Programmable Logic Controllers

I’m unemployed and have seen a few maintenance jobs that state that knowledge of PLCs is desirable. Therefore I’ve decided to learn about PLCs.

I need some help! Please recommend: PLC simulation software, books, DIY kits, videos, etc.

Also, is there a preferred make of PLC to learn?

Thanks.

Buy yourself a telemecanique SR2 smart relay. You can download zelio soft free, and do some practice programs with this and up load it to the plc. Perhaps rig up various switches/ sensors and some lights etc on the outputs and see how it all works. I taught myself pretty much all I know about plc programming by doing this! I then designed a program and built a panel for a milling plant, using various timers, counters etc. it's all good fun and the best way to learn. A SR2 will set you back about £100 Nd you will need a USB cable too, which is bit of a rip off (about £70 IIRc).
Good luck!

There are so many different types. Some software does allow simulation. What I have found is Siemens is a problem. Software very expensive so many firms don't have software and will employ a contractor as cheaper than buying there own software. However this also means hard to get experience with Siemens as you also can't get software at a reasonable price.

The Mitsubishi PLC is easy to program for simple machines but hard with complex machines. The Rockwell PLC with RSLogix software were in the main modular and the method of programming allows you to write complex programs easier than with the more basic system used with most the smaller PLC's but is more difficult to use with simple tasks.

I found http://www.plctalk.net/ was good but after writing a 2000 step program for a concrete press with Mitsubishi to make weights for washing machines I thought I was good and was proud of what I had done. But when I went to University and started using SCADA and rack PLC's I realised I had only scratched the surface there was far more than I thought.

So to add some PLC skills to electrical knowledge is great within 6 months you should be able to write short programs with the simpler units. But if your looking to specialise in PLC's then your looking at least 4 years.

With simple systems like I used much is trial and error. For example to trigger a solenoid to pour wax into a glass to make candles I would as a start guess a time and alter until it was spot on but as I progressed I would write so it auto measured the time required from flags and calculated the delay required allowing for delays so it would run A1 on first run. This was far harder.

So I was involved with installing a car transport system in Vaxhall's factory and I must take my had of to the guys who wrote the program it was built and once we got the PLC's talking to each other ran first time. Very little tweaking to times these guys were really skilled completely different to my concrete press.

When I worked in factories using PLC's we considered if some process needed more that 6 timers then better to fit a PLC as it was cheaper. Writing a small program to print labels is easy but as you move to program to run a bottling plant then it's a really different story.

Thanks for your replies. I plan to watch these videos: http://www.youtube.com/user/plcprofessor/videos

and build something like this: http://www.youtube.com/watch?v=uMaI9H1lVyo

Another idea is a security light system with PIR sensor, an internal light, a radio and an external light.

Software is the big problem. GX_Developer is expensive but Medoc can be down loaded for free. Both Mitsubishi. Although there are specials there seem to be three main types Mitsubishi, Siemens and Alan Bradley (Rockwell) and of the three Mitsubishi is the favourite with electricians and DIY programming.

In the main ladder logic is very like a circuit diagram and although there are some standard ways to do certain processes in the main the electrician (as opposed to PLC programmer) is not required to write programs but only be able to use a PC to monitor the program to assist in fault finding.

Without the program some functions are not what one would expect. I in early days did get caught out. One I remember was temperature control a sensor monitored the temperature of a sealing machine and the element was not heating up. The temperature shown was zero degrees and required temperature was 150 degrees and there was no power to the element and PLC LED's showed the PLC was not calling for heat.

I considered the PLC must be faulty but it transpired the programmer had realised it should never reach zero degrees so had written into the program if temperature is less than 15 degrees no output as clearly there would be a sensor fault.

Makes sense of course but without being able to read the program I did not realise this was the case.

I found using Medoc was in some ways better then GX_Developer as with Medoc I could see the green flash on the icon from other side of the machine so could set up program and manually activate sensors to see if working. In the main this is the limit an electrician goes to there is no need to write from scratch.

However there were some errors. In theroy the PLC is not used for safety circuits although safety circuits are fed into a PLC so it knows when process has been stopped because of a safety feature. I was working on a bottling plant and there was no labels on the uploaded program so first job was to identify what each sensor was. So pressed the E-Stop so nothing would move and with Medoc running went around each sensor in turn and entered the label once identified. However it transpired the E-Stop was only connected to the electrical system and the air system was not covered. So when I triggered a sensor to show bottle in place the pneumatic cap screwer still activated. Really made a mess of my steel rule good job it was not my finger.

As a temporary measure I altered the program so the cap screwer would not work when E-stop was pressed until a pneumatic dump valve could be fitted. I left Jeyes shortly after and as a result never saw the mod fitted so likely it never happened. This is of course always a problem one knows what should happen but that's not always the case.

Much depends on who was before you. Theory is one should document what one does which makes it all easy for those who follow but in practice much of PLC use involves working out what those before you have done.

Having worked as a factory PLC technician for bosch for 13 years and now moved on via several jobs due to bosch relocating to Hungary I can only offer the following observations. I am basically a multikilled technician with electrical bias originally an ex royal navy apprentice who looked after a missile defence system....ended up as a factory technician/fitter.

1. Omron , Siemans, allen bradly are popular choices with Mitsubishi being less used in the industry I have been involved with.

2. the technology has changed a lot since 1997 when I started with Bosch from normal PLC's quite chunky to now small - to various bus and Ethernet communication systems and now soft PLC's ( pc based screens acting as plc's ) and PC controlled machines.

3. ladder programming of any type will get you familiar with how they are programmed but every make uses different software to talk to its pc's and different versions for different age plc's of same make....

4. you can have modern and old plc's in the same factory from all sorts of manufacturers.

So Bosch had their own make and programmes and ways of programming mainly in instruction list. Omron seem to be a popular choice for simple machines and siemens for slightly more complex. It really depends on what industry and company you end up working for. Try to get an understanding of ladder programming and then find a willing company who will throw some training in - sorry I cant be more help.

saladdays said:

I’m unemployed and have seen a few maintenance jobs that state that knowledge of PLCs is desirable. Therefore I’ve decided to learn about PLCs.

I need some help! Please recommend: PLC simulation software, books, DIY kits, videos, etc.

Also, is there a preferred make of PLC to learn?

Thanks.

Click to expand...

I've been writing and commissioning PLC software since 1992, it's taken me around the world working and paid some great rates as a contractor, so I can recommend it

In terms of difficulty it can range from simple ladder logic on basic machines and conveyor systems to complex process systems in petrochem, power stations etc.

I've always specialised in Siemens systems....http://plcforum.uz.ua/ is a website where you could (illegally) download whatever you need for Semens and non-Siemens systems......