Calrec Hydra2, Installation Manual

Page: 35 / 104

CALREC
Putting Sound in the Picture
35
Testing/certification
Calrec strongly recommends that all fibers
are properly tested or certified prior to on-
site commissioning of a system. A certain
amount of signal loss occurs over the
length of a fiber path. If the total loss of
a path exceeds the optical power budget
of the SFPs in use, the system will be
unreliable.
Areasofloss
Signal loss occurs in various areas. Splice
loss occurs in terminations—at the point
where the fiber meets the connector.
Typically splice loss should be <0.3dB per
termination. Poor termination results in
higher loss.
Connector loss occurs at the point where
the connector meets the SFP / optical
transceiver, or another connector, such
as extension interconnects or patch-
points. Connector loss should typically be
<0.5dB per interconnect. Dust or other
contamination between interconnects
and scratches on the end surface
contact point of the fiber will substantially
increase the amount of loss. As such, dust
covers should always be fitted to optical
transceivers when no fiber is connected
and to fiber connectors that are not
landed.
As well as splice and connector loss, the
fiber itself has inherent loss over distance,
typically fiber loss will vary from 3.5 dB
per km for multimode down to 0.4 dB
per km for singlemode. Poor installation
practise and lack of care can damage the
fiber and result in substantially increased
losses.
Fiberhandlingpractise
It is important to follow the fiber
manufacturer's guidelines when handling
fiber and installing fiber runs. Some of the
main points of concern are:
• Minimum bend radii—fiber should not
be bent through tight angles. Tight
angles can cause significant losses
and permanent damage to the fiber.
Fibers may pass initial installation
testing but can fail at a later date due
to stresses on the core of the fiber
caused by tight bends.
• Twists, snags and kinks—Twists in fiber
runs add stresses to the core which
can cause damage over time. Avoid
snagging on other cables or conduit
which will cause excessive tensions
when pulling and can cause kinks and
excessive bends in the fiber. When
routing through angled conduit, provide
enough clearance around corners to
avoid the fibers being pulled sharply
around the inside of the angle.
• Pulling—observe the manufacturers
maximum pulling tension specification.
Use pulling tools and lubrication
where appropriate. Never pull on the
connector.
• Strain relief—fibers should be
adequately strain relieved to prevent
tension on terminations, however use of
plastic cable ties can crush the internal
construction of the cable. Hook-and-
loop "Velcro" straps are harder to
over-tighten, offer more gentle support
and a greater surface area to dissipate
the pressure.
• Crushing—never place heavy items on
top of unprotected fiber.
Ruggedizedfiber
For temporary / re-usable fiber runs , or
runs unprotected by conduit, fiber that
is likely to be exposed to the elements,
snagging or to being stood on, should
always be of a ruggedized / armored type
to protect the internal construction of the
core.
WARNING
Never look into the end of an optical
transceiver or fiber when in use. Laser
radiation can be harmful to the human
eye and should be avoided.
Remember that when disconnecting
a fiber, the transmitting device at the
other end may still be active.
FIBER - GENERAL RULES
Cleaningandpreventative
maintenance
Contamination of transceiver and fiber
mating contact points causes signal
loss and can cause permanent damage
through scratching.
Dust covers should be fitted to all fiber
connectors and SFP optical transceivers
when they are not mated. It is also
important to ensure that dust covers
themselves are kept clean.
When handling fibers without dust covers,
do not allow the ends to come into contact
with any surface, including fingers.
Specialist materials should be used for
the cleaning of mating contact points to
avoid further contamination or scratching.
The following items are low cost and
readily available from camera shops and
laboratory suppliers:
• Canned compressed air—it is important
to use specialist filtered, clean, dry air,
free of contaminants and moisture.
• Isopropyl alcohol. Use with cotton
swabs or lint-free wipes to ensure no
residue is left.
• Lint free wipes / long fiber, low ash
lens paper—needs to be free from
chemical additives. Ensure wipes
and swabs are stored in a clean
environment and are not reused.