OPC/DDE/ActiveX/?

Hello all,

First, excellent forum. You have some very knowledgeable members and moderators.

I have always used Rockwell Software products...RSLinx, RSView, RSLogix, etc. I have a customer that has requested some options for HMI applications. They want data monitors, data loggers, simple troubleshooting tools, etc. I provided a simple verification tool using InGear's ActiveX object in VB6. It was fairly easy to implement and seems fairly stable. We have run into one of the drawbacks of using ActiveX objects for direct PLC communications...after the application was developed and distributed to multiple client machines the customer changed all of the IP addresses of the PLCs. This required modifying all of the IP config files for the applications. Using a server would have kept the interfaces/addresses in one location.

Finally, my questions: What is your experience with the different interfaces? Which do you suggest and why? What vendors to you have experience with?

FYI: I always work with Allen-Bradley PLCs...mostly ethernet communications.

Your comments are very much appreciated.

Interfaces (explained)

When I said interfaces in my previous post, I was referring to OPC, ActiveX, DDE, Etc.

Just wanted to clarify.

We write our own.

We bought the source code to a OPC server and modified to suit our needs. It was still slow. Too slow. We have written DDE drivers in the past but they are old and slow too. Now we use ActiveX controls because they can be accessed by many applications but they are fast.

BTW, just because the InGear activex does not support bootp or dhcp does not mean that all ActiveX controls are the same. An ActiveX control can be very sophisticated. It depends on how much effort the programmers want to put into the nice features like DHCP.

I don't see why so many people like OPC. It is a slug.

I don't see why so many people like OPC. It is a slug.

Click to expand...

I am sooooo glad you said that.

ActiveX:
Fast.
Inexpensive - no runtime fees.
Only a limited number of protocols are supported. You wont find Profibus, ProfiNet, CAN, DeviceNet, ControlNet, Siemens MPI, FF etc. amongst the supported protocols.

I think that ActiveX could be a good alternative, provided you need to make a relatively large numbers of standardised HMI's AND there is an ActiveX for the required protocol.

OPC:
'relatively' slow.
Medium to high expense (*).
Plug-and-play with a huge number of applications.
The greatest number of protocols are supported.

I think that OPC is the only alternative if you need ready made building blocks OR there is no ActiveX for the required protocol.

*: Now both Siemens and Rockwell are providing relatively cheap OPC servers for the masses in the shape of "Softnet S7 Lean" and "RSLinx Single Node".

My personal situation: I would have considered ActiveX if there was one for either MPI, ProfiBus or ProfiNet. But there isn't. I have used Softnet S7 for Profibus in the past and I will use Softnet S7 Lean for ProfiNet in the future.