invalid data decoding in Kepware OPC

Dear all,

I have two analyzers communicating with Kepware OPC through MODBUS serial communication protocol over RS485. i am going to upgrade the HMI and i want to change the communication physical media to be over ethernet.

Existing physical communication is : RS485, two wires connected to female 9 pin port, pin 2 "RX" and pin 4 "Data terminal ready"

upgradation component and the existing situation:
1- using PHOENIX FL COM server RS232/422/485, i convert the physical layer from RS-485 to ethernet.
2- in the PC i use PHOENIX redirector software to create virtual serial com with the same setting of the hardware com that was in using before.
3- through the Kepware OPC i change the communication com to the one we are using.

Observation: communication done and the connection statues is Good, the analyzers are connected successfully to kepsware OPC but the problem that all data coming BAD quality. OPC cannot decode the data.

any one have suggestions what the problem may be or how can i solve the problem.....

thank you in advance
1. The Phoenix Contact FL COMSERVER (serial-Ethernet server) has two models. Only one model supports Modbus, the 2313452. Do you have the 2313452 model that supports Modbus?

2. The DB9 connector is RS-232 only, so your RS-485 connection can not use the DB9 connector. Are your RS-485 signals connected to terminals 5, 6, and a signal ground to terminal 7?

3. Hopefully the analyzer RS-485 signals are A/B, or (+)/(-), or something that is not Data Terminal Ready (DTR) because DTR is an RS-232 handshake signal, not an RS-485 handshake signal.

4. Presumably the network is a multidrop network with daisy chained wiring. Only one analyzer is the end-of-line unit with a terminating resistor and the FL COMSERVER is the other end-of-line device, so it should have its terminating/biasing resistor slide switch enabled.

5. Are the TD and RD LED's blinking green and yellow, indicating RS-485 data transfer?

6. Is the red (error) LED lit?
Thank you Mr.Davied for your reply

1- yes i have this model and in the application configuration it can be configure to be modbus TCP/IP. but i configure is like TCP protocol only

2-i am not sure it is RS232 or RS458 but only two wires is there connected to pin 2 RX and pin 4 data terminal ready.

5- yes plinking but can not read the memory location of the OPC tag.

the following is the error log come on the Kepware OPC

11/11/2020 10:49:35 PM Warning Modbus RTU Serial Unable to read block address [300014 to 300014] on device 'Channel1.Device1'. Unexpected characters in response.
for your point 4 i will check and reply you tomorrow but till that is there any suggestion what i can do.

thank you so much for your reply
1. You must determine whether the analyzers talk RS-232 or RS-485.

Since RS-232 is point to point only, the hardware is likely half duplex RS-422 or RS-485. Getting the right hardware layer is critical. Read the manual for the analyzer and confirm which hardware layer it is using and wire appropriately.

2. You did say how it was wired. DB9 or which screw terminals? These factors go with item 1, above.
Which hardware layer is in use and is wired properly?

3. Non-Modbus serial-ethernet servers do not work with Modbus RTU. Modbus RTU has critical timing features that non-Modbus serial-Ethernet servers ignore. That's why there are Modbus versions of serial-Ethernet servers.

If you want this to work, you need to configure the PC FL COMSERVER with the Modbus features.