andre_teprom

Is there any metrics for performance comparison of PLCs?

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As I am relatively new to the PLC world (I worked with only one brand), and I will probably go to "Hannover Messe 2019", I would like to be able to quantitatively evaluate the performance of other PLCs compared to the one I currently use. One of the reasons for my trip will be to analyze other up to date available solutions. I-m not concerned about costs (software licensing, hardware price, etc ...), I'm more interested to focus on the performance aspects.

Is there any standardized or common use metrics for performance comparison of PLCs from different manufacturers ?

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What performance factor is so critical that you'll travel 1/3 way around the world to find an alternative to what you're using now? 

What does your current vendor suggest for upgraded performance?

In answer to your question, I'm unaware of any standard of comparison.  But I can understand why - so much of PLC's performance is related to how it is programmed.

 

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As for your recommendation to ask for such an advice to the manufacturer of the products I currently use, I don't think they would kindly give it, as they have their own metrics whose criteria for computing it are not disclosed; moreover, I could not find anywhere else their grades, therefore it would not be helpful to use a proprietary scale parameters to compare with products from other manufacturers. 

As for the usefulness to go to that event, as stated above, seeking for news is just 'one' of the reasons, therefore this is not a waste of money and time, otherwise there would be no reason for manufacturers to invest in events like those, but this is getting off topic.

Anyway I was expecting insights with a slightly more technical approach rather than sarcastic. By the way, although relatively new on the PLC world, I have more than 20 years with programming and design of embedded systems, so good programming practices are already present on what I do.

Thanks.

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@andre_teprom: It would be very helpful if you could share some more information regarding what you are looking for... The major PLC brands are more or less the same, some are more leaned towards future functions while others are more conservative. This has of course it's advantages and disadvantages. When it comes to pure processing power, or cycle time, the major brands are not that far apart.

It would help us a lot if you would write a bit more about what you want to accomplish and how you wish to accomplish it. At this point we really don't know if you are using a small 8 input/8 output PLC, or if you're using 8k input / 8k output system - as you can imagine it's very fuzzy and hard for us to give you any kind of tips or advice. Also what is your biggest challenge, or importance?

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@kaare_t: Thanks for the comments, I did not really make it very clear when I was mentioning just "performance" with no additional details. I was concerned on the processing power per second, or something like that. The fact is that the program on which I am working brings together a huge amount of tasks, which are not only interlocking, but rather huge processing in realtime at a high rate. To make things worse, I wanted to gather some tasks that currently run on another PLC so as to have everything on a single hardware platform. Unfortunately, for the initial analysis done so far, this would not be possible at first since at least the main PLC is now running somewhat beyond 50% of its runtime. As for the manufacturer I am currently using, due to NDA issues I can not disclose this information, the only thing that I can share is that it core is based on the X86 architecture and it has built in floating point ALU, which is nice for REAL number calculations.  but this should not matter on the subject in question. Anyway, from all your inputs it is becoming more and mode clear that what I wanted does not exist, and therefore I will have to compare by other criteria the processing capacity of each PLC.

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I have never heard of any charts for PLC's, sadly. Processing power per second is not important, what is important is processing power per instruction. In other words, how long time does the CPU use to process a specific instruction. And of course the base scantime of the CPU (but they are kind of linked together).

The major brands have their scantimes and processing times in their manuals so I think it's a fairly straight forward task. You can then compare your current PLC brand with other brands. Can you upgrade your current PLC brand to a faster CPU?

You know that you can install several CPU's in some rack based PLC's, right? That would offload the main CPU...

When you say your current CPU is running 50% of it's runtime, what do you mean? PLC's have a "base-runtime" (empty program) and except from that it all depends on what you put into the CPU... PLC's are cyclic and not event-based, so everything you put in WILL affect scantime/runtime.

I have attached a small screenshot from a Mitsubishi iQ-R manual that shows some processing times (in uS). Look at these in any manual from the manufacturer...

iQ-r.PNG

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Have seen the similar charts for Siemens too. Another option could be also dividing tasks in the application. In some PLCs it is possible to have both fast tasks and slower tasks. For example, one task with length of 10 ms for turbine control and another with length of 100 ms for SCADA communication. Both running on the same CPU. And then prioritizing among tasks to ensure the speed.

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