Looking for Some Sort of PLC...I Think

There a lots of 'mini-PLCs' around that could do this (about $100-ish), from people like Moeller (the Easy range, also re-badged by Allen-Bradley as the Pico range), Siemens (Logo! range) and Crouzet (Millenium3 range).

One that should do the job is the Moeller Easy512-AC-RC. I'm suggesting this one, because I happened to be looking at the Moeller range yesterday. It has AC mains-type inputs (and is mains powered), relay outputs and an LCD and a few buttons you can use to program it (though it's easier to use a serial or USB cable & a PC). It's got a clock & timer functions built in.

Edit - Just checked - costs a bit more than I'd thought. £89.24 from http://uk.rs-online.com (order code 489-1377).

It would be good practice to switch off the whole room/shop on the isolator if there is one when they leave.

There are all sorts of cheap options...pin timers, central heating timers etc which could be used to give a fixed run time ...or to just switch off at the end of day !(assuming they can handle the load...else you may need to add a relay or contactor) A PLC seems an expensive overkill.

< groan...someone will probably blether on about using inappropriate stuff and safety etc...I'm assuming it is done sensibly with due regard to current ratings and good practice >

Del

Yes, that SG2-10HR-A seems to have just about the same spec. as the Easy512 I suggested. Don't know what the Moeller thing sells for over there, but $89 for the TECO sounds like a good deal.

BTW I don't think you'll need to worry about ladder logic - with all the types of PLR I've used so far, the programming is done on-screen by placing functional blocks (timers, counters, gates, flip-flops etc.) and joining up the inputs, blocks & outputs. If you've done any circuit design before, you'll pick it up in no time.

I must say I'm surprised no-one has come up with the perennial PIC or 555 Timer solutions!

I've got the feeling the TECO thing is something else re-badged, but the nearest-looking thing I can find is a Crouzet which doesn't have as many buttons as the TECO.

Enjoy!

Yea I thought of the PIC idea and a 555 at first.

But I have always prescribed to the theory that "one should never trade parts for labor." In other words If I can spend a little more on a part and less labor its always a good thing. For the customer and for me. Its win-win.

Yea, the software that comes with the teco has a FBD editor as well. In fact now I have played with it a bit, It also has a simulator as well so I will have the programing done before I get the PLR!

The Easy512 is about $149 bucks. So the 79 dollar 24V version of the SG2 is a good deal I think.

I will let everyone know how it all turns out.

Thanks for all the input!

bill12780

My comments about the PIC & 555 were a bit tongue-in-cheek - it seems whenever a simple timing/control problem comes along, someone will suggest it. This is fine for the hobbyist or schoolkid, or someone with loads of time and not much money/pressure etc. etc.

The PLR approach is definitely the way to go here. I agree 100% about the parts/labour trade-off. Grab a PLR, spend half a day learning how to work it, then plumb it in and use it (complete with UL approvals etc.).

Different matter if A) you're working on a (very thin) shoestring of a budget, B) you're doing a school project, or C) you're going to be making 500+ of them.

One little point - do you already have the 24Vdc available? If not, the mains powered version could be more economic in this app.

Hello John,

Yea what you say is true. But were I work budget is attached to every single sentence that is uttered! So MY first thoughts always jumps to the cheap.

I was able to talk them out of a few hundred bucks on this project. One of the versions of our product here is a 24V system and we have OEM 24V powersupplies laying all over the place. I figured it would be a good way to get ride of the one under my desk I have been tripping on for a year. hahahaha!

I will however have to build my own Indicator light. I will have to post a picture when its done. Unless? Someone has a good source for them...

Thanks for the info!

bill12780

LG do a nice PLC range at a reasonable cost. Software is also free.

http://www.lgis.com/main/main.asp

I've got about a dozen or more of these TECO units in my plant that I've stuck in to do little tasks just like you are describing. Great units ...both the 120v and 24v units last. I put them in because I was killing AB PICO units every time I got any spike, anomaly, or one of my guys forgot to open a disconnect when welding in the area.

I have the software and cable somewhere but never have stuck it in my laptop. The things ...like the PICO...are so simple to deal with once you look at it, that you'll find you truly don't need the software.

Draw out the ladder first and, once you play with it with the book in hand, it's simple.

Switchman!

Thanks for this information. Being a noobie at this industrial stuff your post makes me feel a bit more confident! Not only in my choice of unit but also with the programing. Stuff should be here today or tomorrow.

You should change your name from Switchman to Da'Switchman cause you is Da' man! hahaha

I will definitely let you know how it all turns out!

Thanks again!

bill12780

Bill

What sort of power does this thing use? 120 v? 240v? How much current? You might be able to get a timer off the shelf which would shut down power between the hours of A and B (selectable)... I am going to suggest Grainger Associates. They are online, and might even have a branch in Salt Lake City. Sorry, but my catalog is in a box somewhere at the moment. They handle all sorts of industrial items and might have just exactly what you need. Their online might be Grainger.com, but I can't say for sure.

Good luck

another Bill

"You might be able to get a timer off the shelf"

Yea, this was one of my first thoughts. But then I mentioned to the guy in charge of the machine shop that I could program it to shutdown after so many hours for service and have different timed settings and it got complicated all of a sudden.

I really should learn to keep my mouth shut! (My wife says this all the time) But on the other hand--I would not get to learn how to do this and THAT is worth more then anything they could pay me! They can break your spirit but they can't take away your experience or knowledge.

Thanks for the insight!

bill12780

Hello all!

So here is where I am at. I got all my new "toys" and have got a pretty good handle on the ladder logic again..Its been awhile but I think I have it down.

I do have a question to pose to all of you. This might be considered off-topic. But it is the same project.

Just to review. We have a finish-tumbler installed in a room all by itself. There is nothing else in there and is sound proofed!

There are several reasons why we are doing this. The one I am having issues with is implementing "how" the system will work.

Example: Should there be a flashing indicator while the unit is running? Should I install a door switch to make sure the unit is off when someone enters the room?

Basically a safety protocol for this unit.

Can some of you "plant/factory" kinda people give me some advise?

Thanks a bunch guys! You have been great!

When I get it all programmed and installed I will post some pics.

Thanks again!

Bill12780

There's several ways to skin that cat, depending on the level of protection you need (and how much you want to spend). Lites or locks are both easy. If the system has been working forever and nobody has been chewed up, then you maybe are just needing some enhancements in the way of bells and whistles ...or flashing lite. You could simply do a stacklite outside of the door. Red running...green stopped and maybe even do a flasher if the unit has a fault or trip condition. I tend not to use flashing signals unless it's a fault...it's too easy for the brain to become used to it and then not see a non flashing lite.

If you got the 12hr you get 6dc inputs and 4 out I think so you should have enough. If entering the room with the tumbler running is truly (OSHA) unsafe then you can use a cheap maglock or something to energize and hold the door...just make provision (key bypass)for getting in the room. I do a similar thing on a silo I have that has a big Roots blower at the base. Sound Db is way to high even with hard shells on so I maglock the door when running and have a permissive to keep it from starting if the door is open.

Hey switchman,

Thanks for the reply. I was kinda thinking the same things you mentioned. Because like you said its been working forever and nobody I know of has been hurt.

The sound level is very high but I think that the hardshell ear muff they have work pretty well.

I am going to put lights outside of the room like you mentioned. But the only stack lights I could find are cost prohibitive. So I am building my own.

I am adding a emergency kill switch inside the room in case someone is in there and things go bad they don't have to run outside. Although running outside maybe the prudent thing to do? Maybe should re-think location of 911-switch.

This is my first little project of this nature and I will be honest this little TECO unit is really quit neat.

Programming so far has been pretty easy, once I remembered some of the in's and out's. I do have a programming issue I cant quit figure a way around.

I will have 5 different timed setting 5-25min in 5min increments. I was hoping that I could use up/down buttons to adjust time and display it. But I can not for the life of me figure out how. Unless you can give me an idea of how to do it I will have to go to using 5 buttons for different settings.

Anyway, I have rambled long enough. Thanks for the input Switchman! I do appreciate all the help I get here.

Let me know if you have any ideas.

Thanks,

bill12780

Hi, Bill,

I'm sure that up/down buttons shouldn't be too difficult - I haven't used one of these, but assuming it's much the same as all the other similar PLR's around, all you need is an up/down counter + decoder (comparators?) etc. (I may be waffling a bit, but, to reiterate, I'm sure it's possible). If I get a chance, I'll download the software & set up a simulation.

To another subject: do not rely on this thing for any safety stuff (as in safety-related control system). You need to include a hard-wired Safety relay as the Master Control Relay (MCR) to allow the machine to start up, and which can only be reset when any Emergency Stop control is released. Your PLR can supply an Enable signal (allowing the MCR to be reset), and a signal to trip the MCR, but that's about it. Software solutions are generally a no-no for anything Safety related.

It's getting late, & I'm run off my feet at present, but I'll try to find you some references. Try looking up Guardmaster/Allen-Bradley - they have some good info. on Safety systems.

John

Bill,

Having slept on it, I'd say that it's maybe OTT using a Safety relay/MCR type circuit. It's a pretty straight-forward app, and it would double the cost of bought-in gear. Just make sure you have an approved Emergency Stop button or two, and don't rely on the PLR for safety.

A thought about time setting - were you going to use the LCD to display the selected time? It's a bit small (but would be fine if consistent with other controls & indicators around the shop).

An alternative would be a rotary switch for time setting - this would then indicate the set time. To save inputs (so you've still got a couple of spares if needed) you could binary code the time settings onto 3 wires. This would allow you to go up to 8 settings (or 7 + OFF) with only 3 inputs used.

John

Morning John,

As far as the safety switch is concerned. I thought about what you said. So I thought I would just use the stop switch (big red button that has to be physically twisted to reset once pushed) in series with the +24V that runs the PLR. Using the NC contacts it would open this line when pushed. This should shutdown the PLR and disengage the relay that will be turning the power on/off to the tumbler. What do you think?

I gotta say...Your smarter then I am this early in the AM (About 8am here) using a encoder switch would be a great idea. Have to look into this today.

Well I have to prep for a class that I am teaching on Basic Electronics to our service guys. I will deal with more of this latter this afternoon.

Thanks John! appreciate your thoughts!

bill12780

P.S. Oh and don't waste your time writing the logic for me I wont learn a damn thing that way. Just point me in the right direction and kick me in the Butt! I may bounce off a few things on the way, but I will get there! hahaha (Thanks for the offer though)

Hi, Bill,

The twist-to-release button's fine - but you can't use it to shut down the system via the PLR - the diddy little relay contacts in there ain't safety-rated (I very recently had an AB Micrologix with a welded-up relay output). Suggest you get a button with an extra contact block to kill the main power to the machine (as well as the PLR supply). This means running mains up near your +24V line - be very careful to keep the wiring physically separated. Make sure no insulation can get abraded on any sharp edges. Run separate earths from any exposed conductive parts to the Protective Earth point.

Sorry to harp on, but I've been through this loop over & over, and the regs get tighter every year.

My thought for the logic would be to used the binary-coded input to preset a down counter at the start of a run, then use a five-minute timer to decrement it until shutdown time (or use an up counter until count matches coded input?). But there's more than one way to skin a cat...

All the best, John.

You are absolutely correct. NEVER use anything but hardwired mcr for safeties. I have retrofitted most of the lines in this plant due in part to that very reason. Where applicable I do run all my e-stops and permissives into my PLCs for annunciation on my hmi screens, and the operator uses this to quickly clear issues. On Bill's tumbler though, since it has been in service already I don't know if he needs to worry much about control, just bells and whistles. I personally can't think of any reason why I would kill power to the unit though for some control purpose.

On this TECO...they are decent units, comparable to (and maybe built by the same company) to AB's pico... but you only get like 800bits to play with and very very limited basic programming. You can do the switch with 3 wires like you are talking about...it'll work just fine, but that depends on the rest of the input needs since you only have 6. Now, on this PLR, bear in mind that the 4 arrow keys are usable as Z1 to Z4 in the ladder. There is a check box in the program to set them to work. They act as momentary pushbutton so you have to latch them and use that rung as a permissive, along with whatever else controls your appropriate timer, and you'll have to unlatch them. I'd probably use one input switch in combo with the keypad Z bits to get what I needed and the resets. I don't think you can call different register values to write the preset value of a single timer. I'll look (I haven't tried before) but I kind of doubt if you can. At the same line you call the timer you want you can use the HMI function to show on the screen whatever timer value you are on or what ever you want to write. If I remember right the instructions showed a shift function...sequencer...but I never could find the function in the program. That would let you just sequence through and fire your timers with less rungs.

I'll dig around tonite if I have time and find my disk or maybe download it and look.

Bear in mind, I use these things and the pico in pretty (very) simple bell and whistle or super simple control spots where I don't or can't run I/O from a PLC and it doesn't justify a micro plc. But it is not a replacement for a micrologix or other PLC. You'll be happy as long as you don't try to get over complicated.

Hi, Switchman,

I agree that the on-board buttons could be used - I've done this, but only in office & clean lab-type environments. It depends on the conditions in the shop - is there decent lighting? Do the guys habitually wear rigger's gloves? etc. The on-board controls & display are a bit pokey.

If I get a chance over the week-end, I'll try to knock up a simulation using the 3-wire coding (just for the hell of it). Will let y'all know.

John

Good Morning John & Switch,

I do appreciate all you two's help. Your insight and experience is really helping me.

This whole system is really quite simple. In fact I have the program already done. I am sure there are more elegant ways of doing this but its works.

I did not know you can use the buttons on the front of the unit! That is a great option for a different application I will using this for in the next few months. But for "Our" machine shop the thing would be covered in grease in a matter of days!

For the the 911 switch. This is what I plan to do. The tumbler is just a big bowl with a on/off switch. There is nothing else to it to control other then the mains.

So what I plan to do is use a NO high current relay that I will use to control on/off of the unit. I am going to wire the NC contacts of my switch in-line with the 24V DC power supply to the PLR. I have tested this and when you just turn off the power supply it opens all the outputs. So it will immediately (almost) turn off power to the tumbler. (The tumbler does not stop right off anyway so the little time lag we are talking about is really not an issue) Then of course when its reset the program just starts over when the power is reapplied.

I would like to know more on the encoder switch you speak of. I thought I knew what you meant but upon further review I don't.

Right now I am just going to use 5 momentary switches to choose timings between 5 and 25 in 5 min steps. The switch will also be the start button. So you through a main ON/OFF switch and then choose the time and the tumbler starts. Pretty simple.

I am using the display to count down the timer I am mounting the PLR in a box and will cut a window for the display.

I would like to know two things. First, I have looked and read through the users manual but found no mention of the Z1-Z4 for the front buttons. I am wondering if there is a different manual I don't have Could you Email me the PDF of what you have?

Second, Do you know how to turn the back-light on the display on/off? I can find NO reference to the back-light at all in the user manual I have.

Thanks again for all your help.

Have a great weekend if I don't hear from you before then!

bill12780

I haven't got a manual, but this:

.. is where to find the tool, and this:

.. is from the Help system.

Will get back about the coded switch, but in brief, you're looking at a rotary wafer switch, say 3 wafers, each 1P12W.

1st wafer wired as 2⁰ = 1 count (i.e. 1st way open, 2nd way connected, then repeat). 2nd wafer is 2¹ = 2, 1st & 2nd ways open, 3rd & 4th ways connected etc. 3rd wafer (2² = 4) has ways 1,2,3,4 open, then 5,6,7,8 connected.

This looks a mess - a quick circuit sketch will make it clear (I hope!) - gotta go do family stuff now - I'll get back later.

BTW - you're plan for controlling with a PLR output & high-current relay sounds fine - as long as you have a lock-off isolator in there for service. A glitch on say the 24V line, or a fault in the PLR, could fire up the PLR program - starting the motor & mangling anyone unfortunate enough to have a hand in the wrong place.

http://factorymation.info/plr/SG2PLR_UserManual.pdf

page 29 on the pdf from factorymation site shows the menu you get when the teco is stopped. Under the set item is where you can enable the Z bits. In the programmer it is under the operations menu tree down toward bottom is module system set...pg 25 on the pdf. It's also the place to do the backlite.

ok...question for John... I'm looking at the buttons you pasted in. These look totally different from the buttons I am showing. I couldn't find my disk yet butI did download the version from the site last nite. What I have doesn't show the shift function like yours has at the far right. The last teco I put in was somewhat similar in concept to what Bill is doing with needing several timers. I wanted to simply use the shift function on 1 pb and do a sequence output to a y internal and fire different timing. I ended up using the Z buttons(which is why I knew about them) but really just wanted one. My teco didn't have the shift function in it and the program I got last nite doesn't. Now i see yours does. Am I blind? lol

Dang, I hate coooonfusing myself

Hi, Switchman,

I just followed the link from Bill's post #4, & looked for "free download".

This is the "Help -> About..." window:

I guess the config. on-screen may vary, depending on the model of PLR - I went for SG2-HR10-A (the default, I think).

Best I can do - hope you find it!

John

OK, here's a bit of a go at describing a system using an encoded rotary switch for input.

This is the setup with the switches:

The next bit is tricky. As Switchman pointed out (#22), the TECO is rather limited. Some other PLRs (and most PLCs) would have counters that you could preset based on a binary code, or some easy means of comparing a count to the three inputs - there are all sorts of ways, but the TECO seems to be one of the most limited. Then I guess you get what you pay for!

I'd suggest making a 3-8 line decoder. You can copy the guts of the logic from an MM74HC138. You don't need the fancy gating on the ENABLE inputs, but you could use the ENABLE line connected to an input START button. This would then give you the same effect as 8 momentary pushbutton switch inputs.

While your technique of killing the power to stop & reset the system is OK (I've never actually considered doing that!), I think it would be more elegant to have a STOP button. This could just reset all the timers (I'm assuming here that your pushbutton input design used 5 timers - one for each button. If not, please put me right. If I'm on the right track, the outputs from the decoder circuit can now start one of 8 timers, giving 5 to 40 minutes in 5-min increments).

Hope this lot makes sense & helps,

All the best, John.

BTW - you should keep your 911 button to kill motor power via the power relay, but I'd suggest using a NC button for the STOP function I mentioned above, and using a pair of NC contacts on your 911 button in series. This will reset the PLR timers when the E-stop is pressed (ensuring the tumbler won't restart when the button is released).

STOP buttons are conventionally NC (ensuring the stop function can't be overridden (in a traditional hard-wired MCR system), and making it easy to run several in series). START buttons are conventionally NO - running 2 in series gives a simple two-hand control for start-up.

Avoid giving the guys the impression that the E-stop is for stopping the machine except in an emergency - it's bad practice. Hitting an E-stop on some systems can bugger things up in good style, taking hours of lost production time to get the machine back on-line.

John

Nice drawing John...looks right to me. I use that very thing in several places. I personally like Electroswitch brand. check their site. http://www.electroswitch.com/

I've used both the big switchgear industrial sized switches and the "electronic" small switches for many years and they are very good.

OK...i'm still curious about why your program is showing the shift function and mine won't. I think Bill said his doesn't either. In this situation, were it me, I'd want to use a machine running bit off of the original pre-existing control, and a stop bit just like you said. But myself, I would only want one pushbutton and use the shift function to step to each timer as I pushed the button. If I ran 90% of the time at one setting...say15 minutes...I would make that a default so I don't have to select anything...just push the start button. Otherwise tap the pb a couple times until you have the right time displayed on the screen then hit the start. Lots of way to skin a cat though...as long as they kick and howl while you do it.

Ok...i got to get back at it, while my plant is down. I had to wrap a roll of duct tape around my Dell yesterday after it got knocked off a ladder. Got it working (no screen) and now I have an AB touchscreen that was weirding out last week so I need to see if the Dell will load my spare and go change it out. 100 things to do and time for 50...where do you start?

"100 things to do and time for 50..." story of my life!

'Fraid I've got no idea about the elusive SHT toolbutton. As I said, I just downloaded what they had.

Had a quick look at the Electroswitch range - something from eg the 31B series would do nicely. I couldn't see any prices, tho'. I agree that something fairly robust is needed, but the cost has to balance.

My objection to the one- or two-button timesetting arrangement is the display. As I've said, it's OK using the on-board LCD for status info. in the right environment. Using the rotary switch gives both control & indication at the same time.

My objection to the one- or two-button timesetting arrangement is the display. As I've said, it's OK using the on-board LCD for status info. in the right environment. Using the rotary switch gives both control & indication at the same time.

Yes, I totally agree with you there, depending on who is doing the operators job.

I finally figured out the shift function thing. I surely don't get it yet, but I figured it out.

I have about a dozen of these TECO units but have always used the ladder diagram, never had even opened the fbd side. For some unknown reason that is where the shift function is. I have a lot of years of PLC experience but have never dealt with state logic or function block style programming, only ladder. Used to do mainly GE fanuc, now it's all allen bradley.

So, now I have discovered a new toy to play and learn with. I only hope it's not as 'fun' as vb was to learn...

I met this with a Pico (or Moeller?) - lots of the clever functions just can't be used in ladder mode.

Strange.... Mine looks nothing like your does! but the versions are the same---1.9! I even started a new program with the sg2-10 has the unit and nothing changed. Then I thought maybe its the FBD menu. But no it is different yet again!

So I don't know what the heck!

And yes, the link you gave me to the manual is a completely different beast. Yours is like 104 pages. Mine is like 35 and from a place called b&b electronics....There is much more info in here.

I am going home for the weekend. But will be on this like jam on toast on Monday!

Thanks again you guys.

have a great weekend!

bill12780