I integrated PLC TM241 with Universal Robot through Modbus TCP communication. UR as master and PLC as slave. but why wireshark does not capture Request?

Or is there any other software to test the delay time and packet loss?
Thanks

 

The reason is because of how Ethernet switches work. It sounds like you have a PLC, the robot, and a computer running Wireshark connected to an Ethernet switch. Because TCP packets (including Modbus) are unicast messages, the Ethernet switch sends those messages only to the Ethernet port in which the destination device is connected. The switch will not send the packet to your computer if it is not the destination of the packet, and so, your computer will not see the messages exchanged between the PLC and the robot.

In order to allow your computer to see the Modbus/TCP packets between the PLC and robot, you need configure the Ethernet switch to do "port mirroring" to the port in which your computer is connected. Note that not all Ethernet switches can be setup to do this. Alternatively, there are also dedicated Ethernet tap devices, such as these:
https://www.midbittech.com/

For more details, take a look at this article, particularly the Switched Ethernet section:
https://wiki.wireshark.org/capturesetup/Ethernet