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

2.1.2 Bridge With Two Active Elements in Opposite Branches

Bridges can also be constructed with more than one active element. Figure 2-5 shows a sensor with two active elements placed in different branches and on opposite sides of the bridge. This is known as a half bridge.

GUID-20211110-SS0I-2XMN-V39X-BTZMKVM4RQNP-low.svgFigure 2-5 Bridge With Two Active Elements in Opposite Branches (Half Bridge)

Equation 7 calculates VOUT for the bridge with two active elements in opposite branches shown in Figure 2-5:

Equation 7. VOUT= VEXCITATION∙R+∆R2∙R+∆R-VEXCITATION∙R2∙R+∆R= VEXCITATION∙∆R2∙R+∆R

Similar to the bridge with one active element, Equation 7 shows that VOUT is proportional to VEXCITATION and ΔR when ΔR is small. Moreover, the VOUT equation for both bridge types has a ΔR term in the denominator, resulting in the same non-linearity seen in Figure 2-3.

However, the important difference between a single-active-element bridge and a bridge with two active elements is the sensitivity. In the latter case, VOUT is two times larger for a given VEXCITATION. This larger output signal doubles the dynamic range compared to the single-active-element bridge, resulting in a better ADC measurement.