difference between digital and analogue signals

[Ant-plc-man]

CAn anyone tell me the characteristics (or where to find them?) of both analogue and digital signals.

[Steve Bailey]

Post your definitions for both terms. We'll tell you how to put those definitions into the context of the PLC.

[rsdoran]

A digital signal is either ON or OFF

Analog signal can be voltage or current (usually milliamps) that varies in strength..0 to 10 volts 4 to 20 ma

Go READ the book.

[Ant-plc-man]

I really need to know the differences between the two and the main characteristics. You wouldn't happen to know how to calculate the resolution offered by a 12 bit analogue to digital converter with a 10v reference would you?

[PLucas]

Speaking personaly, I would be very reluctant to assist you with your enquiries, I have just read your previous posts and it seems obvious to me that you have not been paying attention in class. Why not go back to your tutor and ask him/her for some assistance, then maybe come back to this forum with your questions. At least then you will be seen to be trying to help yourself. A 24 year old student, what course are you studying? HND or degree? As I feel that by the questions you asked you should have already been taught/know the answers by now

[RDay]

Reminds me of my old days in school. beerchug The teacher would give us a PLC problem to work out. I, like most of the serious students would research the problem, write my code, and debug it. The other guys in my group(if they had showed up for class that day)zzzzz would copy the final solution and we would all get A's. ;) We graduated and entered the real world ready to make our fortunes and our lives dreams come true. :D Today I work in the field I love. I get paid to play with high tech electronics and build the equipment that makes industry move. As for most of my fellow students who hitched the ride along the way, they are box boys and waiters making minimum wage. Kinda brings a tear to your eye don't it? bawling

[Steve Bailey]

You wouldn't happen to know how to calculate the resolution offered by a 12 bit analogue to digital converter with a 10v reference would you?

12-bit resolution is 1 part in 4096. 10 divided by 4096 is approximately 2.4 millivolts.

[Ant-plc-man]

didn't ask for a life story, zzzzz just the answer to the question would surfice. I don't work with plc's and don't want to work with plc's. I only want to pass the subject and get on with more important aspects relating to my area of work. Bet you've got lot's of friends eh!

Would just like to say thanks to those who have tried to help and will hopefully be back to give you my answers.

[Tom Jenkins]

A pilot light or wiggy are either on or off - discrete. A voltmeter indication is proportinal to the strength of the value being measured - analog. Relate this to a PLC inputs and outputs!

[me!!!]

y cant u just tell the homer person the answer??? hey???
and also i needed to know the difference also!!!!

[jvdcande]

y cant u just tell the homer person the answer??? hey???
and also i needed to know the difference also!!!!
Why won't my boss just pay me? I only need the money, not the work.
How does that sound to you? An attitude like this is why student posts don't get the answers they are looking for. Show us some effort and we'll be glad to help out.

BTW I do love my job and I'm proud of the work I do for my paycheck. I got where I am now because of a lot of hard work, both during as well as after business hours.

Regards,

[PLucas]

y cant u just tell the homer person the answer??? hey???


Because we are all prima donnas!!!


i needed to know the difference also

The answer given by Ron (RSDoran) tells you the differences between the two.

If you would like to follow Steve's advice and tell us what you know, then maybe you will find us Prima Donna's are more willing to part with our hard earned knowledge.

Paul

[rsdoran]

Seems people like to play....sometimes the ignorance shown is not false though.

It seems a simple lesson in electronics is desired. Since I am attempting to obtain a better education for myself I do not see a problem with sharing what I do know, it may help me more than others.

Voltage: (Electromotive force) is a POTENTIAL DIFFERENCE between 2 points in a electrostatic field. The unit of measure is the volt.

Digital (or discrete): comes from the word digit, uses discrete which for plcs mean binary using 0 or 1 to respresent High/LOW or ON/OFF. Simple terms the input or output is either High/Low (on or off).

Analog is any continuously variable signal. With a plc a device may send a varying current (0-20ma, 4-20ma) or voltage (0-5, 0-10, etc) and a "converter is used to process this in digital signals a plc can use, usually input to a numeric file.

Resolution is the smallest change it can detect in the quantity that it is measuring...ie 0 to 10volts could be measured in increments of 0, 1, 2, 3 etc or it could use 0.1, 0.2, 0.3....5.1, 5.2, 5.3....etc to 10.

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???
I did leave one point out, Voltage is used as the POWER SOURCE for devices, in some cases an analog device may input 24v but output 0-10volt or 4-20ma. In some cases a device may need a separate power supply that is specifically 10volt. PLCs, in general, can use 110-230vac or 12-24vdc.

Anything else?

[Mark Buskell]

The light switch in your house is an example of digital, either on or off.

The dimmer switch is an example of analog, vary the voltage and directly varies the light output.

[Ken M]

OK, is it just me and old age?

I was educated (no, honestly) long before Mr Berners-Lee invented his wonderful tool. There was no such thing as a forum like this to get answers, information etc. You either got it by going to and listening in class, or, shock horror, reading books. And of course you had to work out which books to read. Usually there would be standard recommended publications for each class, plus some additional reading. One thing that definitely didn't work was going to the univeristy library, striding up to the librarians' desk and demanding "Analogue or digital, which is which, and be quick about it, I need it for tomorrow!"

I may have an antiquated attitude but I get really worried thinking of the next generation of 'engineers' whose approach to life is shown by the emergency posts we get on threads like this. "Let's not do any preparation or planning, let's just ignore the problem till the last day and then we can always say we got no help from others." No wonder I get so despondent during interviews when I'm trying to hire someone. It's not the lack of knowledge that worries me (God knows, there's a squillion issues I'm ignorant about) it's the methods used to remedy this. We seem to have lost a lot of initiative somewhere along the way. There's more information available at my desktop today than I had throughout my entire educational life, and yet the ability to search, select, filter, sort, extrapolate does not get nurtured or rewarded. Let's just ask someone instead.

OK, yet another horse ridden in to the ground. I feel a lot better even if no one reads this.

Ken

[ade]

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]

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]

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]

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]

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]

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]

...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]

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]

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.
http://www.threadbombing.com/data/media/13/useless-troll.jpg (http://www.threadbombing.com/details.php?image_id=4634)

[Mickey]

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]

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]

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]

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]

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]

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!

[MikeDawkins]

i'd like to know which primary school the student is currently at so when they come up for an interview, i will know not to hire them!!!

About Ant-plc-man BiographyStruggling studentLocationManchesterInterestsComputer, footballOccupationElectrical engineer (trainee)

[MikeDawkins]

plus the original post was from 2002 so the "student" is probably out there somewhere..........

[iant]

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.

I have posted a personal message to you....
the answers given to this OP (Original Poster)
was correct at the time.
AND
there was no GOOGLE search engine or wiki so apart from RTFM
there was no easy way.

Also For DABA
This site is operated in memory of its founder Ronald S. Doran


http://www.patchn.com
was RSDORAN's Website he died at 58 in 2007
Still posting and helping people

BUBC
Sorry Mate
GROW UP

[rdrast]

the answers given to this OP (Original Poster)
was correct at the time.
AND
there was no GOOGLE search engine or wiki so apart from RTFM
there was no easy way.


What?
Google is 13 years old. Before Google, there were other search engines as well, and a prolific usenet community.

Wikipedia had its 10th year anniversary in January of 2011, so it too was around at the time of the OP.

/shrug.

[iant]

it wasn't well known in 2002
dont forget we in Aust. are down under

[daba]

....Also For DABA....


You missed the point iant, I was correcting the esteemed Ron's post simply to provide correct data for anyone who needs it. We have to hope that "student-hoover" would at least pick something up.

Ron's posts live on long after his death, and on this occasion his data was "imperfect", or misleading. I will continue to correct such information whenever I see it.

I would personally hate it if I read something on a forum which later (and it doesn't matter how much later) turned out to be incorrect. By posting the corrected numbers I may just do some service to others.

[daba]

I just wonder what OP is doing now....

Last Activity: June 26th, 2002 07:55 PM

[Peter Nachtwey]

it wasn't well known in 2002
dont forget we in Aust. are down under
You better be joking. Where is the smiley that indicates you are joking?

[iant]

:):)

[iant]

is that better Pete