Cable Specifications
Installation Handbook, Autroprime Interactive Fire Detection System, 116-P-APRIME2-INSTAL/DGB, Rev. C, 2016-29-02,
Autronica Fire and Security AS
Page 21
8.4 The Panel Bus Cable Requirements
8.4.1 Characteristic Impedance and Signal Attenuation
When dealing with specification of the Panel Bus cable, the
important issues are the characteristic impedance and the
attenuation of the signal at approximately 100 KHz. These
parameters become more important the longer the cable is.
The parameters are defined by the geometry of the cable. Proper
characteristic impedance is best obtained by a cable with twisted
pairs. For short communication paths (less than approximately
100m) the characteristic impedance is not that important, and
attenuation is low enough for most cables. However, the twisting
improves the cable’s ability to withstand external interference, and
a twisted cable should be preferred when the cable runs in the
vicinity of power cables and power devices as generators,
transformers etc.
Longer paths require twisted pair cable and 100 ohms
characteristic impedance, Cat 5 or similar cable intended for
RS485 transmission.
The characteristic impedance shall be (at 100KHz:) 100 ohm +/-
15 ohm. Note that the characteristic impedance has nothing to do
with the resistance of the cable. It is a property related to high-
frequency transmission, regardless of its length. Typical examples
are antenna cable (300 ohm), video cable (75 ohm).
Attenuation is defined by the wire to wire capacitance mostly, as
long as the wire is at least 0.5mm2. The total attenuation of the
cable length must not exceed 9 dB @ 100KHz. If attenuation is
not specified, normally the capacitance is defined. The capacitance
shall not exceed the specified value in order to achieve the total
communication length.
8.4.2 High-voltage and Noisy Environments
In high-voltage environments (power plants, electrical machinery
etc.) it is recommended that shielded cable is used. In this case,
the shielding of the cable should only be connected at one end to
avoid ground loops. If high-frequency noise is expected (>10MHz),
then both ends should be connected. This may be present close to
radio transmitting equipment or similar.
Summary of Contents for Autroprime
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