Excellent features of Siemens which AB Control Logix Does not have

Phantom75

The most common refrain Ifrequently hear against Siemens is, "It's too complicated" and my answer always is, it's structured and systematic. You have to invest time and effort to understand the system, after that it's a cakewalk.

lalit

But let's take the example of any one if a person is working on AB PLC. If he is experienced for 20 years in AB, how positively he tries to learn any other PLC but it will take some time for him to learn Siemens and he will always try to find AB in Siemens.

fritz

. . . To sum this yet again way to drawn out entry up:
Siemens PLC’s are more logical, more strictand don’t hide anything from you.
Human nature unfortunately favors being a bit lazy and being able to quickly program something without the need to fully understand what you are doing and in this case (and this case alone)A/B programming wins against Siemens programming . . .

fritz

Phantom75 wrote:

The most common refrain Ifrequently hear against Siemens is, "It's too complicated" and my answer always is, it's structured and systematic. You have to invest time and effort to understand the system, after that it's a cakewalk.

Excellent point Phantom75 and the same can be said for the following words from lalit:

lalit wrote:

But let's take the example of any one if a person is working on AB PLC. If he is experienced for 20 years in AB, how positively he tries to learn any other PLC but it will take some time for him to learn Siemens and he will always try to find AB in Siemens.

Let's also not forget that people tend to like what they know (or have experience with).
A/B PLC’s and their programming software are perceived by A/B fans to be “easier”, “more powerful” and more “user friendly” than Siemens PLC’s and I can see where this (WRONG) perception comes from.

For one, ControlLogix PLC’s have a wealth of inbuilt instructions (e.g. Array (file) shift/compare/search/sort instructions, FIFO buffer handling, the hideous “compute” instruction etc.etc.) which far exceeds what you’ll find in the “normal” Step7 instruction set.
There is of course a wealth of SFC’s/SFB’s available to begin with and a considerable amount of IEC blocks, knowing that they exist can of course be a challenge.
I don’t mean to be sarcastic here and its good that these questions are asked, but even in this forum we have questions like “Is there a way to set all values to zero in a DB”, the simple answer is of course “Yes, have a look at SFC21”, but people simple aren't "naturally" aware of these.

And you can of course always develop your own blocks to do what you want to do and neatly put them into libraries (or use blocks created by others such as www.oscat.de).

Secondly, programming of a ControlLogix PLC takes a lot of the thinking effort away from you.
For example, essentially all math and compare instructions exist only as one instruction, whereas Step7 has as set of INT, DINT and REAL for these.
And yes, you can compare an INT with a REAL via the A/B compare instruction (you can even compare STRINGS with the same instruction!).
The compiler will in runtime convert and match the data types and spit out the result.
You can also for example add an INT with a DINT and have the result delivered as a REAL (in one common ADD instruction).
People (who don’t know better) like this nonsense, it does however lead to “sloppy” programming techniques and can cause unforeseen results (note that even the manual actually states that every instruction has so called “optimal” data types which makes the instruction execute faster and requires less memory and these are typically DINT or REAL. There is additionally a long section at the end in the instruction set manual that describes what rules govern the conversion of one data type to another if mixed data types are used).
Anyway, I’ve seen a colleague during commissioning scratching his head why his comparison didn’t deliver the results he thought it should, until he realised that he fell prey to the usage of mixed data types.

To sum this yet again way to drawn out entry up:
Siemens PLC’s are more logical, more strictand don’t hide anything from you.
Human nature unfortunately favors being a bit lazy and being able to quickly program something without the need to fully understand what you are doing and in this case (and this case alone)A/B programming wins against Siemens programming (and for the record, A/B PLC’s are Toys, I am after all entitled to my narrow-minded point of view).

Lastely dear lalit, there are twomore points to add to your main list, which are:
1.)Controllogix PLC's don't have a process image available. If you want to ensure that Inputs stay the same throughout the scan you need to create an input buffer via programming.

2.) NO STL available in A/B PLC's (and if this not the clear winner than I don't know what is, I can't belive I didn't think of this straight away)

Keep up the good work guys

fritz

Siemens PLC’s are more logical, more strictand don’t hide anything from you.
Human nature unfortunately favors being a bit lazy and being able to quickly program something without the need to fully understand what you are doing and in this case (and this case alone)A/B programming wins against Siemens programming (and for the record, A/B PLC’s are Toys, I am after all entitled to my narrow-minded point of view).

gfair

this is why this forum is a great help.

You are absolutely right. It seems like a big family and we all are the members. One word I want to share that, it’s one of the best ways to learn and gather Knowledge.

With best regards

ddg