Troubleshooting - Omron KM50 Communications Manual

Troubleshooting

Check Using the Following Table First
Communications do not operate properly, check any relevant items in the following table before
requesting repairs.
If communications still do not operate properly, contact your OMRON representative.
Problem: Communications are not possible or communications errors occur.
Possible cause
Communications are not wired properly.
The communications cable is
disconnecting.
The communications cable is broken.
The communications cable is too long.
The communications cable is not suitable.
Too many nodes are connected to the
same transmission path.
Terminating resistance is not connected to
the ends of the communications path.
Power is not supplied to the Power Monitor.
Power is not supplied to the
communications adapter (e.g., the K3SC).
The same baud rate and communications
method are not set for all nodes on the
same transmission path (including the
Power Monitors and host).
The unit number specified in the command
frame is not correct.
The same unit number is set for another
node on the network.
There is a bug in the program in the host.
The host is detecting a no-response error
before it receives the response from the
Power Monitor.
The host is detecting a no-response error
for a broadcast command or a Reset
Software command.
The host is sending the next command
before it receives the response from the
Power Monitor.
The host is sending the next command too
quickly after it receives a response from the
Power Monitor.
The transmission path is unstable when the
power supply to the Power Monitor is
turned ON or interrupted, and the host is
interpreting the unstable status as data.
Ambient noise is causing errors in the
communications data.
Location to check
Correct the wiring.
Connect the cable connector securely and tighten the screws.
Replace the cable.
The maximum total cable length for RS-485 is 500 m.
Use shielded twisted-pair communications cables with wires
of AWG24 to AWG14 (cross-sectional areas of 0.205 to 2.081
2
mm ).
For RS-485 communications with 1:N connections, up to 31
Power Monitors can be connected for CompoWay/F and up to
99 Power Monitors can be connected for Modbus. (The host
(e.g., computer) is not counted as a node for these limits.)
Connect terminating resistance or set internal terminating
resistance. Attach terminating resistance of 120 Ω (1/2 W) to
the end KM50-C/-E.
Applied the specified power supply voltage.
Applied the specified power supply voltage.
Set the same baud rate, protocol, data length, number of stop
bits, and vertical parity.
Specify the correct unit number.
Make sure every node has a unique node number.
Use a line monitor to check the command.
Reduce the transmission wait time set in the Power Monitor.
Increase the response wait time set in the host.
The Power Monitor will not return a response for broadcast
commands and the Reset Software command.
Always read the response before sending the next command.
(This does not apply to broadcast commands and the Reset
Software command.)
Allow a period of at least 2 ms after receiving a response
before sending the next command.
Initialize the reception buffer in the host before sending the
first command and after the power supply to the Power
Monitor is interrupted.
Try communicating with a slower baud rate.
Separate the communications cables from the source of the
noise.
Make sure a shielded twisted-pair cable is being used for the
communications cable.
Keep the communications cable as short as possible. Do not
lay extra cable or loop extra cable.
Do not place communications cables and power cables
together. Inductive noise may occur.
If noise countermeasures do not prove successful, use an
optical interface.
Troubleshooting
Reference
pages
1-4
−
−
1-4
1-4
1-4
1-4
−
−
1-4
2-2
4-2
1-4
−
1-5
2-20
4-12
−
1-3
−
−
A-3