PLC Memory Cost

Has anyone ever questioned why PLC memory is so expensive.

I was looking at a CompactLogix 5380 and to go from 1 MB of memory to 4 MB, the cost difference is about $5,000!

What makes that 3 MB of memory so special? Are there other differences in the processors that drive the price up?

https://www.automationdirect.com/productivity/index
The productivity series has 50MB user memory!

Perhaps the problem is the brand? Have you done the same comparison with OMRON, Siemens, etc??


The reason is most likely, people at Rockwell think that if you are going to need more memory, your process will be larger and therefore in theory give you more profit... hence the ludicrous pricing.

The thing is I am used to Rockwell and I like working with it. I don't even mind paying "a" premium for using them, but this pricing structure, especially when you can't even really purchase memory in MB anymore commercially because it's such a small amount, seems absurd.
I just wondered if any of the Rockwell/Allen Bradley folks that post on this board form time to time had any explanation. Though your explanation makes some sense as far as their justification.
In my case, I just want to store recipes on the PLC in a large UDT array. I understand recipes can be stored in the HMI and I'm sure there's a big list of pros and cons regarding that as well. I'm just baffled by the cost of memory in what by today's standards are tiny amounts.

I am not sur for Rockwell but for Siemens.

The difference between a S7-1515 (500ko work memory and 3mo data) and a S7 1517 (2mo work memory and 8 mo data) looks minimal if you only look at the memory.One is sold around 2 000€ , the other cost more than 4 000€.


But I know someone who tried a program that had a 150ms+ scan cycle on a S7-1515, it went down to 6ms in a S7-1517. So there is more than just the mémory. I don't know for Rockwell but I imagine it's the same.

ElectroGuy said:

Has anyone ever questioned why PLC memory is so expensive.

I was looking at a CompactLogix 5380 and to go from 1 MB of memory to 4 MB, the cost difference is about $5,000!

What makes that 3 MB of memory so special? Are there other differences in the processors that drive the price up?

Click to expand...

The assumption is that you need more memory to store and execute more logic, faster.

Yes, it's a dumb assumption in today's world.

Like everything that you do when you are locked into one vendor, just bend over, grab your ankles, ... [in-appropriate description deleted] ..., and be happy they have a product available for you to buy that has enough memory to do what you want to do.

Keep in mind the memory in a PLC has to handle high temperatures (140 F) and 24/365 operation. They are also in integral part of the PLC, not like you can plug in a bigger one like you PC.

It was explained to me by one of Rockwell’s engineers.
When new products are developed, a board is formed consisting of their top OEMs.
They will hash out their needs to Rockwell and usually it is very specific. Hence, more models are produced of a certain type than others and price is reflected.

One example is the little Micro810 controllers. The OEMs wanted a PLC that required a special cable/adaptor to program. They didn’t want a PLC that anybody could hook up to. The little $25 adaptor was born.

The other thing is that Rockwell has such a strong base in the Americas and once your plant is made up of AB controls, your pretty much stuck.
The upside to their tyranny is that other brands will give you stellar deals on their stuff just to get in the plant.
I personally are not installing anything AB anymore, not even a legend plate.