SLAA976 October   2020 MSP430FR5041 , MSP430FR5043 , MSP430FR6005 , MSP430FR6007 , MSP430FR6041 , MSP430FR6043 , MSP430FR6045 , MSP430FR6047

 

  1.   Trademarks
  2. 1Introduction
  3. 2Setup and Configuration
    1. 2.1 EVM430-FR6043 GUI Configuration
  4. 3Test Results
  5. 4Extracting O2 Concentration
    1. 4.1 Note on Achieved Accuracy
  6. 5OpenSCAD 3D Test Fixture
  7. 6References

4 Extracting O2 Concentration

Table 4-1 Spreadsheet Example
A B C D E F
1 Absolute TOF UPS (μs) Absolute TOF DNS (μs) Velocigty of Gas Flow (m/s) Speed of Sound in Gas Medium (m/s) Oxygen Concentration (%) Calibration Parameter
2 132.9382 132.9738 -0.04426 330.936511 21.04397223 14.6
  1. Use TOF values to calculate velocity of gas flow.
    1. For cell C2 “=(0.044/2)*(1/(B2*0.000001) - 1/(A2*0.000001))” – Using Equation 2.
  2. Use TOF values to Calculate speed of sound in gas medium.
    1. For cell D2 “=(0.044/(B2*0.000001) - C2)”
      1. Solving for C in (1) -> C = (L / T12) - V
  3. Calculate Oxygen concentration.
    1. For cell E2 “=100*((1.4*8.314*295.85/(D2+F2)^2)-(28/1000))/(4/1000)” – Using Equation 4.
  4. Calibrate measurements.
    1. Since the oxygen concentration in this measurement is known to be 21% (Air), change the value of cell F2 until Cell E2 equals 21%. In this case, many sample points were taken with air and averaged.
    2. The calibration parameter “14.6” can now be applied to the whole data set.
    3. This calibration parameter is unique to this specific set-up. A calibration procedure must always be performed for any new implementation.
  5. Applying calibrated equation to dataset.
GUID-20201015-CA0I-HLMQ-XPTG-5HMHQFLBC9WD-low.png Figure 4-1 Oxygen Concentration Extraction

As it can be seen in Figure 4-1, the oxygen concentration ramps up from 21% to 93.4%. Based on the manufacturer’s certification report for the specific unit used, our system was 0.8% off from the specified oxygen concentration. This was all achieved using air as a single calibration point and could easily be implemented with the MSP430FR6043.

Table 4-2 Performance and Comparison
Parameter Zirconium Sensor Competing USS Solution TI’s USS
Measurement Range 0.1% - 100% 0% – 100% 0% - 100%
Accuracy ± 3% - 0.5% FS ±3 - 1.8% FS ± 1.7% – 0.5% RD
Power Consumption 1 – 10W 0.6W 660 µW @10SPS
Warm up time ~60s NA NA
Response time 4s – 30s 0.5s 78ms
Output Stabilization time 2 – 10 minutes NA NA
Lifetime 1-3 years > 5 Years > 5 Years