Mesta Automation. Lets say that you want to build your own HMI, because commercial SCADAs are too expensive for your applicationyou need more control over the code and VBA is not goodyou want to protect your know howyou need a better HMI and you cant do it with a normal SCADAand you choose to use. Net and C or Visual Basic. Net. Now the first and most important thing that you need to do is to Read and Write Data to your PLC, and to do this you have 4 choices using Modbus TCP or RTUusing OPCusing open source drivers gpl or lgpl licensed using third party libraries activex, dlls and so onNow Ill try to explain how and when to use these libraries, but more detailed articles on how to implement the code will come later. Modbus TCP and RTUModbus TCP is based on Ethernet TCPIP connection from PLC to PC, there is no need for a custom card on PC, but most of the times you have to buy an additional Ethernet Card for the PLC that support Modbus. MicroLogix 1200 Programmable Controllers Bulletin 1762 Controllers and Expansion IO User Manual. Allen Bradley Micrologix 1200 Plc Software' title='Allen Bradley Micrologix 1200 Plc Software' />In the last 2 years many plcs are provided with ethernet integrated port that supports Modbus, lets say for example Allen Bradley Micrologix 1. B or Siemens S7 1. To communicate to a PLC with Modbus TCP you need a library called n. Modbus download it on the google code site. This library has been tested a lot and its almost a standard for Modbus TCP and RTU, because it uses the same methods for both protocols. Modbus especially TCP is a good way to communicate with PLCs with C and it gives you the most of flexibility, because you build your program and you can run it wherever you want without licenses to pay and so on. If you need some examples, take a look at my article on how to use NModbus with C. Allen Bradley Micrologix 1200 Plc Software' title='Allen Bradley Micrologix 1200 Plc Software' />All manifacturers support Modbus, in particular Siemens s. Modbus TCP and RTU read more about it in the official documentation. For Modbus TCP you need of course the Ethernet card or CPU Profinet version. Allen Bradley Compact. Logix and Controllogix do not support Modbus TCP and Modbus RTU, Micrologix 1. The Allen Bradley OPC Server From MatrikonOPC enables OPC access to PLC5, SLC500, Micrologix, and ControlLogix the most popular Allen Bradley PLCs. Built for those. Load Cell And Strain Gage Input Modules For Allen Bradley PLC. PLC and Instrumentation Communication Software AllenBradley, Siemens, GE, Modbus, and Automation Direct Drivers. Automated Solutions develops and sells software. How to find and download Rockwell and AllenBradley software updates. Where to download Rockwell AllenBradley AB trade show and event session materials. The EZZONE PM Express is an industry leading PID controller from Watlow. The PID Controller includes on universal input and an option for up to two outlets and can. This handbook is a collection of programming overviews, notes, helps, cheat sheets and whatever that can help you and me program an Allen Bradley PLC. When it comes to PLC training courses, we are a leading provider of courses within the UK Ireland. Our PLC and HMI training covers the following manuafcturers and. Undoubtedly the plc Allen bradley and Siemens, are the top global players in this sector. For years I worked with both platforms, and I got my idea, then that is what. B supports both Modbus TCP and RTU. If you need details about Modbus protocol you can check this site. It has a good video and an exhaustive explanation. OPC OLE for Process Control. OPC is the simplest, safest and easiest way to communicate with a PLC. An Opc Server is basically a program that connects to the plc using closed source libraries, and exposes the data in a standard way that is not dependant from the PLC that you use. To use the OPC with C you need to write your own client using the libraries given by your OPC server vendor, by OPC Foundation or you can use third party clients. Usually to write a client you just have to create a group and items that you have to read, and wait for the callback that notifies you when the data that you subscribed are changed. OPC permits also many advanced features, like browse plcs online, browse all tags in a treeview, alarms and events management and so on I think that what you need anyway is simply reading and writing tags with different priority. You can find a simple c client with a video in this article. The best way to communicate with C and OPC is to use the Opc. Net. Api. dll and Opc. Net. Api. Com. dll you can download those 2 libraries from OPC Foundation site or from some open source projects around the web, just run a search on google. You are free to redistribute dlls to your customers but you are strongly reccomended to get the documentation from OPC Foundation website. So whats bad about OPC OPC Server for every pc where you will run your program. COM and DCOM but no one cares because 9. XP embedded or Windows CE. OPEN SOURCE DRIVERS There are some drivers, for the most common PLC manifacturers, that have been developed with reverse engineering of the protocols. Siemens. The most common for Siemens is Lib. No. Dave, a free library that is used the most with Ethernet cards CP3. Its a very common library to communicate with Siemens PLCs and its well tested because of being widely used. It supports also other interfaces I think it supports MPI, Profibus and many Siemens PC Cards. There is also a C driver, S7. Net, that its really easy to get it working and its on Nu. Get you can find an article with examples here https www. A brand new library with many useful features is Snap. It supports many languages C, C, Pascal, Lab. View, etc. Its quite easy to setup and has a great documentation. Another library for Siemens PLC is Dot. Net. Siemens. PLCTool. How To Install Imapsync on this page. Box. Library, that is a layer above Lib. No. Dave to simplify the functions and hide all the interop pain. The sources are full of examples. Allen Bradley. For Allen Bradley you should check 2 libraries written in VB. Net for Allen Bradley Plcs AB DF1 Protocol and Allen Bradley Slc 50. Ethernet Library. Some other libraries written in C for Windows are the ones of Pvbrowser, famous is Tux. EIP ethernet IP stack for controllogix and micrologix and TUX DF1. You can find some information on pvbrowser site or on the tux plc webarchive site Leicht posted those libraries also on github. They are native for Linux but you can compile in windows using Cyg. Win but please dont ask how to. A project that deserves special mention is an almost open source project Advanced. HMI. It contains free drivers written in Visual Basic. Net. The drivers are not open source, but they are free and the interface to them is open source. To use these libraries you need to import them in your C project not in Visual Studio Express edition, you need at least Professional edition or build the dlls and add them as reference in your C project. Advanced HMI anyway offers drivers for Allen Bradley DF1, EthernetIP both Micrologix and Compact. Logix and Beckoff Twincat. Advanced. HMI offers also good looking objects if you are using Winforms, and you can import them same as you imported the drivers. Its really a good project and its easy to get results. You should check it There are some considerations about those drivers they work well but you should consider that in case of problems you are alone with an unkown dll and the quick support is granted only if you pay. Ive already used those drivers with success, before switching to Modbus, and I wrote an article about Advanced. HMI that you can read. Whats good about Open Source driversThey are free and you can debug and improve the communication as much as you need for your plant. You can also write a standard interface like the one provided by Advanced. HMI to access to all PLC data in the same way. The bad side of using this drivers becomes evident with the growth of the complexity because of integration of plcs of different manifacturers. When this happens, OPC is a must. Proprietary Libraries. These libraries are custom dlls or Active. X provided by the manifacturer or 3rd party companies. They are generally not free and they remind me of legacy applications, where every plc had its own library with its own code. Here is a video that explains why OPC has been made and why you should really consider to use OPC instead of third party libraries READ MORE.