PLC system recommendations?

I'll be making a very simplified low cost version of an automatic crate handler.

The bells and whistles version uses National Instruments Compact Rio system, and most of the automation runs entirely on the FPGA part. Thing is though that National Instruments don't sell their low cost single board Compact Rio versions in anything but huge numbers, and the traditional version is way too expensive for a low cost version. Thus I have to make the move to a more traditional PLC for this one.

The simple version will require some 8-10 input buttons, control of two frequency drives for AC motors through analog or digital, an emergency stop system (likely external to the PLC) and include or have the possibility to add RS-232 and more IO later on. A web interface and the option to do logging would be welcome to.

So far the ABB AB500-eco and the Siemens S7 1200 series seems most interesting, but there are certainly others out there as well. The Siemens S7 series do seem controversial though, and is based on old processors.

Any recommandations, experiences and suggestions? The PLC side of things is new to me, so all input most welcome.

I was a consultant to ABB for five years and have great respect for the company. Unfortunately, I don't know much about their PLC's other than that they were very good and very expensive.

Schneider (Modicon) makes a nice PLC but they are overpriced. The programming software is free, which is more than it is worth. It is perhaps the most bloated software program ever developed.

The Schneider software installation puts more than one thousand entries in the registry, and no, I am not exaggerating. It also installs so many background processes that it will crash anything less than a gaming computer.

If you can get Automation Direct (Koyo) in your part of the world that would be my personal recommendation. They have the best combination of price, service, and documentation. The DL06 PLC is about $250 USD and should work for your application.

The only weakness of Koyo PLC's is that you can only use ladder programming. Structured text and other IEC-1131 languages are not supported.

Edit: Almost forgot! Automation Direct has the best documentation for someone new to PLC's.

Doug

FWIW i was told by a controls engineer i know that Koyo actually bought their tech from GE and the older GE stuff its based off of were good components.

you can also download the "Click" PLC programming software for free from them.

Thanks for the tips, I will look into Koyo.

Might want to also look into the Allen-Bradly MicroLogix controllers.

I have mentioned Unitronics in the past.
They have the front panel, display and keyboard built in.
That addition can make it overall cheaper than a simpler PLC where you next have to fabricate and add the HMI.

Actually - Koyo made the PLCs and GE (and Siemens) brand labeled them until they developed their own products for that market segment - after which Koyo hit the market big time via Automation Direct

The Koyo stuff works and is robust and cost effective. When a customer asks for it, we cringe a little because it is seen as being cheap - again, we buy from The best way to buy industrial controls--low prices, fast shipping and superior service.

The Siemens S7 ET200S I/O is very good stuff, but not easy to learn without taking the classes. The I/O is cost effective and compact and rugged. We are using it more and more in machines where distributed I/O makes sense via Profibus or ProfiNet.

It sounds like you will need two drives . . . one thing to consider is the following:

Buy UniDrive SP's and get a logic module - you can write your code in the module on the drive, run remote I/O and you have a complete system. Write the code in statement list, ladder or structured text and switch back and forth between each language. We have done a few small machines like this and it is very cost effective and a large number of 3rd party HMI's are available (we use HMI solutions that put you in focus. - Beijer Electronics / sold here in the US by Mitsubishi) Mitsubishi Electric Automation Inc. - E1000 Human Machine Interface

Koyo is not a big one around here it seems, which makes me a bit worried. Siemens, Omron, AB, Mitsibishi, ABB seems to bemore common.

Unitronics is here, and seems to be a progressive company with a modern product. Not sure I'll need the HMI though. This is supposed to be a low cost thingy. If the price is right though I'll consider it icing on the cake - the concept seem good, and touch screen or soft buttons will save me a few real ones.

(Some of these PLCs seem to have technology from the 8bit era judging by memory and input/ outputs. Is it a marketing differential thing, a reliability strategy, or just steady as you go? Hobbyist microprocessor setups, based on different ARM processors for instance, are inexpensive and have much more of everything. I do of course understand that I pay primarily for the industrial spec components, 24v, enclosure and all that - but with processor and memory prices being what they are many PLCs seem underpowered for the price. Especially the expensive ones: I used to think NI CompactRio was expensive, but that was before I saw what the same money would get me in high end Siemens hardware... Why NI doesn't look seriously at the control market is beyond me. If they would sell the single board Comapct Rio industrial versions as a normal product, and provide normal software connectivity options out of the box, it would be a tough cookie to beat for the price. (Well, then again, they want a fortune for the software part).

Unidrive SP seems to be overkill for this? I just need some standard 1.5 KW induction motors with soft starts and stops. Omron MX2 or the Mitsubishi 700 series drives seems most interesting so far mainly due to included safety functions which will save some hassle. The Omron can also run some programmable logic on its own it seems, but I haven't checked out the details yet.

You can also use the SK drive - sure they are overkill - cost is comparable to most other suppliers and yet the CT drives are far more capable.

BadBeta said:

(Some of these PLCs seem to have technology from the 8bit era judging by memory and input/ outputs. Is it a marketing differential thing, a reliability strategy, or just steady as you go?

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I think it is primarily due to the extremely conservative nature of the people servicing the equipment. They don't adjust well to change.

More important, technicians have good reason to expect uniformity across brands. That's why we still use octal addressing and ladder logic.

Perhaps the reason Koyo hasn't embraced IEC-1131 is because their biggest market is the US.

Doug

motion guru said:

You can also use the SK drive - sure they are overkill - cost is comparable to most other suppliers and yet the CT drives are far more capable.

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With such backing from the guru I had to check some more. We do have a Unidrive representative over here, but it seems they don't live up to the comparable prices part: A SP0205 1.5 KW Univdrive SP cost about USD 1350, a Commander SK is about USD 500, while a 1.5 KW Omron MX2 can be had for about a bit over USD 300. (Siemens and some others a bit less than that again, but then I'd have to buy and install some more safety switches).

As I expect all of them to be able to do the hopefully simple job that is needed I can't justify that high an extra expense.

doug6949 said:

I think it is primarily due to the extremely conservative nature of the people servicing the equipment. They don't adjust well to change.

More important, technicians have good reason to expect uniformity across brands. That's why we still use octal addressing and ladder logic.

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Yes, there is something about not changing a winning team, or repairing what is working. Still, when I compare the hardware with things like this for all of USD 25:

ETSTM32STAMP:

• Includes ST Microelectronics STM32F103 Microcontroller with 512kb Internal Flash Program Memory
• 32-Bit ARM Cortex M3 Processor Bit running at 72MHz or 90 MIPS
• Direct In-Circuit Program Download with RS-232 Connection
• Up to 48 I/O points
• 16 Channels 12-Bit A/D Converters
• 2 Channels 12-Bit D/A Converters
• 1 CAN Channel
• 5 USARTS and 2 I2C Ports, together with SPI (That would be different kinds of serial connections)
• Two 32-Bit Timers with Four Capture and Compare Channels
• On-Board Real-Time Clock with External Back-Up Battery Connection

And there are worse examples - I found this one as it had 2 AO channels and that would come in handy. Others with just one can be had for under USD 10, yet others have web servers and LCD screens. Compare those USD 25 to the PLC world where just an add-on with 2 AO channels seem to cost USD 50-100 on its own. (Of course National Instruments are in their own world entirely - if you want that CAN port the add on module is some USD 1000...)

I can't help thinking that even with industrial electronics they would still be inexpensive in comparison. Where they fall down in mind though is the lack of standardized programming tools. Well, actually they are pretty standardized on C - what they lack is something more effective I guess, and better catered towards control tasks. Like the standard PLC languages.

Holy cow BB - your prices are out of whack compared to what I pay - but then again, I buy 200 - 300 drives a year ranging from 1kW to 150kW in size . . .

I have done several jobs with just the drives (no PLC) running I/O from a Modbus TCP interface on the drive and a inexpensive HMI networked to all the drives via. the built in RS485 ports. Typically very cost effective compared to many of the players you have listed.

motion guru said:

Holy cow BB - your prices are out of whack compared to what I pay - but then again, I buy 200 - 300 drives a year ranging from 1kW to 150kW in size . .

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Yes, that should qualify for special prices. To be fair I guess there is some room for negotiating for me too, and the Omron happens to be on an international introductory offer. That considered I believe the Commander SK could normally be in the same ballpark.

BadBeta said:

I can't help thinking that even with industrial electronics they would still be inexpensive in comparison. Where they fall down in mind though is the lack of standardized programming tools. Well, actually they are pretty standardized on C - what they lack is something more effective I guess, and better catered towards control tasks. Like the standard PLC languages.

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Yes, the language is important. C has the flexibility of assembly language, combined with the user friendliness of assembly language.

IEC-1131 structured text is a subset of Pascal, an easily learned language that was specifically developed to enforce good programming habits. The other IEC languages are also logical and easy to learn.

C will never gain acceptance in an environment where the floor technician has to read another person's code.

Doug

Another Alternative

Unconventional, but interesting nonetheless.

Comfile Technology Inc.

While not mainstream, it meets the OPs criteria, and doesn't cost much. If nothing else, they're fun to tinker with for hobby type stuff. I'm sure a "real" PLC is more appropriate in this application. I second (or third?) automationdirect.com on a value basis.

doug6949 said:

Yes, the language is important. C has the flexibility of assembly language, combined with the user friendliness of assembly language.

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And it doesn't have a history as a language where bugs are easily detected and avoided. Maybe someone should try to make Ruby work with microprocessors? Ruby is an easy going readable language, which in good practice is feature and test driven. Thus you get a pretty much plain english description of what a bit of code is doing, you write what the results of the code should be with some different inputs, and you then write the code itself. If the results from the actual code doesn't match up you'll know right there and then and can do necessary correction before moving on. (Actually you also try to introduce some errors on intent to make sure the tests themselves are correct).

doug6949 said:

IEC-1131 structured text is a subset of Pascal, an easily learned language that was specifically developed to enforce good programming habits. The other IEC languages are also logical and easy to learn.

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Sounds good! I'm old enough to have been taught Pascal at University...

doug6949 said:

C will never gain acceptance in an environment where the floor technician has to read another person's code.

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Second that. Or the programmer reading his own code two months later.

BadBeta said:

Second that. Or the programmer reading his own code two months later.

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- Yes, the average C programmer looks down his nose at ladder logic but then after a year when a bug shows up, they (and hopefully they alone) are enslaved to the machine as they relearn what they did and try to figure out what was wrong - which invariably starts the hero / meat-head roller coaster as they solve problems while simultaneously create other problems for a few cycles before the machine is stable again.

I have programmed in C++ / visual C / Whatcom C / etc . . . symbolic languages are much easier to manage years after the code was written.

Anyone had an experience with the text display PLCs from EzAutomation? (EZAutomation.net) Their PLC with VFD text screen could be nice. (VFDs are great in sunlight and in below freezing temperatures). And they have reasonable priced analog add-ons.

Impractical said:

Unconventional, but interesting nonetheless.

Comfile Technology Inc.

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I've actually looked at them. They use a properitary version of Basic, which might or might not have some gaps. It is a risk anyway. Besides it is a one way street to bother learning the nicknacks of it. Worse though, by the time you've added an interface board and put it in a sensible casing the price isn't that impressive anymore compared to similar offerings. (Add an hour of work to mess about with that and it is no go even economically).

Their big brother series "Moacon" seem a bit more industrialized, but that thing is programmed in C... I don't C that happening.

motion guru said:

which invariably starts the hero / meat-head roller coaster as they solve problems while simultaneously create other problems for a few cycles before the machine is stable again.

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As far as Labview goes spaghetti code takes on a whole new and very visual meaning if you're not disiplined!