Output/Input bits

For example i have PLC with outputs with AO 8bit resolution.
What does it meen, and what influence it gives?

I believe it means you have an Analog Output with 8 bits of resolution.

8 bits means that your full scale of output is either -128 to 127 (Or is it -127 to 128?) or 0 to 255. The more resolution it has, the finer tuned the analog signal can be. 10V/256 (8 bits) is less resolution than 10V/65536 (16 bits).

Edit:

Just to explain where those numbers came from. The bits are how many bits of binary are used for the output.
8 bits of binary is 2^8 = 256.
16 bits of binary is 2^16 = 65536

Tharon said:

I believe it means you have an Analog Output with 8 bits of resolution.

8 bits means that your full scale of output is either -128 to 127 (Or is it -127 to 128?) or 0 to 255. The more resolution it has, the finer tuned the analog signal can be. 10V/256 (8 bits) is less resolution than 10V/65536 (16 bits).

Edit:

Just to explain where those numbers came from. The bits are how many bits of binary are used for the output.
8 bits of binary is 2^8 = 256.
16 bits of binary is 2^16 = 65536

Click to expand...

so more bits meens biger precision of measurement and controling?

Yes.

But it also depends on the accuracy of the devices you are using for your input and output. A system is only as accurate as your least accurate device.

nightex said:

so more bits meens biger precision of measurement and controling?

Click to expand...

Don't confuse resolution with accuracy.

Accuracy is the difference between the "right" value and the actual value. A lot of things influence this, and I've seen 12 bit and 16 bit I/O that had a lot of drift and error.

Resolution is the number of decimal places or digits in the display. It isn't the same as accuracy. You can display a wrong answer to 20 decimal places.

And look at the resolution required. 1/256 = 0.4% If you have a 1% accurate sensor or a valve positioner that is ±2% (which some are) then additional resolution probably won't give more accurate results.