PLC Selection

[MasterCAT 0]

Hello ... I have programmed many PLCs, but I never needed to know the answers of following questions untill yet. I got always the PLC and then I wrote the PLC code. 1. How is the way to select the right PLC? 2. I only found data about user memory and I/O memory. Is the CPU usage also important? 3. How can I determine the memory, if I want to implement a PID controller? 4. Which CPU usage is critical to implement an additional PID controller. Maybe there is a list or tool with the information about the needed memory and the process time, for example for a PID controller. Thank you so much for your answers.

[AndrewG 13]

I would start by thinking about the size of your overall control system. For example, if you want to choose an Allen-Bradley PLC, and you know you have a large control system with a lot of I/O, you probably want the ControlLogix PLC. If you have a smaller system, the CompactLogix. An even smaller system, the MicroLogix. Once you have a rough idea of how many I/O points you will need on your control system, you can start to see which PLC would be a good choice. I'm assuming you want to implement a PID controller by using the PID instruction in RSLogix500/5000. You can create a new project file in RSLogix500/5000, add a sample PID instruction to it, then look at the Controller Properties, there should be a tab showing estimated memory usage.

[chantecler 15]

http://literature.rockwellautomation.com/idc/groups/literature/documents/sg/1761-sg001_-en-p.pdf http://literature.rockwellautomation.com/idc/groups/literature/documents/sg/1769-sg001_-en-p.pdf http://literature.rockwellautomation.com/idc/groups/literature/documents/sg/1756-sg001_-en-p.pdf http://literature.rockwellautomation.com/idc/groups/literature/documents/sg/2080-sg001_-en-p.pdf