New to PLC's...have simple project

[PlasticsDude]

I'm 100% new to PLC's and luckily am starting with a very simple project. I have a machine that has a blower, an electric resistance heater, and a vacuum vessel. I need to be able to turn the blower on/off, control the air temperature (SSR time proportioning), and turn a vac generator on/off and monitor vessel pressure. Other than a PLC itself, what would I need to do this? Would it be cheaper to use a stand alone P-I-D to control temperature, or can a PLC accept a 100 ohm RTD input? Thanks so much for any help!

[Sleepy Wombat]

Never had any PLC experience.... not training... no software....zilch...zippo...nadda...etc.... Just a question,,,whats your back ground... elec techy.. any electrical back ground etc.... The project may be small but some one with no experience in writting ladder etc you have raised a few non beginner types of issues... ie time proortional control of the temperature... analogue controls etc.... Yes you can tackle this a number of ways... all depends on your budget and time...

[PlasticsDude]

I'm a mech E but I do electrical stuff too...laid out a few panels and have a general understanding of how controls work. I expect this will take me a lot more time to do than one of you guru's but even if it takes a month I'm OK with that. I have to start somewhere. Any ideas? Thanks again.

[Ken Moore]

I assume this is for a company project. Does your company already use a certain brand of PLC? Do you have access to the programming software? It will be the most economical to use a PLC that you already have software for.

[PlasticsDude]

It is a company project. Currently we do not use any PLC's, we use custom made boards that our sister company makes for us. That means that whenever I need a simple software change (our machines are pretty simple) I have to rely on an outside guy to get to it when he feels like it. The advantages of a PLC for me are obvious.

[BobB]

Oh boy! A can of worms. I would suggest Omron to you as it is very definately my favourite brand. The software is reasonably priced and great quite frankly. Others will recommend their favourite brands also. I would recommend the CJ1 or CP1 to you for your project. Both of these PLCs have the same instruction set and would make life easier, although the instruction set is awesomely huge. Not much you cannot do in ladder with these. Also a huge library of FBs (function blocks). Software price is reasonable and so are upgrade prices. All sorts of input devices and cards available. Pretty much anything you could possibly want. The CP1 uses block I/O but also uses most of the CJ1 analogue, RTD, thermocouple etc cards. Very versatile.

[gtsuport]

PlasticsDude, Welcome the the Forum! In what part of the US are you located? There may be local support available for your project. To try to answer your inital question, the plc would need analog inputs to handle the RTD and (I'm guessing) the vessel pressure sensor. It may be more economical to use a transmitter on the RTD instead of a separate RTD module if you also have an analog signal from the vessel. As indicated, you will need software to program the plc. The choice of hardware will dictate the software requirement. You may also want some type of operator interface to display and change program variables. Let me know if I am on the right track and we can try to offer some options. Hope this will help.

[PlasticsDude]

I'm in southeast PA. Thanks for the info and the welcome! As far as the RTD, I was thinking it might be cheapest to simply use a stand-alone P-I-D, that way I don't need an analog module for the PLC...although I guess I'll need one anyway for the pressure transducer, so if I have to eat the cost in the end no matter what... Do any PLC's have the analog inputs built right in? As far as the user interface, I just need a screen to show temperature, pressure, and time, and a way to adjust temperature and time...

[JRoss]

PlasticDude, Temperature sensor inputs are different than standard analog inputs. This means you would need a different module for that anyway, at least with Mitsubishi hardware. Not sure what pricing you get for stand-alone PID, but for the Mitsubishi FX series, the FX2N-2LC (two sensor temperature PID control module) list price is $490. The Mitsubishi Alpha series has analog inputs built in. Again, they are only standard analog, not temperature. The temperature module list price is $100. If your application is fairly simple, the Alpha would be a good place to start, as it is less expensive, and doesn't use ladder logic programming. It also has a small HMI built into the PLC that could potentially be used for the interface you're talking about. It is lower end in terms of capabilities, though, so it depends on your application. To truly compare cost with a stand-alone PID controller, though, you would have to compare performance as well. PLC temperature control can be much cheaper, but isn't necessarily as accurate or well-suited to certain applications. How accurate and how fast does the control need to be, and what are you heating? I'm inside applications support for Moxley Electronics, a distributor based in Exton, PA. We handle Mitsubishi product, as well as Athena temperature controls, and I'd be happy to discuss the application with you, make some recommendations, and provide pricing for various options. PM me, contact me through our website, or give us a call (number on our website) if you are interested. Good luck!

[gtsuport]

PlasticsDude, Jeremy brings up some good points. One of my questions is how accurate are you trying to control. The resolution of the analog signal (analog to digital conversion) can become an issue. Setting up a PID loop in a plc can be a scary thing. And tuning can become a job in itself. Support can become an issue also. You should check with local distributors to see what level of support is offered, and if there is a charge for that support. The Omron CP1H offers built in analog input and output in a small plc with a very complete instruction set. I work for a distributor in Michigan, but you can check the www.omron247.com website to find a local distributor. Operator interface choices are many. Depends on what you like. Hope this will help.

[entertron]

Plastics Dude, Welcome to the world of PLCs and the forum. You have received some sage advise and suggestions so far. As stated previously, much will depend on your application and desired results as to whether a dedicated PID controller would be better suited over a PLC with temperature capabilities. The product that we offer that would be best suited for your application would be our Smart-PAK PLUS. www.entertron.com/smart-pak.htm You can download our programming software, which is ladder based, from our home page - www.entertron.com Should you have any questions, all our contact information is available online. Hope this helps. God Bless, Stephen

[PlasticsDude]

Thanks to all for the replies. It looks like I really have my work cut out for me, probably more work than I thought. If it weren't for the RTD and the pressure transducer inputs maybe it wouldn't be all that bad. How long does it usually take to get up and running with PLC coding from the ground up? I really need to get my hands on one and just see if I can even make an LED light up of something...to start.

[OZEE]

This system really doesn't sound that difficult, but I can say that because of 20 years of experience. It's not the type of project that I would recommend as an introductory project. Personally, I like having all of the control in the PLC -- I don't like stand-alone loop controllers in an otherwise-plc-based system. I've been doing this for almost 20 years and am still learning. How long does it take to get up to speed with PLC programming? Depends on your understanding of how the plc works, programming/logic basics, and general aptitude. Perhaps the hardest, yet most essential, parts of plc programming is identifying exactly what you want your system to do. Can you write down a concise statement of how you want it to work? A flow chart of if-then type conditions? That's the basis for programming PLCs. If you can identify it, you're a long way on the path to automating it. If this is your first project, it's really quite ambitious. Start with discrete, then move into analog, then into PID. This part of my reply is based on the combination of this thread along with your other questions. If this is a system you're developing, you need to design it with several things in mind. Does your plant already have PLCs? If so, you probably ought to stick with the same brand. What brands are locally supported? What about training opportunities? You're going to want it!! Honestly I'd move away from proprietary, custom-made circuit boards as fast as reasonably possible! It's gonna come back and bite you hard someday. As much as possible, your control components need to be standard, off-the-shelf, readily available commercial components. just my .02 ...

[JRoss]

Your system is simple in the sense that it doesn't sound like you need any fancy dependencies or controls or what have you. basically, turn things off and on. And you aren't dealing with motion. However, you're getting into PID loops and so forth, which is higher level. In my opinion, if you've dealt with controls before, the most complicated part about that is dealing with the special function blocks! There are lots of settings involved to get things working. I'd start with the online PLC training thing over at PLCS.net. It's a good basic look at the operation of a PLC and how to handle inputs and outputs. You can even use the online simulator there to play around. That should give you a good idea of the learning involved. To go further, you should find local support. If you're willing to try Mitsubishi, I can give that to you. Otherwise, there are plenty of vendors in the Philadelphia area with varying degrees of capability.