SBC vs PLC

[Evnttrggr]

Hi, I would like to have views on using SBC's. When does one opt for this option? I believe that they are good in discrete controls or if you are an OEM ex: wind turbine control systems and need to mass produce a application specific control system. How about having a soft PLC on an industrial computer, like Beckhoff and having I/Os connected to it? When do such designs really make sense? Are they reliable? When using SBC's, can one have different applications (developed in Java/C++) running on it? Then in that case, what is the difference between the SBC and a PAC system, say from Rockwell? I am trying to understand the obvious differences in the two systems and the advantages of using one over the other. Thanks in advance...

[RussB]

One of the biggest differences is that the PAC is a dedicated control which usually uses a dedicated programming platform. With the best of the lot one has at least 5 programming languages to choose from. The GEIP PAC gives you the 5 EIC-61131 programming environments plus 'C' Blocks. Being dedicated there are certain liabilities built in that are not necessarily available with an SBC running a standard OS like Windows or Lynux. Yes there are trade offs so choose the platform that best fits your project. Generally a PAC makes more sense for the one-off or low volume systems and the SBC for an OEM who needs to clone hundreds of systems.

[ianbuckley]

PLCs (or PACs) dedicate the whole processor to the control function. The operating system is designed solely for this purpose. With a softPLC, you are using a processor that was designed to run business applications and dedicating part of its resources to the control function. From what I have seen, how they divide the functionality varies by vendor. Some of them have co-loaded operating systems, and others ride on top of Windows. It seems they have made great strides in the reliability of softPLCs, but I am still skeptical. I know from my own computer use that any machine that runs Windows must be rebooted from time to time. Even if the control function is co-loaded and working while the main OS goes screwy, you lose whatever you are using under the main OS or you have to shut down the control function while you reboot. I am interested to see other responses. Maybe things have improved to the point where my skepticism is unwarranted.

[Evnttrggr]

I too share ianbuckley's skepticism on using soft PLCs on business computers. I have seem OEMs use RTOS and run their own JAVA/C++ based application on the SBC's. But this is a scary prospect when it comes to troubleshooting the system. So, for one of our clients we suggested using something like Codesys or Isagraf. We found that in terms of cost, it was not very helpful and even with volume production, the client was not able to save much through this. So then what would be a good solution? I have not come across many SBC based solution, but surely would like to see some. What I would like to see in them is basically reliability and ease of troubleshooting the code. Does any one has any good ideas?

[DanW]

> I have not come across many SBC based solution, but surely would like to see some.