Siemens SIMATIC NET Operating Instructions Manual page 50

Connection
6.4 Optical channels
For a valid measurement, the partner OLM at the other end of the FO cable must send
normal PROFIBUS frames. This can be recognized based on the LED display of the partner
OLM, see section "LED display (Page 13)".
The output voltages at the measurement sockets are influenced by the following factors:
● Strength of the transmit power of the partner OLM
● Ambient temperature of the optical transmitter and receiver
● Attenuation of the transmission line
● Transmission rate used
The measurement sockets are therefore not intended as a substitute for a calibrated level
measuring device with a calibrated light source. The value obtained only serves to classify
the received optical signals in 3 classes:
● Good (normal operation, green
● Critical (optical link margin reduced, yellow
● Bad (functionality not guaranteed, red
Measure the level with a commercially available, high-resistance, ungrounded voltmeter. The
internal resistance of the measurement sockets is approx. 30 kΩ. A connection from the
measurement sockets or from reference potential to the OLM housing is not permitted.
Note
When an OLM of the SINEC L2FO series is connected, the OLM V4 LED level indicator has
no meaning. The measurement sockets cannot be used.
50
①
): 5 V > U > 240 mV
②
): 120 mV ≤ U ≤ 240 mV
③
): U < 120 mV
Operating Instructions, 01/2020, C79000-G8976-C270-06
Optical link module