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. 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!

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

[jvdcande]

Originally Posted by me!!!

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]

Originally Posted by me!!!

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

Because we are all prima donnas!!!

Originally Posted by me!!!

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