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Difference between Triconex PLC & Other PLC
We are using Triconex PLC in our Plant Emergency Shutdown Systems. As we know Triconex is Fault Tolerant and a very rugged PLC but costlier as compared to other make PLCs
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We are using Triconex PLC in our Plant Emergency Shutdown Systems. As we know Triconex is Fault Tolerant and a very rugged PLC but costlier as compared to other make PLCs

Does that mean that if Money is not adeciding Factor while
purchasing PLC one should always opt for Triconex PLCs ? Is it the best PLC available ??

Why is it that PLCs of other make such as Modicon, Siemens, Allen Bradley are generally not used in Emergency Shutdown System Applications ?

What are the disadvantages of Triconex PLC ?
I suppose one disadvantage is the diagnostics in Triconex PLC is not good as compared to say Modicon......

Kindly guide



By steve young on 1 August, 2002 - 9:57 am

You cannot simply say that one plc is better than anouther. It all depends on the system requirements such as communication, degree of fault tolerance, math capability, Remote I/O needs, programming ease, local support, product certifications/listings, cost, backwards support of legacy products, etc.

I think that most would agree that Triconics makes the most fault tolerant system, but you would most likely get an arguement from many if you were to claim that it is the best at any of the other items list above, or many others not listed.

Ultimately, Triconics, Modicon, Allen-Bradley, Seimens, and the other larger manufactures all offer good products, and selecting one can be a difficult task but should be based on how well the product fits your specific needs.

Keep in mind that triconics probably has the most fault tolerant system, but if you are not going to provide redundant power sources, etc. then you just wasted your money for something you did not need! Evaluate the entire solution, and choose the appropriate solution and products!


I've just joined this forum and this my first take on the topic. Vendors use different architectures to arrive at a certain measurable risk reduction factor. If a Honeywell QMR system is SIL3 and a Triconex TMR system is also SIL3 then should we be worrying about the difference in architectures? Or there's more to it than mere certification?


By Leonard Hamilton on 5 August, 2002 - 12:48 am

Each Safety Shutdown system requires a level of Risk Reduction which corresponds to the hazard involved. After a Safety Integrity Level is determined for a given situation, equipment and procdures must be chosen that will yield the required reliability. Since Triconex, Honeywell FSC, and possibly APACS and GE GMR, are designed to be fail safe, they will usually meet the requirements.
Nearly every PLC manufacturer's products are so durable they become obsolescent before they need to be replaced. Fail Safe PLCs are not always needed but may used because they connect to a Honeywell DCS, or because a good Reliability study is not cheap, or even to make a show of good faith. If you will need to make decisions about safety systems you should learn about Reliability and Safety Codes such as NFPA. Then you will be more able to discern between mere advertising and useful information.
Good Luck

There is a difference between Fail Safe and Multi-Fault Tolerant. In general, any of the SIS offer very good diagnostics. The reason that you do not ALWAY chose an SIS like Triconex, Honeywell or Rockwell ICSTriplex is that it is simply not necessary. There is a reason that the Allen-Bradley/Rockwell Automation Logix Family and Siemens S7 family dominate the PLC global market. They are sufficient for the application they are installed in. They are easy to use, they are very flexible, people are trained on how to use them, they are well supported (depending on the region in the world) and the facilities have inventory for their plant.

By the way Rockwell/Allen-Bradley offers SIL3 fail safe controllers (GuardLogix and CompactGuardLogix) that program with the same software as the rest of their Logix family and they offer two TMR SIL3 Fault Tolerant solutions (ICSTriplex - AAdvance and ICSTriplex - Trusted). It is totally dependent on the application and Safety Integrity Level required, not to mention that if de-energized state would create an unsafe situation, fault tolerance is needed.

By Johnny Mnemonic on 9 August, 2002 - 12:18 pm

Well, one thing that was not mentioned is the fact that triconex has triplicated Processors,
I\O, and power supplies. Something that A/b or modicon doesn't have. Triplex is another triplicated system (which I prefer). And
thats why you have a Triconex on your safety

Johnny Mnemonic

By Kerry Schrank on 21 August, 2002 - 2:24 pm

GE Fanuc also has TMR (triple modular redundancy) in a PLC configuration.

Kerry L. Schrank

Only if your safety system requires a triplicated processor, I/O, power supply, etc. If your safety system does not require this then why would you punish yourself with a Triconex system, which would then require staffing triconex programming engineers to come out and engineer your safety system. A lot of people see the up front glamour of these TMR systems, but what they don't see is the engineering required to program these system, which is a tremendous cost to be added when you have to hire on a Triconex engineer for $200-300/hour.


One more note:

Mention of Fault tolerance in the original mail:

Though conventionally, we use the term fault tolerant for redundant systems, fault tolerance and redundancy are two different things.

Fault tolerance involves your engineering too and is a limited definition, where u have to specify the faults that can be tolerated and to what extent this fault will be tolerated. Viz voltage upto say 500 KV and so on.

Redundant systems are fault tolerant to the extent of internal system failures. If your engineering is not upto the mark, then your total system may not be fault tolerant. And even TMR may not help you. While with good engineering even a simple PLC may function properly.


By Bob Peterson on 23 August, 2002 - 2:17 pm

In the real world, these terms are used much as the term "open" is. They mean whatever the marketing wizard that said it thinks it means. I doubt that you could get any group of engineers to agree what these terms mean other then the term redundant obviously means that there are multiple devices capable of performing a specific function.


Engineering is not upto the mark -
Good Engineering -
I'm sorry, I feel these two statements are misleading.

I got what you mean. But with in the context PLC's capability and performance should be measurable.

That's why they (Triconex) are certified for the safety integrity levels against the required.

In case of your simple PLC their characteristics or their performance are unpredictable and we can not even force it to behave as we required.

These are the fundamental differences.

By Asif Khokher on 21 August, 2002 - 10:47 am


Well! I disagree with you that that TRICONEX has got less diagnostic capabilities than othe PLCs i.e MODICON. Infact, it is the diagnostic also
which makes it SIL3 suitable hardware. SIL is Safety Integrity Level, which is specified for a plant before the develpoment of Safety System
Specifications. AB and MODICON's no PLC is SIL3 certified. TRICONEX is TUV certified for SIL ratings.

It is not the MONEY which decides, it is the INTEGRITY and AVAILABILITY reqiured which defines the specifications. One thing more; If TRICONEX is
not used in a recommended architecture than YES it is waistage of Money upto some limit.

Asif Khokher

By Manikandan on 24 March, 2007 - 9:32 am


ProSafe-RS safety system from YOKOGAWA is TUV Approved and it has more system avaliablty,and much more diagnostics then Triconex.

Triconex is voting system with 3CPU and 3 I/O.
if any one I/O fails with this three one whole leg will fail,
if u see clearly Triconex TMR architecture
voter is presented in output ckt

just think
all three are in one module what is the PFD of that module and common couse error of the ckt.

i am not blaming that system. TMR was good in past days with old technologies.

but nowadays techologiies are improved,
but Triconex is not improving their design.

u cant say which is best PLC in market, based on application only they are different for each other

some of other ESD system avaliable in market
with SIL3 TUV certification

Yokogawa is supplying ESD system with *Pair and spare architecture*

ABB and ICS Triplex supplying ESD system with *same TMR architecture*

AB is 1oo2D
Honeywell and HIMA is QMR.


I have used many PLCs and many safety PLCs (SIS) in the past. None come close to Triconex Tricon, so far.

Even many engineers from major DCS company (Honeywell, Emerson, Yokogawa) would still agree that Triconex is still the easiest and the most robust safety PLC in the market.

James T

By steve burch on 9 May, 2007 - 11:04 pm


You really need to look at the RTP 2500 SIS.
TUV approved SIL 3
2600 years MTTFS
99.99999 availability
10 year simple proof test interval
Extensive Diagnostics
TMR with Controllers in the same chassis, or in separate chassis.
Full DCS Software Suite.

By W. Chadha on 23 July, 2008 - 11:28 pm

RTP 2500 system is the real next generation technology. We saw the demo done by the Indian subsidiary of RTP recently of RTP 2500 system and believe me the system technology is mind boggling. It has built in Proof Test software, unlimited online downloads, unlimited configuration changes, PFD average value is excellent, the HMI package called NetSuite software is a site license - meaning one time purchase by the end customer, unlimited tags, OPC, Historian, Archiving built in - all SIL certified, all inputs to be SOE time stamped, node processors can be separated at 12Kms distance and 25msec reaction time. Hats off to the inventor - a genius system unparalleled to date.

By Vitor Finkel CAP on 9 April, 2012 - 5:47 am

Sorry, but I strongly disagree. This seems to be just an "Infomercial" towards a specific product/vendor, and that is not supposed to be acceptable in this site.

Moderator's note: We do allow vendors to recommend their products in replies to messages. There is no evidence that this reply is by a Triconex employee

There are 3 worldwide known TMR vendors. It is not possible to assure one of them is better than the other 2. There are several SIS PLC logic technologies, such as TMR, complimentary processors, Hardware Diagnostic Channels, etc., And none of them absolutely better than the others.

> I have used many PLCs and many safety PLCs (SIS) in the past. None come close to Triconex Tricon, so far.

---- snip ----


Can you please let me know what are the factors involved in calculating the PFD factor for PLC systems?


You absolutely correct. Triplicated systems need to vote everything 2oo3 in order to meet the required PFD for SIL3. Smarter diagnostic based systems simply don't need to do this to meet SIL3. Your simply paying for hardware you don't need with TMR solutions. Check out the HIMAX system if you want to see where technology is currently up to.

Triconex ESD system practicaly proved popular system in oil/gas/petrochemical process industries.

Triconex hardware part its no issues as per used plants history like Exp (saudi aramco, Sabic, QGPC, ADNOC and etc). and software part also its use and friendly.

Simple network and Interfacing to other systems.

Doha- Qatar

ICS Triplex provide TMR ESD System Trusted, which is better in terms of technology over Triconex. Trusted is having design of fault tolerance through hardware. Fault can be contained and allow system to run.

Trusted is easy to configure and having strong diagnostic.


By Roy Matson on 25 July, 2008 - 12:00 am

I am not familiar with Triconex but I have used ICS Triplex, they may be great for safety shutdown but you would never use one for normal logic. A regular PLC like AB or Modicon is much easier to wire and has better engineering tools for normal logic.


By Claude Lovell on 27 January, 2010 - 8:01 pm

I have to differ with you on this one Roy. I am a turbomachinery consultant with Triconex and have done turbine controls on many different platforms in the past. The Tricon is both the most reliable I've used and it is also BY FAR the easiest to program and troubleshoot. Way far...

Triconex is not the newest or fastest design of PLC on the market...this is because we have a 15 year product lifecycle.... we hang on to what works and works well. But we are unmatched in reliability and longevity of our product.

Yes, TMR is expensive. However, my observation is that on a big project with lots of I/O and engineering (like a Gas Turbine, for example) the difference in hardware price can be as little as 20% of the entire project. On big projects where reliability is important TMR is well worth the premium.

I've visited sites where a Tricon system has accumulated years of neglect and had large numbers of point faults on multiple cards (from years of hard use) and the turbine was running great!

I've done many non ESD projects on this platform and can safely say it is a great platform for any control project that can benefit from reliable hardware.


It is obvious that you have not examined the voter circuit on a Tricon DO. The switches are Darlington pair transistors. The last time I checked, that's considered hardware. "Better in terms of technology" please justify your opinion with more information. Better how?

Hello Mr. Ravi,

It is not a fact that Triconex is the only product for safety applications like ESD & FGS. I used to use Triconex earlier but eventually we replaced all the Triconex systems with other Safety PLCs due to support issue, availability of spares and overall operating costs for maintaining Triconex PLC.

There are now good systems available from Siemens, GE Fanuc, Honeywell, ICS, HIMA in the market at more competitive rates meeting all the functional requirements for ESD and FGS applications as that of Triconex.

We have Honeywell's FSC in one refinery and we are very much satisfied with the performance and support we are getting from Honeywell for the same. In fact the engineering is very easy and we are doing the necessary changes ourselves in the plant. For new expansion we are commissioning Safety Manager for both ESD and FGS applications. We found it is further better than FSC in design and for maintenance.

So don't worry... You are now not dependent on only Triconex.


Triconex has been releasing new modules and supporting two TMR product lines, the Tricon and the Trident. They have a new Communicaitons module which supports Modbus TCP, Modbus Serial, and even embedded OPC (no external OPC server PC required). The Next generation TMR AI modules offer 14 bit resolution, while the next generation TMR DO offers 32 points which are point selectable with configurable open and short circuit thresholds for line monitoring. There are even newer hart solutions for the Tricon and Trident which do not require an external third party termination panel. They have several installations at Nuclear generating stations world wide...even on the reactors (1E Safety).

In my humble should take another look at TRICONEX. Don't beleive what the competition has been saying about Triconex is behind the times. DCS vendors have been offering their inferior safety systems practically for free for years. MAKE UP YOUR OWN MIND...

Dear RAVI,
Please don't forget that PLCs are made more like an empty pages of a book that a programmer or a designer would write on it according to his design of solving a certain tasks. This would mean that a PLC would just be as effective as the programmer. If we would start to compare PLC then more likely there would be a never ending battle of Brands since PLC manufacturers are mostly defending his grounds. As one says a good food recipe would not guarantee the taste of a finish dish but the one who cooks and taste test.

Talking about Fault Tolerant is a very broad issue. One thing is that there are what we call External and Internal Faults. There are also what we call Regenerative Faults and infectious faults. Now designing a fault tolerant system would not lies only on the PLC but you should also look into its auxilliary systems like the power supply, or the Transient protection or the EMI protection and etc. ITs better to look for a good Engineer who can design this protection system than looking for a better PLC.


> RAVI asks about reliability of triplicated PLCs.

The fact is that Triplicating PLCs gains little if you rely on single input signals.

We use triplicated input signals (one for each channel) and a fault diagnostic system, to achieve far higher reliability and fault tolerance than any other system. We control vital power for major banks, and also military installations. It IS possible to remove ALL single points of failure in the control system

Hey, how much does a TRICONEX PLC typically cost for use on a class 1E system?

By Claude Lovell on 27 January, 2010 - 8:15 pm

Wow, that is a really hard question to answer.

In general, you can expect to pay 2-3 times the non 1E price for the hardware. Probably 3-5 times as much for the engineering due to the huge extra burden of QC and such depending on the size of teh project. As someone who works on these projects I can tell you that vendors are not making a killing charging these higher prices... the administrative and regulatory challanges involved in such projects are very significant.

Dear Ravi,

I am also working on the Safety Systems. But what i found is, there are also other brands of PLC's which are less costly for eg. PRO-SAFE, which we can use for SIL1-SIL4. But mostly i will prefer for "Safety Manger (R131.5)". Latest release from Honeywell, its IEC61508 approved and also user friendly. Even for remote sites like Offshore we can remotely perform OLM in running plant. Its MTTF is about 55 years...
so what else you want...

More than 15000 IO's you can configure in single PLC.


Hi Yogesh, Ravi and others,

Have a look at RTP 3000 system ( I have seen the device and we have recently ordered it too. 3 year warranty, one time purchase of software tools, MTTF figure of more than 3000 years - something what every industry dreams of and is a reality with rtp. Have a look and possibly see the live demo from their team. Just wonderful and awesome.


By Troy Martel on 7 December, 2010 - 12:37 pm


How did the RTP 3000 perform for you? Do you recommend the product? I understand that RTP Corp only sells it and does not participate in applying the product, i.e. design, engineering, packaging, installation, etc. Are you happy with the integration firm?



Yes. We are extremely happy with RTP3000 SIS. Hardware is excellent - no qualms about it at all. The System Integrators are good in engineering and installation. Our engineers too did a lot of work to put the system in place. On the product front, nothing can beat RTP3000.


By john stempeck on 4 September, 2011 - 3:23 pm

Raghavan and Troy,

We are trying to understand how often the major vendors of PLC's make major changes to their systems. That is, what is the product life cycle of PLC's (or DCS)? Clearly they want them to last as long as possible due to software integration, etc., but technology seems to be moving at an accelerated pace.