Upgrading relay to programmable

Hello

I have a project to upgrade a bottle capping machine from relay to programmable logic. The existing control is very dated and safety set-up is based upon latching in off the main drive contactor.

I have seven contactors to control; 5 motors, 1 brake and 1 inverter.

I am using Siemens S7-300 CPU 314, SM321 DI 32x24vdc (2 off ), SM322 DO 32x24vdc and IMO Jaguar VXR.

I have compiled the IO table, the panel is wired and schematics drawn up so ready to rock'n'roll once the program is squirted in.

I'm at the stage of compiling the program. As said, this is upgrading an existing machine with modifications such as incorporating a Schmersal (301 LC) Safety Relay. A text display will flag alarms and faults. I could convert the relay logic in some sense but I'd like to take it from scratch.

I've divided the set-up into a number of sections:

Safety [emergency stop(s), guardswitches]
Overloads
Crash stops [clutch lever-switches]
Height adjustment [reversing contactors]
Drive Inch/Off/Auto
Hopper control


How do I go about starting a flow diagram or a way of compiling the program from my IO, please?

Has anyone an example, please?

I know what I want but would like to know how to do it not-on-the-fly (read 'prepared').


Thanks in advance and kindest regards
silva.foxx

Am I to take it that all you programmers program on-the-fly then?

Or... is this restricted access to the Secret Sqirrel Society?

How do I go about starting a flow diagram or a way of compiling the program from my IO, please?

Click to expand...

Silva foxx, I guess the loud silence on your quetion is because there is no known way to get from only your "IO" to PLC logic. The magic missing ingredient is the logic that goes between the "I" (Inputs) and the "O" (Outputs). There is no way for a bystander to determine that logic. You will have to look at the existing relay logic and convert it to PLC logic. Relay ladder diagrams would make it fairly straight forward job. I know how to do it, but I don't know an easy 3-sentence description of how to do it.

Lancie1 said:

Silva foxx, I guess the loud silence on your quetion is because there is no known way to get from only your "IO" to PLC logic. The magic missing ingredient is the logic that goes between the "I" (Inputs) and the "O" (Outputs). There is no way for a bystander to determine that logic. You will have to look at the existing relay logic and convert it to PLC logic. Relay ladder diagrams would make it fairly straight forward job. I know how to do it, but I don't know an easy 3-sentence description of how to do it.

Click to expand...

True!
I wonder if he could post a Sequence of operations for us? That would get the ball rolling.
Assuming you have the I/O Layout and have adressed the I/O Points in the variable list, We could through some ideas if we knew what you need to happen ?

It's all IF,AND,THEN !

silva.foxx said:

Am I to take it that all you programmers program on-the-fly then?

Click to expand...

Well, actually, yes.

But hey, it's made me well over a million bucks, so who am I to complain?

But I will be the first guy to admit that my brain isn't wired up in the normal way.


For the times when I actually do write the program (rather than fix it on the fly like I usually do), I look at the outputs and work my way back to the inputs.

Think of it as creating your flowchart from the bottom up.

So, I would take your motor starter and then add all of the inputs that I felt were necessary to make it run.

I can't help you on the specifics (I've never programmed any Siemens PLCs), but if you would like us to look at what you've got, go ahead and post it.

I do mostly small custom machine controls, so I usually don't do a formal flowchart, but just break the process into sections with the conditions to transfer between sections. Then you can insert the logic, to handle each section.

But, there are different programming styles, and it all depends on the machine, for what works best. The more complicated the process, the more organized you need to be. In the end, keep in mind, the person who has to troubleshoot it later, and the ability to insert a new function later.
-Mur

Simply break it down into steps, as someone already said, a flow chart or similar.

At each step, decide what should happen, what verifies it did happen, and what is required to goto the next step.

What determines that the cycle is complet, and reloops the code etc

I usually break the machine down into its smallest modules, work this out on a sheet of paper, then tie them together.

Did you see it working before you stripped it down?

Thanks guys

Job is done. I winged it and tested it in Siemens PLCSim.

I wasn't looking for someone to fill in the gaps between inputs and outputs. It's annoying that pros here assume you want your homework done for you. Guidance is all that's requested by an amateur.

I was after some sort of graphical representation of planning a program from tabulated IO. I gave no detail of IO so would not expect the program compilation from someone out there. Its often stated 80% prep 20% programming. I was hoping for an example of prep.

Thanks anyway for the responses.

The machine was already broken down as suggested into safety, height adjust, machine drive, hopper control and interfacing.

The previous relay logic wasn't used as an aid. The logic has been tested and is all ticketyboo.

Cheers!

It's annoying that pros here assume you want your homework done for you. Guidance is all that's requested by an amateur.

Click to expand...

If you are referring to lil' old me as a "pro", then thanks for the boost. I did not assume that this was homework, but I did assume that you wanted help to use the IO to write a new program. The reason I assumed that was the highlighted part of your statement:

How do I go about starting a flow diagram or a way of compiling the program from my IO, please?

Click to expand...

I was completely wrong and I apologize for my error. I see now that you were looking for a general approach on how to write a program. The best I can do there is to say that I have not found a general generic approach that results in good programming code.

silva.foxx said:

Am I to take it that all you programmers program on-the-fly then?

Click to expand...

If it has more than 5 IO, I rarely program on the fly.

I've created a video introducing structured programming using flowchart style as a start. The video is simply a start showing the concet and has many more things that need to be done before the program can be considered production ready:

http://www.youtube.com/watch?v=rCa_U6YATTA

Good job Archie !

Archie said:

If it has more than 5 IO, I rarely program on the fly.

I've created a video introducing structured programming using flowchart style as a start. The video is simply a start showing the concet and has many more things that need to be done before the program can be considered production ready:

http://www.youtube.com/watch?v=rCa_U6YATTA

Click to expand...

Perfect... simple. Thanks.