PLC web server hardware

[ToHe]

I need to develop a project where I have to control a PLC from a web application. I have knowledge of web applications, but I have almost no knowledge of PLC. I need to read/write values from/to the PLC and I also have to run local applications on the PLC. So my first idea was to write a web service that runs on the PLC so that I can send requests from the web application to the PLC & vice versa.

Preferably I would like to write the web service in php or java, support for VPN connections would also be a nice feature. Is it a good idea to use a device with an embedded linux distribution or not?

What is the best PLC device that fits my needs?

Thanks in advance.

 

[FreddyNurk]

What is it that you want the PLC to do? Provide IO in a format that you can use with your web server? Local control independent of any process the webserver may be doing (including if it fails)?

Commercial SCADA packages provide some web server functionality to do a lot of what you describe in terms of provide a web service and allow monitoring of IO as well.

 

[ToHe]

The PLC will have to collect & temporarily store data, coming from PLC systems and other local ethernet devices. Maybe even convert ASCII files coming from local PC's.
It will need to store all the latest values so that they can be requested through the webservice.
And it must be possible to control PLC devices through the webservice.

What SCADA packages would you suggest?

 

[dV8r]

I believe we have terminology misconceptions here.
If the PLC is doing all this there is no need for a SCADA, just simple HMI. For a PLC that can do all that you will need one similar to the GEIP PAC, I would recommend the RX3i or RXi. Some of this will Depend on if this is a new or existing system.

PAC -

http://www.ge-ip.com/products/pac-programmable-controllers/c547

SCADA -

http://www.ge-ip.com/products/automation-software-scada/c250

 

[djs]

PLCs are not like computers or microcontrollers. They are specialized pieces of hardware (usually to control some kind of machine). They are programmed using specialized software that is oriented to that functionality. For example most if not all PLCs cannot be programmed in C. If all you are doing is collecting and storing data from other PCs, then perhaps you should look into a different hardware platform.

 

[danw2]

I don't think you want to be limited by a hardware PLC. What you describe is what the class of software generically known as HMI software is designed to do. HMI software typically runs on PC platforms, mostly Windows, some Linux, maybe other O/S's, too.

Each PLC manufacturer has its own HMI software package (Siemens is WinCC, Allen Bradley's is FactoryTalk View) and there are there are 3rd party HMI software package providers, like Wonderware, Ignition or Indusoft.

Many HMI packages now offer web interfaces. And all of them have gotten a security upgrade since the Stuxnet attack.

Commercial HMI software is almost always an OPC client, which allows it to use an OPC server software package to communicate with various field devices because the OPC server has the critical "driver", specific to the protocol the PLC talks. Commercial OPC servers (Matrikon, Kepware, Softing, Iconics) typically allow some form of custom programming for serial interfaces, still common on many field devices that do not use a proprietary protocol. Yes, you pay for an OPC server with as many of its drivers that you need, but unless your delivery deadline is the 22nd century, using a commercial package might well be worth it.

You're certainly entitled to create another HMI software app with its drivers from the ground up, or you could use others' efforts to get results a lot quicker.

The effort to get HMI's communicating between different devices employs an entire segment of the workforce, systems integrators. It is not a trivial task. So you aren't putting yourself to pasture to use an existing commercial product.