ERP-Scale supports SAPODA to provide a direct connection between SAP and the scale without the need for additional software.
For your set-up you could run ERP-Scale on a server in each plant and have it communicating to the scales via TCP. Alternatively you could install ERP-Scale on a PC near each scale and connect the scale to the PC via serial or USB connection.
One installation of ERP-Scale can support multiple scales and multiple SAP instances.
If you require the weight in a custom development, you might find the RFC HU_GET_RFC_DATA simpler to use. In this case you do not require PCo, a simple RFC call is sufficient to get the weight. You can find some sample code here.
You might also consider placing a bar code near each scale with an ID.The operator can then scan this bar code as part of their weighing process. This allows your custom program to identify the scale and communicate with it via RFC. The packing station profile configuration is very helpful in this area.
(Note: ERP-Scale is SAP certified)
Good luck with your solution.
Ian