User Manual PROFview XL 3 Description of Functions and Measuring Principle
3 Description of Functions and Measuring Principle
3.1 The most important measuring functions
The PBT can measure and display the signal conditions of every PROFIBUS station. Any problems with this
station or with the bus cabling can be inferred from the results of the signal quality. The PBT displays the fol-
lowing physical properties separately for each PROFIBUS station:
general quality level (incl. glitch, edge and level error counters)
disturbance-free voltage range (minimum, interference-free differential voltage)
edge steepness
section of the signal waveform (oscilloscope display)
In addition to the physical measurements, the PBT provides online monitoring functions, i.e. the entire bus
traffic is monitored and checked continuously. This also includes the bus cycle time and a counter for illegal
frames.
One of the most important innovations offered by the PBT is the master simulator allowing measuring and
checking already during the phase of installation, even if the master station (e.g. PLC) is not yet available.
The distances (line lengths) to the individual PROFIBUS stations, as well as automatic sorting of the station
and measuring point lists according to the distances, can be derived from the topology determination.
The individual measuring functions are described in detail in the following subsections.
3.2 Measuring the physical bus characteristics
PROFIBUS uses a differential signal, i.e. the actual data signal is transferred via two lines inverted to each
other (A and B). The difference between the two generates the signal digitized by each PROFIBUS transceiv-
er. Any faults occurring there can endanger the correct detection of the bit stream. The PBT provides an eval-
uation of the differential signal in the form of a general quality level, the disturbance-free voltage range and
the edge steepness, as well as by way of the oscilloscope display.
Contrary to the quality level, which provides a general evaluation of the signal quality for the bus, the determi-
nation of the disturbance-free voltage range and of the edges, as well as the oscilloscope display, are useful
aids for targeted fault finding.
3.2.1 General quality level (incl. glitch, edge and level errors)
The quality of the signal transmission is characterized by the level of the differential voltage (between
A and B), the edge steepness, overshoots and undershoots, as well as level dips (as caused by reflections).
All these features are summarized in the quality level value. A reference voltage is changed iteratively by the
PBT such that max. 20 glitch, edge and level errors can occur per 1,000 bits.
Subsequently, the PBT activates error counters for glitch, edge and level errors. These error counters display
the accumulated number of bit errors per 1,000 bits. The following definitions apply:
PROFview XL 5
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