Siemens SIMATIC NET PROFIBUS manual Link Power Margin, Work Sheet

Configuring Networks

Link Power Margin

When calculating the power budget, a link power margin of at least 3 dB (at a wavelength of 860 nm) or at least 2 dB (at a wavelength of 1300 nm) must be maintained.

If the link power margin calculated is lower, the transmission path will not be reliable in its currently planned form. This means that the transmission path may well function when it is first started up since components are normally better than their rated performance (particularly when brand new) but due to aging, replacement of components as a result of repairs and changing environmental conditions, the bit error rate will tend to rise to an unreliable level the longer the equipment is in use.

Note

To avoid possible errors during the installation of the transmission path, when installing glass fibers, the installed sections must be tested during installation and the measured values logged (see Section A-2 “Testing FO Transmission Paths”).

Work Sheet

Section 3.2.4 of this manual contains a work sheet for calculating the power budget of glass fiber-optical links.

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	6GK1970-5CA20-0AA1 Release 2 05/2000