# Which is the Best Redundant PLC???

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#### Ashish Atre

We are looking for a performance/feature based comparative evaluation of redundant PLC systems offered by following manufacturers

1. Allen-Bradley ( Control Logic )
2. GE Fanuc
3. Siemens - 115 H , S7-400H + PCS7

Can somebody help me out with this one.

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#### Amora Fibrianto

1. i don't think AB controllogix has redundancy yet...except software switching ...... but their PLC5 redundancy (controlnet based) might be the good one...... 2. GE-FANUC, has a Genius Modular Redundancy that support TMR (they said...)....their documentation quite good.......check www.gefanuc.com

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#### Berthold Ruhbach

If you are looking for redundancy in order to increase availability and at the same time have safety in mind, you should look at HIMA H51q-HRS. On processor level it is a 2oo4 configuration with all processors running in parallel - no hot stand by. On I/O level you can have redund or single cards. Check out the web site at www.hima.com

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#### ind

Why dont you try honeywell's 620-35 redundant plc's. In case you do not require function blocks and floating point arithmetic, then honeywell is very reliable. But be sure to find out if they plan to discontinue some of the products after being taken over by GE.

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#### tony xie

S7-400H + is the best one for net and web job! tony xie my e-mail: [email protected] shelly industrial automation engineering ltd.P.R.China

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#### Troy D. Scott

Allen Bradley makes the best redundant PLC but, what is the application, is it going to be a "hot swap" with data table transfer???

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#### Burda, Jason M.

I have worked with all three for the past 5 years....although not much with 1 and 3 since 1997. As far as I can tell the performance is all about the same. However, my opinion is that A.B. and GE are the easiest from a software side. Siemens uses three modes of programming PLC's...ladder logic, control systems flowcharts, and state-ment list....which is very difficult to understand and use. If you have no knowledge of PLC's and want to start using a simple system for a simple app....I would go with AB or GE...

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#### CK

Both Omron and Modicon also have redundant PLCs. Maybe you'd want to evaluate those too?

CK

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#### Herry E. Tamba

Dear Ashish Atre, In regard to choose the best redundancy system, they are have their own advantages and disadvantages. You can told them to submit their proposal to you, so you know what is they are advantages and disadvantages both in technical and commercial/ price. But to my knowledge, if you are going to buy complete the PLC system with the redundancy, you better use PCS7, cause it is very user friendly for programming, but you have to choose their best I/o, cause they have some I/O with different characteristic, used their catalog. Hope this info can helping you. Regards, Herry Automation & Control Dept. [email protected]

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#### John Beck

Some questions to ask about the "redundancy" feature of the PLC: 1. Are there single points of failure in the system which will cause loss of control or view of the process should a failure occur? 2. Can you remove and replace a failed component without affecting the control of the process? 3. If you can accomplish item 2, how much effort is involved to bring the replacement module in synch with the operating module? And what safeguards are in place to prevent different versions of the programming from being loaded? Additional questions to ask about the process to be controlled: 1. Are there safety hazards/environmental concerns involved with a loss of control of the process brought about by a failure of the PLC or the removal and replacement of a failed module? 2. Even if there are no safety/environmental problems, what is the cost in lost production and slopped material of a shutdown caused by a failure? Most PLC vendors which provide "redundant" systems only make the processor and perhaps the power supplies redundant, but, for instance, with AB PLC5 redundancy, as with the Honeywell Logic Manager, do not provide for truly redundant I/O. The I/O is the part of the system that faces the "real world" and is subjected to the heaviest abuse from power spikes and other field problems. I/O redundancy is expensive, and the cost must be compared to the cost of an outage. In our facility, we have a mix of non-redundant PLC's, Redundant processors with common I/O, and Triple Mode Redundant systems. We have experienced several failures of I/O cards due to blown fuses, lightning strikes, field wiring problems, but only one processor failure in about 10 years operating. My main concern with the non-redundant systems is having to tell the Facility Manager that it will require $250,000 or more in lost production to safely change our a$2.00 fuse. My vote is for a TMR system such as Triconex, if you can justify the cost of the equipemnt. Contact me directly if you wish to explore these lines of thought more fully. The above are my personal thoughts on the subject. John Beck Pennzoil QuakerState Shreveport, LA

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#### Brian Kukulski

I have used A/B and Modicon redundant PLC's and the easiest to implement BY FAR is the Modicon.

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#### Miller, Chuck (IndSys, GEFanuc, NA)

You will probably find that the best redundancy options are those that are off the shelf, factory supported and third party tested. Some manufacturers offer a range of solutions meeting the requirements of hot standby CPU to fully triple redundant voted systems. Depending on your application requirements these systems can be configured with a wide variety of options and I/O technologies. You can contact 1-800-GE-FANUC or www.gefanuc.com for additional information. Chuck Miller GE Fanuc Critical Control Business Leader (281) 495-0333 Fax: (281) 495-0370 email: [email protected]

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#### Norman Girigorie

I agree with Mr. John Beck. Reading his reply I believe that he is picturing the Triconex PLC as a Safety Oriented System, which it truly is.
The Triconex offers answers to all the questions summed up by him. The Triconex does more than an internal voting (2oo3)of the same input and output signal, but the I/O is not redundant.Hot swap and internal switching of standby modules every hour or so are nice features of it.
If the application for the PLC lies in production/batch processing/ process controlling I would go for for instance the Allen Bradley PLC5 family, especially for the nice instruction sets that comes with that will lend it very good for above mentioned applications.
Siemens comes very close to it as regards to double redundancy and it is one system that I can have a further look at, offers truly I/O redundancy.
It seems that the other PLC manufacturers in the business of the general PLC for one reason or another have not taken up this issue.
Norman Girigorie. Curacao. Netherlands Antilles.

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#### Stale Furuberg

The best redundancy for PLCs is offered by Metso.
Metso's Damatic system outperforms the mentioned PLCs by far. I see that the Damatic system is not on your evaluation list, but it should be considered if redundancy is what you are looking for. Main advantage is that main/reserve process controllers can be located in different areas, thus protecting it from physical damage/fire or short circuits, etc. inside cabinet. When it comes to redundancy, there are also many other important topics, like network layout, power supply, etc. Easy programming as mentioned here, doesn't really have anything to do with redundancy... If it is a large installation, Damatic scales very well and software is designed from ground up to handle very large number of signals ie: 20K-30K. This is very difficult to handle with systems like the S7, which scales badly. For a correct evaluation, more details are needed regarding your requirements.