difference between digital and analogue signals

ade · Jun 24, 2005

Ant-plc-man said:
CAn anyone tell me the characteristics (or where to find them?) of both analogue and digital signals.

ANALOG
In application, let say you have a pressure transmitter with 0-300 PSI input, and 4-20 miliamps output. You connect the output of the pressure transmitter to the PLC analog input module, after some codings in the PLC program, the 4-20 miliamps becomes (say 8 bit) 0-255(decimal) and stored in the data table represented by 8-bits. In analog value, you have many numbers, in fraction of 1, you will have 255 unit of fraction. So in the analog term, you have "in-between" value between 0 and 255, 0-300psi, 4-20mA.

DISCRETE
Again, in application, you have a pressure switch (fro example) that calibrated at 150 psig to pick up the contact either ON or OFF. Then you connect the pressure switch to the PLC Discrete Input Module, and after some codings, the physical input then represented by a single bit in the PLC memory, these single bit can only either ON or OFF. There is no "in-between" value in the discrete term, the only value is ON or OFF, 1 or 0, High or Low.

________________________________
Sorry if there are some mistakes
-ade-

Leadfoot · Jun 24, 2005

I wonder how many of these students looking for a fast answer just to get by, demand an A for the course cuz they paid their tuition?

I quit teaching tech school 16 years ago for that reason. I still read everything I can get my hands on. I wore out an HP printer printing manuals on the PLC's and periphals I have been working with. Oh wait, maybe that is the difference with some of us gray haired antiques and todays students is that we actually can read and comprehend. They expect google to answer the questions. Quick nuke it I want it NOW.

bubc · Oct 12, 2011

sad a holes

I believe the world works and runs a lot better with the exchangment of knowledge.you people are sick.If a young fella wants to better himself why not tell him the answers.you must have struggled through collage seeing that its a problem to release any information you were taught.Its like I had to struggle and suffer so let him.Come on!!get off the stage.

daba · Oct 12, 2011

rsdoran said:
8 bit is 255 divisions
12 bit is 4096
16 bit is 655345
As you can see the higher the resolution the more definitive the precision becomes.

Did I leave anything out???

As we have students looking in on this thread, it's only fair they get accurate information....

Resolution of an 8-bit binary number is 1 part in 256, values 0 to 255 : Sometimes the 8-bit nunmber is "signed binary", which still has a resolution of 1 part in 256, but the numeric range is -128 to +127

Resolution of a 12-bit binary number is 1 part in 4096, values 0 to 4095 : Sometimes the 12-bit nunmber is "signed binary", which still has a resolution of 1 part in 4096, but the numeric range is -2048 to +2047

Resolution of a 16-bit binary number is 1 part in 65536, values 0 to 65535 : Sometimes the 16-bit nunmber is "signed binary", which still has a resolution of 1 part in 65536, but the numeric range is -32768 to +32767

Resolution of a 32-bit binary number is 1 part in 4,294,967,296, values 0 to 4,294,967,295 : Sometimes the 32-bit nunmber is "signed binary", which still has a resolution of 1 part in 4,294,967,296, but the numeric range is -2,147,483,648 to +2,147,483,647

rdrast · Oct 12, 2011

bubc said:
I believe the world works and runs a lot better with the exchangment of knowledge.you people are sick.If a young fella wants to better himself why not tell him the answers.you must have struggled through collage seeing that its a problem to release any information you were taught.Its like I had to struggle and suffer so let him.Come on!!get off the stage.

Mind you, this is a 6 year old thread, and you are just looking to pick a fight, but so be it.

No, it is the attitude of the original poster (and you), which demands that you be simply handed everything on a plate, without putting in any legwork of your own.

Start with Google. Start with Wikipedia. Start with reading your actual books. Then come here, explain what you understand, and ask for clarification of what you do not understand.

When I see that level of "Just give it to me now" laziness, I just add you to the ignore list.

jvdcande · Oct 12, 2011

bubc said:
I believe the world works and runs a lot better with the exchangment of knowledge.you people are sick.If a young fella wants to better himself why not tell him the answers.you must have struggled through collage seeing that its a problem to release any information you were taught.Its like I had to struggle and suffer so let him.Come on!!get off the stage.

When you want to learn, you need at least some minimal knowledge to start learning. In kindergarten, you need almost no previous knowledge at all. In high school, it's common to expect the pupils to be able to at least read and write. For PLCs, a minimal knowledge is some math, say calculating the powers of two, and some understanding of electricity/electronics, say some relay logic and the difference between analog and digital. I wouldn't say that's too much to ask from our side, knowing you'll get some info here for free, for which you have to pay teachers otherwise. When I see how young native English speaking people write down their questions here, I get the strong feeling they're lazy. I could be wrong, it could be it's their teachers who have been too lazy to learn them how to write, but I doubt it.

Regards,

Rube · Oct 12, 2011

bubc said:
...If a young fella wants to better himself why not tell him the answers...

Is it just me or is this statement a contradiction?

kamenges · Oct 12, 2011

That would be correct, Rube.

I've been going through this with my 12 year old daugther this week relative to real-world applications of the Pythagorean Theorem. She didn't like me requiring her to frame the problem herself and do a little research either. She doesn't quite appreciate that understanding the subject is as or more important than the number you come up with in the end. Then again, she's 12. I kind of expected her not to appreciate the process. But bubc and the OP? Not so much

TurpoUrpo · Oct 12, 2011

bubc said:
I believe the world works and runs a lot better with the exchangment of knowledge.you people are sick.If a young fella wants to better himself why not tell him the answers.you must have struggled through collage seeing that its a problem to release any information you were taught.Its like I had to struggle and suffer so let him.Come on!!get off the stage.

Mickey · Oct 12, 2011

kamenges said:
That would be correct, Rube.

I've been going through this with my 12 year old daugther this week relative to real-world applications of the Pythagorean Theorem. She didn't like me requiring her to frame the problem herself and do a little research either. She doesn't quite appreciate that understanding the subject is as or more important than the number you come up with in the end. Then again, she's 12. I kind of expected her not to appreciate the process. But bubc and the OP? Not so much

Similar issue with my 9 year old grandson. While helping him with his Social Studies homework, he had a few question to answer about California. He wanted to read the questions first then look thru the chapter looking for key words to get the answer. I told him we were going to have to read the whole chapter first then answer the questions. Needless to say he didn't like grandpa's method.

TConnolly · Oct 12, 2011

bubc said:
I believe the world works and runs a lot better with the exchangment of knowledge.you people are sick.If a young fella wants to better himself why not tell him the answers.you must have struggled through collage seeing that its a problem to release any information you were taught.Its like I had to struggle and suffer so let him.Come on!!get off the stage.

Clearly you haven't looked over very many of the threads on this site.

Does your teacher give you a homework problem and then give you the answer? Its because you are supposed to work it out - that is how the brain learns. So why would you come here to learn and expect to be treated differently?

Did it ever occur to you that we see you as our future coworker and we want our coworkers to be competent? We have all worked with enough punks that got through school without exerting themselves and by coasting on the work of others. They are a hazard to themselves and their coworkers. Lots of students have come here and shown a little bit of work and gotten a lot of great tutoring. If you want something witout any effort on your part than you have no business in automation. Its hard work. It can also be very rewarding. If you aren't cut out for hard work then maybe you should consider a different career.

I is a noob · Oct 12, 2011

I think OP and then the "guest" that supported him, then the guy that complained about how this forum wouldn't give OP answers are either the same person or a couple of guys who just want to troll this forum, ignore them as feeding into it validates the practice....

Brijm · Oct 12, 2011

jvdcande said:
When you want to learn, you need at least some minimal knowledge to start learning. In kindergarten, you need almost no previous knowledge at all. In high school, it's common to expect the pupils to be able to at least read and write. For PLCs, a minimal knowledge is some math, say calculating the powers of two, and some understanding of electricity/electronics, say some relay logic and the difference between analog and digital.

I was thinking the same thing... I shudder when I see a poster asking basic electrical questions, and then later asking questions that are for a more advanced/experienced plc tech (Or worse yet, he's writing the program). People critisize, when someone is told they need to learn the basics, but you really do need to have some education in these matters. Some just have a part that they are having trouble understanding, and need a nudge in the right direction. But Electrical 101 is difficult to teach in a forum.

Rube · Oct 12, 2011

I is a noob said:
I think OP...are either the same person or a couple of guys who just want to troll this forum,....

I felt that way when I read it early, early this morning and decided not to comment on an old thread. Then it got some traction and I couldn't resist.

My daughters are being brought up to think for theirselves and do for theirselves--in spite of some people might think they need or deserve for free. Hell, I did that--most of you did that. Maybe we should've sat around with our hands out too...

Naw--not a chance.

DamianInRochester · Oct 13, 2011

Did it ever occur to you that we see you as our future coworker and we want our coworkers to be competent? We have all worked with enough punks that got through school without exerting themselves and by coasting on the work of others. They are a hazard to themselves and their coworkers. Lots of students have come here and shown a little bit of work and gotten a lot of great tutoring. If you want something witout any effort on your part than you have no business in automation. Its hard work. It can also be very rewarding. If you aren't cut out for hard work then maybe you should consider a different career.

Wonderfully put!

difference between digital and analogue signals

ade

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