from the Forum department...
Bit resolution on ADC
PLCs and related questions. topic
Posted by automatix on 3 October, 2008 - 5:28 am
Dear friends,

Does anyone know the importance of bit resolution on a AD/DA converter?

If I change a 16 bit resolution ADC module with 8 bit resolution, would the analog data be accurately read by the PLC?

We need to know this because we are afraid it will lead to an inaccurate data reading, which is something that must be avoided in the gas industry.

I really appreciate your willingness to share knowledge or experience.

Thank you and best regards.

Automate. ix at gmail. com

Posted by Rob on 4 October, 2008 - 11:09 am
Well, first you have to understand the difference between "accuracy" and "resolution".

An 8 bit A/D converter may be perfectly accurate. However, it has lower resolution so will not be able to resolve small differences in measurement.

The output of an 8 bit A/D converter has 256 possible values (2^8). For an input of 0-100 % to the A/D converter the output resolution is better than 0.4% (actually its 100/256) and is perfectly good for most level measurement applications.

However, in a 0-10,000 l/min flow range that's a possible error of between 0 l/min to 39 l/min. You need to decide if this is an error you can live with or not. Of course, there will be other errors from things like sensor noise, calibration erors, over & under range etc so in practice your actual error may be slightly higher than this value.

The same is true for an Analogue output.



Posted by automatix on 4 October, 2008 - 9:48 pm
Dear Mr Rob,

i have read your brief explanation about AD/DA converter resolution.

it has also made me clear that i should not change the existing 16 bit ADC into the 8 ones. since our system can only tolerate a very small deviation.

Thank you for your help Mr.Rob

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