In SCADA, we use this thing a lot because there are a lot legacy equipments that are still cabled the old way using differential signal.
RS485 is physical layer (some people says ‘standard RS485’, thats a mistake) communications between the equipment and the host, there are advantages for use RS485 still today:
- Datathrougoutput up to 10Mbps
- Long distances (up to 1.2km) depending of the signal datathrougoutput
- Low noise inmunity
- Master slave devices uses this physical layer via point multipoint, and so on.
I started this fast tracking project about two things:
- I don’t like the quality of USB-RS485 converters
- Have no rugged connectors
- Are not simple to carry
You can download the schematic and board in eagle here
Right now i am in the prototyping phase, and that is what i got.
The PCB size is about a USB Thumbdrive and has protection circuitry. This will not harm you if a reverse current flow over the 485 part (it has happened, on network events of the grid in SCADA).
And now we have the PCB Board. Really tiny, maybe three of them will fit in my hand. Very good finish but now i have to request the parts to make it works.
Once again the same mistake of silkscreen, i have to make the adjustments for the next ones.
Now i have assembled the converter, there is how it looks (pretty well ahh):
Bellow is a simple test of a Nexus Meter 1250 with another of the functional prototypes of the isolated USB-RS485, my test bench is:
- An UPS connected to the power line
- A Nexus Meter 1250 with only phase A cabled to power line and reference Vref
- My Isolated USB-RS485 converter
- A Laptop
- Communicator EXT software (default communication software for Nexus Meters)
To show the functionality i made a video explaining a brief of the work between the PC and the meter