SBAA051A January   1994  – April  2015 MSC1210Y2 , MSC1210Y3 , MSC1210Y4 , MSC1210Y5

 

  1.   Principles of Data Acquisition and Conversion
    1.     Trademarks
    2. 1 System Sampling Rate
      1. 1.1 Error Considerations
      2. 1.2 Aliasing Error
      3. 1.3 How Many Samples per Cycle?
      4. 1.4 Aperture Error
    3. 2 A Few A/D Converter Points
      1. 2.1 Accuracy
      2. 2.2 Selecting the Resolution
      3. 2.3 Resolution
    4. 3 Increasing System Throughput Rate
    5. 4 System Throughput Accuracy
    6. 5 Digital Codes
    7. 6 Summary

4 System Throughput Accuracy

The most common method used to describe data acquisition and conversion system accuracy is to compute the root-sum squared (RSS) errors of the system components. The RSS error is a statistical value which is equivalent to the standard deviation (1σ), and represents the square root of the sum of the squares of the peak errors of each system component, including ADC quantization error:

Equation 3. Eq03_RSS_SBAA051.gif

    where

  • εMUX = analog multiplexer error
  • εAMP = input amplifier error
  • εSH = sample/hold error
  • εADC = A/D converter error

The source irnpedance, data bandwidth, A/D converter resolution and system throughput rate affect these error calculations. To simplify, errors can be calculated by assuming the following:

  • Aperture error is negligible - i.e., less than 1/10LSB.
  • Source impedance is less than 1000 Ω.
  • Signal range is ±10 volts.
  • Throughput rate is equal to or less than the maximum shown in Table 3.

Table 3. System Error Contribution and RSS Error vs Resolution for Burr-Brown Model857KG Modular Data Acquisition System

Error Source Resolutions
8 Bits 10 Bits 12 Bits
MUX Error 0.0025% 0.0025% 0.0025%
AMP Error 0.01% 0.01% 0.01%
S/H Error 0.01% 0.01% 0.01%
ADC Errors Analog 0.02% 0.05% 0.012%
Quantizing 0.02% 0.05% 0.012%
RSS Error 0.283% 0.072% 0.022%