Siemens SIMATIC NET PROFIBUS manual Testing FO Transmission Paths Necessity of a Final Test

Testing PROFIBUS

A.2 Testing FO Transmission Paths

A.2.1 Necessity of a Final Test

The total attenuation of an FO transmission path, particularly the influence of splices, can only be estimated roughly during planning. As a result of inaccuracies when creating the splices and subjecting cables to excessive stress during installation, the actual attenuation may well be higher than the calculated values. The only way to be sure that a fiber-optic link functions reliably and has an adequate link power margin is to measure the attenuation following installation. It is advisable to test every fiber-optic link in which the connectors were fitted on-site and to document the results in an acceptance report.

Attenuation

Attenuation defined as the optical power loss in decibels (dB) is the decisive criterion in optical networks. All system components such as the cable, connectors, splices, couplers etc. add to the total attenuation of a link and with it to the attenuation within the entire network. To measure this attenuation, fiber-optic test units must be used following installation. During the measurements, light with the same wavelength must be used as in the optical transmission system.

Test Methods

In the main, two test methods are used:

1.The Optical Power Source and Meter

2.Optical Time Domain Reflectometer (OTDR)

A valuable tool for every user is also the fiber-optic troubleshooter. This light source sends visible light so that fiber breaks, bad splices etc. can be localized visually.

Some new network components, such as the PROFIBUS OLM version 3 have integrated diagnostic functions with which they can check the quality of the received optical signal.

A.2.2 Optical Power Source and Meter

The attenuation on the fiber-optic link is first measured. All the link components such as the fiber, connectors, couplers and splices contribute to the total attenuation. The total attenuation must be below the available optical power budget between the optical transmitter and receiver. Light sources are available for all normal wavelengths (650 nm, 850 nm and 1300 nm). This means that this method can be used for plastic, PCF, multimode and single-mode fiber-optic cables.

PROFIBUS Networks SIMATIC NET	A-7
6GK1970-5CA20-0AA1 Release 2 05/2000