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[cindy]

Sorry the questions were a bit blunt and formal, I have read the PLC live tutorial and learn't alot. But some of the information I am trying to accuire still isn't evedent. I guess it is the way the question has been asked in the first place. The only thing I can say in response is I'm having a blonde moment.

In the tutorial there was no clear mention of the resolution and relationships between analogue I/Ps and O/Ps or word length. I have read books and donot know where to look next. Please can you even tell me where to start looking? Please!

[Allen Nelson]

As someone else said, Why is it the British schools that get hung up on obscure or obsolete terminology.

First off, I/P and O/P are NOT the standard abbreviations for input and output. If your instructor or text is using it, they're wrong.

I/P is usually the abbreviation for current-to-pressure (usually followed by the word "transducer").

Second, your question is poorly worded (or punctuated). I can't tell if you are comparing analogs to inputs & outputs (by which do you mean bits?), or are wondering about analog I/O (the correct abbreviation for inputs/outputs).

The phrase "Word Length" is also meaningless. 1 Word = 2 Bytes = 16 bits.

All that complaining aside, here is PART of you answer. Analog I/O modules convert an analog signal (which can have ANY value in a certain range) into a digital (binary) representation. Think of the difference between Real Number (analog) and integers.

The most common Analog I/O is 12-bit resolution. This produces converts 0-10 volts into an integer number ranging from 0-4095 ( =2¹²).
14-bit and 15-bit resolution are also common.

with this knowledge, I'll leave it to you to crank out the math as to what % the incoming singal (0-10 V) has to change by to be able to "see" the change in the digital signal. It's different for each bit-length of resolution.