How many bits would an ADC require to measure....

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    Adc Bits Measure
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Discussion Overview

The discussion revolves around the requirements for an Analog-to-Digital Converter (ADC) to measure the output of a preamplifier, focusing on the necessary bit depth, sampling frequency, and data rate for a hydrophone signal characterized by specific sensitivity and capacitance values. The scope includes theoretical considerations and practical implications related to digital circuits and ADC specifications.

Discussion Character

  • Homework-related
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions how many bits an ADC would require, suggesting that the answer is subjective and depends on the desired resolution.
  • Another participant cites Nyquist theorem, stating that a minimum sampling frequency of 8 kHz is necessary to accurately measure a 4 kHz signal.
  • A participant mentions that the data rate from the ADC can vary, indicating that it is limited by the maximum sampling rate of 8000 samples per second but can be adjusted based on user preference.
  • One post references commercially available 16 or 24-bit USB ADCs designed for music capture, noting sample rates between 44 kHz and 96 kHz.
  • Concerns are raised about the quality of cheaper ADCs that may claim to be 24-bit but do not deliver true 24-bit performance.
  • Another participant argues that the analog components may limit the effective resolution to about 7 bits due to precision constraints.

Areas of Agreement / Disagreement

Participants express differing views on the number of bits required for the ADC and the implications of analog component quality on effective resolution. There is no consensus on the optimal bit depth or the impact of component quality on measurement accuracy.

Contextual Notes

The discussion highlights uncertainties regarding the relationship between ADC specifications and the characteristics of the analog signal being measured, as well as the potential limitations imposed by the analog components.

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Homework Statement


How many bits would an ADC require to measure the output of the preamp?
What minimum frequency would the ADC need to sample at to measure the 4KHz signal accurately?
What would the data rate from the ADC need to be at the minimum sample rate?
Given a hydrophone with the following characteristics:
Sensitivity -186dB re 1V/uPa
Capacitance 12 nF
Dissipation factor (AKA Tan Delta, Loss Angle) 0.015

Homework Equations


I am not very familiar with ADC's, numbers of bits, sample rates and data rates. Could someone put me in the right direction by teaching me a little about digital circuits, ADC's, sample and data rates, and bits?

The Attempt at a Solution

 
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lcr2139 said:
How many bits would an ADC require to measure the output of the preamp?
This is a bit like asking "How high is up?". As many bits as you want!
lcr2139 said:
What minimum frequency would the ADC need to sample at to measure the 4KHz signal accurately?
As per Nyquist theorem: 8k samples/s.
lcr2139 said:
What would the data rate from the ADC need to be at the minimum sample rate?
Again: Whatever you want. You cannot get more than 8000 samples/s, but it is up to you how often you read the ADC.

Check out http://www.ti.com/product/ads1291. You can choose between a 16 and a 24 bit ADC - which means a resolution of 15.2ppm or 0.06ppm (parts per million). Consider yourself lucky if your analog part has a precision of 1%.
 
You can buy 16 or 24bit USB ADC intended for capturing music. Sample rates 44kHz -96kHz. Companies like Behringer or Focusrite perhaps. Beware some very cheap ADC may say they are 24 but won't really be 24 bit quality.
 
CWatters said:
Beware some very cheap ADC may say they are 24 but won't really be 24 bit quality.
As I said - the analog part probably won't be better than 1% - which is the equivalent of 7 bits.
 

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