Basic Op Amp Question --- Application is For Boosting IR Photodiode Signal

[alsetalokin4017]

16 bits (over 65 thousand discrete levels) of precision

Resolution != precision. It may provide 16 bits of resolution, that does not mean it will provide accuracy matching that. The datasheet shows a ±3mV total error at full scale input (2048 mV @860 sps), though lower sample rates should improve that, it's not 'over 65 thousand discrete levels of precision' in my opinion.

Let us rather say "Accuracy != precision".  The device isn't much good if it doesn't return the same output level, for a given input level, each time. The mapping between output and input may not be correct (accuracy) but it should be consistent and there should be a consistent difference between , say, output level 32,500 and 32,501 (precision). If you want to argue that the device isn't really a "16 bit" ADC due to that ±3mV total error I can agree with that, ... but then why is it advertised as such?

[pmbrunelle]

Let us rather say "Accuracy != precision".  The device isn't much good if it doesn't return the same output level, for a given input level, each time. The mapping between output and input may not be correct (accuracy) but it should be consistent and there should be a consistent difference between , say, output level 32,500 and 32,501 (precision).

Yup, as long as you can repeat, integral non-linearity often doesn't matter if you're going to do a whole-system calibration... It's not like adc counts mean anything in real life anyway; you need to translate adc counts to real-life units at some point.

The consistency of the difference between counts is called differential non-linearity.

Often, spec sheets will specify "monotonic, no missing codes".

[Potomac]

Some very expensive ADC's for end users

The entry level one is 250 bucks, with 10 or 12 bits of resolution, and 16 ports.  Isn't that very similar to what Arduino has?

https://www.picotech.com/products/data-logger

[alsetalokin4017]

well, I think that the picotech product has a faster sample rate than Arduino can manage ...

[3141592]

16 bits (over 65 thousand discrete levels) of precision

Resolution != precision. It may provide 16 bits of resolution, that does not mean it will provide accuracy matching that. The datasheet shows a ±3mV total error at full scale input (2048 mV @860 sps), though lower sample rates should improve that, it's not 'over 65 thousand discrete levels of precision' in my opinion.

Let us rather say "Accuracy != precision".  The device isn't much good if it doesn't return the same output level, for a given input level, each time. The mapping between output and input may not be correct (accuracy) but it should be consistent and there should be a consistent difference between , say, output level 32,500 and 32,501 (precision). If you want to argue that the device isn't really a "16 bit" ADC due to that ±3mV total error I can agree with that, ... but then why is it advertised as such?

Sorry, this may be a language issue, in my mind a precision component or instrument meant something that's both accurate at the start and repeatable (low drift and noise). Even if accuracy != precision I don't think that without looking at the noise and other errors, we can just assume an ADC to provide meaningful resolution to the LSB. I don't argue that it's not a 16bit ADC, because it is, I'm just saying that the OP shouldn't rely on it to be as accurate as it's resolution, which is a common mistake at first glance.

Yup, as long as you can repeat, integral non-linearity often doesn't matter if you're going to do a whole-system calibration... It's not like adc counts mean anything in real life anyway; you need to translate adc counts to real-life units at some point.

I think it's a bit daunting task, even with proper equipment, to calibrate a 16bit system. I think it's easier to start with quality components for which the response curves and errors are stated by the manufacturer and provide sufficent accuracy out of the box.

[alsetalokin4017]

I agree with that of course. But I still think that for _this application_ and the circuitry that the OP has presented, that no op-amp is necessary and that the Arduino's 10-bit ADC will be adequate to the task.

Should I put some plastic tubing through my breadboarded system's sensing zone and run some cloudy liquids through it? See how small a change in turbidity is actually required to make a discriminatable difference that can be displayed on some kind of output like an LCD screen or the serial monitor? It might be an interesting project for a rainy afternoon.