User Manual PROFview XL 3 Description of Functions and Measuring Principle
3.2.3 Edge steepness
To fully evaluate the transmission properties of the bus cabling and of the individual PROFIBUS stations, the
edges must also be studied, in addition to the disturbance-free voltage range; shallow edges can also prevent
the correct decoding of the transmission signal.
The PBT determines the edge steepness separately for rising and falling edges. To this end, two thresholds
are set at 10 % and 90 % of the signal level determined (differential voltage determined at the bit center, see
Fig. 2). The time required for the differential signal to change between these voltage threshold values is mea-
sured both for falling and rising edges. The rise and fall times are determined with a resolution of 1/16th of
the baud rate used and displayed as a value between 0/16th and 16/16th. This value always specifies the
slowest rising and falling edge of the relevant frames. A measured value of 0/16th means that the level
change takes place in less than 1/16th of the bit width.
3.2.4 Signal waveform (oscilloscope display)
To evaluate signal transitions and to measure reflections, the PBT records a characteristic section of the sig-
nal waveform of a relevant frame and displays it on the oscilloscope of the PROFview XL application soft-
ware. Based on the signal waveform, various cable problems, such as dead-end branches (transient signal
dips), significantly different cable types (long reflections/level dips), short circuits, etc. can be revealed.
The triggering point for recording lies at 50 % of the recording depth and is always to be found on the first ris-
ing edge of a relevant frame. Irrespective of the selected baud rate, the signals are always recorded at a
sampling rate of 192 MSample/s and cover a time range of 12.5 µs with 2,400 points (time resolution: ap-
prox. 5.2 ns).
The oscilloscope display facilitates the evaluation of signal dips/reflections. Based on the height of the dip, it
is possible to infer the changes in the characteristic wave resistance of the cable. The length and the position
of the reflections indicate the distance to the point of interference. Two cursors have been implemented in the
oscilloscope display of the PROFview XL application software for simple measurement of the reflection
lengths and thus distances. The signal runtime is converted into a distance specification automatically. A
mean runtime constant of 4.35 ns/m is used for calculation with PROFIBUS cables.
3.2.5 Measuring cycles and measuring time
The above characteristic measured values for the signal quality are determined by the PBT for each
PROFIBUS station in so-called measuring cycles (see Table 1).
Measured Value Measuring Cycle
Quality level (incl. glitch,
edge and level errors)
Eight iterations with at least 1,000 bits of the station to be measured
(relevant frames)
Disturbance-free voltage
range, edge steepness and
signal waveform
Ten iterations with at least one frame of the station to be measured
relevant frame)
Table 1: Description of the measuring cycles
PROFview XL 7
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