Another newbie...

[extremeintegrations]

Greetings everyone.

My name is Scott and I have 16+ years in Microsoft software development.  My start was VB for DOS and I grew through the years with Visual Basic all the way to VB.NET.  It was then that I jumped ship and turned to C#.Net and I've been developing C# solutions for many years now.

In the past 2 years I started my own company writing custom software and products for database to LED signs.  In the process I'm finding customer needs that require me to bring hardware (plc's and sensors) to the test lab.  I'm VERY new to PLC talk and though I still don't know much of the terminology, I'm about to purchase a Direct Logic system for my test lab and start generating software solutions for my customers. 

I feel many sleepless nights coming soon.  I just wanted to introduce myself and meet people here.  If I sound ignorant like a noobie it's because I am 

[MikeS]

welcome

[Controls Guy]

Welcome, Scott.  Don't worry too much, it's not so much ignorant noobs vs. seasoned omniscient veterans; more like DEGREES of ignorance!   

One thing you'll really come to appreciate is Automation Direct's excellent, excellent manuals.  They're well organized, comprehensive, and actually written by someone who can carry on a normal English conversation, not someone whose native language is Manual.

Another couple of good online resources:

Another poster here has a general PLC site at http://www.theplcguy.com

And http://www.plcs.net has a PLC simulator at http://www.plcsimulator.net.  Till you get a real PLC, you can try out bits of ladder code there, plus there's some tutorials on the concept.

[extremeintegrations]

Thanks guys for all the help.  First of all maybe you can even tell me if a PLC is what I need to investigate.  Here's the problem I have to solve.

I have a manufacturing client that has extruders.  They would like to install 3 counters at different places on their extruders.  They have 33 different extruders so at the least I will need 99 counters (or sensors - whatever you call them).

Now I'm a software developer by trade and I write all the internal software for this client.  We would like to accomplish this.

1.  Install 3 counters (each machine) 
2.  This signal must go somewhere (this is why I'm investigating PLC's).
3.  Write software on a host computer that can read the PCL counters every minute and store these counts in my database.

Now it sounds simple but without a PLC background (or any hardware for that matter) it's becoming complicated. 

Now back to my original question.  Is a PLC what I need?  I'm only looking to capture input (counts).  Are there other solutions that would be better for me? 

[Controls Guy]

A PLC is an excellent choice.  You need to collect information from electrical circuits, aggregate that information, and make it available in an intelligent device that can do digital communication with a PC.  A PLC is perfect.

Other options would be a microcontroller, probably furnished as a completed circuit board (may have trouble getting sufficient I/O count, or industrial level inputs) or a DAQ (data acquisition) card for the PC itself.

One clarification item -- unless you need local display, you don't need three "counters" per line, in the sense of an electronic device that accumulates the counts.  The PLC does timing and counting internally, so you just need a sensor like a proximity switch or photoswitch that turns on and off once per event that you're trying to count.  Then take the signal from those switches and feed them to input modules in the PLC, and let the PLC count actuations using its internal counters.  The PC can then query the PLC and get the current counts.  The PLC can even compute counts/line or total counts if you want it to.

One last item.  Depending on what you're trying to sense and the sensor technology used, you may need to "debounce" the inputs.  When a mechanical switch closes, it actually physically bounces, and the PLC will be fast enough to count each bounce as a separate event unless you filter the events, and even solid state input sensors can do the same thing under certain circumstances.   Sometimes this can be done by configuring the I/O modules, and sometimes it has to be done with timers, so you don't officially accept a count till the input has been on for 20ms or something like that.

Also check the rate at which you need to count to make sure the PLC is capable of counting at that rate.  You may need special high speed inputs to count events if they're very fast (over a couple hundred per second, say).

[extremeintegrations]

Excellent so I am on the right path.  Thanks for all the information.  The counters in this case are pretty slow, maybe 1 every second at the most.

I'm considering the Panasonic PLC which has a webserver module.  My initial thoughts were to have the PLC do its job and build in an XML output on the webserver.  Then have my computer software retrieve the XML from the PLC's webserver.  Another option I'm dreaming up is to have the PLC's webserver (if possible) to do a HTTP post to my application's Web Service.  The Web Service would accept the PLC's xml output and log it to my database system.  Thse are some thoughts.  I'm not sure what is possible to get information out of the PLC to my PC. 

I know there are many brands of PLC's.  The products that I'm developing will be all monitoring products so I only need inputs.  I'm hoping to find a PLC that has purely Input modules and has the ability to get information to my PC in some fashion via Ethernet.  Any opinions?

Thanks
Scott

[Controls Guy]

Not familiar with the Panasonic PLC's personally, but yes, many PLC's do have at least web pages if not web servers these days.  There's a couple ways to get data from the PLC to the PC.  Most brands, including Automation Direct, have at least an optional Ethernet port.

There are various comms products from the PLC makers as well as third parties that will poll the PLC and get the information continuously, either via a serial or Ethernet connection, or vendor specific hardware/comms (such as Allen Bradley DH+).  "Modbus" is a widely used open industrial communication protocol, so called because it was originally developed by Modicon, a PLC maker, but it was released publicly and there's very, very widespread support for it, to the point where today it's viewed as sort of a default open protocol for industrial devices.  (You could easily write a comms driver for it if you wanted to, but you don't have to because there are a lot of them for free or cheap, as a component in a system you put together.  If you purchase an OTS OPC or SCADA product, it will come with a Modbus driver)  In the last few years, Ethernet has become a popular industrial comms medium, and most manufacturers offer Ethernet comms using protocols of varying degrees of openness and varying degrees of support in third party devices, and there's an Ethernet version of Modbus called Modbus/TCP.

Another option, especially if you want the PLC/PC link to be fault tolerant, is email!  Many PLC's, Automation Direct's included, can initiate emails.  So you could have an app on the PC end that parses the emails and puts the data into your database.

Oh, and yes, as far as I know, all PLC brands have input-only modules.