SBOA575 September   2023 INA823 , OPA2387 , XTR115 , XTR116

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Theory of Operation
    1. 2.1 Wheatstone Bridge Sensor
    2. 2.2 2-Amp INA
    3. 2.3 4-20-mA Current Loop Transmitter Interface
  6. 3Simulation
  7. 4PCB Design
  8. 5Verification and Measured Performance
  9. 6Summary
  10. 7Reference
  11.   Appendix

1 Introduction

Following are the design requirements:

  • Use reference voltages of the current loop transmitter to power sensor and amplifier circuitry
  • Total current consumption < 3.5-mA
  • Weight range = 0 to 20-lbs → output current = 4 to 20-mA
  • ±0.1% accuracy

The design goals and performance are summarized in Table 5-2. The measured transfer function and completed PCB design are shown below.

Table 1-1 Design Goal versus Calculated, Simulated, and Measured Performance
WeightGoalCalculatedSimulatedMeasured
Iout (Min)0lbs4mA4.0959mA4.0963mA4.0994mA
Iout (Max)20lbs20mA20.1404mA20.1397mA20.1545mA
GUID-20230802-SS0I-NZG1-GS8M-DJZFBMPVTHMP-low.svg Figure 1-1 Measured Output Current vs Weight Transfer Function
GUID-20230920-SS0I-6ZHC-MLNP-CFMJ1QSQTJQB-low.png Figure 1-2 Wheatstone Bridge to 4-20-mA Current Loop Transmitter PCB Design