MR MESSKO COMPACT - Modbus Communication Malfunctions

9 Fault elimination
975831400/02 EN
Characteristics/
details
Cause Remedy
The receiver mea-
sures a 20mA
loop current that is
too low
▪ A part of the current is run-
ning through a parallel path
▪ Load resistance too high
▪ Supply voltage too low
▪ Device defective
▪ Loop in multimeter and
measure
▪ Check cables
▪ Check receiver (load resis-
tance)
The receiver mea-
sures a 4…20mA
loop current that is
too high
▪ Device defective ▪ Loop in multimeter and
measure
Table11: 4…20mA analog signal malfunctions
9.4 Modbus communication malfunctions (type TTM)
Characteristics/
details
Cause Remedy
No communication
possible (continu-
ous)
Power supply not present ▪ Check cables
▪ Check device supply (18…
30VDC)
▪ RS485 lines A, B not con-
nected or interrupted
▪ Short-circuit A, B
▪ Ground fault A and/or B
▪ RS485 connections
swapped
Info: A = D0 = D+; B = D1 = D-
▪ Check wiring
▪ Take a voltage measure-
ment with a multimeter if
necessary (A against B; A
against Com; B against
Com)
▪ Reconnect A, B if neces-
sary
▪ Modbus address incorrect
▪ Modbus address assigned
multiple times
▪ Baud rate
▪ Parity
Info: For factory settings, see
chapter Modbus RTU
[►Section 11.4, Page 106]
▪ Check parameters (device
and master)
▪ Change parameters if nec-
essary; see chapter Config-
uring Modbus RTU
[►Section 11.4, Page 106]
▪ Device defective -