Why is control logix better than SLC 500 or Micrologix? 3

[eeprom]

Hello,
I've used SLCs and Micrologix processors for years. In the past year or two, I have been told repeatedly by a distributor that control logix is so much better. When I ask him why it's better, he says that I will reduce programming time and its just a better processor. I don't know what to make of those statements. What does it mean that it's a better processor?

A few months ago, I got a demo copy of RSLogix 5000 and a loaner control logix rack. I have used it enough that I could probably build any project on a control logix that I could on a SLC 500. So, after 40 or 50 hours' tinkering with the control logix platform, I see nothing better about this system other than expandability. Of course control logix can handle much more I/O.

A control logix system will cost 5 times more than a similar SLC 500 system. The RSLogix 5000 software costs 4 times as much as RSLogix 500. Can someone who knows these systems please tell me why control logix is better than the older processors?

thanks
EE

 

[djs]

For larger systems the ControlLogix platform is probably better. There are more builtin programming blocks, for example there is a single instruction which will control a two way valve. Most of the builtin instructions are oriented to process control. So it really depends on your application.

 

[catserveng]

I also use a lot of SLC's and MicroLogix, mostly 1200's and some 1500's, recently started getting the same stuff from my supplier.

I support a couple of systems with ControlLogix platforms, in most cases I can see the benefit in some of the larger cogen systems with lots of balance of plant and monitoring, at one smaller cogen site when the ControlLogix failed I replaced it with a 1500 and it worked just fine.

Yeah, the ControlLogix has a lot of extra features, some are pretty neat, others I'm not impressed with, but lately it seems the AB folks are pushing their distributors to try and get more customers over to them.

I have to agree with DJS, depends on your application, but if your doing projects successfully with Micro and SLC's the ControlLogix likely won't be any kind of great improvement.

My two cents, Mike L.

 

[eeprom]

Thanks for your feedback. I don't do any jobs of greater than maybe 60 to 100 I/O. And so far I see the Control Logix platform as a very very expensive version of the SLC system. Granted that there are benefits. But the cost difference in tremendous.

I think some firms push the Control Logix because they get a bigger mark up.

 

[EddieWillers]

From your perspective with small control systems, the ControlLogix probably is overkill. If you had a dozen motion axes and a few hundred I/O points the speed, memory, and functionality would make a difference.

CompactLogix starts to be less expensive when compared to SLC-5/05 systems of moderate scope (100-500; anything smaller and even CompactLogix is often overkill. The newest POINT-backplane controllers that will be introduced at Automation Fair might change that equation even more.

CompactLogix 1769-L32E is my default controller; motion systems get L43's or L61's, small discrete systems get MicroLogix.

As far as the markups, there might be some truth to that. Some OEM users who have been using the SLC for decades get unbeatable discounts that they can't get for ControlLogix because they don't buy any volume.

ControlLogix definitely isn't new; it was released in 1997. I built my last machine with SLC-500 four years ago and have been using ControlLogix, CompactLogix, and MicroLogix since then.

These days I am far more productive in ControlLogix than I am in SLC... it's hard to train myself to be constrained by data tables and the SLC instruction set again.

 

[eeprom]

EddieWillers,
It sounds like you build much larger systems than I do. I work for an OEM and we put together some pretty high end systems, and I have never had difficulty making a system work using an ML1400 or an SLC.

I've heard about the motion control possibilities. But why the expense? A power supply for a control logix rack costs over $1000. How can a power supply be worth $1000. Aside from the transformer and the PCB, there is nothing in a power supply worth more than 5 dollars. I've seen CPUs for more than $10,000. Why isn't this considered price gouging?

 

[EddieWillers]

Low-volume, high-reliability, fanless electronics costs orders of magnitude more than consumer electronics does. The component availability (try to find an exactly compatible PC power supply from 1997, while you can get an exactly compatible 1756-PA2) is one of the things that's built into the price.

Knowing that doesn't keep me from having sticker shock, sure, but when ten minutes of downtime costs the same as a power supply, I don't object for very long.

 

[eeprom]

Downtime can be expensive, and embarrassing.

I hate to be such a nay-sayer. I am actively trying to be convinced that control logix are worth the money. But the downtime argument is one that I hear all the time from my distributor. As if any other product will fail prematurely. I have dozens of siemens 24VDC supplies that have been in the field for 10 years or more without a single issue. I work in one plant that has a modicon PLC from 1985 and it still runs fine. PLCs don't fail very often.

Bottom line is: it is very difficult to justify $1000 for a PLC power supply. I would imagine that the mark up on that would be 300 or 400%.

 

[tygerdawg]

I would suspect that the distributors are being directed to push ControlLogix simply due to business economics. The SLC series is older technology, older form factor, internal knowledge base is getting gray hairs, etc. They want to phase it out because keeping it as an active product line cuts into their profit margin.

I saw the same thing once before when Texas Instruments wanted to phase out their original PLC line. There was such a vast installed base of that particular product, the customers threw a fit. But continuing to make that product to support their customers was a money-losing enterprise for the company.

TygerDawg
Blue Technik LLC
Virtuoso Robotics Engineering

http://www.bluetechnik.com