You should consider something that you are likely to use in the future. In North America, Allen-Bradley is the predominant brand, but there are others commonly in use. If you are in another part of the world, I think it's more likely you will be using Siemens but again, other brands are common. All PLCs function similarly as far as creating logic is concerned, but the development software is specific for each brand and many of them use different programming languages. This stuff isn't inexpensive, though. If you are learning on your own, working out of your own pocket, and just want to understand basic PLC functions, then I would suggest a low-priced unit such as what is available on Automation Direct or other online source. Even through that, you can gather a lot of knowledge and experience.

Brad Waybright

It's all okay as long as it's okay.

As the Bard suggest if out of your own pocket then I'd highly recommend the Automation Direct offerings. If just ladder logic start with the Click series. Use the highest level PLC CPU they offer in that series and that's the Ethernet version. Don't forget to get a power supply.

To round out your training also get their super bang-for-the-buck HMI and figure out that too.

Recommended Powersupply

Recommended CPU (sinking DC outputs)

Recommended HMI

Keith Cress
kcress - http://www.flaminsystems.com

Ditto what Brad and Keith suggested if OOP the go with Automation Direct, they also throw in a free 30 day access to a series of PLC hardware and ladder logic topics.

-AK2DM

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"It's the questions that drive us"
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And, their tech support will answer all your questions without an annual account or a credit card number.

Keith Cress
kcress - http://www.flaminsystems.com