Chapter 13 - Tips and tricks for cable testing
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PROFIBUS Tester BC-700-PB - User Manual
Devices: Please specify, how many PROFIBUS devices are connected to the respective
cable segment (Master, Slave, repeater; typ. not more than 32). The RS485-driver unit of
each PROFIBUS-station acts like a RC-cicuit (delay element) on the cable. In the context
of impulse reflectometry this corresponds to additional 20 cm cable length per device.
Consequently, the combination consisting of connector plus device corresponds to
approx. 70 cm cable length.
Example: A cable segment has approx. 50 m effective cable length and contains 20
PROFIBUS devices, which are connected to the line by means of 12 MBit/s Sub-D type
connectors. Without indicating the number of connectors and devices the PROFIBUS
Tester 5 BC-700-PB will detect a total cable segment length of 64 meters, which
corresponds to a systematic error of measurement of approx. 28 %. The more precise
you will enter the number of connectors and devices into the segment configuration, the
more precise the length indication will be (cable segment length or distance to error).
The cable length detection is optimized for standard PROFIBUS cable type A. The
detected cable segment length will show a methodical error in measurement, if you are
using a fieldbus cable with deviating impedance value.
