AB vs. Modicon

[Daryl 1]

I may have a chance to advise on changing the currently spec'd Modicon Premium system to an AB system, however, I need a few good reasons to justify this. I'd like a few (serious) reason on why I should change the Modicon to AB kit. Why is AB better than Modicon type reason. thanks... Daryl

[Ken Roach 194]

I would have to know more about your business to give a recommendation. I was an A-B specialist for 14 years so I'm not impartial. With my customers who have made the switch between Modicon installed base to A-B, the difference was not in the hardware, networking, or software; it was in the local support they could get from the manufacturer and the distributor. This is most important if you have a large installed base of controllers. If you are an OEM who ships his machines to a far-flung customer base, the most important thing is your abilities in-house and how much hardware you want to stock for your customers. I still hold the company record for fastest hardware replacement; nine minutes from phone call to delivery. I had a fast motorcycle and the road was dry. What's your business like ?

[jmsbama 0]

I have worked in industrial machine repair for 30 plus years and the first question asked when a machine is down is how soon can we get a replacement part. With Allen Bradley parts can be found most of the time locally or next day delivery. Time is money when the machine is down for parts. JMS

[paulengr 44]

This is highly situational dependent. For instance if you are talking about substations, switching to AB is nontrivial. Only the Micrologix supports Modbus directly but the power ratings on the relay contacts aren't great. 1794 Flex IO supports the required power ratings but you have to go through gyrations to support Modbus. So you may face an uphill battle displacing old substation gear with AB. In other areas, it is much easier. The support aspect has already been mentioned. Also don't forget that until recently, AB still supported everything back to the PLC-3 from the early 1970's with parts. Recently they've "finally" started cutting off PLC-2/3 support. The Micrologix line still uses the same programming software as the SLC from the 1980's (though obviously the programming software is vastly updated from that time). Modicon seems to change models (and support) roughly once every couple years which drives Modicon users crazy. Hence when you use AB products, you can seriously expect a product lifespan of 20-30 years minimum. Not so with Modicon. The biggest thing that has withstood the test of time with Modicon is the Modbus protocol that is at this point an industry standard and whose specs are widely published. Since you are talking about plant/process level PLC's then you will be looking at CompactLogix or ControlLogix. Take a very close look at the programming environment. Modicon's environment is most similar to PLC-5 or SLC except that it is not as flexible. ControlLogix programming would look like something out of NASA by comparison. So look closely at this. Second thing to check out is the available IO families and networks. Modicon has Modbus. AB has several others.

[Daryl 1]

Great replies as usual guys. The system that the Modicon kit will be used is a very low volume (3 or 4 items per day) production-style line which takes compacted waste and puts it through a complex procedure to pack it into steel drums. Downtime would be very significant, as I'm sure it is in most businesses, and the longer we're unable to 'produce' packages, the more significant it is. Unfortunately, I didn't have any input to the design process, and I'm sure it's been the case of the contractor being given a fixed budget then told to go get a system, and, as any contractor would consider, they've probably sought maximum profit by purchasing cheaper kit. The support issue for spares is very useful ammunition in having the kit changed if the opportunity remains. thanks... Daryl

[paulengr 44]

In this particular instance then a ControlLogix/CompactLogix may be overkill. It depends on the application as a whole but I'd take a very strong look at the Micrologix 1100 (lowest cost in the Micrologix line) or 1400 (slightly more expensive with more on board IO). You can get a Micrologix 1100 for under $500 new in the box. This unit is easily capable of basic functions and some analog (just have to add IO cards). Expandability is limited but it's meant for the "machine builder" market which is what it sounds like you are talking about. Machine builders are cost conscious and the big player is usually Omron. If your IO starts to exceed this platform significantly, then I'd recommend stepping up to a CompactLogix L2x or L3x. The L2x series has some on-board IO while the L3x series has none. The bigger L4x series gets you into an on-board motion controller. This saves on the cost of a system somewhat if you need motion control and performance is not particularly demanding. One you step into a CompactLogix series processor, you are automatically looking at $2000 or more by the time you add power supplies, IO, etc. As a whole, PLC's are very high reliability items. The best way to insure this as a whole is to fuse all outputs (inputs too if you can afford it). This sounds expensive but if you are buying DIN rail mount terminal strips (the modular 3mm or similar stuff that Phoenix Contact, etc., sells), the cost adder for fusing is almost inconsequential. I buy mine from Omega of all places because they stock it (this is a problem with Wago, Weidmuller, Phoenix Contact, and even Allen Bradley), and they have very competitive pricing. If you have outdoor connections, heavily invest in grounding and bonding, and consider using Joslyn surge arrestors on the inputs (now owned by TNB). Second, put in surge protection and harmonic protection as a minimum. Allen Bradley of all folks sells a very nice compact DIN rail mount surge arrestor/line filter combination unit. If you can afford to splurge on the power side I go for line conditioning which gives you brown-out ride through but not UPS's (batteries have low life spans). These three items (protection from crappy power, protection from dead shorts, and protection from lightning) comprehensively eliminate virtually all the ways I've ever seen a PLC fail. That leaves just water/dust infiltration and heat. For water/dust protection, I have found that Saginaw Control & Engineering makes boxes that are equivalent to or better than Hoffman at a significantly lower price for stainless NEMA 4X, NEMA 4, or NEMA 12 boxes. Once in a while if you have a deeply discounting vendor, Hoffman beats them on price but not often. A phone call and speaking to a real person often nets you a 10-15% discount on Saginaw's web pricing. If heat is your problem, I'm an ex-foundry engineer and I currently work around calciners quite a bit. I have a few tricks up my sleeve but suffice to say that North of 140 F, you are asking for trouble with a PLC although I have run a PLC-5 in an unavoidable situation as high as 165 F, but I don't recommend it as anything made out of PVC starts to fail in short order.

[Daryl 1]

Some great information there, and to be honest, I think it's information that could help me in more situations in the future than just this one. My PLC career is still in it's infancy and experienced information is always very useful as I'm not getting great opportunities yet for gaining hands on experience. Brilliant! thanks... Daryl