Passing Modbus Commands via SCADA system

J

Thread Starter

Jim bartlett

I have a potential customer who has a PA system connected to a SCADA system via a RS485 MODBUS input. I need to connect a PC to the system to send commands to the PA controller. As there is only one MODBUS input to the PA controller I cannot connect the PC to it. Is it possible to connect to the SCADA system via TCP/IP and get it to forward the PCs commands on to the PA Controller.
 
How is the SCADA system connected via RS485 to the PA controller? Computers generally don't have RS485 ports.

Since the SCADA software is the master(?) of the RS485 network, if you want to send commands to the SCADA, it has to be sent to the SCADA software not just the SCADA computer. this is because the SCADA software will generally not share the computer's serial port with other applications.

You could put a Modbus serial-ethernet gateway at the PA controller end. This way the SCADA system and your PC could access the device via ethernet.
 
> You could put a Modbus serial-ethernet gateway at the PA controller end. This
> way the SCADA system and your PC could access the device via ethernet.

This assumes
- that the PC can run or is running Modbus master software. An alternative is having the PC be a slave, where the SCADA continuously polls the PC for PA instruction changes.

- the slave (an RTU slave) can handle two Modbus Masters. Some do, some choke.
 
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