I am at present using my first Siemens PLC for about 5 years. I normally use Omron. I program in ladder as this is usually specified to allow maintenance personel to view the ladder and facilitate quick trouble shooting on a system. The job is for a client who exclusively uses Siemens and at present has a Citect SCADA system with over 100,000 tags in the database. They have many Siemens PLCs networked throuhg the premises. Their engineer has been working with Siemens for over 15 years now and really knows the whole system back the front. He also writes drivers for everything, manufactures his own RTD transmitters and other transmitters of varying types, interfaces etc etc. A very smart man.
He has actually complemented me on getting on top of Siemens as well as I have in the short time that I have had to do the project and described Siemens ans "not very friendly".
I would make the following comments on both PLCs and software and note where the opinions are those of my client:-
1. Having to set absolutely everything up in hardware in Siemens is an absolute pain and there are no easy to use tools to make life easy. With Omron, using CX-Programmer V6.2, you just upload the I/O table from the PLC. To set up various cards there are many tools available to set up all cards just by double clicking on the card in the I/O table.
2. It is very easy to structure the program in both PLCs.
3. Both PLCs offer FB programming and STL is available in FBs for both brands.
4. You can protect FBs with passwords in both PLCs.
5. My client uses ladder almost exclusively but uses STL from time to time when he requires to use it only. He claims that ladder scans faster and I am not in a position to argue that point.
6. Serial communications are extremely easy with Omron to any serial device using a very inexpensive serial card and CX-Protocol software to write the protocol. The serial card even has a trace function on each serial port in Omron where one can trace what is sent and received without the need for an outside analyser. Siemens is absolutely not friendly and far more expensive to achieve the same result. My client has avoided serial communications at all costs with Siemens until I was recently given some excellent assistance on this site as to a far more reasonably priced Modbus interface from Siemens that even my local Siemens rep was unaware of. However it is far more difficult than with Omron and other serial protocols are not easy either.
7. Omron programming software is far more friendly and easy to use that is for sure. Omron also offer a huge number of shortcut keys that can be programmed to work how you want to work. Siemens is very limited, as are most manufacturers. I miss masses of shortcut keys more than anything.
8. Even the very powerfull Siemens 318-2 processor only has 256 timers and then you have to make your own. This is really very few for a large project.
9. The S5 timers are an absolute pain! Many here make their own timers, as does my client, to get away from the S5 timers. Fancy having to program words just to see the PV of the timer! Siemens really should have fixed the timers with the S7 PLC.
10. If anyone thinks that the Omron PLCs are "toys" and not very powerfull, think again. The high end CJ1 and CS1 PLCs have exteremly fast scan rates and a huge number of functions that are vewry easy to use and monitor in ladder. It is my understanding that these PLCs have amongst the very fastest scan rates of all PLCs, if speed is an issue. The CJ1 has 64 bit input and output cards that are the size of a cigarette packet and the CS1 is smaller than the S7-400 and has 96 bit input and output cards. Extremely space saving. Siemens have limited the I/O cards to 32 bits although they are all screw connections rather than plug in. I do find this a bit of a pain and prefer the Omron offering here but many would not. I make my own flying leads away from the plugs but many would not be bothered. The Omron transister output cards are limited to 100ma whereas Siemsns run at 500ma. That does not really bother me either as I only use transistors to drive protected LED indicators and relays with flywheel diodes for either brand.
11. Siemens hardware is generally quite a bit more expensive than Omron.
12. Omron software is far more easy to use and intuitive than Siemens. I hate software that I cannot start to use intuitively straight away these days, although the full software package takes a lot of time to use properly of course. Siemens is definately not in that category but is very powerful as one dicovers what it can do.
13. I absolutely object to the huge folder and file structure that S7 Pro produces. Why? It just fills up hard drives at a million miles an hour. I have a large Omron project for a power station job using 9 PLCs and many remote I/O and the whole file for the project only takes up about 500k on the hard drive and that includes all comments. The printouts use a full box of US fanfold paper so it is not a small project.
14. Omron do have a very good monitoring table function but Siemens is really very good here and better than Omron I feel. However, having to make one of these tables up to force I/O for testing wiring before loading the software is a pain. To force outputs with Omron one can simply call up a 64 bit word in binary and toggle the output with a single keystroke. With Siemens one has to make the table and then write 1's and 0's to the bits.
15. The cost of software is a huge issue for me. I work for myself and struggle to justify huge software prices. This is one of my biggest issues with PLC manufacturers. I Ozz, Siemens charge big money for S7 basic software. I can purchase a full set of software from Omron that includes the programming software to suit
ALL current PLCs, Simulator, NC card software, screen software, Device Net and Profibus configurator and much more for less than it costs for the Siemens S7 basic. I really find that discusting quite frankly but Siemens are no worse than AB, Modicon etc. Omron were not good either until recent times (last 2 years) where they have suddenly realised that a good complete software package at a reasonable price is the way to go. Just have to educate evryone else now. I have absolutely no objection to paying for software tools but it is not reasonable in my view to place the software virtually out of reach of people like myself who work for themselves and find that software that costs several months salary is definately off my purchase list. I also find it strange that many people who pay these exhorbitant prices then run around looking for free software to use for word processing etc. Is this because they cannot afford these other packages after paying for PLC software?
16. It has taken me far longer tp program my current project in Siemens than it would have using Omron. Part of this is due to me being unfamiliar with the software but I have had the assistance of a guy that knows Siemens back the front and I estimate it would have taken twice as long even if I knew Siemens back the front.
Now to comment on a few others posts here
Simple, what is the total price? Structure etc. are secondary questions..
Watch out as time is very expensive. I find that I do not have much time and a speedy software package is very important. It not only means that one takes longer to program a job but another one is waiting in the wings and not getting done either.
They all have their strengths and weaknesses.
People do seem to have a "Siemens = STL" mentality. I have frequently written FCs and FBs using Structured Text (so easy from a development point of view), and then, protect them and call them from LAD. No-one need ever know what's going on inside these blocks if they don't want to.
You can do this with Omron if you so choose. I do not.
I've programmed both (and at least 7 other brands / 20 totally diff plcs) and I'll never do a Siemens again. Debug / actual programming time is at least 3x any other brand.
I would say about double not 3X if using ladder. The ladder tools are not good. The Europeans use a lot of STL and I believe that would, at the end of the day, be quicker and about the same time in both brands. I just do not like STL!!!
Also, in large and complex applications you must buy more Omron PLC's because you will overflow memory.
You have to be kidding!!! I would rather break a system down into small chunks and use multiple PLCs than use a "monster" any day!!! The PLC dies and you lose the whole plant. Distributed systems allow far more flexibility. Also, how do you define memory? All manufacturers define memory differently. I have seen one PLC (no names) that alledgedly had 250k memory. An Omron PLC with 20k memory did the same job. It all depends how it is defined. The 250k referred to RAM, the 20k referred to instructions.
I'm on the opinion, that if you know what you want to acheive, you should be able to do it, independant of the platform that you are using. Sure, every manufacturer does things differently, and the different models have different features / strenghts / weaknesses.
So true. Time can be a killer though.
Generally, I will work with what I have to work with but as I get older I find I am generally restricting myself down to packages that are reasonably priced and fast and easy to program and install in a control panel. Reasonably priced includes hardware, software and installation and commissioning time.
By the way Peter, I have GX-Developer here and it is a bit ordinary quite frankly. Mitsubishi do have 2 good things going for them, definable register areas for retentive/non retentive registers and "drop in" notes in the software, although I have seen programs where this feature was over utilised and was, quite frankly, a mess. I have found the hardware a bit "fragile" over the years.