I am trying to design a system for monitoring a number of PLC-controlled industrial machines. I explained remote monitoring of PLC/Equipment to the factory that hired me, and they put me in charge of "implementing it on our machines" Note that I am relatively new to PLCs but I have worked on FPGAs and Micro-controllers before.

The machines that I am talking about, consist of a few ABB ROBOT waterjets (different models) and a number of gigantic sheet forming machines. All of these machines are controlled by S7-300 PLCs and most of them have HMI panels (with MS Windows) connected to them. I am free to re-program their PLC's or add/remove other PLCs to them if it is needed. (I have access to the source-codes)

At first I thought connecting PLCs to a network is as simple as putting a PC on a network. There are a lot of "Factory Floor Supervision" solutions and SCADA products on the net, so I assumed that it is relatively straightforward to do so.

It looks like I have to configure PLCs to connect to a network, add ethernet modules to the PLCs, (use some kind of OPC server) so that they send the variables that I want, then connect them through a network switch, and then convert and show the data that the OPC server has gathered, remotely. Am I right about the process?

I also assume I have to spend some debugging time, "hunting" the variables that need to be monitored remotely. Can I find the address of these variables through Simatic Net?

 

> "I explained remote monitoring of PLC/Equipment to the factory that hired me"

My first thought: why "explain" something you don't yet master properly? ;-)

Networking PLCs is not trivial.
Briefly, in your case check first:

- analysis of network family: Profibus DP, Profibus MPI, Ethernet.
Profibus port is standard on all S7 CPUs but you need special hardware to connect a PC to a Profibus network.
Profibus MPI is the standard programming port.
Profibus DP is fieldbus oriented: you may run some data transfer on it, but be aware that you might somehow interfere with the fieldbus network (devices , motors, valves, etc) and stop the PLC. Ethernet port is available only on some CPU models, otherwise you must add an expensive Ethernet card (CP) to each PLC

- analysis of protocols and connection type ("transparent" S7protocol, coordinated/uncoordinated data transfer, etc). Choice depends on the device(s) you want to be the "data collector(s)" and on the grade of "transparent vs. confined" PLC memory access you want to allow.

- analysis of what data you want to read and write. You must go through each PLC program and identify relevant data. You may even need to write some code (e.g. calculate parts actual process time, idle time, production counters, etc.)

- available CPU communication resources might be another possible issue, check in each PLC project how they have been configured and how many are free.

On the networking HW side, I suggest you to evaluate "IBH Link S7++" or similar products to easily reach Profibus CPUs using the floor LAN. IBH products come with a free DLL you can use programmatically in PC-based applications.

Snap7 at sourceforge.net is another interesting mean (Ethernet only) to connect multi-platform devices to S7 PLCs. Have a look at its web page, for S7 communication is there briefly but clearly explained.