SBAA532A February   2022  – March 2024 ADS1119 , ADS1120 , ADS1120-Q1 , ADS112C04 , ADS112U04 , ADS1130 , ADS1131 , ADS114S06 , ADS114S06B , ADS114S08 , ADS114S08B , ADS1158 , ADS1219 , ADS1220 , ADS122C04 , ADS122U04 , ADS1230 , ADS1231 , ADS1232 , ADS1234 , ADS1235 , ADS1235-Q1 , ADS124S06 , ADS124S08 , ADS1250 , ADS1251 , ADS1252 , ADS1253 , ADS1254 , ADS1255 , ADS1256 , ADS1257 , ADS1258 , ADS1258-EP , ADS1259 , ADS1259-Q1 , ADS125H01 , ADS125H02 , ADS1260 , ADS1260-Q1 , ADS1261 , ADS1261-Q1 , ADS1262 , ADS1263 , ADS127L01 , ADS130E08 , ADS131A02 , ADS131A04 , ADS131E04 , ADS131E06 , ADS131E08 , ADS131E08S , ADS131M02 , ADS131M03 , ADS131M04 , ADS131M06 , ADS131M08

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Bridge Overview
  5. 2Bridge Construction
    1. 2.1 Active Elements in Bridge Topologies
      1. 2.1.1 Bridge With One Active Element
        1. 2.1.1.1 Reducing Non-Linearity in a Bridge With One Active Element Using Current Excitation
      2. 2.1.2 Bridge With Two Active Elements in Opposite Branches
        1. 2.1.2.1 Eliminating Non-Linearity in a Bridge With Two Active Elements in Opposite Branches Using Current Excitation
      3. 2.1.3 Bridge With Two Active Elements in the Same Branch
      4. 2.1.4 Bridge With Four Active Elements
    2. 2.2 Strain Gauge and Bridge Construction
  6. 3Bridge Connections
    1. 3.1 Ratiometric Measurements
    2. 3.2 Four-Wire Bridge
    3. 3.3 Six-Wire Bridge
  7. 4Electrical Characteristics of Bridge Measurements
    1. 4.1 Bridge Sensitivity
    2. 4.2 Bridge Resistance
    3. 4.3 Output Common-Mode Voltage
    4. 4.4 Offset Voltage
    5. 4.5 Full-Scale Error
    6. 4.6 Non-Linearity Error and Hysteresis
    7. 4.7 Drift
    8. 4.8 Creep and Creep Recovery
  8. 5Signal Chain Design Considerations
    1. 5.1 Amplification
      1. 5.1.1 Instrumentation Amplifier
        1. 5.1.1.1 INA Architecture and Operation
        2. 5.1.1.2 INA Error Sources
      2. 5.1.2 Integrated PGA
        1. 5.1.2.1 Integrated PGA Architecture and Operation
        2. 5.1.2.2 Benefits of Using an Integrated PGA
    2. 5.2 Noise
      1. 5.2.1 Noise in an ADC Data Sheet
      2. 5.2.2 Calculating NFC for a Bridge Measurement System
    3. 5.3 Channel Scan Time and Signal Bandwidth
      1. 5.3.1 Noise Performance
      2. 5.3.2 ADC Conversion Latency
      3. 5.3.3 Digital Filter Frequency Response
    4. 5.4 AC Excitation
    5. 5.5 Calibration
      1. 5.5.1 Offset Calibration
      2. 5.5.2 Gain Calibration
      3. 5.5.3 Calibration Example
  9. 6Bridge Measurement Circuits
    1. 6.1 Four-Wire Resistive Bridge Measurement with a Ratiometric Reference and a Unipolar, Low-Voltage (≤5 V) Excitation Source
      1. 6.1.1 Schematic
      2. 6.1.2 Pros and Cons
      3. 6.1.3 Parameters and Variables
      4. 6.1.4 Design Notes
      5. 6.1.5 Measurement Conversion
      6. 6.1.6 Generic Register Settings
    2. 6.2 Six-Wire Resistive Bridge Measurement With a Ratiometric Reference and a Unipolar, Low-Voltage (≤ 5 V) Excitation Source
      1. 6.2.1 Schematic
      2. 6.2.2 Pros and Cons
      3. 6.2.3 Parameters and Variables
      4. 6.2.4 Design Notes
      5. 6.2.5 Measurement Conversion
      6. 6.2.6 Generic Register Settings
    3. 6.3 Four-Wire Resistive Bridge Measurement With a Pseudo-Ratiometric Reference and a Unipolar, High-Voltage (> 5 V) Excitation Source
      1. 6.3.1 Schematic
      2. 6.3.2 Pros and Cons
      3. 6.3.3 Parameters and Variables
      4. 6.3.4 Design Notes
      5. 6.3.5 Measurement Conversion
      6. 6.3.6 Generic Register Settings
    4. 6.4 Four-Wire Resistive Bridge Measurement with a Pseudo-Ratiometric Reference and Asymmetric, High-Voltage (> 5 V) Excitation Source
      1. 6.4.1 Schematic
      2. 6.4.2 Pros and Cons
      3. 6.4.3 Parameters and Variables
      4. 6.4.4 Design Notes
      5. 6.4.5 Measurement Conversion
      6. 6.4.6 Generic Register Settings
    5. 6.5 Four-Wire Resistive Bridge Measurement With a Ratiometric Reference and Current Excitation
      1. 6.5.1 Schematic
      2. 6.5.2 Pros and Cons
      3. 6.5.3 Parameters and Variables
      4. 6.5.4 Design Notes
      5. 6.5.5 Measurement Conversion
      6. 6.5.6 Generic Register Settings
    6. 6.6 Measuring Multiple Four-Wire Resistive Bridges in Series with a Pseudo-Ratiometric Reference and a Unipolar, Low-Voltage (≤5V) Excitation Source
      1. 6.6.1 Schematic
      2. 6.6.2 Pros and Cons
      3. 6.6.3 Parameters and Variables
      4. 6.6.4 Design Notes
      5. 6.6.5 Measurement Conversion
      6. 6.6.6 Generic Register Settings
    7. 6.7 Measuring Multiple Four-Wire Resistive Bridges in Parallel Using a Single-Channel ADC With a Ratiometric Reference and a Unipolar, Low-Voltage (≤ 5 V) Excitation Source
      1. 6.7.1 Schematic
      2. 6.7.2 Pros and Cons
      3. 6.7.3 Parameters and Variables
      4. 6.7.4 Design Notes
      5. 6.7.5 Measurement Conversion
      6. 6.7.6 Generic Register Settings
    8. 6.8 Measuring Multiple Four-Wire Resistive Bridges in Parallel Using a Multichannel ADC With a Ratiometric Reference and a Unipolar, Low-Voltage (≤ 5 V) Excitation Source
      1. 6.8.1 Schematic
      2. 6.8.2 Pros and Cons
      3. 6.8.3 Parameters and Variables
      4. 6.8.4 Design Notes
      5. 6.8.5 Measurement Conversion
      6. 6.8.6 Generic Register Settings
  10. 7Summary
  11. 8Revision History

4.6 Non-Linearity Error and Hysteresis

Non-linearity error is the deviation of the output curve from the expected full-scale straight-line output as the bridge output increases. This non-linearity results from the characteristics of the bridge resistive elements and is different from the bridge topology error discussed in Section 2.1.1. For example, a resistive bridge element may be more non-linear if it exceeds a certain range or load. Bridge data sheets often characterize non-linearity (see Table 4-1) and suggest limiting the maximum load to keep non-linearity small.

Similar to non-linearity error, hysteresis is a small error that changes with the bridge output. However, this error may be different depending on whether the bridge output is increasing or decreasing. The addition of hysteresis to the non-linearity error is known as the combined error. The combined error is the maximum error from the straight line ranging from no load to the maximum load conditions (increasing and decreasing). Figure 4-2 graphically shows the non-linearity error, hysteresis, and the combined error.

GUID-20211110-SS0I-QFBM-KZWB-CJP9DZVRPGHR-low.svg Figure 4-2 Hysteresis, Non-Linearity, and Combined Error

Non-linearity error and hysteresis are not easily calibrated. These errors may be different from unit-to-unit such that calibration requires many measurements across the full range of the bridge operation. However, these errors are typically much smaller than offset and full-scale errors. It is also worth noting that an ADC can contribute a non-linearity error, though this is generally negligible compared to bridge non-linearity.