PLC technician questions?

I have been hard at work on my Electronics tech. course. 12 more exams, 30 something more books and I graduate with a ET diploma. I am looking at more training that might help with gaining employment and commanding better pay. I have been reading up on how PLC technicians are in demand. There is a local college that is actually very respectable that offers a PLC course online. Great idea? Will it help gaining employment and making more money? Are PLC's really, really hard to learn? Thanks for the help, I appreciate any help you may have.

The PLC itself is easy to learn. The first one I used programmed in "relay ladder logic" and was so stupid-simple it was actually frustrating, because you couldn't write a subroutine or even a very sophisticated conditional statement. The new ones give you a console to work with (instead of punching in a gazillion cryptic codes) and allow for graphic user input (so you can put the stupid relay diagrams in) as well as having better access to the processor itself (ability to do loops, subroutines, and read table data).

The difficult part is the process control itself. This can involve integrating or differentiating a signal with respect to time, juggling more than one variable, "characterizing" motor curves and sensor data, etc. But most of the work is just reading switches and triggering valves with delay times.

Thanks for the help, and I feel much less intimidated than before. Anyone else have anything to add? Good idea, bad idea, have to have this training? Anything? Thanks

Any employer that hires a PLC tech for that specific job will want someone with experience in the particular PLC's they have. If you learn A-B PLC's you will probably use about 15% of that knowledge on some other PLC's like Mitsubishi's for example. An employer with a specific need will want a tech with specific skills.

This is all not encouraging but I really do want to learn how to troubleshoot PLC's so I probably will take the course anyway.

Its hard to convey "how hard is it to do PLC stuff" in English language. Kind of like trying to explain sex to a virgin. You just have to do it. All the different platforms have different little idiosyncrasies but they are all based on the same principle, relay ladder logic. learn that (which is so easy it's almost boring) and then it's just a small learning curve (how to set up backplane, address I/O, create timers, search, crossref, compare, how to not download, etc.) with each different platform, no different than when you have to learn a new version of windows (well actually a little harder than that, but you get the picture).

Then there's higher level PLC stuff that deviates from the traditional ladder stuff, text based writing of code & whatnot where some programming experience is helpful, but even then it's not so hard as to be unlearnable.

If you've got the time and the money to take the training, take it. But remember, a lot of companies will pay for this type of training, especially if they have lots of different types of PLCs they can't expect you to know everything.

The plant I work in didn't send me to any training, but they also don't stand over my shoulder while I'm trying to figure it out, saying "are you done yet, are you done yet?".

duffy said:

The PLC itself is easy to learn. The first one I used programmed in "relay ladder logic" and was so stupid-simple it was actually frustrating, because you couldn't write a subroutine or even a very sophisticated conditional statement. The new ones give you a console to work with (instead of punching in a gazillion cryptic codes) and allow for graphic user input (so you can put the stupid relay diagrams in) as well as having better access to the processor itself (ability to do loops, subroutines, and read table data).

The difficult part is the process control itself. This can involve integrating or differentiating a signal with respect to time, juggling more than one variable, "characterizing" motor curves and sensor data, etc. But most of the work is just reading switches and triggering valves with delay times.

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A better explanation than most. (no emoticon for thumbs up)

I've been doing PLC's off and on for 25 years. I'm no wizard but have worked with stuff like a 5TI dating to the mid-70's that took up a 6 foot long panel thanks to just 4 inputs or 4 outputs per I/O module. As a math guy with a Karnaugh map exposure to digital logic, it made just enough sense to me that I always ended up the PLC every 6 months or so guy in the office. I'm once again the only guy in the office of 20 or so who can break down a PLC program.

The 5TI didn't support anything beyond the most trivial documentation and nothing beyond a master control set and master control reset to implement anything like a subroutine. Our program effectively went just one subroutine deep: call stop, call run, or call jog. For troubleshooting we knew the inputs were supposed to operate in sequence and the outputs were supposed to as well. That made inserting another state either confusing or complicated. There were also the early 70's screen printers that had their ladder logic, probably about 20-25 rungs worth, implemented with 3PDT and 4PDT relays.

If you can master state diagram to plc program translation, you will have mastered a lot. The ability to successfully structure process control in such a manner leads to far more stable code than the average script kiddie is capable of.

cachehiker said:

The 5TI didn't support anything beyond the most trivial documentation and nothing beyond a master control set and master control reset to implement anything like a subroutine.

Click to expand...

I bet at one point someone had to have looked to someone else and said "remind me again, why we are using this thing instead of relays."

I figure call run, call stop, and call jog would have each required a 6 foot rack and about 200 relays to hardwire.

Every subsequent logic change would've required a substantial amount of rewiring.

The 5TI console at least allowed you to display and edit the ladder logic graphically instead of mnemonically. IIRC, I only ever had to make one substantial change. I had to add a lead frame cutter and a warning light to the end of the process. Detect the reel is nearly full, start flashing yellow so the operator would have an empty real ready, cut the lead frame when the reel was full, and then spool an additional ten feet or so before it stopped and started flashing red. The machine used to stop and wait for the operator to manually cut the lead frame and change the reel before restarting. It took about a day's worth of head scratching to increase the machine's daily capacity by about 1%.