Little PLCs not to sneeze at...

[Skogsgurra]

We live in an old iron and steel district. There is an old blast furnace in the village and we are restoring it (tourist thing). It is all volunteer work - so we are supposed to work very hard and doing nights as well as holidays - and we do.

We have got a lot of scrap from nearby industries. For the blast machine (Bagge 1880 model) we have got a frequency inverter (SAMI GS), a PLC (brand new Siemens LOGO!) and I also talked one of the grandchildren into letting me have his little RC car. I needed the radio gear to make a wireless control for the machine.

It was when I started working with the PLC that I discovered that these little ones have a lot going for them. Security is one of our tougher challenges in this project. We do not want children to be able to start the rather heavy machine and we can not allow it to run uncontrolled when batteries are low in the hand transmitter.

So there is a code that has to be entered within a certain time. There is "heart beat" supervision. There is automatic shut down after a certain time and there is a start warning with a five second window when the thing can be started. And lots of similar things. We are also contemplating a speed supervision that checks that things are moving as they shall - if not, something might be stuck in the machine. Or no machine any more...

I have just finished the main part of this. And I still have about 80 percent of the capacity left for future use. Speed supervision is not implemented. It will probably eat another 20 percent.

We got this unit for free, but I have looked at the prices and they are real low. I could easily pay more for a standard time relay. Just one time relay! And this little creature has tens of them. Plus lots of other functions. Plus, of course, normal logic blocks. I like it. I have seen that Telemecanique (Schneider) has a similar thing. But never got one under my nails. Anyone used that one? How is it? How do they compare?



Gunnar Englund

http://www.gke.org

 

[fangas]

Yep, they're pretty nifty.

I don't know about getting them overseas but, the PLC line from automationdirect is probably the best bang for the buck out there. They're on the web at

http://www.automationdirect.com

They might be sold overseas under the Koyo name.

I've never experienced a hardware failure and their software is great. Documentation is also excellant. I highly recommend them

I've never used a Telemecanique so I couldn't tell you much about them.

Ed

 

[Skogsgurra]

Thanks for the tip, Ed.

I did not know about the Koyo PLC. They have a lot more functionality w/ regard to Motion Control and fast I/O. I will try to get one of those. Can you use anything other than ladder? Logic diagram would be nice.

Gunnar Englund

http://www.gke.org

 

[fangas]

You're pretty much stuck with ladder, Gunnar. They do have a feature they call Stage build into it. I wouldn't think much about it though. Their software is highly intuitive. Real easy to use. Actually, it's the eastest I've ever ran.

You can download a demo of it from their site. Play with it some. I think you'll like it.

Ed

 

[skills]

While it still uses ladder logic instructions as it's instruction base; using the stage approach with sg, conv, divrg, block, and call allows you to write larger programs with many parts that are very easily managable. I make up functions with these stages that I keep sort of as a library then I call one when I need it. I like this approach as I don't have to write much anymore. I just add functions or write new ones. It's cool.

You can always find some of these DL205 Direct logic units at auction on Ebay. We get quite a few there.

 

[Allphase]

http://www.crouzet.com/corporate/m2/uk/index.cfm

http://www.mitsubishi-automation.com/

http://www.idec.com/usa/index.html

These are a few Smart Relay manufacturers that feature function block programming