Replacing PLCs in Industrial Applications with Microcontrollers

Thread Starter

daljeet795

Joined Jul 2, 2018
274
My background from embedded System. I have hands on experience with microcontroller. I am not familiar with PLC and it's programming. I do not want to learn PLC programming. I want to stay with Microcontroller.

I want to replace PLC with microcontroller in conveyor belt application.

For an example

My guess they are using PLC so Can I replace PLC with microcontroller for airport baggage handling system?

In practically, Is microcontroller suitable and efficient for this project as compare to PLC?
 

Dodgydave

Joined Jun 22, 2012
8,469
Ask yourself the question, if was possible it would have already been done, since there are ready made plcs with software written for this type of automation, Siemens, Allen Bradley, etc..easily programmed with more memory and powerful processors, why re-invent the wheel..!!
 

kubeek

Joined Sep 20, 2005
5,622
PLC is ready made for the purpose. You would have to develop and test your own input and output circuits, overvoltage protection, EMC conformity certification, possibly also failsafe features.
I don´t think it is worth the hassle developing your own, unless you have a lot of airports to which you could sell your system.
 

Papabravo

Joined Feb 24, 2006
12,498
My background from embedded System. I have hands on experience with microcontroller. I am not familiar with PLC and it's programming. I do not want to learn PLC programming. I want to stay with Microcontroller.

I want to replace PLC with microcontroller in conveyor belt application.

For an example

My guess they are using PLC so Can I replace PLC with microcontroller for airport baggage handling system?

In practically, Is microcontroller suitable and efficient for this project as compare to PLC?
You are about 25 years too late. PLCs are built around microprocessors not only for the supervisory functions, but also the low level I/O devices. Everything is connected with robust multi-level networks. IMHO you have zero chance to break into this market without a massive amount of capital. I'm thinking 3-5 billion. The global factory automation market is in the ballpark of 400 billion so that sounds like a great deal of risk for a marginal payoff. Here is the other problem: the people in the plant and the contractors they hire understand ladder logic, the fundamental programming method used in PLCs. To get them to switch to another paradigm has been tried before and met with fierce resistance.

Good luck with your plans - let us know how it is working out for you.
 

MaxHeadRoom

Joined Jul 18, 2013
19,163
I want to replace PLC with microcontroller in conveyor belt application.
In practically, Is microcontroller suitable and efficient for this project as compare to PLC?
For industrial control systems you cannot beat the PLC, not only does it have I/O already conditioned for most types of equipment interface, but its biggest feature,IMO, is the ability to trouble shoot using the ladder program display, with all rung I/o high lighted when active.
This was the reasoning behind the original concept by GM, for the ability for shop floor maintenance personnel to reduce the time taken in trouble shooting.
This is not to say you could not control with a Micro, just that it may turn out to be less efficient later on when equipment failure happens..
Max.
 

Papabravo

Joined Feb 24, 2006
12,498
For industrial control systems you cannot beat the PLC, not only does it have I/O already conditioned for most types of equipment interface, but its biggest feature,IMO, is the ability to trouble shoot using the ladder program display, with all rung I/o high lighted when active.
This was the reasoning behind the original concept by GM, for the ability for shop floor maintenance personnel to reduce the time taken in trouble shooting.
This is not to say you could not control with a Micro, just that it may turn out to be less efficient later on when equipment failure happens..
Max.
PLCs are already run by micros! Why does anyone think there is a difference!??
 

MaxHeadRoom

Joined Jul 18, 2013
19,163
I assumed the OP wanted to use a his own micro design to simulate a PLC, As I stated, the difference for me in a DIY version compared to the features already of the PLC whereby with the acompanying design software, the ability to display the ladder together with its maintenance diagnosis features on a PC screen may take, a great deal of work, re-inventing the wheel.
A micro controlled system without these features would be severely limiting.
Max.
 
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Thread Starter

daljeet795

Joined Jul 2, 2018
274
My bad, selected unsuitable example

For example
Vision system to sort screw on conveyor belt
Vision system to sort good and bad bottle cap
Vision system to sort good and bad box

I want to replace PLC used to sort the product on conveyor with micro-controller

Is microcontroller suitable and efficient for those project's as compare to PLC ?
 
I want to replace PLC used to sort the product on conveyor with micro-controller

Is microcontroller suitable and efficient for those project's as compare to PLC ?
Suitable? Yes it can be done, but it will take a much greater work and time period to implement, is it worth re-inventing the wheel? also what about the lack of maintenance features already mentioned?
Max.
 

Papabravo

Joined Feb 24, 2006
12,498
I assumed the OP wanted to use a his own micro design to simulate a PLC, As I stated, the difference for me in a DIY version compared to the features already of the PLC whereby with the acompanying design software, the ability to display the ladder together with its maintenance diagnosis features on a PC screen may take, a great deal of work, re-inventing the wheel.
A micro controlled system without these features would be severely limiting.
Max.
As a practical reality of the market our TS would have to duplicate the whole ladder logic paradigm. He would be at least 3-5 years from product launch and in that time the market would have moved on. AFAIK he has literally nothing to offer on the subject.
 
My PLC experience is limited to looking over the shoulder of a co-worker who as programming one, but one very big feature that I saw which is not in any plain microcontroller that I'm aware of, is the programmable logic itself! AND gates, OR gates, etc.. With a PLC, at least the one he was using, you build the equivalent of actual low level logic circuits, and that is wrapped with a microcontroller. It was actually very cool and as soon as my request for the 25 hour day comes in I'm going to learn how to program one! :)
 
.. It was actually very cool and as soon as my request for the 25 hour day comes in I'm going to learn how to program one! :)
One cheap(er) way to get in to it is via https://www.automationdirect.com/systembuilder they offer the S/W free also.

.. With a PLC, at least the one he was using, you build the equivalent of actual low level logic circuits, and that is wrapped with a microcontroller.
As well as implementing them, a large part of my experience has been replacing huge cabinets full of control relays used on shop floor automation with PLC control in enclosures 1/10th the size.!
Programming via boolean ladder logic.
Max..
 
Learning to program a PLC will take less time and effort than building your own, even the simplest microcontroller device with I/O. I know because I did both. My Arduino PLC was a good learning experience, but the end result is a piece of crap. One of the lessons I learned in that endeavor is don't reinvent the wheel (unless the wheel sucks, which in this case it doesn't).
 

MaxHeadRoom

Joined Jul 18, 2013
19,163
On the VERY odd occasion I have built my own, it is for small projects that doesn't warrent the expense of PLC, and using the Opto22 I/O board modules to round it off.
The modules come in 5v 24v opto isolated input and fused outputs , relay, transistor, Triac AC/DC etc with LED status indicator. 4 to 32 I/O count, mix and match.

For very small projects there is also the programmable relay, just a miniature, low I/O PLC.
Max.
 

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I think the other big advantage of a PLC of a microcontroller is the reliability. I work for a system integrator and we routinely replace PLC's that have been running 24x7 for 20+ years. And these customers expect the same type of uptime of the new system.

While an airport luggage conveyor isn't as 'high stakes' as a furnace full of molten glass that will cool and destroy the furnace if the controls fail, I personally wouldn't want to have to explain why 200 people couldn't have their bags because a non-industrial controller decided to release the magic smoke due to something stupid happening.

Favorite startup story so far - we just finished a week of long days getting a mixing system cutover from a PLC-5 (1980-1990 tech) to a Control Logix. Literally one more I/O point needed investigated as a valve wasn't working. My customer said he would take care of it and, unfortunately, dead shorted a 120 VAC output to ground and threw sparks everywhere. Entire panel went dark.

We all thought the PLC was toast. Nope. It was fine, put a new fuse in the panel and the system was good as new. Most microelectronics wouldn't be as forgiving without some serious protection circuitry being designed.
 
My bad, selected unsuitable example

For example
Vision system to sort screw on conveyor belt
Vision system to sort good and bad bottle cap
Vision system to sort good and bad box

I want to replace PLC used to sort the product on conveyor with micro-controller

Is microcontroller suitable and efficient for those project's as compare to PLC ?
I wouldn’t consider a PLC for vision based resolution. A dedicated vision system, communicating with a PLC for actions would be fine. A ‘microcontroller’ Would unlikely serve as a vision system.
 

dendad

Joined Feb 20, 2016
3,072
Years ago, we built a vision system with the Harris RTX2000 FORTH chip, used to sort half peaches in a cannery. We even made our own cameras. This drove our own designed I/O boards for shaft encoder input and kicker driving to eject the peaches to the appropriate belt. All this was custom hardware, and programmed in FORTH.
Later, the RTX2000 board and camera were replaced with a Linux box with video capture card and a commercial camera. All off the shelf parts.
The RTX2000 was a magic chip. It could sort the fruit quite well, and it ran at only 20Mhz.

One of our success...
In automation the real bang for the buck is when you can replace miles of home-run wiring with a network cable. Now you have a real in.
Our UNIMOD series of boards did just that. They were marketed as "Wiring Eliminators". Used for building management, and they are still going strong after 30+ years. The main failures are electrolytic caps drying out. These boards has 16 I/O each, and allowed the interconnects between floors in multi story buildings to be run in fire proof network cable, not great multi core runs like it used to be, that having all the switch and contactor cables run to the basement. This saved a heaps of money.
UMDC1.jpg
This is the UMDC, the "slave" part. Many of these can be on the network.

Then, the UMH or host. This had the wiring matris stored in flash memory and that could be easily altered as required.
UMDC1.jpg


But we did put a fair bit of work into making the I/Os pretty tough. An had good protection on the power supplies. Custom hardware can work, but a big problem is support in the long term.
I am retired now, sort off, and will finish my last 6 x Super Unimod boards (SUM) for a customer so he can have spares. After that, no more.

EDIT: The SUM boards also can run on the network, and have 8 x inputs, 8 x relay outputs and 4 x Analog inputs.

There is a lot to be said for PLCs and ladder logic (I have never used it myself) in that when the hardware dies, a replacement can be found, even from another brand, and the program grown into it fairly easily.
The room for custom hardware still exists, but you do need to make it as bulletproof as you can. Industrial environments can be pretty harsh.
But trying to replace an existing working solution with your own custom version is not the way to go. Look for something that does not work well and try to fix that.
As an example, we did a custom Mag Flow water meter for irrigation, the Irriflow...
Irriflow.jpg

And earlier, the M300 for industrial applications..
M300.jpg
Both these filled a need in the market. And PLCs could no do this.
So, look for something that neesd a fix, not one that is working well.
 

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