I am using Omron PLCs on a project and just wanted to give my opinion. I've liked them so far, except for their documentation and manuals.
Project
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Collect fault data from around 30 PLCs from the plant floor and bring them into one PLC. All PLCs are Omron CS1G-H Ethernet networked using the ETN11 card.
Pros
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1) Very good communication and data exchange capabilities (once you learn the setup)
2) CX-Programmer is easy to use after you spend a few hours with it. But, although it has online edits, there isn't a function to test your edits like you do in RSLogix. You just make the edit and send it to the PLC.
3) I think they have free tech support (I'm not sure), but Jay helped me out whenever I got stuck.
Cons
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1) I admit that I didn't read every word in the ETN11 manual and the CX-Programmer User guide. But I think the information is scattered around the manuals and its hard for a beginner to find all the information in one place and its a little confusing. The PLC is called a PC (Programmable Controller) and it gets confusing when they talk about communications to a PC (personal computer).
2) Compared to AB, there is lack of an online Knowledgebase, white papers and the help within CX-Programmer is not as good. The Instruction help does not give an example, which would really help a beginner.
Some of the things that I learned which were not explained well in the manual in my opinion:
1) Auto Adresss Resolution in the Unit Setup can be used only if all the PLCs are on the same Ethernet network segment. If you have to go across Ethernet network segments, you are limited to 8 network segments per ETN11 card and 32 PLCs in total. We ended up using 2 ETN cards because we had to communicate to 10 different Ethernet segments.
2) When you transfer the Unit Setup to the PLC, it overwrites the IP Address table for all nodes on that FINS network. In other words, all the PLCs on a FINS network share the same IP address table. This can create a problem if someone adds a new node to the network and unknowingly downloads the IP Adress Table to other nodes on the FINS network.
3) And when creating the control structure for FINS commands (SEND, RECV), if the manual had specified that the Unit number of the CPU be used, instead of just saying Unit number, it would have saved me a weekend