Siemens SIMATIC NET PROFIBUS Betriebsanleitung PDF herunterladen (Seite 45)

Installation and Maintenance

5.6 Receive Level of the Optical Channels

SIMATIC NET PROFIBUS Optical Link Module OLM V4.0

Operating Instructions, 01/2013, C79000-G8976-C270-03

5.6 Receive Level of the Optical Channels

Figure 5-11 Position of the level

recording connections

The receive level of the two optical channels CH2 und CH3 can

be measured using a standard voltmeter via the measurement

sockets. The voltmeter can be connected and disconnected

while the device is operating. The OLM is protected against a

short circuit at the measurement sockets; data transmission is

not influenced. The receive level of the two optical channels can

be read in on a PLC using floating high impedance analog

inputs.

This allows

– the incoming optical power to be documented, e.g. for later

measurement (aging, damage)

– a good/bad test to be carried out (limit value).

The measurement must be performed with a high-resistance, ungrounded voltmeter. The ground connector

must not be connected to the housing; otherwise the data traffic could be disturbed. 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 receiving levels in the following diagram:

Figure 5-12 Relationship between measured output voltage and signal quality

Measured voltage / V

Receiving level at 660 nm / dBm

Receiving level at 860 nm / dBm

Receiving level at 1310 nm / dBm

-4-6-8-10-12-14-16-18-20-22-24-26

-12-14-16-18-20-22-24-26-28

-18-19-20-21-22-23-24-25-26-27-28-29

0,8

0,2

0,4

0,6

1,0

1,4

1,7

2,0

2,5

3,0

3,5

4,0

0,1

Function not guaranteed

Optical system reserve reduced

Normal operation, level sufficient

1 2 ... 40 41 42 43 44 45 46 47 48 49 50 ... 63 64

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