| Author |
Message |
seyyah
Joined: 07 Oct 2001
Posts: 578
Helped: 1
|
 11 Jun 2009 20:07 panasonic plc vb.net communication |
|
|
|
|
| It is standart interface or something that simplifies connection and developing systems on it but i wonder what possibilities does it offer? Who develops it and does it change according to the manufacturer? How is it its architecture generally or what is the logic behind it simply? Thanks
|
|
| Back to top |
|
 |
FvM
Joined: 22 Jan 2008
Posts: 5044
Helped: 752
Location: Bochum, Germany
|
12 Jun 2009 7:11 what is opc |
|
|
|
|
1. See http://www.opcfoundation.org/
2. My personal (somewhat polemic) definition:
From it's origin, OPC is the dubious attempt to abuse the Microsoft Windows RPC (remote procedure call) mechanism as an automation protocol. Nevertheless, it has been the most important vendor independant automation protocol since a decade. Meanwhile, OPC has grown out of the MS RPC limitations by adding new concepts as XML. OPC has powerful features as engineering units for process quantities, that are missing in most automation protocols.
3. As it's most serious disadvantage, OPC is not simple. It's feeding a whole industry of consulting companies...
|
|
| Back to top |
|
|
PLCMentor.com
Joined: 26 Mar 2009
Posts: 23
Location: North Carolina, USA
|
15 Jun 2009 15:07 vb .net opc |
|
|
|
|
| In the simplest sense, OPC is a tool that can enable software manufactuerers to connect to a variety of different field devices. SCADA and HMI systems today usually work in layers. You have a developer of a graphical system that allows people to monitor a process. The system may need to communicate with several different field devices. OPC allows third parties or the manufacturers of the field devices to design a software module that communicates effectivly with their device. In turn that software module is written in a standard manner that allows a variety of different software packages to access the information that it provides. So you have the OPC complient driver communicating with the field device (ie, a PLC) and the graphical software package (ie, Wonderware) talking with the OPC driver.
|
|
| Back to top |
|
|
servodude
Joined: 25 Jun 2009
Posts: 1
Helped: 1
Location: Left Coast
|
25 Jun 2009 14:12 is opc basically equivalent to odbc? |
|
|
|
|
Mr. PLCMentor has provided the definitive explanation of OPC. I have one addition to add in my own uneloquent way:
OPC also allows the user to NOT need SCADA software. I have written numerous Microsoft Visual Basic, Visual Basic .NET, and C# operator interfaces (screens) all using OPC middleware.
I have used OPC drivers for Panasonic (Aromat), Mitsubishi, AutomationDirect, and Omron PLC's. If you know how to program in any of the Microsoft .NET languages, you can use an OPC driver to connect to a PLC.
My only "problem" with OPC is that it is ridiculously expensive. Most companies charge $500 or more ($795 is a common price point) for their OPC driver. The "justification" is that it is cheaper to buy the OPC driver than it would be to buy a more expensive SCADA package.
This is a specious justification at best. I know what it takes to write a driver, the "secret" is you need the communications protocol for that particular PLC. ALL PLC manufacturers have a communications protocol (if it can talk to a PC), so all they have to do is take that information and program it to the OPC foundation requirements. It is NOT $795 a copy worth of effort, and EVERY programmer (who knows anything about the automation market) knows that.
|
|
| Back to top |
|
|
seyyah
Joined: 07 Oct 2001
Posts: 578
Helped: 1
|
26 Jun 2009 19:09 disadvantage of opc |
|
|
|
|
| Ok i think it has different aspects. A scada program can also use an opc based program to connect to a drive over modbus for example, right? How is the mecahnism works in that situation?
|
|
| Back to top |
|
|
FvM
Joined: 22 Jan 2008
Posts: 5044
Helped: 752
Location: Bochum, Germany
|
26 Jun 2009 23:57 Re: What is OPC |
|
|
|
|
Needing OPC middleware and paying considerable amounts for OPC drivers is the other side of using an extravagant complex protocol. (My point 3 above).
When interfacing MODBUS through OPC, you basically need an OPC enabled MODBUS Master, either a separate software component acting as standalone OPC server or an existing automation component, that implements the OPC interface as an added value.
|
|
| Back to top |
|
|
Google
AdSense
|
26 Jun 2009 23:57 Ads |
|
|
|
|
|
|
| Back to top |
|
|
wh00per
Joined: 14 Jul 2009
Posts: 12
Location: Canada
|
14 Jul 2009 16:42 Re: What is OPC |
|
|
|
|
In my opininion, OPC is for process controls the same thing as ODBC is for databases .. A common way to access them.
As a member of the OPC foundation, you have free access to all standards defining the communication. Else it's a bit hard .. however, if one needs a quick immersion in the topic and knows a little programming, visit http://gray-box.net
If you need papers .. ask! Somebody out-there will definitely answer.
|
|
| Back to top |
|
|
