beating the plc scantime for multiple machine

Hello guys,

Do you have any suggestions or considerations when programming multiple machines running all at the same time? I am using Allen bradley plc with rslogix 5000 as the software. I am thinking whether the program is fast enough to accommodate multiple machines. do you have any tips in programming or with the hardware?

Thank you in advance.

at the end of the day the program scans through its rungs top to bottom.
the more rungs the longer the scan time.
Also the more memory that is consumed.
One issue is - should you loose power on your main processor
(or a major fault) you will loose all your machinery.
your call on that, not a good idea in my mind.
it is more common to run smaller field PLC's
should you require to centrally control those
do so by an E/net system to a central processor.

thank you for your reply...yes you are right.

lets say in the program, I have a main routine calling each subroutine. And each subroutine there is a machine running. I have 4 machines running all at the same time. what is the best and efficient way of programming it?

From a memory standpoint, you probably want to modularize as much of the code as possible. This means using AOIs and the like whenever possible. Is there one chunk of code you use over and over? Don'y copy/paste, use an AOI.

From an execution standpoint, it is often useful to call different parts of your program in multiple tasks, that execute at different rates. Your motion control needs to be done quickly, but other things like slow temperature PIDs can wait (maybe only once a second). If your HMI only updates at once a second, you don't need to run the code that handles the animations every 5 ms. Any code you execute more often than you have to drags the rest of the system down.

Any optimization requires you to analyze your code and really understand what the code is doing, what it SHOULD be doing, and how it interacts with other components. The other side of the coin is that once you understand your code, you can re-write the sections that will help the most. There quickly reaches a point where further optimization won't help much, and it is vital to be putting your efforts in the right place. I can't count the number of times that I've seen customers worry about their PLC scan time, only to explain to them that the PLC wasn't slow, it was that the 3rd party gateway they monitored it with was only set to update every 2 seconds.

How many IO points in each machine? In total? What size will the program be for each section?
How fast will the machine run - what is the fastest response you will require?

Run each machine as a separate program with tags aliasing the IO in each program scope.

That way your code will be portable between machines. Make a change in one and you can copy it straight to all the others or if they are identical you can cut and paste the whole lot.

AIOs are nice when everything is finalised but are a complete **** to work on while developing because you can't modify without going offline and downloading everything again.

thank you for your replies..

Yes, I will use AOI in order to minimize the program. but I have to be sure with my codes and I already tested it.

If running all the subroutines all at the same time, Is there going to be a problem that I may encounter in the future?

Do I need to repeat the subroutines just to be on the safer side?? because the scan of the plc goes from top to bottom of the program.

This kind of objective is new to me.

Thanks again in advance.

Can you unpack your post a bit, femnoble? What do you mean by "repeat the subroutines?"