On-Line, Real-Time, Programming...

[emokar]

Yes, Yes , Yes, of course!...

 

[kamenges]

Originally posted by jstolaruk:

Well, you challenged my statement, you might as well cough up your reason for calling it nonsense.

I think you guys are having a semantic Simatic disagreement.

Technically I'm with jstolaruk on this one. Unless the new family of processors has changed this the original S7-300 line (314, 315, etc) didn't perform online editing in the way most people view online editing (the Rockwell method). As jstolaruk points out you can't download to a function that you are actively monitoring. At least you couldn't in V5.2. If you are allowed to now it most likely because Step7 suspends monitoring while you download the function then re-activates it without the user seeing the change.

Having said that, the Siemens active download is seamless as far as I can tell. I have personally never come across a case where I have seen any noticeable effect of a download.

Originally posted by Peter Nachtwey:

Ah, the big question. If your PLC compiles all the code into one big block then you will need to change how the code it compiled.

I think the 'classic' AB plcs (PLC5 , SLC5) may have cheated a bit. I think those designs ran an onboard interprettor and generated instructions on the fly. That's one of the reasons the Siemens S5 was so much higher performance with basically the same hardware. It ran compiled code. That doesn't change the fact, however, that the new code needed to be called instead of the old code. The mechanics of that would need to be similar whether compiled or not. As a side note, the PLC5 would run into online edit issues if it was nearly out of memory. If you were trying to edit a large rung with complex instructions you may be able to edit it offline and download but not edit it online due to lack of memory.

Originally posted by Peter Nachtwey:

I also think that most PLC companies are moving away from hot plugable cards so I don't see it as the competitive issue that on-the-fly edits are.

Interesting position. AB just brought this in as an officially OK thing to do with the CLX platform. So is AB just 20 years behind the curve or did they see something in the marketing data that everyone else missed?

Keith

 

[JesperMP]

Well, you challenged my statement, you might as well cough up your reason for calling it nonsense. I may learn something about S7 that will help my efficiency debugging. ☯

OK. Here goes:

Since long, the PLC memory itself is no longer the scratchpad in which instructions are inserted one by one when the programmer presses keys on his handheld terminal.
Today, you edit the program on a PC and it is downloaded to the PLC.
On AB, you edit one rung at a time, and when you hit the ENTER key, it is downloaded to the PLC (*).
On Siemens, you edit a complete block at a time, and you have to manually initiate the download of the block to the PLC.
Point: Technically AB and Siemens are not so different behind the scenes. One is not more online than the other.

Arguably, AB gives you a more fluent feel when programming, you dont have to do so many keypresses or mouseclicks in order to achieve the same.
However, ABs online editing could also be improved. It has hit me uncountable times, that I forget to move the cursor to the start of the rung and then activate the green tickmark to accept the edit. When I then later "test" and "assemble" my edits, some rungs are not included. Someone mentioned that there should be an "finalize all edits" button. I aggree to that.
Point: AB and Siemens are very different. AB may have a slight lead in the productivity department.

I think that this is what you mean to say, that it is a more of a hazzle to do edits with Siemens than with AB. I aggree, but the reason you state is not correct. I also think that if you sum everything up, the difference is not so great.

AB has a genuine advantage over Siemens due to the test and untest feature. No other PLC that I know of has a real undo/redo functionality.

*: You can also insert one instruction at a time, but what really happens is that the entire rung with the new instruction is downloaded and replaces the old rung.

edit:
I shouldnt have used the word "nonsense". However I see sometimes the statement that Siemens is "not really editing online you know" used as a way to derate them. Thats why I felt I had to correct you.
I could have said "ABs online view is not really correct you know". And we dont want to start an argument about that, right ?

 

[Peter Nachtwey]

Correction, CLX modules are hot swappable.

I think the 'classic' AB plcs (PLC5 , SLC5) may have cheated a bit. I think those designs ran an onboard interprettor and generated instructions on the fly.

Whether one uses an interpreter or not makes no difference as to changing code on-the-fly if you have the right computer that use position indpendent code. One can just as easily jump to a block of true machine code.

Interesting position. AB just brought this in as an officially OK thing to do with the CLX platform. So is AB just 20 years behind the curve or did they see something in the marketing data that everyone else missed?
Keith

I just asked by hardware engineer and he said that Control Logix cards can be hot swapped but the program may fault.
The hardware engineer was specific about what would happen if a motion controller was removed. However, one better stop the process before pulling the motion controller anyway.

 

[jstolaruk]

Point: Technically AB and Siemens are not so different behind the scenes. One is not more online than the other.

Maybe, but it feels more offline than online for the reason that Keith pointed out:

As jstolaruk points out you can't download to a function that you are actively monitoring.

And you point out:

AB has a genuine advantage over Siemens due to the test and untest feature.


Darn, I was hoping you could show me a trick that would make S7 feel more like the AB method.

Frankly, its a little scary making changes and downloading while the processor is running and not monitoring the changes or being able to undo them quickly. So, I usually imbed a temporary contact that I can energize manually that will enable the new logic and disable the old while I'm monitoring. Its exactly what I do with the older SLC and Micrologix processors that don't have online editting. So from the user prospective (me), it feels more like offline editting then online.

 

[PeterW]

It does make me laugh when I see statements knocking Siemens because its not Allen Bradley.

Thing is, over here Bradleys play second fiddle to Siemens.

At the end of the day ALL PLC's have their good and bad points and peoples preferences are biased to what they know.

Better the devil you know is the saying, is it not!

 

[jstolaruk]

It does make me laugh when I see statements knocking Siemens because its not Allen Bradley.

Thing is, over here Bradleys play second fiddle to Siemens.

At the end of the day ALL PLC's have their good and bad points and peoples preferences are biased to what they know.

Better the devil you know is the saying, is it not!

Oh don't get me wrong, I'm not knocking it. And I agree with you 100% on the good and bad points. As an example I prefer working with ProTool Pro than PanelBuilder.

 

[geniusintraining]

I would like to ask the forum if anyone has every experienced any problems with online editing...

Yes, I have seen where the switch between old and new code has caused jumps in the scan time that causes PLC based motion control to have difficulty..

I have noticed this with Automation Direct and Siemens ('S5'only), there is sometimes a noticeable change in the scan and the outputs are interrupted...But I have not noticed this with the SLC (504) do you think this is due to the changing of a single rung/bit verses a segment/ladder?

 

[PeterW]

I'm scratching my head now.. ... yep thats me, I have the worlds worse memory, I've only recently been using Modicon and thinking is that it??


or was it the old Square 'D'?...

or maybe TI..


Which PLC actually made the changes and came true in the logic as you wrote (and monitored!!) it.

Probably more than one!!

I remember Square 'D' allowed you to place contacts anywhere on the screen so you could monitor its state.

 

[Tom Jenkins]

"The first thing we do, is we kill all the lawyers." Thomas Moore (himself a lawyer!)

I can't address the liability implications, Stephen, but apparently other manufacturers have been able to reconcile themselves to this, since I know Siemens, Allen Bradley, and Modicon offer some kind of on line editing on at least some models.

I've often wondered if some of the PLCs that offer this have dual memory areas, or if it is interpreted code vs. compiled. I myslef don't know.

As far as "gotchas" in modifying the program with incorrect logic, it is a real consideration, of course. However, I'm not certain this is any more of a problem than bad code that requires the processor to be dropped out of run mode before downloading. The only difference is off line editing delays the inevitable discovery of what you did wrong.

 

[kamenges]

Originally posted by JesperMP:
*: You can also insert one instruction at a time, but what really happens is that the entire rung with the new instruction is downloaded and replaces the old rung.

I don't know enough about the actual mechanics of an edit download. AB may download a whole rung at a time. However, both the old rung and the new rung are resident in memory at the same time. You can begin an edit session with an AB plc and lose your connection half way through the edit. When you reconnect the edit will still be there just like it was before the connection loss. The old rung is only erased from plc memory when the new rung is accepted after testing.

Again, this is largely semantics. The online changes I have made with the Siemens S7-300 have appeared seamless to me.

Keith

 

[Money4Nothing]

I didn't care for online editing with any PLC until I started using AB's Control Logix platform. Its far and away the best control architecture that I've ever seen.

$

 

[Ron Beaufort]

from Tom Jenkins:

The only difference is off line editing delays the inevitable discovery of what you did wrong.

I’m pretty much in agreement on that score ... there’s more about that particular aspect of the discussion in this post ...

also, it’s easier to understand the “when/where/why/how” of Allen-Bradley if you use their terminology:

case in point: we don’t “download” just one rung ... instead we “accept” a rung ... in many (but not all) instances, this “accepting” operation does NOT require shutting down the system ...

the word “download” should technically be reserved for the operation which completely REPLACES one ENTIRE PROGRAM with another program ... any “download” always requires completely stopping and then later restarting the process ...

finally, there's much more (too much?) on the AB end of this subject here for anyone who has an interest ...

 

[optimus2861]

Use it, need it, want it. Stop an entire process just to, say, add a new transmitter? Program a flow totalizer? Add a time delay to something that didn't have one before, or vice-versa? Insanity.

 

[jstolaruk]

finally, there's much more (too much?) on the AB end of this subject here for anyone who has an interest ...

oh yeah, I forgot about that one. There must have been blood on your keyboard after publishing that dissertation.