Hi All,

I am curious if others have had problems with Micrologix PLCs being really touchy about AC power. I had a rash of ML failures a while back with "loss of retentive data" failures. That time around I replaced 4 PLCs and they were covered under a recall of ML1000s for bad memory. OK, PLCs are not supposed to fail, but anyone can have a supplier problem. Lately, I have had another rash of failures and AB does not want to cover them or talk about warranty. Bzzzzt, wrong answer. So I have been replacing them with Mitsubishi PLCs until I can pick another brick, so to speak. I get a little cranky after paying the AB premium and getting shook down for support and then they won't stand behind their product. I looked around on the web and it seems others have had this problem. I have a ML1100 that predictably faults on power up after a power outage. So I did a test. I have an assortment of other vendor's brick PLCs that I have either salvaged or replaced for one reason or another. Install a line cord, plug into an outlet. Repeat until you are satisfied that AB has a problem. Is anyone else seeing this?

So, I have been looking at bricks lately. AD is fine except the ones that have sensor power built in aren't competitive on price. The Mitsubishis are OK but are kinda spendy and local support and availability isn't that great. So I called the other big electrical house locally and they carry Modicon/Telemecanique. I wanted to buy a Twido to play with, but they loaned me one and sent the _free_ software with it. The Twido brick is another brick, and the software is closer to the Mitsubishi and Koyo stuff than to RSLogix. Of course it's thousands of dollars less. But, I like what I see on the Open front. It uses Modbus and Modbus/TCP of course, and their whole attitude just seems less hyper proprietary. What I don't understand is why they are such a rarity in my part of the world. Before I commit, I'd like to hear a few opinions from the most opinionated bunch of guys I know. :^)

Regards

cww

 

I am partial to Automation Direct, having had great luck with them over the years. Have you looked at EZAutomation? I have no experience with their PLCs but their MMI products are good. The PLCs look decent, have Modbus comms, lots of I/O, and are priced reasonably.

 

I normally prefer to use transistor outputs instead of relays, as relays don't seem to last very long on newer model PLCs. I also prefer to power the PLC, sensors, and outputs off a single DC power supply (DC/DC/DC), so I don't worry about the on-board supply. Using a DC supply probably adds a lot of filtering and isolation from the AC lines which may help reliability. The capabilities (or presence) of the on-board sensor power supply would not be an important criteria to me.

I've used the Siemens S7-200 series quite a bit, and not had any real problems with the hardware. The S7-200 series closely resembles a Japanese style PLC (Koyo, Mitsubishi, etc.) but with IEC addressing. It has no relationship to the S7-300/400 (or S5). The big problem with the S7-200 (or S7 300/400) is that Siemens seems to have a phobia of working with anything non-Siemens except on very limited terms. They don't "play well with other children". If that's a problem for you (and I suspect it is), then I wouldn't recommend their product line.

Given what you have said, I suspect that Modbus/TCP capability is important to you, as it seems to be the only open vendor independent Ethernet based protocol available on PLCs. Omron has a protocol of their own which they do document in detail. It is useful if you want to have a PC talk to one of their PLCs, but it doesn't seem to be used by anyone else though.

I don't know the Twido's communications capabilities very well, but I would suggest looking carefully at how the Modbus/TCP actually integrates to the Twido PLCs. On many small PLCs the communications between add-on modules and the CPU is very slow, which means you can't necessarily do things with it that you would like.

 

I like the Automation Direct stuff too. I wish they had a low end with 120V power and sensor power built in. That's handy for add ons and the
small ad hoc projects that come up. I use their PBs and switches a lot since AB (and others) went to the all plastic junk that drops it's contact blocks to the bottom of the enclosure.

Regards

cww

 

Boy, no kidding. You would think they were lepers, or afraid everyone else was a leper or something. My experience is that their "official" position is that if there's not a Siemens device that can do it, then it's outside the bounds of reality and best left to the science fiction writers to talk about. Never mind that Endress+Hauser might have one on the shelf that they can ship today. And if you do try to get outside the bounds, their official position is that it won't work, even if you get to do so.

I have more fun at the dentist.

Michael

--
Michael Batchelor

www.IndustrialInformatics.com

Industrial Informatics, Inc.
3281 Associate Dr.
N. Charleston, SC 29418

843-329-0342 x111 Voice
843-412-2692 Cell
843-329-0343 FAX

 

Every time I need to work with Siemens I get the feeling they think that I should be begging them to allow me to use their stuff and promising to obey. They must have some mystique that I am missing, because they seem to have a lot of fans in Europe.

Regards
cww

 

Yes, I have had two MicroLogix 1000 units to fail within the past 6 months. The first one I should have returned on warranty but did not bother with the hassle, as it was a new installation and only ran for a couple of weeks. Both units failed from error (S:1/13 fatal internal hardware error). It took a few attempts to even establish communications to extract the fault.

I agree with holding higher expiations on AB products as you do pay a premium for using their products. Both failed units were also manufactured in Korea SERIES E FRN1.0, if this has any relevance. The second unit failed on a similar application. I still use the units in new installations with limited confidence. Our “Standard” is AB so I have been using the new 1100 series with good results thus far.

In the past I have had great results with Automation Direct and Omron on small applications, and when given the choice of vendor selection especially on a limited budget A-D is great. If performance and longevity is desired Omron is solid.

WM

 

The interesting part is that I replaced the AB with a Mitsubishi in the machine where I have replaced the AB twice for this problem. So far, I have no faults. I too have used an 1100 for its Ethernet capability. That one only starts cleanly about half the time when we have a power outage. It will usually start with another power cycle. I'm still shopping. I've informed management that AB is not an option until they get their act together. At least in the MicroLogix line. I haven't had this problem with the SLCs, but they aren't economic at low point counts. I suspected the power, but we have many brands of PLCs around and none of them give me this kind of grief.

Regards

cww

 

In reply to Curt Wuollet: I have a suggestion that doesn't directly address your questions, but might help with one of your current problems. With regards to the AB 1100 that doesn't always start on power up, I had a similar problem with a different PLC (Siemens S5-115). What we ended up doing was to install a small on-delay timing relay in the AC power to the PLC to delay the PLC starting up until several seconds after AC power returned to the machine. This seemed to cure the symptoms completely.

The problem seemed to be related to the AC voltage recovering slowly or fluctuating during start up. Some PLCs have had design problems with their power circuits where they have uncertain behaviour when the voltage is in the "grey zone" between "on" and "off" (in our case, the PLC would lose its program). This problem seems to be worse in some machines than in others (possibly because of various capacitive or inductive loads also powering up). It isn't just cheap PLCs that have had this problem. The S5-115U that I mentioned above was a particularly expensive CPU.

This isn't something that you should normally have to do, so that doesn't excuse AB from having a problem in this instance.