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

[jstolaruk]

Online editting is definetly a time saver when commisioning new machinery and practically a neccessity if the equipment is interlocked with neighboring equipment (robots, etc). The more complicated (i/o) the machine, the bigger the payback in time savings not having to stop it to download-edit-upload.

I agree, "online editting" with Step7 isn't truely editting online. How could it be if I'm making changes offline, uploading, and then have to re-connect to see the results? The only savings is that I didn't have to stop the processor.

 

[Ken M]

What about changes to hardware ?

I've seen Siemens make reference to a facility on their upper-range controllers (as used in the PCS7 process control system) having something called CIR - Configuration In Run. I've never used it so I don't know much about it.

This appears to be not just the ability to download modified code to a CPU, but to physically add or remove I/O modules and download new hardware configurations and relevant code, while keeping the existing plant running and in control all the while. I guess companies with genuine 365/24 operations (oil/gas/petrochem) would have this kind of need with plant outages maybe only planned every two years or so.

Ken

 

[rPraveenkum]

Finalize All Edits in Program

This feature will be good one instead having classic Accept pending edits, Test edits, assemble edits

 

[IO_Rack]

Do I use it? I use it almost exclusively for modifying existing programs.

Do I need it? Probably not, but it most certainly saves valuable time in the high speed production world.

Do I want it? Absolutely.

Speaking from an Omron perspective (possibly others, I don't know), you have to be very careful with some of the older processors... even some of the newer ones depending on the speed of your inputs and PLC scan time.

The Online Edit will increase the time of PLC scan to a point an input may be missed. Depending on your application this could be disasterous.

 

[cntrlfrk]

Yes, Yes, and Yes here also. I mainly work in processing plants where 'scheduled' outages only come maybe once per year. I hear A-B is coming out with the ability to add cards on the fly. That is the only other thing I miss about DCS control systems

 

[Stephen Luft]

Terry,

Thanks for posting this topic. It was something I was considering posting yesterday. We are currently in the planning stages for a new controller and one of the features I am considering is online editing.

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

Personally, I see potential problems with modifying code while the process is in operation...and therefore am extremely conservative/cautious about considering such a feature.

For any of you techies out there, just how would one design a controller that offers online editing? Our concept would be to have dual memory on the hardware side. Not quite certain how it would be performed in firmware just yet, in that we haven't researched it.

Based on the responses to date, it is needed most in process applications whereby the equipment is running continually. Many have stated that they don't need it, but it is nice to have..."a time saver"

I would think that once a machine is commissioned, the actual ladder code probably wouldn't be modified, but rather the variable information (timing), which can be done rather easily through an interface or PC. I would also think that to modify online while the process is running, one would have to be extremely confident in their programming abilities...one OOPS could cause major damage.

From a manufacturer's perspective, I would be offering a feature that if not used properly or used by someone with limited experience could make Entertron liable for damages. All the disclaimers in the world can't protect you...lol. Our basic view is that any new customer, whether completely new to PLCs or a pro, will have a learning curve with a new PLC, in that every ladder editor and features are different.

If anyone would like to enlighten me as to the nuts and bolts of online editing, I would be interested in learning more, so to be able to make an informed decision, for our new product.

"Adding cards on the fly"...are you referring to I/O cards or memory cards?

If we are talking about memory cards...I can see that in that some already do online editing. If we are talking about I/O cards...that would concern me.

In both cases, the manufacturer is presuming a certain degree of knowledge on the part of the customer. To change I/O while a process is in operation mode presents endless possibilities for disaster.

I look forward to participating further in the discussion.

God Bless,

 

[jstolaruk]

I would think that once a machine is commissioned, the actual ladder code probably wouldn't be modified, but rather the variable information (timing), which can be done rather easily through an interface or PC.

Depending on the industry and the application, this statement could be true or farthest away from the truth.

If you consider the industry I'm in, the customer 99% of the time will buy the material handling from one vendor and then each machine will be from other vendors depending on their strengths and bid price. The size of the equipment doesn't allow it interact with each other until its actually on the customer's floor. Though a lot of the interlocks and timing can be designed ahead of time, there is still the requirement to debug it onsite and to make changes for interlock debugging and to optimize cycle times. Online editting is a neccessity in this phase of the project.

 

[TimothyMoulder]

Unitronics does not support on-line editing. What they do have is the ability to download to a running PLC without stopping it. They do this by downloading the new program into a separate section of memory, the switching from the old to the new in between ladder scans.

In certain instances, they cannot do this, and will force you to stop and reset - yes, they warn you first. Most noticibly if you change a major function block like Modbus Config, or if you use the Search & Replace function while editing offline.

Online edits is one of a short list of things I wish they offered, like tag-based addressing and user-defined function blocks, but all of these would be major code changes to Visilogic, so I don't complain.

TM

 

[rdrast]

Online, Editing?
Use it?
Absolutely. Every day.

Need it?
Definately, We cringe anytime we get a piece of trash equipment that does NOT allow online edits.

Want it?
In the few places we have piece-of-trash controls without online editing, yes.

We are also taking advantage of the later ControlLogix firmware in allowing us to plug in NEW I/O modules, activate them, and update our systems without interrupting the existing process.

I don't want to go back to the dark ages.

 

[kamenges]

Yes. No. Yes.

I don't do process stuff so shutting down a machine to make a program change isn't a real issue. I like having online editing but it isn't a requirement. But it is convenient.

And I don't see a real significant controlability issue with online editing. If a programmer makes a change that is going to cause a crash that crash will happen whether the change was online or offline and downloaded. It'll just happen a little sooner with the online edit.

Granted, this assumes there is no significant processing discontinuity when the change is made.

Keith

 

[cntrlfrk]

"Adding cards on the fly"...are you referring to I/O cards or memory cards?

If we are talking about memory cards...I can see that in that some already do online editing. If we are talking about I/O cards...that would concern me.

In both cases, the manufacturer is presuming a certain degree of knowledge on the part of the customer. To change I/O while a process is in operation mode presents endless possibilities for disaster.

Adding I/O cards on the fly. We try to plan ahead for any possible projects that may come up, but it seems like there is always a project where you end up a half-dozen I/O points short. So then we need to take the whole plant down to stick an I/O card in the rack and configure it. (Plant managers don't like that!) Or even change a card type from digital to analog, or from DC to AC or 8 point to 16 point etc...

 

[JesperMP]

I use it, I need it, and I want it.

... and was suprised to interface with a SLC500 and find that it didn't support it.

SLC5/01 and SLC5/02 dont have online editing. SLC5/03, SLC5/04 and SLC5/05 do have online editing. For that reason avoid the SLC5/01 and SLC5/02.

I once decided to use a ML1200 in stead of an SLC500 in oder to save a small amount of money. Big mistake ! Never again.
(Today I would have tried the new ML1100, but it wasnt available back then).

I agree, "online editting" with Step7 isn't truely editting online. How could it be if I'm making changes offline, uploading, and then have to re-connect to see the results?

Without going into details, this is nonsense.
ABs online editing is better than Siemens, but for other reasons.
It is the true undo/redo functionality that makes ABs online editing stick out from the rest.

 

[RMA]

If we are talking about memory cards...I can see that in that some already do online editing. If we are talking about I/O cards...that would concern me.

Stephen, the ability to hot-swap I/O cards has been a feature of what are now called DCS systems for over 30 years. The first time I met it was with the Kent (now ABB-Kent) K90 systems in 1972. On those the only things you couldn't change on-line were the DEC PDP-11 CPU, the Interface card connecting the CPU to the Kent I/0 section and a couple of the main control cards for the I/O system. All the rest of the I/O cards and power supplies, including the Kent printer and paper tape punch/reader cards could be hot-swapped.

Sure you have to know what you're doing, but if you don't you shouldn't be doing the job anyway. After all, even if you can stop the plant/machine to make your modifications, unders certain circumstances, if you've made a mistake, you could still cause extensive damage on start-up.

 

[Peter Nachtwey]

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.

Personally, I see potential problems with modifying code while the process is in operation...and therefore am extremely conservative/cautious about considering such a feature.

Nothing is absolutely safe. I think it can be made safe from a vendors point of view but if the customer downloads bad changes they will be bad whether on-line or off-line.

For any of you techies out there, just how would one design a controller that offers online editing? Our concept would be to have dual memory on the hardware side. Not quite certain how it would be performed in firmware just yet, in that we haven't researched it.

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. The code must be compiled in sections that can be downloaded in piece if need be. I would bet that Rockwell compiles their ladder a rung at a time whereas Siemens downloads whole funcitons or funciton blocks. You can see that Siemen's method could cause problems if short on memory and a big block needs to be down loaded. In both cases I think the program is is the form of link lists. There definitely must be some sort of indirection. The new code is downloaded and between scans the point in the list is changed to point to the new code. This means that code cannot be compile for any particular address location because you don't know where it will end up. In addition, there must be extra memory where the new code can be downloaded. There must also be a way of freeing up the old code so that space can be used again. This will required some sort of garbage collection. It can be very simple and it must not interfere with the PLC scan in a noticeable way. There must also be a method of finding memory in the heap to allocate new space for new code. This has all be done before. There is no trick if you look at how operating systems allocate code. You may just allocate code and never reclaim the old code. When all memory is filled up then you force the customer to reclaim the code by activating a garbage collection routine that requires the PLC to be off. This is simple and I believe some Siemens PLCs use this method.

Based on the responses to date, it is needed most in process applications whereby the equipment is running continually. Many have stated that they don't need it, but it is nice to have..."a time saver"

I have customers that will not use MicroLogix because they can't make on-line edits. They buy the older SLCs instead.

I would think that once a machine is commissioned, the actual ladder code probably wouldn't be modified, but rather the variable information (timing), which can be done rather easily through an interface or PC. I would also think that to modify online while the process is running, one would have to be extremely confident in their programming abilities...one OOPS could cause major damage.

That is because your smaller PLC get used for smaller projects. When commisioning a saw mill or still mill you don't want to stop to download edits.

From a manufacturer's perspective, I would be offering a feature that if not used properly or used by someone with limited experience could make Entertron liable for damages. All the disclaimers in the world can't protect you...lol. Our basic view is that any new customer, whether completely new to PLCs or a pro, will have a learning curve with a new PLC, in that every ladder editor and features are different.

That is why you must make sure that download code doesn't interfere with the scan. I think the edito on-the-fly feature is safe. Anybody can download bad code. The only thing you will be doing is making it possible for anybody to download bad code anytime.

If anyone would like to enlighten me as to the nuts and bolts of online editing, I would be interested in learning more, so to be able to make an informed decision, for our new product.

This varies from PLC to PLC. The TI and old Modicons were rather simple. The Rockwell software allows one to have many edits pending. It is the the most versatile on-line editing method but it has more key stokes to get the job done. There is a procedure to it.

"Adding cards on the fly"...are you referring to I/O cards or memory cards?

This is a different topic. We made motion controllers for PLC too. The only motion controller that are hot plugable are the Modicon PLCs. Adding a new card will cause an in rush of current. You need to add inductors between the back plane and the DC to DC power supplies otherwise adding a card can cause the PLC to fault when it detects a low voltage. The PLC power supply must also have better regulation. Hot plugable cards is some that is designed in, not added on.

If we are talking about memory cards...I can see that in that some already do online editing. If we are talking about I/O cards...that would concern me.

In many cases the PLC will fault because some I/O can't be read. However, this is a nice feature. I do a lot of testing here and I am very sloppy about turning off power when in the office.

In both cases, the manufacturer is presuming a certain degree of knowledge on the part of the customer. To change I/O while a process is in operation mode presents endless possibilities for disaster.

I look forward to participating further in the discussion.

God Bless,

I don't think it is as bad as you think. I just think that it isn't necessary and not near as important as on-the-fly edits. 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.

 

[jstolaruk]

Without going into details, this is nonsense.
ABs online editing is better than Siemens, but for other reasons.
It is the true undo/redo functionality that makes ABs online editing stick out from the rest.

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. ☯