Micropack FDS301 - 4.5.2 Video Cable Selection; 4.5.3 RS485 Cable Selection

4.5.2
Video
The video cabling should be a twisted pair stranded cable with an overall screen. Where multi-
core cables are used then individual screened twisted pairs are recommended. The cable should
have the following characteristics:
Table
4: Video (Twisted
Pair) Cable Characteristics
The maximum cable length is dependent on the cable manufacturer’s attenuation specification,
which is approximately proportional to conductor size.
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Cable
Characteristic
Characteristic
Impedance
Capacitance
Conductor
Resistance
Attenuation @
1MHz
Inductance
Nominal
150R
50nF/km - - - - - -
Absolute Limit
90R to 150R
100nF/km
150R
6dB 7mH/km
The characteristic impedance of a transmission line is a function of the physical dimensions of
the conductor and the permittivity of the dielectric (the insulation), at high frequencies this is
approximately equivalent to:
Zo (  )  L

 C
E
q
uation 1: Characteristic Im
p
edance
Calculation
For maximum performance the video output of the FDS301 is designed for differential twisted
pair operation. For single ended output a Micropack VTP4 or differential to single ended balun
should be used.
4.5.3
RS485 Communication
The RS485 communications cabling should be a twisted pair stranded cable with an overall
screen. Where multi-core cables are used then individual screened twisted pairs are
recommended. The cable should have the following characteristics:
Table
5:
RS485
Communications
Cable
Characteristics
The maximum cable length is dependent on the cable manufacturers’ attenuation specification,
which is approximately proportional to conductor size. The characteristic impedance of a
transmission line is the same as for the video above.
micro
p
ack.co.uk
Cable
Characteristic
Characteristic
Impedance
Capacitance
Conductor
Resistance
Attenuation @
1MHz
Inductance
Nominal
120R 50nF/km - - - -
- -
Absolute Limit
90R to 120R
100nF/km
120R 6dB
7mH/km
L = Cable Inductance (mH)
C = Cable Capacitance (uF)
Zo = Characteristic Impedence (Ohms)
FDS301 Flame Detector FDS301 Safety and Technical Manual
20
Ref: 2200.5009 Rev: 2.3 ECN 4434