Do you have another DLtech DT-9xxx converter? Because the scale is essentially a server, but because it is RS232 it is designed to be a point-to-point device. However, on the RS-485 network side of the DT-9xxx you can have multiple nodes. So if you have an extra DT-9xxx converter, you could put the PC on that network and have it send the Q\r\n string, and then the scale would respond and the PLC would see the scale's response. The only problem would be getting the PLC to ignore the Q\r\n string. Or instead of the Q\r\n you could have the PC send the "start to stream command" and then the PLC would see a continuous stream of data.
This is only an idea for bench testing. The right fix is to get the PLC to not put the two [00 03] bytes on the wire. I suspect the PLC is sending the entire string object, not just the string, and the string object comprises two items: a 16-bit integer length of the string ([00 03]), and the three characters of string data themselves (Q\r\n).