PLC Resolutions and relationships

Hi, im currently learning PLC's at college and was wondering if anybody could help me! as part of an assignment iv been asked to describe the resolution and relationships between analogue inputs and outputs and word lengths? this means nothing to me and i am totally confused! any help would be much appreciated!

Bryan

These are Edexcel files pertaining to the HNC certification, the info may be there:
http://www.freestudy.co.uk/plc.htm

I've only messed with plc's since 1988.

Your question has me stumped.

The nice thing about this place is that you can come here and learn a tremendous amount by osmosis.

regards.....casey

Actually you probably do know the answer, its just the way the question is asked that makes it difficult.

Just think about the differences between 8, 10, 12, 14, 16 bit ect..and how resolution is converted to digital.

Thanks Ron:

You just have to explain it to me in Ebngkish, or Caseyese, or something.

from the "big picture" hint department ...

Greetings Bryan,

if you’re totally confused, here is something to think about that might help you sort things out ...

suppose that I have to measure the level in a tank of water ... the tank holds 0 gallons when empty ... the tank holds 250 gallons when full ...

suppose that I have a transmitter connected to the tank ... suppose that this transmitter gives a 4 mA output when the tank is empty ... suppose that the transmitter gives a 20 mA output when the tank is full ...

now for the PLC’s resolution ...

suppose that I can only afford a PLC input module which has 12 bits of resolution ...

question 1: using only positive binary integer numbers, how many steps can this module use to represent the level of the tank? ...

question 2: how large (in gallons) will each of these steps be?

now suppose that I have more money and that I can afford a PLC input module which has 16 bits of resolution ...

question 3: using only positive binary integer numbers, how many steps can this module use to represent the level of the tank? ...

question 4: how large (in gallons) will each of these steps be?

the basic idea: the more money ... the more bits ... the more steps ... the better the resolution ... the finer the “slices” that my PLC will be able to recognize and control ...

suggestion: post your “best guess” answers to the four questions above and we’ll see how well you’re coming along with this “resolution” topic ...

and finally ... welcome to the forum ...

Wow, Ron.

Are you teching currently? If the answer is no, have you considered teaching? You can be a good lectuer, you know.

regards
ST

Wow, Ron.

Click to expand...

I second that...
I always enjoy reading your posts.
Thanks again.

You just have to explain it to me in Ebngkish

Click to expand...

Honest guys, it loked fine with the new bifocals.

Like I say often, enginers can't spell.

regards.....casey