Rockwell Automation 1757-FFLD Linking Device Configuration Manual - Manual (Page 110)

Publication 1757-PM002A-EN-E - June 2006
5-4 Troubleshooting
Poor Fieldbus Signals Poor signal quality can inhibit the optimization of your fieldbus network.
Below is a list of common causes for poor signal quality:
Cause of Poor Signal Result
Wrong type of cable Can attenuate the signal below the low AC cutoff limits. Also, this could lead to cable length being
too long.
Too long of H1 segment Tends to attenuate the signal below the low AC cutoff limit by inducing inductance. Also, the
length, along with the number of devices, can create a power problem.
Missing terminators Causes ringing, which will enlarge the signal outside the high AC cutoff limits.
Grounded /shorted signal wires Causes the signal to be 0 volts.
Bad terminator or junction block Can ground/short/load the signal which will cause the signal to be low or 0 Volts.
Improper shielding Causes shorts with signal wire, which will cause the signal to be 0 volts. Dressing shields with
shrink-wrap will prevent this situation!
Bad device or transmitter Causes short or load down the H1 segment.
Bad connectors Can drop transmitters off the H1 network intermittently or permanently.
Too many devices, which combined
use too much current on a
H1Segment Reduces the voltage below 9 V DC because the power supply or power conditioner cannot supply
enough power to the H1. Also results in small power dips from the AC supply. Ideally, the system
should be kept at 11 to 12 VDC at the lowest so that there is some safety margin for the devices in
the event of a poor power condition.
The power supply supplies too much
voltage Can shut down devices or damage them, make sure your power supply with the conditioner only
supplies 32 V DC out of the conditioner output terminals.
Noisy power supply Causes data loss and reset of devices when the low 9 V DC cutoff is reached.