I am entirely new to the OPC-UA world.
I need to establish a proof of concept of how to allow our ERP to communicate with PLCs. I am evaluating software that acts as an OPC-UA server (it is working). I found about Milo and got the code working in Eclipse. Looking at the examples, I got a toy program connected to the OPC-UA server and doing... something.
The basic plumbing works, but I can't figure out where to start with OPC-UA and Milo. I have not been able to find introductory material to help me make sense of it all.
Is there documentation about the architecture of OPC-UA and how Milo implements that? Is there a better way to go about it than looking at the examples to figure out how things should be done?
Documentation for Milo is one of the next major things to tackle now that we've got a release published to Maven central. Even once that documentation exists, though, it will assume some knowledge of OPC UA.
There's a somewhat expensive green book called "OPC Unified Architecture" available on Amazon. I haven't read it myself, but I've heard other people mentioned they have. It's probably a lot easier and cheaper than trying to learn OPC UA from the specifications.
edit: Seems there's a couple other cheaper alternatives now too.
The Milo project has a gitter channel and a mailing list you can ask questions on as well.
Related
I'm wondering if for simply communicating with a PLC, like reading and writing tags, do I need all of the other heavy lifting that comes with an OPC-UA server?
I've tried writing a simple server in Python that talks to the PLC, but I get denied when requesting information from the PLC.
The Controllogix PLC I'm attempting to communicate with uses Ethernet/IP to communicate, so why doesn't a simple server/client script work? What is required exactly to communicate with an Allen Bradley PLC or PLC's in general?
There is quite a bit required to communicate with a PLC.
Each vendor has a driver, there are firmware compatibility considerations. Different protocols to think about.
OPC-UA makes it a bit more generic, but OPC-UA still has a set of things to work around when setting up communications.
Most of the OPC products I've worked with, needs to have their security adjusted to allow anonymous communication. It's generally bad practice to do this. (A network intrusion would be able to read/write to your automation layer) There is certificate signing and some encryption business that needs to be turned off if you're looking for simple communication. (Again, not a good practice but ok for learning)
After all that you have to have a notion of how your PLC is set up on your OPC server, there are channels, devices, namespaces etc. You'll point the OPC client to some opc.tcp://:
If you got this far you're almost done, I'm assuming your OPC server is running and has tags configured at this point. You can use your OPC-UA API to do a read. It can return just the value, or you can get an object back with tag health, timestamp, and a bunch of other data. Depends on the implementation. After that you can do subscriptions, writes...whatever else you need.
TLDR: OPC server not required, but may be the easiest method. Turn off security. (But turn it back on before exposing your control layer to the net)
I am also a little late to this conversation. If you are interested in coding your own solutions and don't want to use any of the commercially available standards, AdvancedHMI is a "mostly" open source solution written in VB.NET which is 100% free and provides communications to many different PLCs including the ControlLogix platform. Since I see you are programming in Python you may also be interested to know that the project does work under Mono on the Linux OS. I have used it to write gateways between EthernetIP and ModbusTCP and to pull data serially from OEM devices and push this data to a CLX PLC.
The forum is full of many helpful hints and is very active and supported.
Just trying to give you another option. DDE, NetDDE, FastDDE, OPC, DCOM, Suitelink.... These are all good, but mostly a pay to play adventure. As a programmer, it seems ridiculous to have to pay such an excessive amount of money just to talk to my hardware, IMHO. Sorry for the rant. Have Fun!
Update - Just wanted to also suggest the following open source project written in python:
https://github.com/dmroeder/pylogix
I have used this to write small programs for communicating with CompactLogix and ControlLogix. (Even to/from a RaspberryPi!)
Depends on several factors, if you want something simple to program you can opt for Modbus/TCP I think some AB PLC supports it without extra hardware.
However if you want something with more security for example for industrial use then OPC UA would be better choice but the programming has a complexity far higher than Modbus, even using the libraries of OPC Foundation or others. There is the option of using a commercial or free (if any) OPC UA server to save work, then you will need to program the client side only.
With Ethernet/IP it should also be possible, but the problem is that there is no clear specification and even different AB models talk different Ethernet/IP dialect ! , it is also far more complex to program than Modbus.
I am a little late to this discussion, but there are a couple commercial tools that make this a bit easier. The one that comes to mind for me when you say you are using python is Cogent's data hub. It is certainly not the cheapest tool out there, but they have already done all of the heavy lifting for PLC/PC communications & security.
If trying to read CLX data using Python, there are several open source implementations that will save you a lot of work. Such as this:
https://github.com/dmroeder/pylogix
If you use .NET and Visual Studio, you can use AdvancedHMI
to be able to read and write OPC Tags to ControlLogix platform is done via its communication Driver RSLinx. RSLinx acts as an OPC Server, it will need to be configured to communicate with the PLC and run on a networked PC on the same LAN. Several flavours of RSLinx are available (for WAN/VLAN also) but essentially this is the communications driver you need to talk to AB PLC's
I have an application whereby I need to read data from a PLC into a database and whereby I need to develop my own application to do this. I just need to read 5 values from the PLC and log it to a DB. I have a demo OPC server running and can access it via UA or DA.
After looking at many different approaches I settled on using an OPC server to connect to the PLC and then to write an OPC client to interface to the OPC server and then write the data to the DB from my app. My language of choice is C# with .Net and the only licence fee I am able to pay for is for the OPC server from my PLC vendor.
What I am however finding extremely frustrating is getting the right info on OPC to get started. I dont want to buy any stacks but would prefer an open source stack. The information seems very fragmented and all over the place. Most of the info about OPC seems to be hype about how easy it is to use etc.
The best post on Stackoverflow that I could find is: Noob guide to OPC: how to write a C# Hello World client? and some of the links are not active any more.
My question is therefore are there any good tutorials showing how to build and OPC client from scratch in .net and what is the best open source SDK to use without having to buy a vendor's stack?
Is DA also worth learning or should one stick with UA?
The big question is why is OPC so frustrating when its marketed as being so easy?
It would also be nice to have a nice high level guide on the theory that one needs to know to build a client. I do realize that with time its possible to eventually figure this from the resources available but with limited time to make sense of all the scattered resources a quicker guide would be helpful.
Stick with OPC UA.
Luckily for you, the OPC Foundation's C# reference implementation has the capabilities of both stack and SDK, whereas other language reference implementations are typically just stack functionality.
The code is available on GitHub: http://opcfoundation.github.io/UA-.NET/
If you're not a member of the foundation the code is available under GPL2.
As for your concerns about the ease of use and marketing... I assume it's because OPC UA is marketed towards end users, who will just be hooking up various OPC UA compliant applications, which is easy. As a developer I think its fair to say there's a little more assumed about your ability to figure things out... from code examples, the specifications, books that are available, etc...
I want to set up a SOA platform to demonstrate the key ingredients of it. Not knowing much about this topic, this seems to be an difficult task. I hope someone can clarify some points for me. I am aware that SOA has no exact definition, but I am trying to get some sense into it.
What are common platforms and development tools? Everything seems to have a little bit SOA in it, but I am searching for the big ones. Something like that?
platforms: IBM WebSphere, SAP NetWeaver, RedHat Jboss SOA, HP SOA, systinet software, Microsoft .Net
development tools: Eclipse SOA, NetBeans SOA, Visual Studio
What are the key ingredients of a SOA platform? I figured something like this:
Service Registry, Enterprise Service Bus, BPEL-Engine, Application Server
Can I mix components from different platforms? I especially don't get the concept of the application server which every platform contains. Is it just an Java EE Environment?
I want to set up an environment for experimenting and demonstration. It should be based on some opensource SOA platform and developed with Eclipse SOA. I want to create a few services (with for example basic math operations), a Registry and a BPEL controlled process. What SOA System is suited best for me? Easy to learn, maybe good tutorials?
Any answer to any question would be awesome and be greatly appreciated.
1) & 2)
See this article and you may understand exactly what it is.
3) it will be a little hard unless you are extremely fast developer/deployer & configurator - I'm talking you work as fast as 10 people for a few months. Why not use existing examples ? Like Google for example
I would start with Apache Axis/2 and Tomcat for you server environment.
And the splendid SOAPUI utility as your client. Moving on to real Java/C/perl/php/Python/C# or whatever clients as the server side develops more.
Don't bother with the heavyweight commercial servers like until you have a specific need for them as the installation and configuration is usually really tedious and most of their functionality is available from Apache.
I want to try developing an XMPP server component using XEP-0114: Jabber Component Protocol.
Which server do you recommend and why? I'm talking about ease of development, community support, documentation, examples, etc.
That's a hard question to answer, because I doubt there are many developers involved in developing across multiple XMPP projects and languages.
I can throw out a few personal perceptions but... I could be off-base!
What you're really looking for is which libraries would be recommended for component development. All the servers support the component protocol, so all you really need is a socket connection to the server and some helper routines to make the repetitive stuff like message parsing easier.
Where the server might matter is if you need tighter integration.
For example if you want your component to scale the same way as Ejabberd then you'll probably want to use exmpp.
If you need to deploy your component alongside Openfire into Java only enterprises, then you'll probably want to use smack.
If you are familiar with Python and want to prototype quickly use Wokkel.
I don't think documentation is going to be great for any of the libraries (haven't looked at them all though!) but that shouldn't be a huge burden. All you really need a good book on how the XMPP protocol works and then some sample code from the library and it's fairly easy to move on from there.
For an easy-to-use testing server I like openfire. Good instructions, easy to hook in components, and a good web interface for administration. Debugging is more of a "tail -f" on the logfiles, slightly java-ish.
I've used XCP professionally, but that's really for commercial use. It works well but if that's not your target deployment it's not worth the effort. I'm not sure if you can buy it separately any more.
I tried using ejabberd and I gave up quickly. I found the documentation for setup and administration awful. The config files are not self describing and there's no good walk through on the ejabberd site. It may be able to even fry my eggs in the morning for breakfast, but I couldn't get past install with the time I'd allotted to it.
For Openfire, there is something called Whack, which is a Java library for creating server components (XEP-0114).
Since the communication is over sockets, I presume the same code should work for any well designed XMPP server (such as ejabberd). However, I have only tested it with Openfire and it works quite well.
Is there anyone who has used or looked into using Jitterbit as well as BizTalk? If so, what are some pros and cons of each, and which one did you go with as your final solution?
Specifically, I'm looking for SAP integration, but any input would be appreciated.
Like Rob I have not heard about JitterBit until reading your question (thanks!), I have, however, been working with BizTalk, almost exclusively, for the past 9 years; for that reason I wasn't sure I should be responding, but as Rob did, and nobody else has, I figured it's worth a couple of cents....
From the little reading I've done it seems to me that JitterBit, apart from being an open source, which has it's pros and cons, is trying to lower the entry barrier by offering a relative simple solution with the promise of rapid development and drag-n-drop approach "with no custom code".
I'll take their promise at face value, as I know nothing about it, although I have my doubts, so let's assume developing with JitterBit is really easy, there's one thing I can clearly state - developing with BizTalk isn't.
But, and that's a bit but in my view, developing with BizTalk is somewhat difficult not because Microsoft did a bad job at it, on the contrary - developing with BizTalk is somewhat difficult because Microsoft wanted to create a tool that could realistically allow enterprises to solve their BPM and integration needs well, and, in my experience, these problems are almost never simple, so Microsoft had built a server that has many capabilities, is very strong and very flexible, at the cost of complexity.
So, while any experienced technical sales guy can give you a demo of an integration scenario that is very simple, and is developed in a few minutes using a lot of drag and drop and configuration, even in BizTalk, but is this a realistic enterprise-level solution? was it a realistic scenario that was demonstrated? from my experience the answer is almost exclusively no; the problems tend to be complex, and their require a more robust solution.
So, I guess the bottom line would be - if you're looking for a one off solution, and open source is something you guys work with - JitterBit is definitely worth looking at, seeing if it's capable of helping out and has, indeed, a short learning curve (it would be important to look at maintenance, monitoring, trouble shooting, instance management etc)
If, however, you believe, as is often the case, that your solution would grow to become a BPM/integration platform in your organisation, and you need something more robust - I would put my money on BizTalk being a better candidate.
I've done a fair bit of integration with SAP, starting with the old SAP DCOM connector. More recently I've been involved in the selection of an integration platform to serve in an Enterprise Service Bus pattern.
We did web service samples to connect to SAP on a number of platforms, including BizTalk, Mule, Netweaver, Webmethods and Tibco. Webmethods won out based on licensing and capability, though BizTalk and Netweaver both had very high marks.
Jitterbit was not part of the evaluation - in fact I had to look it up to be sure I understood your question.
If your goal is just to be able to call an RFC, the .NET SAP connector works well.
If your goal is to expose a web service to wrapper a process in SAP, then BizTalk is good, but I recommend you see if your organization already has netweaver licensed as there are many web services available directly from SAP with no coding.
My recommendation is to avoid Jitterbug and Mule for the enterprise for now - unless Open Source is actually a popular thing at your place of employment. Netweaver and BizTalk are very robust, polished products.
If you are looking for something you can ship easily, then Jitterbug may make more sense. Though generally I'd recommend you define it as a web service call, and look to your customers technology stack for the most appropriate integration technique.
More context of what you are looking to achieve will enable a more accurate answer.
Michael,
We use Jitterbit in our organization and we've been very successful with it in various projects. Our SAP projects use XI and Jitterbit has dramatically simplified the ability to integrate web service interfaces with the various protocols it supports.
In addition to an excellent price (and we now subscribe to Jitterbit for support) we realize great value out of the support service. If we have any questions during our implementations they seem to provide all the subject matter expertise included in the support cost, so we're quite self sufficient.
We still have many other integration solutions in our company including VB and Java programs; it's a mess, but we don't believe that any one platform will meet all of our different divisions' needs. We have been using open source, specifically Linux and Apache for many years now, although IBM and Microsoft are also prevalent here.
We went with Jitterbit as it supports protocols needed to integrate any modern system and with SOA / Web Services being our stated direction Jitterbit was a great fit for what we needed.
Given that Jitterbit is Open Source, I would encourage you to download it and try it out.
I will say it simply, I have been using biztalk and was one of the people that helped validate the 2006 training course. Biztalk by far one the best server applications for Business process that is available today. You do also have to factor in the price point is ridiculously low compared to what else is out there.