Installation and Maintenance
5.1 Installation
SIMATIC NET PROFIBUS, Optical Link Module
Operating Instructions, 07/2008, A2B00065774O, Edition V1.5
29
surfaces are ideal for good contact
between grounding elements. With tin-
plated surfaces, the necessary contact
must be established using screws. Painted
or varnished surfaces at the contact points
are unsuitable.
¾
Shield clamps or contacts must not be
used as strain relief. The contact to the
shielding rail could deteriorate or be
broken altogether.
Optical link power budget, aging and environmental requirements
When using OLM V4.0 devices, make sure that they are not exposed to high
temperatures for no good reason. The aging of the devices increases radically in
high temperatures. The same applies to the connected fiber-optic cables. They age
faster under the influence of temperature and high humidity. The deterioration
caused by humidity especially applies to plastic fiber-optic cables.
The described deterioration of devices and fiber-optic cables is offset by the link
power margin. This is obtained from the difference between the receiver sensitivity
and the minimum input optical power (see section 4.1) along with the cable
attenuation that derives from the maximum operating distance.
Example:
OLM/G12, wavelength 860
nm, fiber 62.5/200
µ
m
P
send
= 13 dBm
P
receiver
= 28 dBm
optical link margin
= 28 dBm-13 dBm= 15 dBm
max. line length
= 3 km
attenuation
= 3.5 dB/km @860 nm
max. line attenuation
= 3.5 dB/km * 3 km= 10.5 dB
optical power margin
= optical link power budget
–
max. line attenuation
= 15 dBm
–
10.5 dBm= 4.5 dBm
This link power margin may not be infringed on by the user, because it may lead to
errors at the optical interface!
You should also remember that the maximum line lengths are only valid for
unspliced cables. If splices are used in the configured plant, their loss must be
added to the cable loss.