New to PLCs, specific project, need advice

I'm working on a very interesting project where a couple of IT guys and myself are working on developing a computer system that will monitor the status of a couple hundred switches (just ON or OFF) over the span of three floors of a hotel that is being constructed.

Our computer system development is being completed in the next few weeks, aside from this part. We need a PLC system (or something) that will allow our system (programmed in Java) to simply look at a database with the statuses of all of the switches and see which ones are on and which ones are off.

Simple, right?

Good! What is the easiest way to go about this? Both hardware and software.

I got a quote from an Automation Direct technician, the hardware looks fine, but then when we got to the software, I found that the only software that reads their devices use OPC (OLE for Process Control). My software can't read a windows based system like that. I need more of an open-source, java compatible approach to the software.

So now I'm back to square zero. I got a suggestion from someone else of some other PLC company, Opto22, but they also use OPC to talk to their PLCs, and they seemed to be more expensive for simlar products.

If anyone has put together a PLC system that takes data from switches and reads them into software, using something other than OPC, or if you have any other ideas, I, and my co-workers, would appreciate it very much.

- Bret

I just did something similar recently where I detected switch transitions and time stamped them. I then broadcast the message over UDP where a client then stuck the info in a database to analyze later. I would be surprised if your software couldn't do something like that.

Look at Triangle Research, INC. They have just the thing for you here. I believe your specific's about the JAVA shouldn't be a problem since their software was developed on the JAVA platform. They would be able to help you with all the hardware/software idea's you could need.

The website is www.tri-plc.com

**** I am not a tri-plc.com representative, just an OEM that uses their products.

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Thanks.

What you described (S7) is exactly what I need to do, but I need to have my system "look" at the data in real time and update a display based on what it "sees".

Could you let me know a bit more about how you did this? Like what software, what hardware, etc...

I checked the website that was mentioned in the second reply, TRI PLC, those applications look so complex compared to what I need to do, such as pouring concrete using PLCs! I just need to see if a couple hundred little switches are on or off!

What sort of product would you recommend? I checked on their web site and from what I can see a T100MD+ would work. What do you think?

BretB said:

Thanks.

What you described (S7) is exactly what I need to do, but I need to have my system "look" at the data in real time and update a display based on what it "sees".

Could you let me know a bit more about how you did this? Like what software, what hardware, etc...

Click to expand...

I use S7 PLCs, and what I used would be overkill (this was just a tiny part of what I do in this processor), but just about any PLC with an ethernet connection could do it.

As for "real time", define real time. I would be able to send out the status of the switches about every 10ms. Would that be fast enough? No matter what software you use, there is nothing that just "looks" at the status of the switches. Even PLCs that are directly coupled to the switches experience some latency in the network and back plane of the IO cards.

...

Okay so I'll check out the S7 web-site, I'll just google it.

Real time to me means that once every few seconds (5-8 seconds max) each switch has been checked and it's status updated on the main display. That's all i mean. I don't need "instant" and I know that's not really possible.

If the hardware you used would be overkill, do you have a recommendation of something that would work?

Thanks.

Sure, any of the S7 300 series would work. The "PN" models have integrated ethernet, which would be useful.

But since your app is pretty basic, I would make some call with local suppliers and see who can offer the best support in your area. Or, maybe a place like Automation Direct would be a good choice.

That's funny you say that. Automation Direct is where I started and all looked good, aside from the connection with their software. That was the problem. Their equipment only uses OPC or DDE, niether of which work with my application programed in Java.

So I'll keep looking, unless someone out there has non Win32 software for looking to a PLC and getting their status.

I am currently checking out the tri-PLC web-site as "1973" suggested, but those seem very complicated. At least with Automation Direct, they could just tell me "you need A, B and C and the price is X". I don't know what is what when I go through the tri-plc web site. They may very well have what I need... ?

I guess I'll check with one of the Tri-PLC people who may be able to help me.

Any other suggestions or advice would be welcome though.

But I assume you wouldn't have to use AD's software. If they have an ethernet card, I would think you could program it to send either UDP or TCPIP messages. I've connected to dozens of SCADA systems with PLCs over the years, and haven't used an OPC server on a job yet.

Hmm... That's good to hear. And that's good on the hardware side if we stick with AD. It's already spec'ed, priced and looks good from that end. I would like to stick with AD on hardware.

The thing now is the software. Sure I could program a UDP or TCP/IP messaging system to this guy - if I knew how. I am sure I could figure it out, it's just some weeks added to the project that we can't really afford.

Maybe that's what the Triangle Development people can do with their apparently Java based software. I'll have to check that out.

Why JAVA? I would guess its because its what you IT guys know. Maybe you should ask them how they would like the data. I would guess a database maybe SQL database? Can they use an active X control? I am sure there are options that will work for you.

Because we are using Java for the entire enterprise development and per experience OPC and DDE are both hard to communicate with to Java.

I am sure we will find something that will work too - I just can't find it by trial and error, I need to know before I go.

Here is a couple of links to Siemens info that should help get you started. They have some good examples. I would love to see what you come up with. I did some work like this a few years back using Automation direct and a custom ap in Delphi. I used DDE to get the information from the plc's then put it in a database. The delphi ap would also generate html to display in a webpage. I used Java Script to display the data in a graph. It all worked but after everyone on the company network started seeing the real data it got shut down. Good luck


https://a248.e.akamai.net/cache.automation.siemens.com/dnl/DQ1MDc0NQAA_16832609_HB/IT-CP-Info_e.pdf


https://a248.e.akamai.net/cache.automation.siemens.com/dnl/DM4NDEzAAAA_24843906_HB/mn_it-cp-infoprgm_76.pdf

https://support.automation.siemens.com/WW/llisapi.dll?func=cslib.csinfo&objaction=csopen&objid=21687867&nodeid0=21687867&caller=view&lang=en&siteid=cseus&aktprim=0&extranet=standard&subtype=133300

There are several PLC's that can handle communicating through basic TCP sockets. Just set up a simple protocol for your PLC and Java application to 'talk' through. Then you can bypass the OPC bit.

I'm not a big fan of OPC, and have used this approach several times.

"couple hundred switches" = couple hundred I/O = big project.

Most small and cheap PLC can not be configured for soo many I/O.