Siemens SIMATIC NET Operating Instructions Manual page 49

Measuring the receive level
1. Measure the level with a high-resistance, ungrounded voltmeter.
2. Do not connect the ground connector to the housing; otherwise the data traffic could be
disturbed.
3. To meet the EMC requirements, the length of the connected measuring cables must not
exceed 3 m.
The quality of the bus traffic can be estimated based on the receive levels in the following
diagram:
①
②
③
Figure 6-1
Optical link module
Operating Instructions, 01/2020, C79000-G8976-C270-06
Normal operation, level adequate
Optical link power margin reduced
Function not guaranteed
Relationship between measured output voltage and signal quality
Connection
6.4 Optical channels
49