User Manual

Appendix - "Bus analysis" mode
141
12.14.3. Measurements (Profibus PA)
Diagnosis
Use this table to troubleshoot problems on a measurement :
Measurement
Description
Diagnosis
VOffset
Offset measurement on the Data
signal

Too many devices on the bus

Cable length not compliant with standard

Faulty power supply
 …
Vpp
Peak-to-peak measurement on the
Data signal

Termination problem

Cable length not compliant with standard

Faulty junction connection (oxidation, bad
contact, etc.)

Significant noise (check the cable route, ground
braid not connected, faulty chassis-ground, etc.)
 …
TRise
Rise time between 10% and 90% of
the Data signal amplitude

Cable length not compliant with standard

Unsuitable or damaged cable (the rise and fall
times increase with the cable impedance)

Termination impedance incorrectly positioned
 …
TFall
Fall time between 90% and 10% of
the Data signal amplitude
Jitter
Measurement made using the bit time
total.

Significant noise (check the cable route, ground
braid not connected, faulty chassis-ground, etc.)
 …
Time Data
Measurement made using the bit time
total. The bit time is measured on one
period (Manchester coding).

Significant noise (check the cable route, ground
braid not connected, faulty chassis-ground, etc.)

The cable length is not compliant with the
standard

Unsuitable or damaged cable
 Termination impedance incorrectly positioned
Distortion
Measurement of amplitude distortion
as defined in the IEC-61152 standard.
The max overshoot level is compared
to the signal peak-to-peak value.

Unsuitable cable impedance

Termination problem (if there is no termination,
major overshoot and the opposite if the bus
impedance is too high)

Significant noise (check the cable route, ground
braid not connected, faulty chassis-ground, etc.)
 …
Noise-Ripple
Search for the max. peak-to-peak
value for signals between 7.8kHz and
39.1kHz on the dead time part of the
bus, i.e. its power supply

Excessive noise between 7.8kHz and 39.1kHz
on the power supply (check whether the power
supply is faulty, check the cable route, ground
braid nit connected, faulty chassis-ground, etc.)
 …
Noise-HF
Search for the max. peak-to-peak
value for signals between 3.91MHz
and 25MHz on the dead time part of
the bus, i.e. its power supply

Excessive noise between 3.91MHz and 25MHz
on the power supply (check whether the power
supply is faulty, check the cable route, ground
braid not connected, faulty chassis-ground, etc.)

…