Technical Q's

[controllers]

I know now all the business questions to ask when picking a plc line, but what are the technical questions I should be interested in.

Thanks,
Joe

 

[ICman]

Unless you have some overriding desire for something particular, you need answer only some basic questions:

1. Does the PLC do what you need/want it to?
2. Is it expandable? [This is a little tricky. You want to be able to add I/O (at least 20%), without having to buy a different processor, more racks, etc.]
3. Can you (or your technicians) program it? Is the language "common"?

There are several other questions, but most depend upon your particular needs:

4. What is the processor speed? [How fast can the PLC read a point, perform the logic, and change the output?]
5. How big is the footprint?
6. Where can the PLC be mounted? [i.e. hazardous area classification]
7. Direct wiring, or does it need a marshalling panel/terminal strip?
8. Availability of service, parts, or help?
9. What kind of communications are offered?
10. What is the security scheme?

... and there are more, but these are what I would look for. I'm sure others will fill in whatever I missed.

. . . Steve

 

[skills]

As with anything in this world, you must have an objective in order to enlist the aid of another thing or person. The PLC system generally possesses enough flexibility to cover most errors in application, but, does so at some hidden or unanticipated cost. Most plcs that I have used could generally to replace any others, the few differences being the paradigm of the application developers. The plcs are generally targeted to those who are reluctant to leave discrete logic or to those who would rather build a microcontroller SBC to control the system. Therein lies 99.7% of the differences in 'brands' that I have observed. Beyond this, there are a couple hundred small and obscure variations in offerings that make one choice easier than another; but, it doesn't preclude other systems from satisfying the primary objective! Hope this clears things up!

 

[skills]

I quess I meant to say that at the level of your question, it strikes me as similar to the query of "what do you want in a good car?" Answer, of course, is "everything I can get and keep it cheap!!!" It really doesn't strike me as a real technical question as much as "what's your way of making a good hamburger". What I look for generally causes me to discount the very selection of some of my counterparts doing the very same job, but approaching in a 'roundabout' way. Isn't that funny?? I've always thought so. Simple answer is, every plc with appreciable market share is targeted toward someone and when they meet up they form a supplier-customer relationship. I like multi-program-lanquage capability and specialty module availability. Some people like to use systems that have multiple development program systems. Everyone's different and electrical engineer's are all different in their strengths, this allows a plc provider to distinquish himself with an offering to a 'sect' that others aren't addressing. A super-techie isn't impressed by what a spec-head would find interesting. I hate AB products; but, many users, strangely enough, seem to like them. That excites me because, the good stuff is cheaper because of the hungriness of the 'better' in my opinion, lines. I, personally, can build and program an single board computer to do much of what I do as fast as I design plc systems; but, my customers would not be able to support and upgrade them as requirements changed. Any plc will be a fit somewhere to someone or another!! That's the bottom line.

 

[davidvinch]

The AutomationDirect catalog has a really nice section devoted to picing the right plc. They also seem to get a lot of awards for customer support. No I don't work for them
but their catalog has answered a lot of my questions.
Regards,
Dave

 

[skills]

The above point is correct. AutomationDirect was voted #1 for Best in Service in 2001-2002-2003 by Control Design Magazine. They offer more support than anyone I am aware of.
This is a reader's choice award and it reflects well on their commitments.