1
2
~ 26
200 m
110 m
~ 24
320 m
170 m
-
350 m
190 m
-
400 m
220 m
~ 22
500 m
250 m
~ 20
500 m
400 m
RS-485 interface
19.2 kb
500 m
500 m
500 m
Number of read heads with
heater
3
4
1
70 m
50 m
15 m
110 m
80 m
30 m
130 m
90 m
35 m
150 m
110 m
40 m
180 m
140 m
50 m
270 m
200 m
70 m
62.5 kb
500 m
450 m
400 m
2
3
4
10 m
7 m
5 m
15 m
10 m
7 m
17 m
12 m
8 m
20 m
15 m
10 m
25 m
17 m
12 m
35 m
25 m
17 m
187.5 kb
300 m
275 m
250 m
35
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