Modbus RTU comunication issue

[cooldjmc]

Hi, i’m getting a comunication issue in Comunicator after some modbus rquests that are workink ok, i get this error messages:

2019-06-17 17:00:09 Communication session with the Device 4 “Compresor 4”, type: KpModbus, call number: 4
Request element group “Comp-DATA”
Send (8): 04 03 00 00 00 5D 84 66
Receive (5/5): 04 03 BA 00 00
Receive (186/186): 00 5C 00 01 00 01 00 00 00 00 00 00 00 00 00 00 00 00 00 01 00 01 00 01 00 01 00 01 00 00 00 00 00 00 00 00 00 00 00 28 00 24 00 1F 00 00 01 87 00 00 00 0C 00 04 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 15 00 12 00 02 00 08 00 28 00 2C 00 25 00 10 00 00 00 00 00 00 00 00 00 00 00 00 00 00 02 E2 01 4B 00 00 00 05 00 00 00 00 02 03 02 03 00 00 00 00 00 00 00 39 00 00 00 00 00 00 00 00 00 00 00 4B 00 00 00 00 00 00 00 00 00 00 00 17 00 00 00 00 13 70
OK!

2019-06-17 17:00:10 Communication session with the Device 4 “Compresor 4”, type: KpModbus, call number: 4
Request element group “Comp-DATA”
Send (8): 04 03 00 00 00 5D 84 66
Receive (5/5): 04 03 BA 00 00
Receive (186/186): 00 5C 00 01 00 01 00 00 3F 3F 00 00 00 01 02 00 00 00 00 00 00 01 00 01 00 01 00 3F 3F 3F 3F 01 00 01 00 00 00 00 00 00 00 00 00 01 00 28 00 24 00 1F 00 00 01 87 00 00 00 0C 00 03 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 3F 3F 00 00 00 00 00 00 01 02 04 08 00 00 00 00 00 00 00 80 00 00 00 00 00 00 00 15 00 12 00 02 00 08 00 28 00 2C 00 25 00 10 00 00 00 00 00 00 00 00 00 00 00 00 00 00 02 E2 01 4B 00 00 00 05 00 00 00 00 02 03 02 03 00 00 00 00 00 00 3F 3F 00 39 00 00 00 00 00 00 00 00 00 08 00 4B 00 00 00 00 00 00 00 00
CRC error!
Request element group “Comp-DATA”
Send (8): 04 03 00 00 00 5D 84 66
Receive (0/5):
Communication error!
Request element group “Comp-DATA”
Send (8): 04 03 00 00 00 5D 84 66
Receive (0/5):
Communication error!

2019-06-17 17:00:14 Communication session with the Device 4 “Compresor 4”, type: KpModbus, call number: 4
Request element group “Comp-DATA”
Send (8): 04 03 00 00 00 5D 84 66
Receive (0/5):
Communication error!
Request element group “Comp-DATA”
Send (8): 04 03 00 00 00 5D 84 66
Receive (5/5): 04 3F 3F 03 BA
Incorrect PDU function code
Request element group “Comp-DATA”
Send (8): 04 03 00 00 00 5D 84 66
Receive (0/5):
Communication error!

2019-06-17 17:00:18 Communication session with the Device 4 “Compresor 4”, type: KpModbus, call number: 4
Request element group “Comp-DATA”
Send (8): 04 03 00 00 00 5D 84 66
Receive (0/5):
Communication error!
Request element group “Comp-DATA”
Send (8): 04 03 00 00 00 5D 84 66
Receive (0/5):
Communication error!
Request element group “Comp-DATA”
Send (8): 04 03 00 00 00 5D 84 66
Receive (0/5):
Communication error!

2019-06-17 17:00:23 Communication session with the Device 4 “Compresor 4”, type: KpModbus, call number: 4
Request element group “Comp-DATA”
2019-06-17 17:00:23 Error communicating with Device 4 “Compresor 4”: Error writing data: Uno de los dispositivos conectados al sistema no funciona.

2019-06-17 17:00:23 Close serial port COM4

2019-06-17 17:00:23 Open serial port COM4
2019-06-17 17:00:23 Error executing the communication channel actions before session with a device: Error opening serial port: Access to the port ‘COM4’ is denied.

2019-06-17 17:00:23 Unable to communicate with Device 4 “Compresor 4” because connection is not established

2019-06-17 17:00:24 Open serial port COM4
2019-06-17 17:00:24 Error executing the communication channel actions before session with a device: Attempt to open serial port can not be earlier than 5 seconds after the previous.

2019-06-17 17:00:24 Unable to communicate with Device 4 “Compresor 4” because connection is not established

2019-06-17 17:00:24 Open serial port COM4
2019-06-17 17:00:24 Error executing the communication channel actions before session with a device: Attempt to open serial port can not be earlier than 5 seconds after the previous.

2019-06-17 17:00:24 Unable to communicate with Device 4 “Compresor 4” because connection is not established

2019-06-17 17:00:24 Open serial port COM4
2019-06-17 17:00:24 Error executing the communication channel actions before session with a device: Attempt to open serial port can not be earlier than 5 seconds after the previous.

[Mikhail]

Hi,

How the devices are physically connected to Rapid SCADA server?

[cooldjmc]

Hi, are conected with USB to Rs485 converters, there are 2, each one conected to a USB port on the mainboard. Each converter pulls 2 RTU Slaves. But the test i made is only with one slave active.

[Mikhail]

The log says that there are problems with a converter:

2019-06-17 17:00:23 Open serial port COM4
2019-06-17 17:00:23 Error executing the communication channel actions before session with a device: Error opening serial port: Access to the port ‘COM4’ is denied.

[Mikhail]

May be other application uses the same port COM4.

[cooldjmc]

Thank you for your answers. what i don’t understand is after this:
2019-06-17 17:00:23 Communication session with the Device 4 “Compresor 4”, type: KpModbus, call number: 4
Request element group “Comp-DATA”
2019-06-17 17:00:23 Error communicating with Device 4 “Compresor 4”: Error writing data: Uno de los dispositivos conectados al sistema no funciona.

2019-06-17 17:00:23 Close serial port COM4

the COM port remains blocked and no other app can open it, also if i try restart the computer it won’t restart remains on “Shutting down windows ” screen and i must reset it.

[Mikhail]

Seems like hardware problem. What USB-COM converter do you use?

[hethongscada62]

Dear Mr. Mikhail.
I am creating a new project “Smart ScadaFarm” on Raspberry Pi4. It is running but not unstable. Maybe all my devices are connecting to RaspberryPi4-server via Rs485-WiFi converter. Is that the cause of instability?.
Now i want that all these devices will be connected to Raspberry Pi4 via RS485-USB converter. Can they connect to Pi4? How will i configure?
Thanks and best regards

[Mikhail]

Hello,

Is that the cause of instability?

You should provide communication logs to check.

Can they connect to Pi4?

Depends on the converter. I can’t suggest a particular. As I know, many of them work with RPi.

[kumajaya]

I recently have a bad experience with Moxa NPort device for transmit Modbus RTU over ethernet in RFC2217 mode. I have to compile Moxa Real COM driver for a stable communication. Working flawlessly after.

[Mikhail]

Using Moxa NPort, I prefer TCP server or TCP client mode.

[kumajaya]

@Mikhail Today I realized how simple NPort in TCP mode. Thank you.

Not actually NPort device I use here but a GSM modem from Moxa with a serial port. With a private IP from GSM operator, the only option to access it is via OnCell Central Manager. OCM map the serial port to a local TCP port.

[Mikhail]

If you use GSM modems, you can try a mode when Communicator is TCP server, and a modem is TCP client, so a modem doesn’t need static IP address.

[kumajaya]

I’ll try it @Mikhail. For now I accessed it from Node-RED using node-red-contrib-modbus. I have to enable TCP in telnet mode because got incorrect Modbus stream in default TCP mode.

[SGG]

Hello Mikhail and team,
I have rapid scada connected to 6 modbus devices through rs485…they all worked and communicated effectively at first…2 days later, I observed that only the terminal (at the end of the daisy chain) device is communicating. When I turn off that device, it picks the next terminal device and communicates with it properly…I later changed the “number of request retries on error” in the communication parameter from the default 3 to 20 and all the device started communicating. I observed that for some devices, it takes about 14 retries before a response is sent by the device.

I dont know what might be caussing this, although, I suspect I need to insert a terminating resistor of 120ohms…kindly help me with any suggestion from experience.

[Author]

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