Newbie with questions.

Hi,

Can you help me out with a few questions please.

1: What is meant by the following statements

Delay Off?
Delay On?

2: Design a simple circuit that will transfer the status of the thumbnails to the 7 segment display, whenever the IP switch 000.00 is opened. The transfer should only happen once per switch operation.

I haven't a clue where to start.

Any help would be greatly appreciated.

Thanks

MM

Well, I won't do your homework for you, but I'll try to get you going in the right direction.

Look at the words. "Delay" means to wait. "On" or "off" are states; that is, relays can be in one of two states, energized (on) or de-energized (off).

As far as the second question, you'll have to give us more information. Is this supposed to be a PLC? I'm assuming it is, since you posted it here, but by the wording, it could be a programming (as in C+ or FORTRAN) question or even an engineering problem calling for a circuit design.

What is shown in the thumbnails? What kind of equipment are you supposed to be working on?

a new term has just started!

Oh dear, we are just one week into the new school year starting and we have our first student post.

MM

Can you tell us what you think the terms delay off and delay on mean?
That should be pretty obvious, but to give you a clue I will tell you that they are to do with timers.

Your second question you will have to try and figure out for yourself, have a go at it and post your code here and then you can let us tell you where you are going wrong, then again you might find that you have it right. As the transfer should only occur when the switch is opened you will need to use a 'one-shot', if the PLC you are using doesn't have a one shot function you will have to roll your own, I am sure that one shots have been discussed here before, so have a search of the forum for some examples.

Paul

P.S I see Don answered while I was busy 1 finger typeing

For the answer to the first question, refer to your textbook in the chapter that discusses timers.

As to the second one, I'm really surprised that it is included in an introductory course. The conversion of thumbnail data to a format compatible with with seven segment displays involves the keratin function. There aren't very many PLCs that include the keratin function in their instruction set, and even when they do, it is notoriously difficult to tune. It's the sort of function that you can learn in a day and spend the rest of your career trying to master.

Hey Steve!

I've never even heard the term "thumbnail data."

What does it mean? Links are welcome. Maybe I've done it, but didn't call it that. Who knows?

Paul,

I'm still thinking that the Christmas Lights questions were the first students.

Thumbwheel

I think the original post meant thumbWHEEL data.

Marc

Thumbnail data is like a thumbnail sketch, but it is rasterized into JPG format.

DonsDaMan said:

Paul,

I'm still thinking that the Christmas Lights questions were the first students.

Click to expand...

Don, they seem to be American students not British!

The British students ask some classic questions, search this site for HNC and you will find out what I mean.

HNC students are a source of such fun and embarressment to us 'other' Brits.

Paul

A crumb

Here's a possible hint on the second problem.

The word is thumbWHEEL, not thumbNAIL.

As far as where to start -

It's the same thing we've told students over and over again. It starts with:

1) Make a list of all your inputs and outputs.

You are going to have to find out / decide, how the thumbwheel is wired to the PLC. My guess is BCD (look it up), but it's only a guess.

The same goes to your 7-segment display. Will the PLC drive each segment, or will you be wired (in BCD fashion?) to something with a bit of smarts to it?

You used a plural in your "thumbnails". How many do you have?

Try breaking down your task as follows:

1) Get the PLC to recognize the number set on your thumbwheel in a single register.

2) Prove that your logic is good, by toggling the input switch ("00.000"). I suspect that you have wired the thumbwheel to the same input card as the switch. Only the thumbwheel, and nothing else, should affect the destination register.

3) Focus on the output. Make the 7-segment display display what you want to display. Don't have any code driving the number you want to display, just manipulate the PLC memory space.

4) Now that you have some experience under your belt, try to write a program that does "One-shots". If the PLC has an ADD function, try to have it add one register to another and put the results back in the second register. Play with ladder logic until you understand how to make this happen only once when the switch is closed, but not every time. This will do more to get the concept of "PLC scan" into your brain than anything we could do or say.

5) Put the peices together. Simple.

Good luck, and post again if you need pointers

Hey, pointers I know about. We used to call them "indirect addressing." What fun they were! I understood them the first time I used them, then had to learn them again when C came out... man! It took me like 6 months to finally make the brain-connection that pointers were just indirect addresses.

I bet I asked some stupid questions THEN, too.

Yeah... I know you weren't talking about pointer-pointers.

I'm betting all the used text books at HNC have "www.plcs.net" written somewhere in the first chapter.

American students don't count? Well... maybe. We really don't like math. But we can usually COUNT, at least.

Thanks, I will have a look at it.

Thanks again for all your pointers

Opps!