1.What is number of slave devices which connected to the master device?
2. What is the loop total distance and maximal length between devices?
3. Compare port setups between the master and all its slave devices: baud rate, format and parity (for new installation)
4. Check for duplicate devices’ addresses.
5. All slave devices should be corrected to one chain , the RS-485 loop cannot be spitted.
5. Type of cable: shielded twisted pair.
6. Shield of each segment must be grounded.
Shield of each segment should be connected into SH terminal to only one device.
See illustration below:
First segment of the communication cable: Shield connected to SH of device#1 and grounded, but not connected to the master.
Second segment of the communication cable: Shield connected to SH of device#2 and grounded, but not connected to SH of device#1.
...
7. Communication cables should be installed separately from power and current measuring cables.
8. Only one master can to connected to the loop. What is the Master Device type?
9. Only one client in ethernet can send Modbus TCP requests to specific slave device via the Master device at specific time.
10. Termination resistors 100-120 Ohn between ‘+’ and ‘-‘ of RS485 cables: On Master’s side and at end of the loop.
If the Master device is ETC-II or ETC2002, it has a termination resistor inside, but on end of the loop termination resistor is required.
11. Are there specific hours when connection is interrupted?
12. Connection to which devices interrupted? Is communication interrupted to same devices every time?
13. Can you split the loop temporary to find which device of segment of communication cable is causing the issue?
14. When connection to some device is interrupted, do not restart the device.
Else stop temporary requesting on the SCADA to all devices in the RS485 loop and test communication using PAS. Does it response?
