Compare Mitsubishi and Allen Bradley PLCs

Can anyone with experience on BOTH the Mitsuibishi iQ platform and the Allen Bradley ControlLogix/CompactLogix platform provide opinions why one is better than the other? Are there any watch-outs or warnings with the Mitsuibishi iQ platform?

support was a real issue for me with Mitsibushi vs AB you get fast support with AB particularly if you pay the tech connect contract. The cost is higher however I find its a reliable platform. I've had extreme difficulty in getting the same support from Mitsibushi

Bill, welcome to the Forum.

Great info, thanks. Again, if anyone can provide details regarding their vote then that too is greatly appreciated.

If your project uses a lot of communications then read this

My opinion is communications weighted. Rockwell makes it easy. Just about anything can be done with a MSG block or the I/O can be configured to magically appear as in Ethernet/IP IO. Mitsubishi is almost brain dead. One must write code to monitor status and copy data to and from 'intelligent' modules. One can argue that the data structures for the Mitsubishi have similar data as that in the MSG block but the MSG block has all the fields there and you fill in the ones you need. One must get out the manual and figure out what needs to be placed where in the Mitsubishi.

I rate all the PLCs pretty much by how much support they require to access our products and then how well they work. Rockwell is at the top and Mitsubishi is just above Siemens at the bottom. GE is down there too.

The last time I worked with a Mitsubishi was about 4 years ago and I remember that the support staff was stumped by a simple question. What is the best way to communicate to our controllers using a serial port. For Rockwell it would have been RS485 using half duplex DF1. Mitsubishi had no equivalent method and it took them two weeks to fess up.

BTW, I think it took only about 4 hours to write the half duplex DF1 code for the communicating with a Micrologix or SLC5 just reading and writing 16 bit registers.

http://forums.mrplc.com/index.php?showtopic=6090&hl=Mitsubishi
I don't forget or forgive. Once on my s-list you smell forever.
That was about two weeks wasted. I implemented one of the protocols only to find that the PLC couldn't initiate commands. I had asked their tech support and told them what I planned to do. They didn't know about the limitation.
I ended up using the binary in and out blocks but could only talk to one controller at a time. I had to make up my own application layer inside the binary packet. It worked but it required a lot of code on the PLC side and could only talk to one motion controller at a time. There wasn't any nice queueing like the Rockwell MSG blocks unless you wrote it yourself.

I don't think you guys really appreciate how much that MSG blocks.

The other problem I came across was the limitations of CC-link simply put you required to use CC-link rated cables in order to have a reliable chance of communicating. With other protocols the cabling was far more flexible on which one you could use. The only other one I found as dependant on specific rated cables was Profibus (seimens)
The other nice advantage AB has over most other PLC manufacturers is the ease of its software. Out of all the ladder lanquages I've studied AB is the most intuitive and easy to troubleshoot and program

Your vote and opinion/experience is important!

Actualy you do not need to write code for a lot of modules some of these being ASI, Analog etc. there are utils such as configurator where you just set where you want the data to appear, AB have recently restricted suppliers, try to beat you into a tech connect contract & simular platforms are far more expensive from AB.
I agree that AB has better documentation but being in this trade for over 30 years & currently working at a plant that has many types of plc (AB & Mitsi being the predominant types) can confirm that the mitsi's seem to fair better in this harsh enviroment than the AB, we have more mitsi's than AB but the repair/replacement cost is far higher for AB.
Then again anybody from over the pond would probably be biased towards AB just as germany probably prefer siemens.
I'm not biased towards any well known plc platform as I have worked with most but this observation is based on years of experience.
The main problem with most systems nowadays appears the continued "improvements" to hardware & software i.e. versions where on a regular basis you have to upgrade your software, upgrade firmware without a real choice which causes real headaches for engineers on the front line where they have the production manager breathing down their neck wanting the plant running again.

Still looking for you opinions and vote in this poll...

The older Mitsubishi controllers were a bit of a pain to set up for analog. Seems I would forget the half dozen or so steps needed to set up an input and would have to drag out the manuals every time. Also, the assortment of functions are not very intuitive as to what the data format is - again I would need to pull the manuals for a refresher.

I guess I've been lucky with the quality of local support which has been readily available and supportive. For older established hardware much of the documentation is still in "Jenglish" and leaves much to be desired.

We have dozens of tools with a wide range of models and vintages and I have found the Mitsubishi equipment to be very robust.

I would agree that AB is a much better choice in any distributive control network. CC-link is very limitted in I/O count.

Surely the answer to your question cannot be answered unless we know what your application is; are you looking at a one off project? to standardise for a complete factory installation? will you have different types of applications? how many I/O?, 3rd party interfaces, eg. HMI, SCADA, etc? the list is endless.


In my experience, in the UK, Mitsubishi tend to be cheaper and have a bigger instruction set, particularly for machine control, sequencing, etc. (having said that I usually like to keep instruction use to the basics which makes it easier to implement similar programs on other platforms).

Mitsubishi manuals can be difficult to understand; most of the information is there but not always where you'd expect to find it and Japanese-English translations are not always very easy to comprehend.

I can understand why Peter had a problem with tech support; I guess a lot of the in-depth knowledge on the Mitsi is in Japanese. I doubt if all the technical info on the product has been successfully translated into English.

My other gripe about Mitsubishi is the fragility of its relay output cards, particularly when driving inductive loads; as long as you know this and use interface relays then it's not a problem.

I prefer the speed of on-line editing with a Mitsubishi; I'm not a big fan of the RS method which involves 4 steps instead of 2 with the Misubishi.

I have heard people disliking GX Developer but I have no axe to grind any more than with RS Logix.

I have not come across any reliability issues with either platform (Misubishi A series and AB SLC 500) I don't think the new platforms (Q series and Control Logix) have been around long enough to make a judgement call.

I agree with Parky about hardware and software "updates", I think AB have more guilty of this than Mitsubishi in the past.

I would guess that there are far more 3rd party products that will readily interface with AB, particularly in the USA.

If I were forced to standardise on one or the other, I'd probably go for Mitsubishi, mainly because of price but also, in a weird sadistic kind of way I've grown to prefer them over AB.

I agree with a lot that burnerman has stated... but I like the lay out of RSLogix 5000 (ver 16) more than GX Developer (ver 8.55) I put the versions because they may have changed some and improved but these are the versions I have to compare.

Last I looked Mickey was the only one voted they are the same... and for the most part he is correct, they both can do the same, just like a car can get you to from point A to point B... a little faster or slower but they all move you

Look at support in your area/plant, if you are installing a system and they/you have CLX or GX then stay with that system

At my former employer I installed every type of system I could find... I did this just to learn them all at the time I did not think that I would use this in the future... but it sure has helped me a ton for what I am doing now

The Q series is a far better platform than the FX range, especialy if you use GXIEC Developer it's more structured & contains a lot of functions that are not in GX, however as they have kept the code simular so that both GX & GXIEC can be used it means you really have to keep the source file as they are not strictly compatible, saying that if there is enough memory in the plc you can store the packed database in the plc so it can be uploaded, although changes will have to be downloaded again in the packed DB.
AB is certainly a nice platform but expensive in comparison & since I have been using the Q platform since 2002 8 years is plenty of time to iron out any bugs (not that I have found any real bugs yet).
Also there are some IEC handling blocks for analog on FX as a free download.

I appreciate everyone's response. This is great info - keep it up!