PLC assignment help needed

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Hi everyone new to this,

I've been working on a college assignment for instrumentation engineering and have been given a design task. I've been going through it but I don't really understand designing programs, in this case ladder logic. Any assistance would be brilliant and any additional general help on PLC Programming would be appreciated, as I really enjoy PLC topics but seem to struggle.

Heres the problem given:
There is an industrial oven on your site used for heating bearings for motors in the repair workshop and the bearings are heated up to a normal temperature of 80 degrees celcius.. Lately electricians in the repair shop have been asking for local indication of the process.
1) When the beaing is placed in the oven and a door switch is made as the oven door is closed the light should indicate amber for 5 seconds.
2) After the 5 seconds the oven automatically heats up and the red light comes on for 30 seconds indicating a bearing is being heated up.
3) After 30 seconds the oven is switched off and the bearing is allowed to cool inside the oven with an amber light on for 10 seconds.
4) This is replaced with a green light for a further 15 seconds and then the green light goes off meaning the bearing can be removed safely and retaining enough heat to place on to the motor shaft.
5) Try to incorporate any safety interlocking with the door switch and alarm conditions to enhance your program.

Ive got as far as point 2, using a retentetive timer in step 1. As I said earlier any assistance would be appreciated and any explanations to help me better understand PLC's/Design.

Thanks in advance, JM

JM,

You probably don't yet realize that there are hundreds of different models of PLCs, and they all are slightly different so that a program for one may not run on another. To help you, please list your class PLC brand and model, and your software name and version. I suppose this happens because instructors treat programming as if it is generic and THEIR version is the only one that matters.

You should also make a first try and post that here as a PDF print-out file, or a ZIP file of your actual PLC program.

I've got as far as point 2, using a retentetive timer in step 1.

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Do not start by thinking about the "input" devices, such as door switches, and 5-second timers. Instead list your outputs, the goals for your program, such as:

"READY TO HEAT (AMBER LIGHT), PLC Output xx:xx",
"OVEN HEATER & RED LIGHT, PLC Output xx:xx",
"SAFE TO REMOVE (GREEN LIGHT), Plc Output xx:xx".

If you put a rung in for each output, then you will have them all turned on a working. Now all you have to do is figure out how to turn them off at the right times, and back on at the right times (as the result of various (4) timers, switches, and other inputs.

Hi, thanks for the fast reply. I have left my plans at college. The PLC's I use vary but they are all Mitsubishi's, mostly the FX series. Yes, we are only taught one type of ladder logic I didn't know there was others until I posted this on another thread. My original plan in ladder log looks something like this (just the amber light part up to now).

I currently have this | | OPEN, |-| CLOSED

X000 T250
--| |--------|-|---------------------------------(M1)---

M1
--| |--------------------------------------------(T250 K50)---

X000
--|-|--------------------------------------------[RST T250]----

M1
--| |-----------------------------------------(Y000)----

I may have written this out wrong.

Thanks in advance, JM

As in any PLC program, use address descriptions and rung comments to describe WHAT each instruction IS or DOES. That makes it readable to anyone (or yourself) trying to figure out what is going on.

Sorry. TS250 is a retentetive timer and holds its charge until reset, which is why the RST 250 is there on the rung. T250 K50 is the timer and times 5 seconds. The M's are auxillarry relays. The M1 contact energises when the corresponding M1 coil is energised. Finally the last M1 contact will also energise when the timer starts and will light the amber light (y000) for 5 seconds. I forgot the comments so sorry if this just sounds foreign. This is as far as ive got really.

Most students make the mistake of trying to get too far ahead of the logical process. Start simply with the 4 Output rungs (including a way to STOP the process). These are your goals; where you are going; the actions that you want the PLC to perform. All other instructions are the bells and whistles that modify or change these PLC outputs. Then add the 4 timers with the correct settings. Only then add the "finishing touches" to control each output.

Hi. Appreciating the help and tips, becoming clearer. Like you say i'm probably just over complicating it. On the picture does it say 'MO' on all the rungs? Not very clear sorry.

JM

Yes, I put the RUN RELAY MO on each rung. That is just a place for you to start adding your timer logic. Maybe on some rungs you will not need MO. It controls the system STOP and START functions. Never start anything until you know you can stop it at the right time.

PS: You might try ZOOMing your screen to see the rungs better. I can read all the text in that picture on my screen, but my screen is large for my poor eyes. If you do your logic correctly, you should not need a retentive timer or a timer reset instruction. Non-retentive timers will reset when you remove their trigger input.

Maybe you can read this LogixPro simulator version. I ran and tested it for all your conditions. A Mitsubishi version should be similar but not identical.

Yes I understand that thanks. I will convert it into mitsubishi and run/test it. Thanks for all your help Lancie. Much appreciated

JM

On the picture does it say 'MO' on all the rungs? Not very clear, sorry.

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One reason that PC users are unable to read text on their screens is that they have their Windows Control Panel Display Screen Resolution settings too high. Your monitor has xxxx-zillion pixels, so you got to use them, right?

I have found that when I help friends or family with computer problems, that invariably I cannot read the titles below the little icons on their Windows Desktop. Their screen resolution is maxed out so they can see pretty pictures in the background, but cannot read the text. Lowering the screen resolution setting results in a smaller physical viewing area, but readable text. I keep my monitor set for 1024 x 768 pixels, even though it has much higher settings. I had rather read and KNOW what file I am opening, rather than guess. I do not ever put in any pretty picture background either, setting the "Screen Saver" to "(None)". If I want to see a pretty picture, I will buy one and hang it on the wall.

Lancie1, i think there is also the solution to not seeing text on computer screen of using two magnifier classes in frame that can be placed on your face so that they are supported on three points, nose and ears..

But the real problem in this case clearly is low quality screenshot (picture compression) and small picture, viewed in any resolution its not that clear it indeed says M0 in many places.

I will convert it into mitsubishi and run/test it. Thanks for all your help, Lancie. Much appreciated.

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Let us know how it turns out. Post your final version for future students. Also your instructor may be lurking in the twilight here. Many do to find out which students need help!

But the real problem in this case clearly is low quality screenshot (picture compression) and small picture, viewed in any resolution its not that clear

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Yes, these are the allowable limits on this site. Still, with my 1024 x 768 screen resolution, I could easily read the text in my posted picture. Higher resolution gives more area but less text readability.

Lancie1 said:

One reason that PC users are unable to read text on their screens is that they have their Windows Control Panel Display Screen Resolution settings too high. Your monitor has xxxx-zillion pixels, so you got to use them, right?

I have found that when I help friends or family with computer problems, that invariably I cannot read the titles below the little icons on their Windows Desktop. Their screen resolution is maxed out so they can see pretty pictures in the background, but cannot read the text. Lowering the screen resolution setting results in a smaller physical viewing area, but readable text. I keep my monitor set for 1024 x 768 pixels, even though it has much higher settings. I had rather read and KNOW what file I am opening, rather than guess. I do not ever put in any pretty picture background either, setting the "Screen Saver" to "(None)". If I want to see a pretty picture, I will buy one and hang it on the wall.

Click to expand...

Lancie1,

If it's just the text under the icons on the desktop, there is an alternative to lowering the screen resolution. Under Display Properties, on the Appearance tab, you can change the Font Size. Three choices Normal, Large Fonts, Extra Large Fonts. These settings should produce results at least as good as changing the screen resolution and might even be better. It depends on what your monitor's native resolution is and what you had it set at.

Regards,