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For my work, we have to control a 50 kW power-station and coordinate different components, including some safety-critical sensors, reactions, etc.

I am considering to use a PLC as a master controller. We have about

  • 30-50 digital I/O (with 10-15 special safety elements)
  • 10-20 analog I/O

The details are not yet completely clear. Nevertheless I was looking for a PLC solution for it, and I don't have prior experience with PLCs myself (but I do with microcontrollers). At first, I looked into the Wago 750/753 Series, which offer some modularity. But then, people often recommend the Siemens S7 PLCs.

This time, it is to build a prototype, but we might expect 5-40 products delivered if everything runs fine.

What is the experience with the Wago PLCs, and how do they compare with the Siemens? And what would an alternative be?

  • 2
    I would suggest that if you have no experience with PLCs that you seek an expert. Designing, spec'ing, and implementing safety critical systems with no background in the technology is not even remotely a good idea. – enderland Sep 11 '15 at 15:22
  • Enderland has it right. Good question, bad idea. – ArtOfCode Sep 11 '15 at 15:38
  • @enderland, my post might be misleading in this respect, but I am not in charge of the system design, neither the electrotech part. Just the programming. We don't have PLC expert in our company, as we have a MCU-based solution for most of our applications. Nevertheless we have some who have some experience programming it. We can find some allright, I just wanted to see if someone had any suggestion about different PLCs. – bilbo_pingouin Sep 11 '15 at 19:12
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You could do worse than look at the compactrio.

http://www.ni.com/compactrio/

NI has invested thousands of person-years in this proven, validated, certified, and rugged hardware and software platform that tens of thousands of customers have deployed. With industry certifications and wide-temperature range, thermal, EMC/ESD, and shock and vibration testing, the rugged CompactRIO platform helps you to deploy reliable systems that last. Plus, benefit from a wide-range of services, outstanding customer support, and the industry’s most extensive ecosystem.

NI are usually very helful. NI hardware was used in the large hadron collider so I expect it would suit your application.

  • We did that. Indeed the NI elements are very good... but a bit too good for us. And in particular too expensive. But for an application where measurement precision is crucial, those are great modules. – bilbo_pingouin Apr 18 '16 at 19:11
  • @bilbo_pingouin Yes, misread your question. 50kW is not a lot, still neither is £1035 ,(sine.ni.com/nips/cds/view/p/lang/en/nid/213089). Did you look at compact RIO? – SeanJ Apr 18 '16 at 22:10
  • We did, but including the IOs we wanted, the price was much above the concurrence. Which is explained by a higher precision. – bilbo_pingouin Apr 18 '16 at 22:18
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If someone stumbled on this question, they might be interested to know the result.

So we contacted various companies, and at the end we compared the products from the following companies:

  • Waco,
  • Jetter,
  • NI (Compact),
  • Siemens.

Our choice went for the Siemens products. So we acquired a S7-1512SP F-1PN, which had F-DI/F-DQ modules which allowed us to work with sensors in an Ex-Zone environment.

The deciding criteria for us were: Ex-Zone, CAN communication and price.


Much later, someone recommended Unitronics as alternative, but we haven't tested it for reasons beyond the scope of this question.

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