why do plc's have so little memory still?

I have more memory on my cell phone than some of these top dollar plc's.

memory cheap.

why why why?

additionally, why an M340 ethernet card over 800 hundid?

and why the input card 7ms. if i program an arduino w/o an input filter, i click a micro switch pcb button and get thousands of inputs on one push.

To put it simply without going into a lot of detail: It mainly has to do with the processor that is used and how many addressing lines it has.

Since PLC's rely on passive convective cooling, you are limited in speed, hence you are limited in the addressing power. If you are limited in addressing power, you are inherently limited in the amount of memory that you can address.

This isn't to say that you can't get a PLC with a decent amount of memory in it. A lot of the newer PLC's have a fair amount of memory. For example, the Productivity line from AutomationDirect has 52 Meg! Even the newer Do-more line has several Meg in it.

Honestly if the PLC is designed properly, you don't need Gig's of memory space. A Meg or more is quite sufficient for the majority of applications.

Now if you want to store full documentation, drawings, pdf's, etc... then the PLC will need more memory, but for most applications a few Megabytes is quite sufficient.

As to why hardware is expensive, manufacturers don't get to sell to the consumer market where fractional percentage profit margins will net you a few million dollars. Plus there is a lot of extra protection built into a PLC module that is not there on consumer grade stuff.

As to why inputs are somewhat slow, your Arduino has no protection on it. A bit of over current or any transient will wipe it right out. A PLC can handle some amount of nastiness, it has to. The Arduino, not so much.


TLDR; Industrial components =/= consumer grade components. And for a good reason.

1) i wouldn't be complaining about lack of memory if i didn't need more. you say megs? my micro sd in my phone has 32 gig. pretty sure that not the biggest. probably under 20 bucks.
2) that is why i'm not using the arduino. i fail to see how protection has to do w/ such speed differences.
3) automation direct is kinda the harbor freight of automation.
4) yes, i obviously appreciate the robustness of industrial components. the arduino ref. was just me saying wtf? (probably more like saying: how did this yugo just beat my hellcat in the quarter mile?)

What Icky said.

And these
*Reliability
*Need, it doesn't need to be 64GB (or more) as in a SD card in a phone today

I use controllers up to 256MB, usual two of those to control 300MW CFB boilers with all subsystems, ca 2000 I/O. Safety system excluded (separate system/controller).

There are PLCs that have SD card slots to allow for the storage and retrieval of larger amounts of data/recipes. Look at Wago 750-880 for example.

Ken

Dirt said:

What Icky said.

And these
*Reliability
*Need, it doesn't need to be 64GB (or more) as in a SD card in a phone today

I use controllers up to 256MB, usual two of those to control 300MW CFB boilers with all subsystems, ca 2000 I/O. Safety system excluded (separate system/controller).

Click to expand...

lol, i've never had the problem, so it must not exist logic.

kvogel said:

There are PLCs that have SD card slots to allow for the storage and retrieval of larger amounts of data/recipes. Look at Wago 750-880 for example.

Ken

Click to expand...

actually am. the wago's are impressive. i'm complaining about the 3k plus rack of the schneider m340. my only complaint is cost and memory. these things have been robust sans the modbus port. and the unity software has barely any bugs. they rock, minus my two complaints. but we might end up going to the wago. flying up to wisonsin for the august class.

over $800 for the ethernet card?

located data is what is killing me. not storing ascii in the plc. that would kill it.

ganutenator said:

lol, i've never had the problem, so it must not exist logic.

Click to expand...

Kewl. But in a later post you're talking about a specific brand/model not mentioned in topic? (except ethernet card). You'll have to choose a PLC brand/model that fits the bill. I thought you meant in general, very sorry!

As icky pointed out, the passive cooling is a big limiter on the processing power. The 1518 from Siemens is about a foot wide, and from what I've heard the reason is that it needs a massive heatsink to run at the 1ns instruction time they advertise. Even if you add gobs and gobs of memory, your program can only execute so fast. I think PLC manufacturers feel that there is a certain maximum scan time that most customers will tolerate, and it isn't profitable to add too much memory past that.

As kvogel, many PLCs come with expandable memory today. Siemens makes you use their own SD cards, but you can get a 32GB one, if you want to do lots of data logging or recipe storage.

You ask about IO update times: Most PLC guys WANT that input filtering, to protect against spurious signals. The ones that want fast data buy high speed cards. They can get pretty fast; I've seen analog cards that can update faster than 50 microseconds.

A number of other posters list some other requirements, like industrial robustness, etc.

To me, it really comes down to this: if there was enough demand for it, at least ONE of the PLC manufacturers would have products like what you're looking for. Instead, profitability is all about trade-offs, and they just think there isn't demand.

M340 has been a pretty amazing upgrade from Quantum for us and it costs half as much.

like you said the unity software is solid and worth paying a bit extra for over the lower end platforms.

if you want to save the 800 for the ethernet module just use the ethernet CPU and program the modbus data exchange yourself.

What are you doing that needs more than 65,630 16 bit located words or that exceeds the capability of the 32mb flash card, then transfer the relevant data to/from located space when you need it externally?

I remember AB PLC3 days....128MB memory module was over $10,000.

Respectfully, this is all total ********. There are industrial rated (either to 70 or 85 °C) single board computers, with faster processors than any PLC, with onboard FPGAs, with gigabytes of memory, and no active cooling.

There is no good reason except to make you buy a more expensive PLC, plain and simple.

****-poor example: https://www.embeddedarm.com/products/TS-7250-V2

Or, other reason, most PLCs are using MS-DOS era technology still. I still can't believe that most can't do double precision floating-point arithmetic.

I agree. Total BS- PLC manufacturers are colluding against the market.

Same mindset with anti-features. They design one PLC that can do everything (motion, 256 ENet connections, etc) then disable those features incrementally throughout the line to make you pay more for what you need.