Help with PLC communications to application understanding

Crumpet

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Join Date
Mar 2022
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Wales
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5
Hi,

To give some context of the situation and why I'm posting. I started a PLC module as part of a general engineering course last year and the teacher for the subject quit 2 months in, since then the lesson basically hasn't happened because they didn't get a replacement. With a month remaining we suddenly get handed a boatload of coursework to complete without having any support, lessons or resources. Or else risk the whole course grade. So it's full on panic mode and I'm actually considering taking legal action

Anyway, for the most part I'm getting through it but one part I am really struggling with is communication technologies related to various applications.

Firstly I have to find 4 specific applications and do a review of their common communication technologies.

Secondly I have to do an evaluation of avaliable fieldbus technologies for three industrial applications and then avaliable eithernet technologies for three industrial applications.

I've been trawling the Internet for days and I have gathered plenty of info that covers communications in general but it's all very broad and non-specific to any selected applications. (Protocols, networks, topology, transmission media etc.) I have written about these individually but have found next to nothing to explain how these apply with the pros/cons in order to speak about how and why one is better than another to each application.

For example I was looking too go for cnc machines, air con, robot manufacture, cement industry, glass industry, bottle plant etc. Now I'm getting quite stressed about it and getting overwhelmed with the amount of information and not actually getting anywhere with it.

Shot in the dark but is anyone able to offer some help? Before it's said, I'm not looking for anyone to do my homework for me, just looking for guidance, direction to resources or anything that might get me on the right track.

Thanks for reading.

Crump
 
I hope that's not the actual language in the course assignment because that sounds like a complete waste of time for beginner. Yes, you can tell your instructor I said so.

They are more like questions in an interview for experienced folks to gauge the level of experience and the individual's thought process.
 
There isn't an instructor she quit 6 months ago. Just pre written course work questions that'suddenly been dished out by the course leader who doesn't even teach the subject. And yes that is the actual language covering two questions
 
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They've given you the wrong coursework. I did the PLC module as part of my HNC and it was basically a few questions on I/O, digital analog signals, differences in types of PLC, then a traffic light program.
 
This is also HNC/HND. Those are all things we've covered, communication applications is the final assignment.
 
Or else risk the whole course grade. So it's full on panic mode and I'm actually considering taking legal action
I would have already taken legal action and would seek to claim back the money you're paying for no service received. This is the definition of breach of contract or possibly fraud if you let it go for long enough.

Firstly I have to find 4 specific applications and do a review of their common communication technologies.

This is silly because the communication technology isn't chosen based on application but the instrumentation and brands used on the overall solution to increase diagnostics, reduce engineering time and have, in theory, a more reliable solution. EthernetIP or Profinet will be chosen based on the whether the main controller is Rockwell or Siemens, not because it's an oil rig or plastic making plant.

Secondly I have to do an evaluation of avaliable fieldbus technologies for three industrial applications and then avaliable eithernet technologies for three industrial applications.

One example you can bring about is the use of Foundation Fieldbus in Hazardous Areas (or ATEX) since it's certified to be used there which for the time being other protocols aren't.

You could approach the transmission media for example although that's not protocol dependent.

The other possibility would be to write how modbus is still used and in many cases is the solution since most devices will "understand" it due to being so common with all sorts of devices. The fact that is, to an extent, an open standard helps as it allows products to make it to market without paying license fees. The downside of this is that it's not set in stone and there are quirks to how is implemented.
 
The best way to help you is to brainstorm with you to get things clearer in your mind and narrow things considerably.


Looking from a bird's eye view and then drilling deeper until it reaches implementation level and you know you've gone too far; next iteration limit the scope to and remove anything that is too detailed.


Why communication?
To get data (or for control) you need information from somewhere/something to somewhere/something or somewhere/someone.



How critical is the data, (security, reliability, redundancy)?


How fast does the data transfer have to be?


Oh, when we talk about speed, size immediately comes up, how much data are we talking about?


The last two questions bring up the question of distance, how far does that date have to travel?


The last three questions alone can help you split up industries, small production plants, oils and gas, mining, city infrastructure like hydro and water/waste.





What form of communication are there:
Wired and Wireless


We can use Wired and Wireless as the top of two pyramids and see how far down we go down with each.
Wired: Serial and Parallel .


Wireless: I guess GSM and what? Where is Damica1 when you need him. He does a lot of this stuff. MQTT, maybe?



Drill down serial communication with MODBUS which has few protocols, CanOpen and what else.....USS, DeviceNet.

Why serial communication,





Industrial Ethernet (would be nice to define what that is, for yourself, it may guide you in your research for applications)

Protocol, what are few of them and how do they differ?
Do we need to know physical layers of each, I doubt it
PROFINET, Ethernet/IP, Ethercat, OPC-UA,

As to how they differ, I wouldn't get bogged down in the technical structure and focus on things like:


Each hardware manufacture (PLC and related hardware) seem to have a preference and they either invented/designed the protocol or embraced it for use with their hardware.
Meaning, an OEM is unlikely to choose communication protocol and rather choose the hardware as a whole. If a machine manufacturer gets excellent price, service and reliability from Siemens they're going to be using PROFINET, PROFIBUS.
And as mentioned above, MODBUS is supported by a few of them.

Again Siemens seems to support MODBUS TCP/IP bettter than MODBUS RTU.



Ethercat pretty much goes with Beckhoff, Ethernet/IP with Rockwell. And the same applies, if a customer specifies Rockwell hardware, the OEM is using Ethernet/IP , DeviceNet, etc.




Then what about integration of different protocols?

That is usually challenging, there are some converters out there that solve some of those issues.




Another idea to go about this is to pick any three industries as your main headings then analyze each one's communication requirements.



Small production line: say each line with 20-30 motors, likely MODBUS or CanOpen, cheap and slow. Used to changing speed, maybe to start and stop and error monitoring.


Larger plant, multiple sites: Industrial Ethernet of some type.


Remote sites: Mining, Oil and Gas, Infrastructure. May need wireless, MQTT.
 
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