Most Important Features

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Thread Starter

Dean Norton

Just a general question regarding what you feel are the most important features in selecting an PLC and/or distributed I/O solution. If you are looking for a new solution to outfit your plant or some new machine, what are the top 5 features that would make you consider another vendor? Looking for your feedback. Thanks in advanced.
 
1. Support
2. Diversity
3. Completeness of tools
4. Reliability
5. Upgrade path

At the plant level and even with most machines the cost difference between manufactures is so minimal you want to look at it but you can not use it to base your decision on. Especially at the plant level. Basing decisions on price can cause you to hit the wall with the platforms limitations.
 
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Tugrul Guclu

I'm a newbie in PLC and having some problesm with selectiong one, Siemens or Schenider etc.

But what I look at in our project (tunnel automation)
PLCs
-must support redundancy
-networking
-fiber optic connection
-enough number of digital and analog I/O
-failsafe working
 
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Lynn at Alist

My view is most PLC and I/O modules do what they need to do.

Although I now work mainly in Ethernet/Serial data comms I started doing integration work. So my list is a bit system-oriented - if I were investing in a large capital upgrade I'd want the most future-friendly equipment. I'd assume I'm not sure what I'll need 2 years from now, so I'd avoid things which are "perfect" today as-is but may not be what i need in a few years.

1) protocol: How many 3rd party vendors support? I'd say a minimum of 3 would be required before I'd consider a product worth investing in. Not that you need to buy 3 - it's just that IF/WHEN you find problems with one (or the main vendor) you have "options".

2) open protocol spec: I won't buy anything "general" if the vendor doesn't publish the protocol spec. The days of secret/closed protocols are over, yet a few companies don't quite get it. Avoid them & help the market evolve!

3) media diversity: How easy is it to communicate over wireless? Fiber Optics? Ethernet? Cellular modem? Again I'd want future flexibility. Perhaps today you only need that 1 Coax cable, but what about next year? Who wants to pay $5000 for a pair of Coax to Fiber Optics converters because only 1 or 2 companies makes them?

4) termination style: I don't have a preference here, but there are various options: the lug-to-screw, wire-in-compression-cage, stripless, terminals-on-product or terminals-by-ribboncable, etc. What fits your style of engineering & technicians work habits? What works in a wafer-fab may not work in an iron foundry or oil platform.

5) local support: some people like web shopping & email support - up to you. But I tend to like someone local I can "borrow" stuff from to test things etc. Worst case be able to go into their lab and play. Brand "A" may be technically better than Brand "B", but if you'll find it easier to get your job done with Brand "B" because of local help, I'd vote for Brand "B".

best regards - LynnL www.digi.com, Snr Prin Engineer for email address see: http://www.iatips.com/contact.html
 
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William Sturm

PLC: on-line program changes.

Many processes are too expensive to shut down for a simple logic change.

I/O: easy to use terminals for connecting field
devices.

Too often with small PLC's, people wire to separate terminal blocks, which is a huge waste of time.
 
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Ranjit Nambiar

1) Open scalable system
2) No Proprietary protocols , it should be platfrom dependent and not protocol dependent
3)communication to the devices / instruments that are already existing in the plant (in Hardware and software)
4)Support online 24hrs
5)Maximum Uptime .

The fundamental problem with PLCs are that one does not communicate to the other seamlessly ,
Wheras platforms like PXI is a open platform and
with LabVIEW and DSC Toolkit you can even communicate to PLCs from the PXI , not only PLC even GPIB Instruments , RS 232 , USB , Firewire ,and any other standard commication .

LabVIEW with PXI is the ideal choice also because of the backplane features in PXI like local bus between modules , star trigger , 10Mhz Clock , trigger bus , for precise synchronization and timing .

National Instruments also provides RT on the PXI platfrom where you can download a code from a desktop machine and your PXI system cause it is running on RTOS only executes your downloaded code for maximum determinism .

feel free to contact me ([email protected] )for any further technical details you may require on this .

Ranjit Nambiar
 
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Starride,

Thanks for you input. Just a couple of questions though:

1. Cost between manufacturers is minimal... There is a real-life example that I can share where PLC Brand A (probably most popular PLC in the marketplace - care to guess) - cost approx $5,000 (list) for CPU, Ethernet Card, Power Suppy, and 8 slot rack. This is without software or additional I/O. And the same package from brand W PLC for less than $1,000 (list)with a full IEC 61131-3 software suite.

2. Support.. what are your thoughts here? Free support, 24/7 support, local support, other.
 
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In no particular order:

1. Cost per I/O point.

2. Bus bandwidth, as well as suitability of bus characteristics and
topology to my application.

3. Physical size (panel area and total volume per point) as well as
dimensions of typical assembled rack.

4. Object oriented paradigm, ala AB Control Logix or others.

5. Linux hosted programming tools.

6. Sometimes, compatibility with specific HMI hardware, or availability of third party (i.e. Kepware) OPC drivers.


--
Steve Myres, PE
Automation Solutions
(480) 813-1145
 
The reply from starride is very concise. The only things I would add would be look long and hard at networking of PLCs as some systems are not very good. Generally I prefer a proprietary network solution that is token ring based.
You can make or lose a lot of money with poor programming software. I always look for function key support in preference to getting RSI from a mouse with the "drop and drag" system. It is also very slow.
 
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Thanks for all your input. I would like to invite others to contribute and keep this post alive. We could even take the opposite of this question and answer the question - which features that many control vendors tout/stress are not important buying features?
 
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Steve Myres, PE

On December 27, 2003, Dean Norton wrote:
> 1. Cost between manufacturers is minimal... There is a real-life example that I can share where PLC Brand A (probably most popular PLC in the marketplace - care to guess) - cost approx $5,000 (list) for CPU, Ethernet Card, Power Suppy, and 8 slot rack. This is without software or additional I/O. And the same package from brand W PLC for less than $1,000 (list)with a full IEC 61131-3 software suite. <

Tell us a little more about brand "W". Which languages from IEC 61131-3 are supported? How is the selection of I/O modules, electromechanical ruggedness, general fit and finish? How long has the product been available for purchase? Are there some kind of reasonable number of units in service for sufficient time to trust it for reliability?

> 2. Support.. what are your thoughts here? Free support, 24/7 support, local support, other. <

I don't often need tech support, but when I need it I need it. I think some of the major manufacturers stub their toe on this one. I would like to see more techs available, so that a higher percentage of support calls can be taken on the spot rather than require a call back. A little higher standard for the techs would be good too, and/or an easier method to escalate the call to the next higher level tech. I've actually spoken with techs that knew less about certain aspect of their own product than I did. Extended hours would be nice as well, as it's a pain to be starting up a machine at 9:00 pm and not have support available, or at cost when it's free during the day. Tech notes available for download on the net have alleviated this problem to some degree.
 
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On December 29, 2003, Steve Myres, PE wrote:
> Tell us more about brand "W"..
Q:Which IEC 61131 languages?

A: ALL - Function Block Diagram, Instruction List, Lader Diagram, Structured Text and SequentialFunction Chart - at $600.00 site liscense!

Q: How is the selection of I/O modules, electromechanical ruggedness, general fit and finish?

A: Selection is great - granular 1, 2, 4, or 8 channel modules and over 100 types - digital, analog, special function. Reggedness is good. Fit and finish are great - small compact design very functional.

Q: How long has it been available and what about applications?

A: The PLC has been around for about 3.5 years. However the I/O has been around for about 10 years. I/O and PLC look the same - same housing and use same I/O modules.

There are plenty of references if you are intersted - just email me at [email protected] or call me at 1-800-647-7245.
 
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