Siemens SIMATIC NET Operating Instructions Manual page 35

Optical power budget, aging and environmental conditions
When using OLM V4 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. These age faster under the influence of
temperature and high humidity. The aging effect caused by humidity applies in particular to
plastic FO cables.
The described aging of devices and FO cables is counteracted by the link power margin.
This is obtained from the difference between the receiver sensitivity and the minimum input
optical power (see section "Technical data (Page 73)") along with the cable attenuation that
results from the maximum coverable distance.
Example:
OLM G12, wavelength 860 nm, fiber 62.5/200 μm
P
Send
P
Recv
Optical power budget
Max. cable length
Attenuation
Max. cable loss
Link power margin
This link power margin must not be used by the user, because this may well lead to
functional disruptions on the optical interface.
You should also remember that the maximum cable lengths are only valid for uncut cables. If
optical couplers are used in the configured system, their coupling loss must be added to the
cable loss.
Optical link module
Operating Instructions, 01/2020, C79000-G8976-C270-06
= 13 dBm
= 28 dBm
= 28 dBm - 13 dBm = 15 dBm
= 3 km
= 3.5 dB/km @ 860 nm
= 3.5 dB/km * 3 km = 10.5 dB
= optical power budget - max. cable loss
= 15 dBm - 10.5 dBm = 4.5 dBm
Mounting
5.1 Installation guide
35