SoftPLC vs. True PLC

[marks1080]

Hello All. I work for an offshore oil and gas company, and we have a FPSO (floating production storage and offloading) currently in service. We have contracted a company to provide us with a simulation environment for the I&C onboard the ship. Basically we have an exact mock-up of our control system in a training room.

The system consists of HMI servers, OPs stations, and an Engineering Station (along with an instructor’s station). That we use as a training environment for our technicians. Also, we have connected with this a HYSIS simulation computer and several Emulation PC's. The HYSIS engine is simulating plant conditions, while the emulation PC's are simulating logic solvers (PLCs)... ie: this is a "soft" PLC, which we use as a test bed.

The purpose of the training simulator was stated - to train technicians. The purpose of the Test Bed is to be able to test new software updates/downloads and see how they interact with the system. It is very important that any software changes are tested extensively before being implemented in the plant.

We currently have another test facility under contract that is an exact mock up of what we have off-shore on the plant - true "Hard" PLC's. This is currently where all of our software changes are tested before being implemented.

I would like to know if anyone has any insight on how a soft PLC system compares with the actual thing (hard PLC). I've been hearing different opinions from different people regarding this. Some say there is no way to truly test the impact of a software download using soft PLC's, I have documentation from a company, that has since left the project, saying that the soft PLC's should be able to do the job just as well.

As any downtime in this kind of industry can cost millions of dollars, my recommendations on whether our soft PLC test bed will suffice or if we should purchase our own hard PLC test bed will be scrutinized to death.


Any help or insight would be appreciated on this. I've left out some specific information here... If it would help, I can post more detail about our systems.

marks

 

[richs]

Hiya-

You mentioned:

"As any downtime in this kind of industry can cost millions of dollars, my recommendations on whether our soft PLC test bed will suffice or if we should purchase our own hard PLC test bed will be scrutinized to death."

Isn't that answering your own question? Better to err on
the side of caution?

In addition, having a set of PLC in an active, running
training simulation seems to be a pretty good way of
having "hot standby" spares available to be, to coin
a phrase, in "active depot testing", ready to be yanked
from the test bed and flown via jet to wherever needed.

Just my 2 cents worth.

Cheers,

Rich S.

 

[djs]

Hello;
Depending on the manufacturer of the PLCs and soft PLCs, there might be some small differences between the soft and the hard. An example of this is the A-B ControlLogix line. There are small differences in the way the two handle math.

 

[Skogsgurra]

I agree 100 percent with Rich.

The reason to use soft PLC is to save money on hardware. I think that a test station for new software is the least place to save money on just that, if your downtime costs anywhere near the cost of the PLC. Not to mention more than the PLC.

Your soft PLC supplier can promise complete compliance between soft and hard - but what are his promises worth? And who will be sorry when one of those "minor exceptions" show?

An alternative would be to use soft PLC in the test station AND on the platform. Then you have identical set-ups in both places.

Gunnar Englund

http://www.gke.org

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

 

[marks1080]

richs:

Yes, that was my thought as well... This is really being blown out of proportion by some people in managment (non-engineers).

I was speaking to a certiafied Siemens technician regarding this as well. He does a lot of the software testing for any ICSS code changes before they get uploaded to the plants control system. He is using a full PLC mock-up for this (rack mounted hard PLCs). He also said that if he had to be responsible for testing code changes on a soft PLC he simply would not do it. His biggest concern was in regard to any possible interferance while uploading the new changes. It is required that any uploads go in seemlessly without any undesiered affects or downtime to the system. He said that this can not be garunteed using soft PLCs, as the nature of the device is different in itself. If anyone can point me towards information supporting this claim it would be a great help (I know what he's saying is more than likely correct, but I need some concrete evidence.)

Now on the contrary, I have an old contract here that states that when our test system (soft PLC) was purchased that it would be able to perform all task of the hardware based test bed. This is what the managment (non-engineers) are seeing and asking why we don't use the soft PLC system that we have already purchased, instead of contracting out the hardware based PLC system (at a high cost a may add).

Again, thanks for any help! I really appreciate everyones input.

Regards,
marks

 

[Beggar]

Presuming that you've got the Siemens stuff installed at your site, you might start by getting a letter from Siemens stating that they strongly advise against using a software simulator.

On a system much much smaller than yours, I have had similar problems. I was running a 315-2 DP processor and was using the Siemens PLCSIM software to ring out my software changes. In one case, I started using one of the system OBs and it worked fine on the simulator. When I put the code into the PLC, the system continued running but the logic based on that OB never fired. When speaking to the tech support guys I discovered that the 315-2 didn't support that OB. So, while the code worked fine in the simulated 315, it didn't work at all in the hardware 315.

In my case, all it cost me was a few hours of wasted programming time and a couple hours of downtime on the machine while I was trying to figure out the problem. In your case, your costs would have been substantial, it sounds.

This is very much a case of penny wise, pound foolish.

--------------------
How much do YOU owe?

http://www.brillig.com/debt_clock/

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[marks1080]

Thank you Beggar for your reply.

Another interesting point for this situation... the Training simulator and Software based PLC test environment were provided to us by Siemens. It would be hard to convince them to give me a letter saying it isn't suitable for our use, when in turn that would almost be like them saying they didnt meet our inital contract requierments... This one is a real pickle .

I've been instructed to be as objective as possible on this. Also, a lot of the players in this job are not technical people, more business and contract types...

I know the short answer to my problem is that No, the softPLC is not sufficient. But I can't bring this to upper management in a report without specific reference to proof. We've paid almost 3 million for this softPLC test environment, and it would look bad on a lot of people here if it was discovered that more or less it is useless for our needs.



... ands there's so much actual work that needs to be done in the meantime too lol...

 

[richs]

Hi again-

In my particular branch of engineering, our "archtype" is
the cartoon character "Dilbert", a long suffering engineer
who is drawn by an actual engineer, a local fellow who in
real life (before he quit and just draws now) was/is an
electrical engineer at our local power company.

One of the major thorns in Dilbert's life is his boss, a
"pointy haired boss" (PHB).

One of the things that I have found is that PHB's are
typically cowards. Typically, they don't have any qualms
of spending large amounts of company money if they
percieve that it would help save their precious hides.
Nor do they have any qualms about hanging your ass out on
the line if it makes theirs look better.

A power point slide or two, as to cost/risk benefit, and
if possible, tieing the decision to *THEIR* jobs, usually
can sway them over to your particular view. Which is,
of course, to the good of the company.

As a contractor, ROTFL.

Seriously, after wiping the tears of laughter from my eyes,
the Siemens contract, the risk factor of a training
simulation vs. a simulation of a real time situation? If
error with the training simulator, you find it in the
classroom and change the software. You simulate a
field application and you find it in the field! I think
that you can easily point out the difference to the PHB's.

Tie that into a Valdez situation (where the cost of the
cleanup, political loss, and "intangible" costs of such
a failure) and I think you can wrap the ribbons on the
package. Throw in a couple of words about going to great
lengths to preserve our earth, that no cost is too great
to save the brine shrimp in the area and a few other "green"
weasel words. And SAVE that presentation. So, if your
ass gets caught in a wringer later down the road, you
can trot it out and say:

"See, I did everything I could to make this a safe thingie!"

Damn, it's the people engineering that's tricky. Real
engineering is FUN. Maybe I've been in the business too
long.

Hope this helps. Sorry about the rant.

Cheers,

Rich S.

 

[Beggar]

Boy, you're in a bind.

At the very least, you should put together as strong a report as you're able and make it public. If something does go wrong then at least you're on the record as having identified the potential problem.

Your simulator is probably fine for training. The issue really comes with the validation of code modifications. That's where the potential for a problem is much higher.

For what it's worth: So far as I understand it, the FDA requires software validation to be done on IDENTICAL hardware. A simulator just can't possibly predict every possible combination of I/O state, interrupt conditions, memory loading, etc, etc, etc. If it's a critical system, a simulator just won't do.

The alternative that your bosses face is allowing the system to be taken offline for a time period sufficient to validate the new software on the actual hardware.



--------------------
How much do YOU owe?

http://www.brillig.com/debt_clock/

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[dieselvette]

(sorry this is a little off-topic)
"...One of the major thorns in Dilbert's life is his boss, a
"pointy haired boss" (PHB)..."

If Dilbert's writer is a local, then you must know who his real PHB is/was. So then I must know, does he really have pointy hair?


"...Damn, it's the people engineering that's tricky. Real
engineering is FUN..."
So true!

Nic Van Engen
Electrical Technician

 

[richs]

Hi dieselvette-

Again OT, no, sorry. I read about it in the San
Francisco newspaper. It's been a while, but the author
if I remember correctly worked in the San Ramone area.

A quick check on google says that he worked for the phone
company, not the power company. My bad.

A couple of wiki entries:

http://en.wikipedia.org/wiki/Scott_Adams

http://en.wikipedia.org/wiki/Pointy-Haired_Boss

http://www.annonline.com/interviews/961021/biography.html

Hope this helps. Of course a search for the Dilbert
cartoons is left as an exercise for the student......;-)

Cheers,

Rich S.

 

[marks1080]

hahaha richs... i just wasted 20mins going through wiki links Funny though... and actually explains a lot of the BS related to my problem... although I think i'll leave the terms PHB and REMF out of my final report...

marks

 

[richs]

"although I think i'll leave the terms PHB and REMF out of my final report..."

Good thinking! I knew we could count on you! ;-)

Best of luck. It's a tricky situation and we all sympathize
with your situation.

O.K. this is getting bad. I went to google to find out how
to spell sympathize.

Anyway, best of luck!

Cheers,

Rich S.

 

[marks1080]

There are bound to be a lot of upset people with this final report... It's more a contractual cluster-f**k than anything to do with engineering.

The actual answer to the problem is quite simple... and anyone half decent engineer would be able to figure it out without going to any other resources. The biggest problem I have to get around is convincing some PHB's that they basically wasted 2 million bucks

marks

 

[richs]

Hi marks1080

Welcome to the wonderful world of engineering. There's a
book out by a soils engineer. It's been around a long time,
and it probably isn't really worth the read too much called,

"Engineering and the Art of Not Being Sued"

or some such thing.

Nah, the PHB's didn't *WASTE* a couple of million, they
research done just was not very cost effective.......

O.K. here comes the trickiest part of engineering, convincing
them without your toes getting stepped on (or CYA if you
prefer) and still get them pointed in the right direction
WITHOUT them thinking you are a "loose cannon".

Here all the lack of ethics of a "smarmy" salesman should
be dredged up from the dark side of your soul and plaster
a big friendly smile on your face while you give your
cheerfull and "upbeat" report, all the while thinking:

"these idiots couldn't find their way out of a wet paper
bag with both hands and a map!"

Mark, this requires the best poker face that you can put
on in the situation. Against your better instincts, you
still have to "sell" your report.

Remember, it is easier to draw flies with honey rather than
vinegar.

We can let our true feelings out whilst amoungst ourselves,
but to the bean counters and PHBs, we have to seem like
a "team player". And we have to play on "their" team,
with their vocabulary. Sigh.

Best of luck on the report and followup. Keep us posted
as to the results.

Best of luck!

Cheers,

Rich S.