Data Server for HMI - Current Best practice?

[harryting]

Had a philosophical discussion with a colleague of a related discipline today and I want to get the opinion of the folks here.

The most common HMI like Wonderware, iFix, etc. all comes with their own data driver for AB and ModBus, etc... However, the days of using those drivers seems to be gone to me and they are all implicitly recommending using OPC instead.

My coworker doesn't view the included data driver as separate component. So he is thinking using the included driver rather than OPC eliminate a data hop so the data path is simpler. I disagree for two reasons I can think of:

1. The "included" driver does add another "hop" which is simply unavoidable. it's not really any different than running through OPC.

2. Most vendor haven't updated their driver for decades and migrated toward using OPC. Making the OPC solution actually more reliable.

What do you folks think?

 

[mk42]

Regardless of below, big fan of OPC, as long as it's OPC UA. Old School OPC can take a long walk off a short pier. It can add cost to a system, though.



1) I'm willing to bet that the performance difference would vary from system to system. I could definitely see OPC adding a small amount of delay between the PLC and the HMI, with an extra hop: PLC -> OPC server -> OPC client driver in SCADA -> Screen vs PLC -> AB driver -> Screen. Depends on teh respective sampling intervals, although it wouldn't make a noticeable difference in most things.



2) The vendor may not have updated the driver in a while, but if it worked 10 years ago, what needs to change? Modbus is still the same. There may be new flavors of EIP, but are any of them more efficient?


I guess it could just be that the driver was bad (or works well but has bad performance) in the first place, and they don't feel like going back and making it not suck.

 

[Phil Buchanan]

Just to add a little alcohol to the mix.

If your OPC provider is a 3rd party like Kepare you are introducing another hoop into the circle of blame.

For example, if you have Wonderware for your HMI and Allen Bradley for your PLC and Kepware for your OPC in between and you have issues the Wonderware is going to point the finger at AB and KEP and if you have a PLC problem they are going to point to Kep and Wonderware, etc.

The more vendors you add the more awesome it gets so just something else to keep in mind.

 

[JesperMP]

We have been using OPC DA for approx 15 years, slowly transitioning to OPC UA.
The OPC server/client is not limiting for us, but our needs are probably low-medium (however growing rapidly).
We have chosen to use the OPC Servers from the original PLC manufacturers. We mix OPC Servers from Siemens and Rockwell with no problems.

N.B. We do not use the OPC UA Servers that can be run from the PLCs themselves as Siemens offer. On the lower-end PLCs the performance is too low.

 

[Ken Moore]

An advantage of modern OPC servers is the advise mode. Instead of constantly polling tags at a set rate. The OPC server advises the client on which tags have changed since the last inquiry, and only sends the changed tags. Much more efficient, and you can inquire at a fast rate, without having the bandwidth concerns of old.

 

[ynpmoose]

There is also a cost issue. Wonderware's drivers are included in the cost of any license that has IO enabled.

I echo Phil's concern. I single point of contact, a single support contract makes life easier.

I'm not sure where you're getting the non-update concern though. I know Wonderware's drivers are updated to keep up with new models and firmware changes, especially for AB and Siemens. They also have new drivers for MQTT and Web Services, plus encrypted Suitelink. As MK42 said, things like Modbus don't change, so there's not really much to update.