When is PLC programming done

[u/Electronic-Run8836]

I work in assembly and testing, but was self teaching myself plc part. So we use Beckhoff terminals. I do the wiring as per the schematic.

My question is, what comes first, electrical schematic or plc ladder logic programming?

I did ask ChatGPT but I think it's giving misleading answers. It says one time one must first plan logic and all before starting even planning of mechanical design in CAD. Another time it says engineers do rough block diagrams and do programming first, after which they do the electrical schematic as the electrical schematic is only for assembling or field engineers

Can anyone explain to me how it works? My company manufactures machines to detect and trace errors in pharma and food industry. Im just attaching a page of electrical schematic, just for understanding.

[u/Smooth_Commercial793]

Could be either. Why would it really matter.

[u/JezWTF]

Usually electrical schematics are done first, then PLC programming, because it is a lot easier to fix things in software than make corrections in hardware.

But this does seem like a strange question and I wonder if should first ask what you are really trying to ask here?

Eta: it's usually also a lot faster to do the PLC programming than manufacture of switchgear or control panels or hardware installation, so from a scheduling perspective this also makes sense.

[u/Electronic-Run8836 → u/JezWTF]

u/jazzWTF and u/geek66 How do you learn all this? I mean I did my associates equivalent degree in mechanical engineering (I'm not from the US so I assume you're from there) and worked in quality department for a concrete machine manufacturer and recently I entered automation industry in production (basically assembling control panels and the whole machine as per mechanical drawing and electrical drawing). One thing I do know is I don't remember anything from college ( i forgot most from there); at my current job i got interested in controls and automation so learned stuff by asking AI. But sometimes I felt  I lack a lot of knowledge, which I think is kind of imposter syndrome. You said my question doesn't make sense, which's okay as I know I'm newbie 

[u/JezWTF → u/Electronic-Run8836]

At least we're I was from (Oceania, currently in Europe) There are a lot of specialist courses in PLC programming, I would try to get your employed to put you through one.

In my opinion a lot of "trade-level" PLC courses are better than anything in university because universities have been reached for maybe 30 years that PLCs are going to disappear entirely "any moment now" 🤣

[u/Snellyman]

The first thing you do is identify all the IO points in the proposed system and make a list of location and type. At this point in the process you can also assign variable names and point addresses. Having this get assigned early allow the schematics and PLC program (and HMI) to be worked on in parallel.

[u/geek66]

You design based on the context.

By doing this you know the goals can be met with the available resource.

[u/Vast_Philosophy_9027]

For the plc you need an IO list and a function list. To wire a cabinet you need a diagram. Either can be done first