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Looking for Opinions on different PLCs

Looking for Opinions on different PLCs

Looking for Opinions on different PLCs

I only have experience with Mitsubishi and Allen Bradly PLCs, so I could use some advise as to what would be a good PLC to go with on my next project.  I am replacing an old Texas Instruments (Siemens)PLC which is stricly used for monitoring purposes in a chemical plant... Inputs are mainly RTDs, thermocouples, some discrete alarm points, and 4-20mA from pressure transducers...  So I need 250 - 300 points, lots of rack space.  Since the PLC is not used for control, I can get away with using a fairly simple (featureless) but robust PLC.  

The only other requirement is that it be compatable with iFIX SCADA software... or have a equivalent manufacturers  software package.  I have a quote on a Siemens replacement (500 Series) but the cost is fairly steep.  I am looking for a cheaper PLC which will do what I want.  Eg. maybe OMRON, AB, ABB, IDEC, etc...  Anyone have opinions on what is cheap and good???  Thanks.  This forum is a very helpful tool for me, a newbie to the Plant Engineering game!

RE: Looking for Opinions on different PLCs

     The most inexpensive PLC that I know of is Koyo. The web address is www.automationdirect.com
     If you are only using it for I/O, perhaps you can go a different route. Several companies offer stand alone I/O modules which can be scanned by your iFIX system. I don't have their anmes off-hand, but if you like I can try to find them.

RE: Looking for Opinions on different PLCs

One option, which djs mentioned about inexpensive plc's. I recently helped design a system with a guy who was doing something very similar.

iFIX is DDE/OPC compliant. You run KEPdirect (ethernet based OPC server) the iFIX package becomes the client. This allows all of automationdirect's (Koyo) i/o to be used as dumb i/o. No processor required, so the speed is increased. And since this is ethernet, the amount of i/o is almost unlimited.

Look up KEPdirect at the website:



RE: Looking for Opinions on different PLCs

I would take a look at the DL240 from Automation Direct and look at Lookout Direct which is a dandy Scada system. I think you can use up to 255 points with a 240, if not, use a DL250. Lookout is really cool and I discovered it while I was burning a computer with Blunderware on it. With a DL240
$158, 9-slot rack $130, I/O 16input $72 and around $700 for Lookout 100 point, you should be done for about $1100. Just a thought, hope it helps.

RE: Looking for Opinions on different PLCs

For a breathing air project I'm working on, I needed two small PLC's to control the air purifiers. I checked with AB about the micro (around $400). It would still have to be programmed in ladder logic. I was hoping to find a small PLC that I could program on my PC in my office using logic blocks.
I found just what I was looking for. I purchased two Millenium II (by Crouzet). A controller with 8 DI's & 4 DO's was $123. The complete kit with controller, software and com cable was $198.
They have controllers with more I/O also. The controllers can communicate to each other and also by modbus.
The programming is great (and fun). Just point, drag and drop blocks or wires. It's a lot like Triconex Trident programming.
You can test and watch the program run on the PC or on line with the PLC. These little PLC's are great! check them out.
www.crouzet.com. Drop a reply back to let me know what you think after you check these out.

RE: Looking for Opinions on different PLCs

Crouzet really has something in the Millenium. I use this too and my mechanics and technicians love it. Plus, the software is free.

RE: Looking for Opinions on different PLCs

Stock Solvera Forry, Cleveland, Ohio has some PLCs that are primarily used for Precipitator Controls.  Minue driven, no programming experience required, very robust (snow, ice, heat, sulfur, flyash) and relatively inexpensive compared to Westinghouse, Bailey, Siemens.

However, the Forry does cost more than the Crouzet.  I gotta check that out myself.  Anyone else tried the Crouzet?

RE: Looking for Opinions on different PLCs

Stick with something you know. Eliminate the learning curve. What about either a MicroLogix 1500 with a couple of CompactLogix expansion cards, or a simple CompactLogix system.

Since you're familiar with AB, you probably already know the software. The price difference in the hardware will be offset by the lack of a learning curve.

RE: Looking for Opinions on different PLCs


I agree with arte and skills. We are an OEM company and 1 year ago developed a new product that needed to be as inexpensive in design as possible and reliable. Our higher end design incorporated an Omron CPM 40 with expander modules. I found the Millenium unit, and it fit our requirements very well in both cost and reliability. Our end product operates in an enclosure, outdoors, from Louisiana to Canada, (temp.extremes) It is extremely easy to program even for non PLC types.

RE: Looking for Opinions on different PLCs

I was just wonderin if these AB fans are getting paid commission for turning every inquiry into an Allen Bradley ad or promotion?

RE: Looking for Opinions on different PLCs

How about Profibus remote I/O. If your not doing any control and you just want to monitor I/O , you can use remote I/O to bring in your information and use just about any HMI you want with a Profibus PCI card. I'm sure you were quoted the Siemens 505 solution so you can use your existing I/O with a new 545-1106. This solution shouldn't be that expensive unless you were quoted new modules with the system. The logic is almost a straight conversion from the old PM550 or 5TI sequencers and you can upgrade your I/O slowly as it fails so the total price doesn't impact you right away. This would also offer the least amount of downtime with your existing system.

RE: Looking for Opinions on different PLCs

I have happily used Koyo for several years in several applications. While very good off the shelf software is available, the flexibility of creating the control interface in Visual Basic allows each control/monitor point to stand alone, as it were, without bringing the rest of the system down during a catastrophic failure of a field device or communication link. One may, alternatively, produce one program to handle all control points, but I've found the independent avenue quicker to deploy and tweak. A big benefit to writing the control program yourself is that what you wish to be done is created quickly and tuned for each application as opposed to having to select the best fit from that which is offered in a package and subsequently settling for the results. Logging may be addressed in a case by case fashion to collective and/or independent files with individual or shared time periods. As ctolbert mentioned earlier, all interface with the PLC can be performed over an ethernet connection or several other protocols from RS-232 on up. The time to create the interface is money well spent when the burden of control is handled by the computer running the program and the PLC, freed of overhead tasks, rapidly executes I/O communications requests.

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