Chapter 1 Before Installation
8 BMTW-SVN01F-EN
IMPORTANT
Due to the high precision required when performing fiber-optic termi-
nations, Trane recommends that only qualified technicians with the
proper equipment handle all terminations and splicing.
Optical-Link Loss Budget
Every fiber-optic link has some signal loss (measured in decibels). Many
factors affect decibel loss, including:
• Length of fiber-optic cable
• Transmitter optical output power
• Operating wavelength
• Fiber attenuation
• Fiber bandwidth
• Receiver optical sensitivity
The decibel loss between any two devices is based on how well the termi-
nations or splices are made. The decibel loss can vary from 0.5 to 2 dB. A
clean splice results in increased performance. For example, the fiber-optic
ARCNET card that Trane supports has a power budget of 10 dB. The
decibel loss for fiber-optic cable provided by Trane is 3.75 dB/km
(1 km = 3280 ft). Precut fiber-optic cables and professionally spliced and/
or terminated cables should ensure minimal decibel loss.
To calculate the system loss, subtract the cable loss, splice loss, termina-
tor loss, and patch panel loss from the power budget. The example below
shows typical values for the ARCNET communication link:
power budget – system safety margin = available budget
10 dB – 3 dB = 7 dB (available budget)
available budget: 7 dB
cable loss: – 3.75 dB (1 km at 3.75 dB/km)
allowance for splice loss: – 1 dB (2 at .5 dB)
allowance for end connectors: – 1 dB (2 at .5 dB)
allowance for patch panel: – 1 dB (2 at .5 dB)
excess margin: = 0.25 dB
Note:
Use glass fiber-optic cable for long distances, interbuilding
cabling, and/or other areas of high electrical noise, such as petro-
chemical installations, electronic rooms, and near hospital NMR
or X-ray rooms.
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