choosing a PLC

Hey guys,
I need some rules, advices, good references about the way of selecting a PLC or PAC for a special purpose. Generally, what specification should be noticed to choosing a PLC. In addition, I want to choose a PLC to control a gas compressor station or at least to control a gas turbine (turbocompressor). In fact, I want to know do I need to obey any standard to choose a PLC (except safety standard which they are used in ESD)
Thanks,

In a PLC's most basic form they all work the same. It is just the user interface that becomes a choice for choosing a PLC. Some are more powerful in terms of ease of use, and more expensive. I personally would stick with either an AB Compact/Control Logix, or a Siemens PLC. I personally prefer an AB PLC. I feel strongly that their software is much more intuitive than other brands, and just as powerful. But if you are a siemens Koolaid sort of guy then that is an option that is good too.

A good place to look and do an initial comparison of PLCs available in North America is plccompare.com.

The term PAC is a differentiation without a difference. The term was coined by Bob Mick of ARC, a market research company, back in the early 2000s. I believe that his definition had to do with what he saw as an emerging product category that utilized a standard bus structures that would allow multiple vendors to provide plug in CPUs and IO modules. That really never developed. I have tried to find the definition through Google searches and have come up empty. Various manufacturers call certain products, PACs. If you look at different PACs from different companies, you'll see that they have nothing in common. What they are using the term for is the high end of their PLC line.

For your application, you'll need to look at your functional, distribution, communication and programming requirements. There may be cost issues as well.

For safety issues, you really need to get ahold of applicable safety standards for the applicable industry. You may need to take precautions outside of the PLC.