Technical data

www.westermo.com Theoretical and general applications 45
Calculation of resistance
When you do not know the resistance of the cable you can use this formula:
Q=RxA/I
Where Q = resistivity for the material to be used. For copper you can use
0.017 µ Ωm, or 0.017 x 10
-6
. R = the resistance in the cable, A = cable cross section
and l = length.
The formula is easy to use with solid conductors. With multicore the cross section of
the conductor is multiplied by the number of conductors.
Cross section = radius x radius x pi.
Two symbols for capacitance
There are two different symbols, nF/km or pF/m, which are two variants of the same
unit measurement. nF stands for nano farad which is 10
-9
Farad per 1000 metres
(0.62 mi). pF stands for pico farad which is 10
-12
Farad per metre.
n.b. All speeds and distances have been calculated based
on cables with standard values for resistance and imped-
ance.
In field installations the transmission distance may vary
depending on cable quality and local conditions.
kbit/sbit/s
TD-32
TD-34
TD-23
4.0
500
187.5
115.2
100
38.4
19.2
14.4
9.6
4.8
2.4
1.2
600
Mbit/s
501005001 2 4 6 8 1012 141618202224
Leased Telephone Line
10mA balanced current loop (W1)
Fibre optic
RS-422/485
20mA current loop
RS-232/V.24
B A C K