Rosemount 3095FB - COMMUNICATION PROBLEMS; ALARMS AND CONDITIONS

Reference Manual
00809-0100-4738, Rev DA
May 2006
Rosemount 3095FB
5-2
COMMUNICATION
PROBLEMS
Table 5-1 identifies the most likely causes for communication problems with
the 3095FB transmitter.
TABLE 5-1. Communication
Troubleshooting
ALARMS AND
CONDITIONS
If an alarm or error condition exists in the 3095FB, it will be displayed in the
Modbus registers (Section 3: 8.1.1 in the Modbus Protocol Guide located in
this manual). Specific alarm conditions can be viewed via the Configurator
User Interface software (see the Diagnostics > Error Info... selection).
NOTE
Alarms are not logged or archived. The alarms and error conditions displayed
on the Diagnostics > Error Info... Info screen indicate the alarms present at
the time of command invocation.
Symptom Corrective Actions
No communication
between the User
Interface Software
and the transmitter
Check for proper voltage across the power terminals of the transmitter
(7.5 – 30 V dc).
Check for intermittent shorts, open circuits, and multiple grounds.
Verify the RS-485 bus is terminated with 120 Ohm resistors at each
end of the bus.
Verify the RS-485 bus is NOT terminated at points other than at each
end of the bus.
Verity that the RS-485 converter is connected to the A and B terminals,
not the power terminals
Test the opposite polarity connection to the RS-485 bus.
Verify identical baud rates for computer and transmitter.
Verify the correct COMM port is selected.
Verify the laptop computer is not in low energy mode (some models
disable all comm ports in low energy mode).
No communication
between the
transmitter and the
Modbus host
Check for proper voltage across the power terminals of the transmitter
(7.5 – 30 V dc).
Check for intermittent shorts, open circuits, and multiple grounds.
Verify the RS-485 bus is terminated with 120 Ohm resistors at each
end of the bus.
Verify the RS-485 bus is NOT terminated at points other than at each
end of the bus.
Verify the power wiring and RS-485 bus wiring are not switched.
Verify identical baud rates for the RTU and transmitter.
Verify you are talking to the correct transmitter address.
Possible noise on the bus - switch both "A" and "B" pull-up switches on
the comm board of only one transmitter to the "on" position
(see Figure 2-5)
The turnaround time for the transmitter may be too fast for RTU. Try
using a longer time (see page 4-7)
The RTU may be polling too fast and cutting off the transmitter
response messages. Try adjusting the polling time on the RTU.
Verify the software for the RTU is functioning properly.
Transmitter is not
sending meaningful
data
Verify that the 3095FB is transmitting floating point data in the correct
format for the RTU (see page 4-10).
The RTU may have register addresses referenced to 0 rather than 1.
Try subtracting or adding 1 from register addresses when polling.