Can a PLC do Sequence of Events? 2

[bdn2004]

We are looking to put in a SCADA system on our power system. We contracted a place to give us a proposal and they recommended we wire the alarms from the field to an annunciator panel that will provide the Sequence of Events snapshots. From there the same points on the annunciators will wire to a PLC to provide constant monitoring.
And we have to get this fiber optic gizmo to provide a sychronous clock signal into each annunciator and PLC.

I mostly understand the reasoning and function of each part but wonder why a PLC couldn't just do it all?

 

[Skogsgurra]

It depends on what temporal resolution you need - and how fast the PLC can react. With your needs on the right side of the PLC speed limit, I see no problem - apart from the work involved.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[danw2]

Why? Sequence of Event recording is a specialized task. Those packages designed specifically to do that, like Ronan's, will will implement more quickly than generic devices that need to be programmed and integrated to get the same end result.

 

[djs]

AB ControlLogix has specialized I/O modules that do sequence of events. I believe that their resolution is down to about 1 millisecond. Very little programming is needed, just to read the data from the I/O module.

 

[bdn2004]

djs,

I saw something on that online on that, and in part prompted my question. That resolution is the same as the annunciator.

Don't you think it would make more sense to just wire directly into the PLC instead of going first to a remote annunciator? But there is an existing annuciator with all the wires right there....but we could just re-use it and output to it from the PLC....

And too this setup is multiplied by about 50 throughout our site spaced from nearest to farthest about 1500 feet. The sychronization is important which is provided by a satellite signal. Do PLCs also have these synchronization modules that could daisy chain from PLC to PLC?

I can see the scenario where the info available at the 1500 foot away PLC is part of the sequence of events that prompted an annunciation at the 5 feet away PLC.

 

[bdn2004]

http://www.ab.com/programmablecontrol/pac/controllogix/applications.html

to answer my own question it looks like the AB will do 100 mS resolution, the annunciator that has been proposed is 4mS. Looks like AB has some work to do if they want to compete in that market.

 

[ScottyUK]

Depends what you're trying to record. A-B's card is likely fine for some applications. Your annunciator has some way to catch up on the 125us resolution of the 1980's WDPF turbine control system SOE card.


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If we learn from our mistakes I'm getting a great education!

 

[PLCMentor]

Actually there may be some misunderstanding in the thread here. Looking at the page that bdn2004 references, the AB guys brag about being able to discern between events on the 100 microsecond level not 100 mS. Is the annunciator you are looking at operating at 4 milliseconds or microseconds?

I guess that means we can beat the 80's after all Scotty. Still cant beat the 60's and early 70's for music though...

Russell White, P.E.
Automation Technologies, Inc.

http://www.AutomationNC.com

Automation Help

http://www.PLCMentor.com

 

[bdn2004]

Wow....PLCMentor has found not a misunderstanding but a major error that could change the design. Thanks PLCMentor.

After reading further on the annunciator, its resolution
is 50 mS standard down to 1mS if you want to pay for it. I'd link to the page but you have to have a password to get to it. There is nothing mentioned about uS.

AB wins after all....in a landslide.

Now back to my original question. If the PLC can do all the I/O, the SOE, why can't it also do the synch clock function too?

 

[bdn2004]

again to answer my own question...it does do that!...that is the synch function.

 

[PLCMentor]

Also quoting from the site you posted:

"Simple Global Positioning Satellite (GPS) integration using HiProm's 1756-HPGPS module allows geographically separate systems to operate with the same correlated time values."

Cut sheet here:

http://www.hiprom.com/Pages/Product...cument Publish/1756HP-GPS+IRIGB Datasheet.pdf

I've never had to do anything like this, but it looks like an interesting app.

Russell White, P.E.
Automation Technologies, Inc.

http://www.AutomationNC.com

Automation Help

http://www.PLCMentor.com

 

[bdn2004]

Thanks.

I guess you would stick one of these into each one of your PLCs? There is no need to daisy chain a clock signal from one PLC to another....? That's how I take it.

As you called it earlier this is third party too. I guess that is common in PLC world and is perfectly fine?

 

[PLCMentor]

I didnt look at it too closely, but that is my impression also. I am always aware when I use 3rd party modules. It is done all the time and since rockwell lists this module as a solution for SOE on their website, they are essentially endorsing it for this application. I dont know the manufacturer of these modules so I would do a little research on them to find out who they are.

Russell White, P.E.
Automation Technologies, Inc.

http://www.AutomationNC.com

Automation Help

http://www.PLCMentor.com

 

[djs]

I believe that you need one GOS module in each rack. It reads the internal CPU real time clock value and at intervals matches it to UDT time from the GPS satellites. I believe that the clock signal is only available on the rack side bus.

 

[bdn2004]

you know what I'm wondering now is if I can wire all of our various field I/O into these SOE cards. The original plan was to replace the existing dumb annunciators and meters with smart devices. The smart devices would do the SOE function - but only with the I/O that is wired to it. The same points along with many others would be wired to the PLC just to show status.

Many of the annunciated points are wired to a control relay contact that is activated by as many 10 different field devices on one production line. So an alarm could mean 10 different things, then the fun begins. I know this sounds primative but when you are talking literally 1000's of devices its not easy to upgrade without spending gazillions of dollars.

But since all the wiring is already coming into these control relays it seems easy enough to replace the control relays with a terminal strip, wire the devices directly into into the SOE cards in the PLC, link all the PLCs together and voila I've got full status of the system and have full SOE. Am I oversimplifying this? Is there limitations in computing power of PLCs to do such a thing?

 

[djs]

You might want to check with AB to see if SOE is possible on remote I/o racks.

 

[PLCMentor]

bdn,
I think you can probably do the SOE on remote racks, but I think it would be worthwhile to have the ab guys come in to talk with you concerning your project. I think you have narrowed down what you want to do and now you need to get them in and grill them about what this card can really do. I would think they would jump at this chance.

Russell White, P.E.
Automation Technologies, Inc.

http://www.AutomationNC.com

Automation Help

http://www.PLCMentor.com

 

[bdn2004]

Actually I did just talk to the A/B guys and they were very helpful. From our initial conversation this is what the A/B cards are supposed to do. He is going to lay out a proposal free of charge based on the I/O I provide. He said these wire just like conventional I/O points. - I'll find out if it is possible to put them in the remote I/O racks - that's a good question to ask. The cost of the modules is a little less than double. He is to provide me with limitations on the system...max points allowed.

He did mention that they would recommend a CIP Synch module, that is either fiber or copper to get the GPS signal...the GPS module you found may be a better option there. Any experience with CIP Synch?

All this to me is but one option of three. The consultants plan another and the third....

An integrated system made by Schwietzer Engineering Labs exclusively for SCADA systems. From what I understand SEL has the market on SCADA in the utility world. However I can see the advantage of using A/B because everything else in the plant is A/B and many people know how to work on them.

Thanks PLCMentor and djs for the help.

 

[PLCMentor]

My rule of thumb with my clients is to stay with what they have unless there is some overriding factor to change. If your facility is standardized on AB then I would stay with AB.

As far as the help goes, this was interesting for me also. Feel free to contact me if you need to discuss this more freely. I think we have taken this to the extent a forum can cover a subject.

Russell White, P.E.
Automation Technologies, Inc.

http://www.AutomationNC.com

Automation Help

http://www.PLCMentor.com

 

[ScottyUK]

If you guys do go off-forum please drop a note back regarding the the outcome of the dicussion with A-B. I'm sure a few others might be interested in if / how a distributed SOE recorder can be built.


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If we learn from our mistakes I'm getting a great education!