Comparing PLC/SCADA to LabView?

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Thread Starter

Chip Hinde

It used to be a simple task to decide when a small and simple LabView solution with SCXI or other National Instruments hardware would be
best or when a PLC/SCADA solution was needed. I used to use the analogy of "If you want a word processor, you could buy one with all the
functionality built-in (the SCADA with PLC solution) or you can buy a programming language and build the functionality (the LabView
solution). I also used to ask customers if they could tolerate the computer hanging up from time to time and that would make the decision
for them to go with a computer control or PLC approach.

Now it seems as if the boundaries between the two are not as clear. National Instruments has its Real Time processors for PXI and FieldPoint. It also has the LabView Datalogging and Supervisory Control Module add-on that brings some SCADA functionality to LabView (no longer need to build it up).

I prefer my PLC. I loved the "Why I love my (P)athetic (L)ittle (C)omputer" post in a previous thread and taped it up on my office door. But I fear I am losing my arguments against the LabView users at work. What is left to defend my PLC? Our applications are usually small bench to pilot scale processes with less than a 1000 I/O points. Some, but not all processes have some safety significance due to the materials we process.

Does anyone else have experience with both PLC/SCADA and LabView and have some advise to lend?

Thanks,

Chip Hinde
Los Alamos National Laboratory
 
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Curt Wuollet

> It used to be a simple task to decide when a small and simple LabView
> solution with SCXI or other National Instruments hardware would be
> best or when a PLC/SCADA solution was needed. I used to use the analogy of
> "If you want a word processor, you could buy one with all the
> functionality built-in (the SCADA with PLC solution) or you can buy a
> programming language and build the functionality (the LabView solution). I
> also used to ask customers if they could tolerate the computer hanging up
> from time to time and that would make the decision for them to go with a
> computer control or PLC approach.

Labview comes on Linux now, which eliminates the hangs and crashes. Labview is especially suited for test applications and instrumentation.
If you don't need precision measurement or signal processing, the PLC would probably be easier. But, it you need the functionality of PC cards
or want to do complex math and diverse measurements, Labview is gonna get the nod. They are sorta aimed at different markets, but yes, things are getting blurry.

> Now it seems as if the boundaries between the two are not as clear.
> National Instruments has its Real Time processors for PXI and FieldPoint.
> It also has the LabView Datalogging and Supervisory Control Module add-on
> that brings some SCADA functionality to LabView (no longer need to build
> it up).
>
> I prefer my PLC. I loved the "Why I love my (P)athetic (L)ittle
> (C)omputer" post in a previous thread and taped it up on my office door.
> But I fear I am losing my arguments against the LabView users at work.
> What is left to defend my PLC? Our applications are usually small bench to
> pilot scale processes with less than a 1000 I/O points. Some, but not all
> processes have some safety significance due to the materials we process.

Again, the bad reputation of PC control is almost entirely due to the use of fragile software. I do custom code because I need to do things that Labview doesn't, but people I trust say the speed and reliability are very much improved on the Linux platform and are much more competitive with dedicated realtime hardware and PLC's. I was impressed with the eval I did. For what PLC's do well, they are hard to beat. These days it's often a stretch. Some classes of problems will be
easier on each.

Regards

cww

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Chip,

The lines between PC and PLC are becoming very blurred, but the Labviews of the world are still not robust enough for me to place into a
demanding production area. I too use Labview, but mainly for laboratory instruments where it is not a real big deal if they have to reboot once in
a while. I don't know if the safety thing really matters anymore because all safeties should be hard wired anyway, unless by safety you include
false triggering of I/O, which I haven't seen as many issues in PC based systems today. I believe that you still must use good judgement for each
job given to you, but each case must be reviewed on it's own merits and what the customer desires. There are some very good PC based systems being
designed today and they are becoming more and more robust so you will always need to evaluate both architectures. And, I don't ever think there
will be a common solution for all applications. Just my 2 cents.

Dale
 
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Skye Controls

I have used LabView many times but after programming C/C++ VB, and Visual C++ I think LabView sucks. it uses a ton of over head, does not process threads as efficaly as VB or the other I listed, also there G-programming controls are garbage as well, to create a global var you need to create another vi or sub vi, I am sure anyone who has used a real programming software before and has tried to use slabview can relate. I would go with the plc they almost never die, hang up or need to be re-booted so you can move valves/tooling to a safe position...
 
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Erick Sutanto

If you program LabVIEW with a lot of global variable, I don't think you have adopted their graphical programming paradigm completely. In the beginning, I was doing freestyle LabVIEW programming and it was a mess. If you learn to follow their programming best practice , you will start seeing that LabVIEW can be very powerful. I understand the skepticism, but in fact LabVIEW is used to control very complex high tech systems nowadays.

Effective LabVIEW Programming
http://www.ntspress.com/publications/effective-labview-programming/
 
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PLC Programmer

LabView to me is a complex and highly advanced approach to controls when compared to PLC's.

Obviously PLC's are perfect for simpler controls requiring lower level of complexity. Ladder programming adds to its ease of application in the field. We would only go for this in case of regular conditional switching programming.

LabView on the other hand is highly specialized for complex computation in controls such as multi-state variable controls.
LabView provides that mathematical complexity and Easy to program GUI.
But the software is costly (Initial investment though and compatible with many controllers not only PLC's )

LabView has a wide window of application. PLC/SCADA is industry specific. That's how I could differentiate them.

Programming with C/C++/VB is going to be a challenging task when it comes to complex mathematical functions. If you have a time constrain and limited workforce for programming and task is to design complex systems such as RT controls for Satellites etc, i would vouch for LabView.
 
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