A guy at Rockwell called me yesterday. When I take those calls it never know if it’s going to be good news are bad news. Sometimes they call with an opportunity. Sometimes it’s an old friend who wants to chat. AND sometimes they’re complaining about some marketing piece or a blog piece that they thought was unfair, inaccurate or misleading. They’re always misguided when that happens.
It’s a lot like when my daughter calls. I know it’s an emergency and she wants me to cart one of her kids from here to there or she needs money. A call at work is never something I look forward to.
This call was about Linux and how his customer could get access to ControlLogix tags from a Linux application. Now using Linux to access ControlLogix is something I happen to know a lot about.
Linux is incredibly popular for lots of embedded application. Ease of use. Cost. Security. Open Sources for lots of things. There are quite a few good reasons for developers that are building plant floor HMIs and such to use Linux. I get that kind of call every day.
So I went through all the good reasons why the RTA software to move tags in and out of a ControlLogix PLC from a Linux application is such a good tool. Here’s what I told him:
1. Real easy-to-use API. After you open the connection with the PLC all you have to do is to fill a structure with the tags you are reading or writing and pass it to us. We process it and do a call back to your application with the result. Couldn’t be easier.
2. Support. When you call here for support you talk to the guy that wrote the software not some flunky that was playing the guitar last week.
3. Business Model. It’s a one time cost. You can ship unlimited binaries.
4. Linux Interface. Our software has a single file that adapts it to the Linux Sockets structure. That’s all we need from Linux so it works with any brand of Linux. In fact, it will work with any BSD compatible TCP/IP stack.
5. Speed. We can do a transaction in about 25msec or less. In a transaction you can cram in as much data as the PLC can handle. That’s about 500 bytes worth. If you have real long tag names, you won’t get many in the packet. If you have short ones or array tag names, you can do quite a bit.
Lots of System Integrators are building their own custom SCADA tools instead of using Wonderware or something else like that. It’s not that they dislike Wonderware, it’s just that they can make a much more integrated and custom SCADA tool by writing it themselves. And they also have something they can sell to the next customer.
For guys like this, Linux is the a great solution and the RTA EtherNet/IP Tag Client is the best way for them to get ControlLogix connectivity.