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PLC brands comparison

PLC brands comparison

PLC brands comparison

I hereby invite all you to suggest the best by your opinion PLC brand and family.

The suggestion should be argumented, not just a personal preference.
Another words, mention at least one property that makes this PLC a better choice than another ones.

Let's limit the subject to single unit PLCs, the rack type being out of scope at this time.

I think, such poll would be interesting for many of us, experts as well as beginners.

RE: PLC brands comparison

This isn't a fair contest. What do you mean, "...rack type being out of scope"? That eliminates many good ones.

What's the application? Is a faster PLC better than a PLC with more memory or capability? How many I/O? What type?

How about technical assistance and on-site service capabilities? Or warranty? Are they important?

You've left yourself open to way too many variables.

Look at sales results for the most popular (I think probably A-B and Siemens).

RE: PLC brands comparison

   I think that most people will argue their favorite as the best thereby rendering any real net gain of insight rather mute; because, many of us simply associate our first experience with the best and never objectively consider alternative systems on par with others. This phenomena is called impressioning and is what causes a duckling to impute maternal charge to the first animal it sees upon birth. As regarding, ease of use, our first experience generally wins hands down, because our learning ability is diminishing as we age, there are lots of names for this condition.

    I use all the systems in the survey cited above because my customers all have their "best" ideals and I'm spending their money to make them happy. When I am spending MY money, we use a different "best" because I want maximum punch for the dollar spent without giving up the required performance in field.

    I teach PLC system design on about 12 different systems and whatever a newcomer sees the most and learns the first is "best" to him/ her every single time.

    This is how I would pick the best in a contest. Take a novice and give him a real world system to design with all the revelant literature from each of the surveyed systems. the one that he can quickest satisfy the given requirements is the best for that particular application in that situation. Of course, that is spoken like an automation contractor, which I am. Each system is targeted to some end and probably excels strictly in that end or they missed their mark in development.

   That's my 31/2 cents worth!!

RE: PLC brands comparison

As an aside, I reviewed the survey and have concluded that the best plc is probably not what people are voting in this anyway. In east Asia, I would expect to see %33-40% Omron market share in numbers, In Europe and ultra heavy industries, like STEEL and Aluminum, I would expect to see
around %40 Siemans market share. The survey looks like small to mid-range manufacturing companies talking about what their BOSS had installed in some integrated equipment when it came in the plant. I think people are simply naming what they have seen in a cabinet. Many systems with large followings such as Klockner Moellar and Reliance aren't even listed and I see this in as many places as Allen Bradley in Arkansas.

RE: PLC brands comparison

For small, powerfull, cost efficient PLC's, try Automation Direct,(www.automationdirect.com/store/Shopping/Catalog/PLC_Hardware).

Small form factor
Easily configured
Power efficient
Wide range of sizes for required use

No, I am not a salesman, just an observer. We have used several PLC's in our company, and the Automation Direct PLC seems to fit well in the small to mid-range applications.

RE: PLC brands comparison

I see by your reaction, gentlemen, that I have to clarify my request a little.

I clearly asked not to use personal preferences as arguments.
Neither do I think that sales statistics reflects the brand/model quality or value.

The goal of this poll should be exactly to reduce the effect described by Skills, when the first used is considered the best.
Another phenomena is what I call the brand preference inertia.
And very often the reason is that your information about another brands is obsolete.

The reason to evaluate only single-unit PLCs is that I meant small-to-medium projects (128-255 I/O max) and reasonable price (under $1500, excluding software).
This is the class of AB Micrologix 1500, not SLC.
The scan time is not a big consideration, though may be an argument for the choise.

Ideally users of two or more brands should compare them and indicate advantages and disadvantages of each vs anothers.
By the very nature of such method, a user of only one brand has nothing with this poll as an author.

Best regards

RE: PLC brands comparison

I'll start myself, comparing AB Micrologix 1500 to Mitsubishi FX1N.

Both are single unit expandable PLCs.
The hardware is very similar by price with more I/O extensions, but the FX1N tends to be less expensive for less I/O numbers, especially without extension.
Maximum number of I/O is 255 for FX1N and 156 for ML1500.
The advantage of ML1500 transistor main unit is several relay outputs, while the FX1N main unit is homogenous by the outputs type.
The FX1N main unit inputs are configured as sink/source all at once, while the ML1500 inputs are grouped in several groups.
The largest main unit of ML1500 is 28I/O.
The largest main unit of FX1N is 60I/O.
The ML1500 largest extension modules are: for ML1500- 16I/O each, FX1N- only 8I/O each.
FX1N exists in AC powered version.
Also, FX1N of any type features a built-in stabilized 24VDC/600mA service power supply. With AC powered PLC this may eliminate a separate power supply for small project.
The FX1N has an inexpensive option of the programming port duplicator card, which allows the PC to be connected without disconnecting the MMI unit, if any.
FX1N high-speed outputs are isolated and may be used as sinking or sourcing each.
Both models feature two analog setting potentiometers on the main unit.
The special modules choise looks little wider for FX1N.
Expect the FX1N with extension modules to occupy more rail than ML1500 when extended over ~128 I/O.

Programming and sofware.
The programming software convenience is strictly individual, but the Mitsubishi software is less expensive and not copy protected.
Even the legacy DOS software may be used for FX1N programming.
The Mitsubishi software does not require additional communication driver to communicate with standalone PLC, while for the Allen Bradley you need the RSLinx installed and configured.
Mitsubishi programming cable is expensive, but I suggested a link to the inexpensive replacement in one of my posts on this forum.
ML1500 has NO online programming or editing- a big inconvenience during debugging!
FX1N may be programmed online except for interrupts.
The ML1500 has bigger choise of internal devices (T,C,B)and their quantity is virtually unlimited (limited only by the PLC memory), all the devices may maintain their status with power off.
The FX1N has limited quantity of each type device, each timer resolution is predetermined.
Only part of the FX1N devices maintain the status with power off.
On another hand, FX1N features 32-bit counters, lacking in ML1500, and almost any instruction may be defined as 32-bit.
ML1500 instruction set looks wider for sophisticated math calculations.
6 high-speed inputs may be assigned to interrupts on FX1N versus 4 on ML1500.
Both feature 2 high-speed outputs (frequency pulse train or PWM each), but FX1N allows more control over the frequency pulse train, like direct frequency change on the fly.
Unlike the ML1500, the FX1N has no forces that can override the program execution- any device may be directly written online; it will be, however, processed according to the program logics and may be altered by the program at any time.
FX1N outputs may be altered online when the PLC is not running, unlike the ML1500.

Well, enough for the beginning.
Correct me if I forgot to mention something important.
And ask questions about FX1N, if any.

Best regards

RE: PLC brands comparison

I have experience with the following brands and models of PLCs. They are Allen Bradley PLC 5, SLC 502,503,504,505,Micrologix 1200, Ge Fanuc 90-30,Omron CS1-G,
Modicon compact,Modicon Momentum,Automation Direct Koyo 305
I find The allen Bradley brand of PLCs to be fairly easy to program. The programming software (RSLOGIX)is very well structured. Programs can be generated very quickly as vertical and horizontal lines are automatically generated.
there is no need to insert extra rows in order to create branch instructions. The I/O tables are automatically generated after the PLC back plane is configured. Generation of bit tables is easily accomplished. I love the manner in wich Allen Bradley addresses I/O. It is extremely intuitive. for example an input address I:1/0 is an input address denoted by the letter (I) that resides in slot 1, terminal 0. Other PLC manufacturer's such as GE Fanuc,Modicon,and kOYO use the following. Where is the logic in these conventions?


One of the aspects I do not like when using Allen Bradley brand PLCs is the fact that many programming devices such as the PIC,PCMK card, and others are available to interface a PC with the PLC. Other PLC manufacturer's provide only a serial cable used to interface the PLC with a PC, thus the complexity involved with setting up a communications driver is non existant. Just give me only one methosd to communicate between the PLC and my laptop!

However the fact that Allen Bradley provides a host of communications drivers for communicating with ethernet device net and such is very nice, as it is integrated into RS Linx. With other PLC manufacturer's these drivers must be purchased sepearately.

It is also failrly easy to make online changes to a program.
When using the PLC 5, SLC 503,504, AND 505. The Micrologix 1200, and SLC 502 PLCs do not allow online changes.

I/m going to stop for now. I have to get ready for the work day. I will dicuss the likes and dislikes of the GE Fanuc PLCs in my next post

bets regards, plcsavvy.

RE: PLC brands comparison

It would seem from "xyzz" posts in this thread that he is trying to get us to "vote" for the Mitsubishi FX1N.

As an OEM we have used numerous PLC's for our customers and there is no doubt that each have there place for many of the reasons specified in the above posts.

The market for the smaller PLC's [rackless/shoebox w-expansion]is extremely competitive. They all have very similar capabilities in hardware and while the instruction sets may be different between manufacturer they can DO the same thing. I would suggest that hardware COST is now completely irrelevant.
The cost of programming/documenting/maintaining the PLC software is the key factor. We have standardized PLC's from Rockwell Automation NOT because they are necessarily the best or most advanced units but because their software IS  far ahead of ALL the competition.
"plcsavvy" notes it is very well structured, intuitive. I would add that the ability to modify file types and size in memory offers extraordinary flexibility to the programmer versus fixed memory locations found in most other PLC's. The ability to define each machine function in its own separate identifiable file sure beats one huge long ladder diagram.

Yes RsLinx does stinx. But let's face it, when you get used to it it works fine.

My biggest gripe is the inability to do on-line programming changes on the MLX1200 or MLX1500. "xyzz" definitely is right on that one.

RE: PLC brands comparison

I'm wondering if those parties heralding the intuitiveness of RSLOGIX have used DIRECTSOFT to a large degree. I use both, albeit, I don't use RSLOGIX as much and I find it uses
unusual paradigms for memory. I develop a lot of microcontroller system pic, AVR motorola, and intel stuff and DIRECTSOFT appears to match most of the software development for computers, regardless of use. With regards to PLCSAVVY's observation of memory/ I/O reference, it seems that DIRECTSOFT uses the convention used in most any microcontroller development system. X's are input and Y's are outputs is fairly standard algebraic notation based on the cartesian system.

  Both systems edit fine I suppose, I used both in parallel
 to pick the most efficient, quess?

   The points QUIPPDUDE makes are interesting; but, I've never found a need to adjust memory size of resources to cause me much trouble because DIRECTLOGIC provides enough of all these resources you don't have to dink with it in the first place, DL systems aren't stingy like that, which is really why that ability is required anyway!

   As regards his statement about long ladder programs being cumbersome, That's why STAGE programming is provided, so you don't have them anymore if it is applicable.

    Software wise, DIRECTSOFT is way ahead of any development software under $10,000 with the exception of Think-n-Do.

RE: PLC brands comparison

Hey, you might get a better response if you asked which was the WORST PLC.

I'd vote for the Honeywell LogicManager, IPC-620. Most expensive and weakest program I've seen. I don't think they make it anymore (Honeywell switched to the A-B Contrologix platform). Thank goodness!

RE: PLC brands comparison

Well, many thanks to mister X, he really worked hard on this one.

One thing that belongs to the past is the "No Licences" feature of GX-Dev.  The newer versions come with a site licence.  You install it and then you need to supply them with a key generated by your PC and then they give you another key to unlock the software.  What a pain!

At least one could copy the master disk of AB.

I still will use version 9.11B and older for they still can be copied.  Hey, I have a laptop too!

I was out of town a few weeks ago and in a hotel room I installed this new GX-Dev. version...

Since the software detected that I had GX-Dev. installed earlyer in my laptop, it locked the program and I could not use it anymore...

The features I like about the Fx serie is the ease of use and programming.

Want a OSR, add P to the function.  That is nice.

The down side... If one has never established the configuration of an special extension module... the writting and reading of buffer meory areas in those can be a little tricky.  I get many calls about this.

Also the way that Forces (Mitsu) do not work when the bit is in the program is a pain.

As for OMRON, another brand that I use, I really kinf a like some of them functions.  The table compare is very good.


The best printing goes to AB (Zoom + many extras)
The best Online monitoring goes to Mitsu (fast)
The best software to program via the web goes to Mitsu (almost not com loss)
The best software goes to AB (unbeatable for thos shoeboxes)
The worst software goes to AB (don't tell me RSLinx of not RSLogix) the fact that they are separate is irrelevant.

RE: PLC brands comparison

As promised, here are my thoughts on the GE Fanuc 90/30 PLCs. I find that the versa pro software environment is for the most part well designed. I like the fact that you can issue commands (pneumonics to create ladder logic.This speeds program development. Once learned your fingers can fly across the keyboard. Some of you may say that you can do this with Allen bradley PLCs as well. I have to agree, but not with the ease and speed of versa pro.I praise Ge fanuc for their one serial interface for communicating to the PLC and laptop computer. Only one driver to configure!
One major complaint I have with the GE Fanuc PLCs is the use of the words store and load. These are used to down load and upload. Don't ask me what each means. I can never remember and always need to look for the meaning in the help files,if it has been sometime since I last used a GE Fanuc plc. Another complaint I have is the fact that Timers and counters automatically encompass three consecutive registers. One register is used for the accumulated count, another for the preset, and another to address the counter.
Believe me it can be a major pain in the butt, if you use these registers elesewhere in your program (overlap). I do like the plug in communications modules that GE Fanuc provides. there are so easy to configure and very robust.
Getting the software to print a program that can be read can be a daunting task the first time around. After that it is a piece of cake.
All in all I like using the GE Fanuc PLCs.
Modicon however is a different story.

I do use Direct Soft 32 and Skills is correct that the I/O addressing scheme follows the convention used by most microcontrollers as does the use of watch windows or in microcontroller terms the watch directive. I too design microncontroller related devices.

But let me ask you a question. Can you. using other manufacturer's PLCs, know exactly where to look on the PLC for an I/o point that is addressed as x10 or y13 without first referring to an electrical diagram?

You can with the Allen Bradley PLC.

best regards, PLCSAVVY


RE: PLC brands comparison

Those are great points made by plcsavvy, and I got a great deal of insight into fanucs software development systems. I also had an epiphany as I read it. Angels didn't come down and dance around my head; but, I did see something cool. In looking at different peoples preferences, I saw why 2-3 different software tools would gather different types of people. Each of these different systems are designed to appeal to different needs.

    Your favorite plc system is dependent, to a large degree; on what else you do, where you do it, and your primary focus. I spend around 30% of my time designing microprocessor systems for hot rod cars and such. These embedded tool suites all condition you a certain way.

  As I read the above statement concerning the association of a program element with a rack slot, I agreed that some are far more direct in presenting that info; but, from a development side don't value that feature.

   I had thought, GEE, that's right; but why would you care unless you were maintaining someone else's design.
   I configure and designate all memory variables, accum, timers, counter, constants, and I/O points and words, before I even know how I'm going to write the procedures. That's the way most any microcomputer programmer would do. In 2 days I couldn't easily tell you where clamp_valve_1 is connected to the rack. At this point, I don't care! I'm going to treat it the same regardless. When I'm performing troubleshooting, I wish for more convenience!

    Microchips aren't slot oriented and worrying about physical location gets in the way of rapid development. Just as the AB ControlLogix system allows someone to write control software that doesn't even know what kind of cards, racks, or slots are available/ he just uses data/ I don't even think of the way to find that point then. Now, when I have to replace a broken wire.... It's a different story.

RE: PLC brands comparison

This response is limited to a the programming of a few of the brands that I have worked with over the last 20 years or so, so probably completely off topic!
The examples are all 'old' and to be honest I have not seen a great improvement in capability with the newer systems.

Allen Bradley (2/30 was the first I used, 1983ish)
Fantastically powerful ladder diagrams, IF you use the advanced instruction set. The brilliant idea that you can use equivalent instructions on bits, bytes, and even arrays.
Design the data tables right and the code can be very fast and small and powerful. The secret is in the data structures and the advanced instruction set.

Siemens S5
Huge flexibility - for example Function blocks make it possible to write your reusable standard modules that can be instantiated in higher level blocks.
STL is worth learning. It can approach assembler - good if you like to code at the low, fast level.

Texas APT
Almost object oriented higher level environment that preceded IEC1131/3 by a decade. Great for control loops and SFC's. Dont mess with the ladder that APT generates.

ABB Sattline
(It was a PLC when I first came across the company)
More object oriented than any control system I have ever worked with. Where is the global tag database? Buried in the objects.
But, create a control object (with it's graphics/HMI) and it can be replicated wih a few clicks

RE: PLC brands comparison

Here are my thoughts concerning the use of Modicon PLCs.
the types I have experience with are the compact and momentum series. First let me say that the compact is a rack type PLC and the momentum is not. The programming software I am accustomed to using is PROWORX NXT. This is my least favorite PLC programming software. This software is the most unfriendly and poorly laid out PLC programming software I have ever encountered.To start with, when enetering ladder logic, you must drag and drop every signle instruction, including,horizontal and vertical lines! Can you say very slow program development? Another feature I hate about the sofware is that when using a momentum PLC, the serial drivers required for communication between a laptop and the plc do not function correctly. Once online with the PLC, the driver will lock up your computer with any attemp to perform a search or simply scrolling through through your ladder program. The only method of communication that works is a modbus plus network. For this you need to purchase a $1000.00 MBx pcmcia card, modbus plus cable, and either t-taps or modnus plus 9 pin d sub connectors. Take it from me the t-taps are a major pain in the arse!  Sorry guys there is no driver available for the wIN 98 operating system. GOOD thing I just received a new laptop with XP pro!
Another complaint I have with this software is when dealing with modbus plus, it is possible to send a program that is meant for plc 2 for example to plc 3. Imagine the head aches resulting from such a situation as this. This situation is worsened when performing a read from the wrong plc and writing over an existing program written for a separate plc on the modbus plus network. A word of advice " make copies". Wouldn't it be nice if the folks at schneider automation would have provided a program compare to prevent such an impending disaster. The point to remember with modicon PLCs is that you can buy better but you won't pay more. Another major complaint I have with the momentum PLCs and the use of proworx is that the i/o adresses and bit mapping is reverse of what you would normally expect. For example the top most input on the first 16 point input card of a momentum plc is addressed as 10016 not 10001 as you would expect! What a nightmare it was to discover this interesting feature. The only solution at that point was to renumber the I/O addresses on the electrical schematic and change the descriptions in the plc using the global replace feature. By now I am sure you are convinced that I dislike using modicon PLCs. best regards, plcsavvy

RE: PLC brands comparison

   I've noticed noone has offered their thoughts of Keyence and the Visual PLC. Are there any users here that view Keyence as being out front with some of their innovations? I've only used these once; but they don't give up much to anyone else that is out there. I've also noticed that noone has cited IDEC as being the best brick, while I don't care much for these, I expected some people to. I'm going to say that, for my purposes at the moment, the DL205 family and more specifically the DL240 processor is the best small size plc I've ever used. Yes, there are other companies that may offer some feature that it may lack, today, but, seriously, if it was important to the project agenda and the realization of our goals, we'd go get one of those. The DL240 can do anything that I've ever seen a small plc do and much more.
    The limitations that exist in it merely provide a market for its big brother, the DL250. At $259, I've never even heard tell of a plc that alleges to have the backbone, and sheer power and speed it has. Try 4 autotuning PID loops that run on the processor, 7.6K ram, floating point math, PID fill-in-the-blank profile generators, High-low alarming without code, configurable drums, ability to run 7 remote racks? Any takers on a sub-$1000 processors with similar capabilities?

RE: PLC brands comparison

I have had experience both in programming and specifying numerous brands of PLC's including Siemens, Omron, Mitsubishi and have had plenty of opportunity to compare them to many others. While it isn't a shoebox micro the very best I have worked with and specified is the Giddings & Lewis MMC and PiC series. One software application for all Plc's, backward compatible with earlier versions. MMC starts at ~64 I/O and 2 axis true motion control including circular interpolation, function block programming, expandable to ~3000 I/O using digital and analog block I/O. Ease of programming as described by hardcore A-B and other users. They can support up to 32 servo axes complete with fast inputs. Not cheap but great in terms of performance. Plc's are good at controlling machines but generally come up short in motion applications. G&L on the other hand is an excellent motion controller that can also handle machine control. There is a difference.

RE: PLC brands comparison

I made a mistake in my post, the maximum number of I/O in FX1N system is 128, not 255.
Sorry for desinformation.

RE: PLC brands comparison

My 2 cents worth. I work with Mitsubishi, AB, GE-Fanuc, Hitachi and Omron.

GE-Fanuc is not too bad although the instruction list is bit limiting. Ethernet with Global I/O is quite good as the Global I/O runs as a separate layer on TCP/IP. Setting up Modbus RTU communications is not the most friendly thing to have to do with the Horner card, although it works well when written and commissioned properly.

Mitsubishi GX is a pain with having to get another password, as previously mentioned. I also got caught with the lockout. What a pain. GX will also not convert some of the software developed with older versions of programming software. I got caught with SC and had to download from the PLC and recomment the whole lot. Try remembering what you did 3 years ago.

Hitachi is bearable but once again a poor instruction list.

AB is OK but the programming software is very expensive and not as flexible as I would like. The SLC500 has a reasonable instruction list but could be more extensive. My biggest grumble is that the last SLC I used was one of the higher end processors but only allowed 2 expansion racks and then one has to go to slow old remote I/O. Support for busses is quite good. Device Net is a big plus, as it is with Omron. Both PLCs have a good workable configurator. I use Device Net quite a lot.

Omron have one set of software to programme all PLCs in the range, with the exception of the ZEN programmable relay. CX-Programmer is very configurable, powerfull and not very expensive. The instruction set in the CS1 and CJ1 is the most extensive I have worked with in the medium sized PLC range and helps reduce development and commissioning time. Huge numbers of I/O available, dependant on processor, and up to 7 expansion racks for the CS1. the CJ1 mounts on a DIN rail. No rack required.
The other thing that is becoming important is the available space in control panels. Unfortunately, the space taken up by infrastruture in buildings is being reduced to very small spaces as it is not leasable. The important thing these days appears to be to squash plant rooms up and expand leasable space to make money. The CS1 is about the same size as the SLC500 but has 96 bit I/O cards. Saves racks. The CJ1 is about the size of a cigarette packet and has 64 bit I/O cards. Space is becoming very important and these 2 PLCs can save lots of it.
The other things I find very good with Omron are networks, (Controller Link is very powerfull and easy to use) and serial communications. They have a set of software called CX-Protocol which allows one to simply set up serial communications with virtually any device through a serial port. There is also a trace function so that one can trace and trouble shoot any serial comms. There are 2 serial ports on the serial card and one can run a different protocol on each port.

RE: PLC brands comparison

I design for an OEM to the paper industry worldwide. Back in 1990 I conducted a thorough weighted analysis of the major brands with respect to the types of equipment we supply. Some brands were strong in features we would not use, but weaker in offering the mix of I/O that we would use (e.g. we use far more OUT than IN, which is not typical). You cannot answer this question without some boundary of applications.

We selected Siemens as the clear choice. About a year later we found that our customers in the US did NOT like Siemens. What a hard lesson. Now we use what our customers use. In the US it mostly AB, Siemens in Europe, and OMRON in China.

RE: PLC brands comparison

Hi all,

I had read all posted in this thread; I had found it very informative! Thanks to all of those who contributed.
Any way, I would like to ask your opinion on the following PLCs:
I have to choose between the ABB AC800F or Siemens S7 400 PLCs for my current project. Initially, I was going to use Schneider Electric's PLC. But commercially, both ABB & Siemens could offer much better pricing on their PLCs.
I had never used neither ABB nor Siemens's PLCs before. However, I had lots of experience with the Allen Bradley PLC 5 & SLC 5xx PLCs. I am looking for any pitfalls and disadvantages only not the "so-call" great features from each manufacture. ( I had enough of that from the sales men)Any comment/suggestion/warning would be greatly appreciated.

RE: PLC brands comparison

I would not suggest any brand of PLC so as not to be partial. However, I suggest that you may be able to get an idea of what brand is the best by searching the web for the installed base of the different brands. You can search for websites of system integrators or automation contractors/consultants and find out what brands of plcs they have used for their different projects.

RE: PLC brands comparison

I've written programs for Siemens TI505 (using Ti-Soft and PLC Workshop), Siemens LOGO!, S5, S7-200, and S7-300/400), various Modicon boxes, IDEC, Direct Logic, Allen-Bradley SLC and ControlLogix, and Square D (I think that's all of them). What I would choose if the decision is mine varies depandant on what the local I&E tech is capable of working with, the amount of IO, and the complexity of the task. For my money the Siemens TI555 is the easiest to implement. It has built in analog alarm blocks and PID loops. The Special Function program capability is handy for specialty programs like gas and liquid flow calcs or creating an interface to a 3rd party serial port with non-standard data packets. The Ethernet card made by CTI for the TI series is easy to program. I have 14 TI545's and one TI555 (with 6 RBC's) networked together in one of our gas plants using this card in each processor rack. There are over 125 PID loops and nearly 200 analog alarm blocks used plus over 1,000 lines of ladder logic and 18 Special Function programs on the TI555 alone. 10 of the PLC's transfer data to the TI555 using peer-peer over the ethernet backbone. I also have two S7 remote IO racks connected to the 555 via the Profibus port on the 555 processor. We used a fiber optic profibus network for that. There are also 5 independant, 6000 plus tag Wondware nodes on this network. Once connected to our WAN (RAS, VPN, or Direct) I can remotely connect to any PLC on the network and troubleshoot a problem or even program (don't like to do that.). I also have the latest Wonderware app on my laptop so I can see what the operator is seeing from anywhere on the WAN. CTI also make a serial comm card (various flavors but we use the 2573-MOD modbus card mostly). The serial card configures very similarly to the Ethernet card. There are 4 ports per card. 2 can be used for MODBUS RTU (RS232  RS485 multidrop) and two for MODBUS ASCII. Typically, in a data concentrator application, we use Port 1 as a MODBUS RTU slave and Port 3 for the MODBUS RTU master. If we need more Master ports for devices that do not use the same baud rate we just add another card. This system has proven to be very reliable (Zero downtime in 5 years). So, for large systems where I want to emulate DCS functionality and provide an easy to learn programming environment for the local tech I would chose the TI model from Siemens and Workshop software from Fast-trak Softworks.

For smaller or single processor jobs I like the Siemens S7. If it's ethernet card was able to handle the density of ethernet traffic that the CTI ethernet card can it would be my first choice. The S7 offers many options on programming language including Statement List, Structured Text, Ladder, Function Block, and ??? one I obviously don't use :D It allows you to create and compile your own blocks which greatly speeds application developement. For instance, I have a block that I created for lighting a pilot on a burner management system. If I have a 10 burner heater, I call the block 10 times and populate the inputs with the correct addresses for each pilot. Outputs and intermediate operations are stored in data blocks. I also have a pseudo AGA7 calc block (110 internal variables) that I can use in lieu of a MODBUS connection to a flow computer. The S7 is a good data concentrator and MODBUS RTU Slave or Master is easily implemented. Using ProTool integrated with Step 7 it is very easy to develop an application for a local operator interface (touch panel, text display, etc). If I had one complaint it would be that their PID loop is incomplete at best. I've taken their block apart and if I can ever find the time I am going to modify it.

The S7-200 is my first choice for small applications. Especially if I need a MODBUS slave. It's easy to program and has a myriad of features sometimes not found on larger PLC's

I like the Direct Logic line of PLC's. Their PID loop is very robust.

My least favorite? Allen-Bradley. I do not like their programming software. I hate the way they name IO. The aforementioned systems all have a clean import / export feature that I make use of. I am a documentation fiend and I hate having to type information twice therefore I create my IO map in Excel, including symbols and descriptions, and then import that info into the program. Allen-Bradley's import / export feature yields a file cluttered with useless nonsense. When they implemented the ControlLogix line they almost got it right. There are a lot of things that I like about this line however their import / export feature is horrible and they blew it big time with their implementation of Structured Text. What good is Structured Text when there is no way to easily (note that I said easily) associate variables with the instance of the block. The blocks are not compiled and there are no instance variables. Each variable has to have a tag. The tags are not auto-generated. Why is that a big deal? Using my pseudo AGA7 block as an example- There are 110 variables associated with this block. If I implement it in the ControlLogix platform I have to manually create 110 variable tags for EACH INSTANCE of the block. Plus, I have to edit the instance of the block to point to the correct variables (can't use the same variable every time). I could use indirect addressing to mitigate this somewhat but all 110 variables per instance would still have to be generated. I was frankly very disappointed in the way that A-B implemented Structured Text.

RE: PLC brands comparison


Good feedbacks on the Siemens PLCs....I take it that you haven't came across any ABB AC800F/AC800M before?
Anyone else's has any things to add to either ABB or Siemens PLCs?
Thanks in advance,

RE: PLC brands comparison

As a plant engineer and maintenance manager it is necessary to use what fits best with the rank and file. Ge-Fanuc is the easiest for my electricians to use. It is already here and all of the electrician use it. All simple jobs have Ge-Fanuc 90-30. Software is not overly expensive. We have 4 Siemens S5's and it is universally disliked. S7 fares a little better. Software is costly. The six AB SLC and Micro and 5000 all are not liked by the electricians but liked by outside contractors who use AB. I hate their addressing methods. Software is too expensive. As for others I have experience with, IDEC is great. It is easy to program, software is free if you buy a small PLC. Phone support is incredable and so far free. Some old Square D can be programmed with IDEC software. I have used it in Mexico and it took about 10 minutes to get the plant computer guy along with his electrician to use it. I have no Omron in this plant but like it. Omron is very powerful and it uses a simple address system. Very logical. Can not mess it up. Omron plc's seem to like math. It likes networking. Commucating from here to Ireland is as easy as the next office. Price is usually lower than AB or Siemens. Omron is the largest logic control manufacturer in the world. I can see why. If I could start everything over in this plant 50 plc's would be IDEC or Omron.

RE: PLC brands comparison

Hey Wylde,

I understand your electricians frustrations with the S5. Especially if they are using the Siemens software. But, the S5 a rock solid box. I have one that I will eventually change to an S7-200 but only because the S5 will eventually be mature (might be now come to think of it)and support may become an issue. You might want to look into Fast-Trak softworks S5 programming software for the S5. One of it's strengths is that it will convert some of the statement list commands into ladder which is usually more familiar to electricians. It all depends on how the STL was written and what commands are used. STL (statement list) is a very powerful language but I know a lot of people that hate it. I love it. I don't know as much about it as I would like but every chance that I get I write something in statement list I do. Sometimes I use it just because it's available (S7).

Fastrak is at http://www.fast-soft.com and you can dl a demo of their software there.

I'm with you on AB addressing. It's like they think that we like to type or something I wish that everyone would take the tac that Fastrak did with their software. No clicking and dragging. Just start typing the address in the rung and you get a NO contact. Hit the / key and it changes to a NC contact. Hit the O key and you get an output. Type SET and you get a SET. RST and you get a Reset. If there was a programming drag race event the 505 with Fast-trak's software would win hands down

The IDEC is a sweetie but the last time I programmed one it was like the Direct Logic box in that there are no online edits. You have to shut whatever it controls down to be able to download the program changes to it. The box I used was an FA3S so it's possible that IDEC has improved in that respect. I have no idea.

I recently did a project where I replaced an old Square D with a new S7-315 and a WW interface. There was no documentation. No IO list. Nothing but wire numbers with no meaning. It was quite a challenge to determine what went where but that's my favorite thing to do so I had fun. By the time I was done (first Square D for me) I had cleaned up the original Square D program and fully documented it and there was really no need to change it as the problems that they were having were related to trash left in the program when the plant was reworked a few years earlier. The Square D line must have been pretty high end in it's day. I really liked it. Too bad it's mature.

Samske- No ABB for me. Not yet anyway. Counting panel software and Wonderware I think I have 18 different PLC/HMI software packages loaded on my laptop The IT people took over our software purchase / maintenance operation a few years ago. They still can't get my stuff right so it would be fun to add a few more PLC/HMI's to the list

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