On-board troubleshooting
15
Low signal level or missing signal
A transmission error can be caused by a low signal level. One possible cause for a low
signal level is that the other half of the differential signal is missing. Also, the entire
signal can be missing. You can measure the signal levels with an oscilloscope.
It is not recommended to use a multimeter, as it does not properly indicate
the status of the transmission line.
To find out whether the transmission error is caused by a low signal level or a missing
signal, do the following:
1 Set the vertical amplification of the oscilloscope to 2v/div or 5v/div and the time
scale to 1µs/div or 500 ns/div.
2 If you need to measure line A, connect oscilloscope channel 1 to pin 1 and channel
2 to pin 2 of connector M1. If you need to measure line B, connect oscilloscope
channel 1 to pin 4 and channel 2 to pin 5.
3 Connect the ground of the oscilloscope channels to PE (module front panel).
4 Set the oscilloscope for a differential measurement (channel 1 - channel 2) and
determine the cause of the problem by the resulting waveform.
The following figure shows a normal waveform that indicates no transmission errors.
Figure 4.1: No transmission errors
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