Getting into PLCs

[Dannyx]

Good day folks. Over at this new workplace of mine, "big boss" we'll call him ,constantly thrives to find new and "creative" ways of increasing income and increasing the range of services we cover. More often than not, he starts off with average joes like yours truly and slowly trains them or turns them into pros in some field or another, which is a thumbs up for this chap - giving people the opportunity to learn is not something your run of the mill definition of "boss" does, let alone in a big company like this one. Some tend to keep a stiff upper lip towards this approach, no doubt, as they likely think this "litters" the industry with untrained and unqualified personnel, but that also means TWO thumbs up for this guy for giving all of that a middle finger and being like the Schindler of the job market, wrangling mediocre people and giving them a chance to do what they like.

To make a long story.......even longer it is now my turn to be involved in a project which seemed intimidating at first, but turns out it may actually be doable, despite seeming ludicrous at first.

So: a large water treatment facility in our city has reached out in search of someone who can provide setup and maintenance for some of their equipment, electrically and electronically speaking (they may actually require plumbing services as well, but that's not my field). Now imagine my reaction when I heard of that Big Boss, being the visionary and eager chap that he is, has instantly taken them up on this offer, so he took me along with him on a "business meeting" of sorts with the facility's manager where the two of them had a heart-to-heart discussing financial issues as well as what the project involves. Their manager assigned us a worker to takes us on a tour of the facility and show us exactly the equipment in use and what needs to be done to it. Honestly, there's really not much to say: I was expecting something like a huge space with gauges and displays all over the walls and filled with the sound of whirring motors and I was mentally preparing for the challenges that lay ahead, for obviously I know squat about such things....how could you blame me ? Ever since I've started working in the field of electronics, I've only done household stuff, never industrial, so I was rather taken aback by Big Boss's confidence in putting ME (your 1.83 tall - 53Kg skinny chap ) up front and center with these guys basically saying "he's our man for this job"

In reality though, while this facility may have such advanced equipment elsewhere, no doubt about it, in this case it's nothing special: a couple of fenced areas here and there around the compound have some deep holes dug into the ground, kinda like wells, and these house a rig consisting of a vat in which dirty water accumulates and it's then aired out by an air compressor which bubbles in air from the bottom and that helps separate the sludge and debris from the water somehow and then the clear water is dumped out into the canal which this compound belongs to. There's several facilities like these spread throughout the length of this canal from what I understood.

You can now see where this is going: the treatment process as well as anything "below ground" is irrelevant and beside the point. I only mentioned it as a curiosity. What IS important is the automation and probing of these vats: every X hours/days, whatever, the compressor is supposed to come on and bubble the dirty water for Y minutes. When this is done, a valve (or several) open and a pump throws the clean water out in the waterway. This requires some sort of automatic control mechanism for each of these stations. There IS such a system already in place and it works to a degree but it requires some maintenance (some of the vats no longer work and are overflowing with sh!t, quite literally due to the pumps in them failing of becoming clogged), so granted, this isn't a project which we build from the bottom: there is something to work with. Most of these stations are functional and we'll use this available technology to study and understand the system. As I said, we went on a field trip to see these things in operation and have a look at the control panel, which consists of a display+keypad unit to display various sensor readings which are way beyond the scope of the project right now, some relays, MCBs, contactors, but most importantly the brain: the PLC. This particular one is a XC3-14R-E (PDF included). Remember, I had absolutely zero experience with stuff like this, but I was able to grasp the concept surprisingly fast, in less than 1-2 days, thanks to the internet and some very helpful YT vids. You can see the COM interface plugged into the PLC which communicates with the panel there. The panel itself is a TouchWin OP320-A-S. From what I understand, the panel and the PLC are programmed individually and are THEN connected together via that COM cable and if done right, everything should sync up and communicate. Basically it's like an Arduino just without the code part: the proprietary program does the coding for you. You just have to input some parameters and use a surprisingly intuitive graphical interface. The videos I watched in this series were for a SIEMENS PLC, but the concepts seem to be the same. This "XC" family uses a suite called XCP PRO. I even grabbed a copy of it and the manual to study myself, despite not having the actual hardware readily available. The pinnacle of this project shall be implementing some sort of remote monitoring system to allow the head office or whatever to monitor the different parameters of these stations without having to go down into the field, which is what happens at the moment. A communication+software solution has to be implemented, but that's not TOO critical at the moment, though certainly worth the discussion....why not.

Anyone here with experience with PLCs who is willing to share ? Share what exactly, you may ask. Tips, tricks, warnings (don't touch 3 phase 380v with your bare hands while standing in a pool of mud ), do's and dont's, the usual, as we usually do here at BC. Some good and easy reads perhaps, for someone who doesn't have a degree in electronics, random thoughts...you know. Cheers guys.

[sam_sam_sam]

Danny x

You should have fun your new project with PLCs

Here is how I tackle new equipment and PLCs and Micro Controller and servo drives and sensors

The first thing you need to know and understand is how the system is suppose to work ( very important thing to know )

The second thing is that I will google the PLCs model number and the other component in the system to understand how they work and also contact tech support for the company who made the device to get more information most of the time they are willing to work with you

You find on most PLC that there is a LED light on each input and each output this is very helpful when troubleshooting a PLC it tell if your input is being activated or not not on the output it will tell you the same thing BUT do not trust this because your LED will light but you have no output power this where your meter comes in handy

( Which you look like you are on your way to understanding how the system works)

This is how I have learn how to work on these types equipment
Yes it does take some time to learn what you need to know to fix the equipment but after some time goes by you will not need to use tech support as much

I hope this helps if I can help you with something feel free to ask I will try to answer it for you

I did not read the hole manual for this PLC but the parts I did read in some detail I like this manual it dose go into some detail on how to program it that can be very helpfully in troubleshooting what wrong with it

To me it is well written

[redwire]

PLC's are annoying in that it's big money in a plant and everybody has $$$$$ in their eyes.
You have to buy the PC software and yearly licences. Very expensive, custom cable etc. This is to connect and modify any ladder logic, and sometimes the HMI is a second PC program and cable. So price this out.

You need to get the point or tag list as it is called, a spreadsheet showing all the I/O points and their names. Also to see if the PLC is maxxed out, no spare I/O exists, which is the first thing you check for when doing additions. The little PLC might be to small to do more.

The electrical wiring diagram is also important to know the I/O. What is an analog input, digital in or out, relays etc.

Some plants are "sloppy" and they make modifications to the process but do not update the schematics, so there can be surprises if they added a sensor or something.

See if they have any backup copies of the PLC program too. Another consultant might be hiding it.
Some PLC software can work in reverse- reading out the program from the PLC and exporting the tag list and the program.

The main safety hazard is start or stopping the PLC. It might do nothing or it might start up the bubbler sequence, or start a chemical pump every time. Testing new software is not easy, in the plant. I usually buy/borrow a new PLC and test my program in the office.
Careful the panel has enough room for a bigger PLC. It's one of the surprises that can make giving a quotation difficult.

[sam_sam_sam]

Originally Posted by redwire

PLC's are annoying in that it's big money in a plant and everybody has $$$$$ in their eyes.
You have to buy the PC software and yearly licences. Very expensive, custom cable etc. This is to connect and modify any ladder logic, and sometimes the HMI is a second PC program and cable. So price this out.

You need to get the point or tag list as it is called, a spreadsheet showing all the I/O points and their names. Also to see if the PLC is maxxed out, no spare I/O exists, which is the first thing you check for when doing additions. The little PLC might be to small to do more.

The electrical wiring diagram is also important to know the I/O. What is an analog input, digital in or out, relays etc.

Some plants are "sloppy" and they make modifications to the process but do not update the schematics, so there can be surprises if they added a sensor or something.

See if they have any backup copies of the PLC program too. Another consultant might be hiding it.
Some PLC software can work in reverse- reading out the program from the PLC and exporting the tag list and the program.

The main safety hazard is start or stopping the PLC. It might do nothing or it might start up the bubbler sequence, or start a chemical pump every time. Testing new software is not easy, in the plant. I usually buy/borrow a new PLC and test my program in the office.
Careful the panel has enough room for a bigger PLC. It's one of the surprises that can make giving a quotation difficult.

This is very true

[Dannyx]

Originally Posted by redwire

Some PLC software can work in reverse- reading out the program from the PLC and exporting the tag list and the program.

Correct. Looking through the software for this one, it can do this apparently (or at least the "download" button is there). I don't know if it's down to the PLC itself or the software.

Originally Posted by redwire

Testing new software is not easy, in the plant. I usually buy/borrow a new PLC and test my program in the office.

Of course: my boss has already set his eyes on a couple of those keypads and PLCs to buy as our own in order to prototype on them, which is a no brainer: you simulate stuff before sending 380v in there

[Curious.George]

Originally Posted by Dannyx

Anyone here with experience with PLCs who is willing to share ? Share what exactly, you may ask. Tips, tricks, warnings (don't touch 3 phase 380v with your bare hands while standing in a pool of mud ), do's and dont's, the usual, as we usually do here at BC. Some good and easy reads perhaps, for someone who doesn't have a degree in electronics, random thoughts...you know. Cheers guys.

The "problem" (IME) with PLCs is that they are dumb. They model a bunch of independant PARALLEL "circuits" (ladder rungs) without any real concept of time or history.

So, while an I/O might be able to signal that it has become disconnected or shorted (or other GROSS faults), any diagnostic ability beyond that is almost impossible to implement because the "rungs" have no concept of time/history.

E.g., if a sensor becomes detached from the manifold it was intended to monitor, a SMART observer would notice this -- because it's sensed state is unchanging, over time ("Gee, the web is still 82.3 degrees -- despite the fact that we've increased the temperature setpoint by 5 degrees in the last hour!")

Anything "clever" has to be done in dedicated modules (e.g., running a PID loop IN ladder rungs is just plain silly). So, you have this mix of dumb "circuitry" and smart "modules" (with cryptic interfaces).

And, are still left with whatever capabilities the system designer THOUGHT you would need (tail wagging dog).

When you're "system" is done, as an exercise, rewrite it in C (or some other HLL) on some "imaginary hardware" to see just how much cleaner a non-PLC implementation can feel... E.g., you can write a PID loop in a paragraph of text -- and spend just as much text interfacing to the "registers" in the PLC's PID module to do the same. And, you can instantiate 100 copies of that PID loop without having to buy 100 PID modules!

[Dannyx]

That sounds a bit over my head ATM, but rather than giving up on the project in favour of someone else, I say I commit to following it through as much as I can to see what happens If I get gummed up along the way.....I don't know

[Curious.George]

Originally Posted by Dannyx

That sounds a bit over my head ATM, but rather than giving up on the project in favour of someone else, I say I commit to following it through as much as I can to see what happens If I get gummed up along the way.....I don't know

There's no reason to "give up"; rather, just make sure your expectations of what can be (reasonably) accomplished with the technology remain in step with the technology's capabilities.

E.g., if I'm measuring the rate at which some item in the controlled process is moving, I want to know how far and how long (time). If I can't measure both of these, then I need something else in the system/design that guarantees I won't have to measure ONE of them. For example, ALWAYS checking the position at fixed, immutable time intervals. So, if the item moves farther than it did in the last time interval, it must be moving FASTER!

But, if you can't be guaranteed that THIS time interval will be EXACTLY the same as the LAST time interval, then any deductions you make based on distance traveled are dubious... it may look like the item moved 10% FARTHER but are you sure the interval wasn't 10% LONGER??

You can compensate for this (even in a PLC) but it's a lot more convoluted than it would be in a procedural language/system where you inherently KNOW that the interval WILL vary (and, as a result, you make sure you have a means of measuring it and factor all that into your design/algorithm)

Obviously, if you're using this sort of information to drive a control loop ("Hmmm, it's moving too slow! Increase the drive to the conveyor motor!"), then the value of your control algorithm becomes suspect. Your attempt at ADDING control can actually make the system LESS controlled.

[Dannyx]

ATM I'm trying to focus strictly on the task at hand, which is deciphering this exact hardware and how it's programmed, because there's still a lot of stuff going on beyond that seemingly simple user interface. Not having any experience in the programming field (remember, I'm a translator by trade, technically speaking ) it's a very steep learning curve, bits and bytes and junk and stuff....the relatively broken English (though I've seen worse), doesn't do us any favours here either, but now I'm being picky and blaming others for my own incompetence....

[Curious.George]

Originally Posted by Dannyx

ATM I'm trying to focus strictly on the task at hand, which is deciphering this exact hardware and how it's programmed, because there's still a lot of stuff going on beyond that seemingly simple user interface. Not having any experience in the programming field (remember, I'm a translator by trade, technically speaking ) it's a very steep learning curve, bits and bytes and junk and stuff....the relatively broken English (though I've seen worse), doesn't do us any favours here either, but now I'm being picky and blaming others for my own incompetence....

I'd, instead, focus on the problem that "they" originally tried to tackle and how their solution has been "inadequate". You don't want to take ownership of a design that isn't up to the task:

There IS such a system already in place and it works to a degree but it requires some maintenance (some of the vats no longer work and are overflowing with sh!t, quite literally due to the pumps in them failing of becoming clogged), so granted, this isn't a project which we build from the bottom: there is something to work with.

Figure out why the system/process is failing, first. Is there something missing from their approach to the automation? Has something changed, over time, that wasn't accommodated in the original design? How could you possibly detect these problems without being on-site?

You may need to retool the solution to avoid being in the same predicament, later. That might mean replacing the PLC, some actuators or sensors. Silly to understand how to program hardware that may not be "up to the task"!

[Dannyx]

Of course, there's a lot of work to be done there and anybody, even if they're a completely random bystander could tell you this even after a superficial look at these sites. I didn't snap pictures of these sites (we weren't allowed to, we could only photograph model numbers and electrical stuff which was of concern to us and us alone), but these things are relatively minimalistic. The control side is not housed properly do begin with: they're sitting out in the rain and exposed to the elements, so that's one cause of the failure: it seemed fairly damp in those boxes, despite having a gasket around the door and I highly doubt they devices are rated for outdoor use, as you can clearly tell by the control panel in the first picture whose display had gone black - it didn't exactly enjoy being rained on I believe. You can also see in the upper left hand corner two of the MCBs for the three phases had tripped from an unknown cause, even though I could hear the compressor placed directly below the box pictured still whirring away somehow.

I'm sure that when the producers of designed them, these filters were properly thought out. It goes beyond our jurisdiction somehow to try and figure out the mechanical/chemical side of things, like if the sieves or whatever were not meant for such a high volume, or they chose improper sites for their install where the soil is unstable and drops down into the filter bath or whatever, stuff like this. We only care about the control. Can it be done differently ? No doubt about it: even an Arduino could handle it I'm sure: turn X on, run 10 minutes, turns X off, wait 10 minutes, repeat 24/7. Do we WANT to do it differently ? Most likely not: the price point has to be kept as low as possible by reusing existing equipment to begin with (so that our company can actually calculate an offer for these guys) and secondly implementing new hardware may not be possible from a policy standpoint, as we may not be allowed to modify the specs of these control panels, plus the time factor is also a constraint: designing something from scratch is tougher than improving what is already there, despite what you said in your final line...and it looks like it IS up to the task, just not taken care of very well and maybe not unlocked to its full potential. Like I'm sure it can read sensors and interface with a communication module or something, but a lot of skill and time is required to implement such "extra" features.

[sam_sam_sam]

Originally Posted by Dannyx

We only care about the control. Can it be done differently ? No doubt about it: even an Arduino could handle it I'm sure: turn X on, run 10 minutes, turns X off, wait 10 minutes, repeat 24/7. Do we WANT to do it differently ? Most likely not: the price point has to be kept as low as possible by reusing existing equipment to begin with (so that our company can actually calculate an offer for these guys) and secondly implementing new hardware may not be possible from a policy standpoint, as we may not be allowed to modify the specs of these control panels, plus the time factor is also a constraint: designing something from scratch is tougher than improving what is already there, despite what you said in your final line...and it looks like it IS up to the task, just not taken care of very well and maybe not unlocked to its full potential. Like I'm sure it can read sensors and interface with a communication module or something, but a lot of skill and time is required to implement such "extra" features.

I have seen this before that you can not really change of there system setup
you can only get it back up and running

That is why I made the comments earlier about learning the system and how it is setup with all of its sensors and the other support systems

[Dannyx]

Originally Posted by sam_sam_sam

learning the system and how it is setup with all of its sensors and the other support systems

My point exactly

[sam_sam_sam]

Originally Posted by Dannyx

You can also see in the upper left hand corner two of the MCBs for the three phases had tripped from an unknown cause, even though I could hear the compressor placed directly below the box pictured still whirring away somehow

A couple of things to check one is the over loads working correctly check each leg on the contactor to make sure that the amperage are very close if they are not very close look at contacts of the contactor and make sure that they are not pitted

One last thing is to use a mega-ohmer to see if motor winding are not shorted or leaking voltage to ground if the reading are not in the good to very good this can cause all kinds of problems

One last thing is if the controller is shutting down the motor can also happen

Or is the controller particularly bypassed which is maybe why you hearing it run

[Dannyx]

Originally Posted by sam_sam_sam

One last thing is if the controller is shutting down the motor can also happen

The only way for the PLC to shut off the motor would be by turning off its contactor, which I think wouldn't trip a breaker because a circuit is being OPENED, not closed (to say it's got inrush problems or something). Still, can't quite figure out why the motor was still running, unless it was running on one phase which would certainly not be possible, or at least not in this configuration....
Could be that MCB is for something different entirely and the schematic on the side wall of the box which I snapped a picture of but haven't posted till now (I did now) doesn't correspond to the physical layout of the devices in the box. Have a look. Not particularly great quality, but if you zoom in enough you can make things out pretty clearly. Not sure how those 4 contactors at bottom operate. I figure things like that out by testing them i.e. playing with the contactor on the bench and doing continuity measurements. It instantly becomes clear, rather than relying on random codes like A1, A2 etc, which mean nothing to me...
"SIG" here refers to "breaker" in case you couldn't figure it out, as that's the only word in there that differs grossly from the English "MCB", whereas the others are close enough that you can suss them out, such as "butoane" or "releu" which mean "buttons" and "relay" respectively....no trouble there...

[sam_sam_sam]

Who makes these contactors because there numbering is pretty standard but there is some parts that are not standard like ( 22 )

A1/A2 is the coil for the contactor

What is the reason for them not to show the connection to A2

It also in not showing the control transformer/ power supply for the contact-ors or am I missing something because I do not see it

I have not a configuration setup like this

Do you whether or not this motor is more than one speed if this motor is more than one speed it will not be a good idea to play with the contactors you will burn up the motor

I go back to work on Monday I will show you a wiring diagram that shows things a lot better and easier to read

[redwire]

The PLC wiring looks straightforward.
Four output relays drive the Meta-MEC GMC-16M's which are a contactor and bimetallic overload relay built into one.

One for the 3-phase pump motor, set to 5A trip.
Three for some 1-phase loads, set to 0.5A trip, with oddball L2-4T2-L3 connection to fool it to thinking it's 3-phase or something.
All contactor's auxiliary switches 97, 98 are all in parallel to one indicator light.

If a pump is staying running then there is a ghost to get rid of.

[sam_sam_sam]

Redwire

Thanks for explaining that to me I have not seen a setup with the contactors setup that way

Or a wiring diagram showing the overload and contactors as one unit all wiring diagram that I have seen they show them separate

[Dannyx]

No, I don't think the motor is multi-speed, though I was expecting to see some form of star-delta switching, but from what I see there isn't any. I don't know which way the motor is wired though, because I didn't open the cover for the connection block at the top to have a look at how the shims are placed between the winding terminals.

[MixMasta]

This is some kind of shitty Chinese PLC. Based on everything you have said here on this forum thread and your background my advice to you would be not to waste your time and the customers time. Move on.

Sorry if this sounds blunt.