# Measurement Uncertainty and Compliance Evaluation Applied to Natural Gas Moisture
## 3 Results and Discussion
### Uncertainty Evaluation  
Between 13 September 2024 and 20 September 2024, 10 dew point (\({}^{\circ}\)C) and pressure (bar) results of natural gas from the Portable Moisture Analyzer--PM880 were collected to validate the algorithms of the developed MS-Excel spreadsheet. After the pressure data were converted to psig, the MS-Excel spreadsheet developed, which is attached as Supplementary Material in this study, calculated the moisture values and their respective expanded uncertainties, as shown in Tables 2 and 3. In the spreadsheet, the input quantities in yellow, cells H2 and H3, are the dew point in Celsius degree and the pressure in psig, respectively, of the natural gas.  
To calculate the expanded uncertainty of moisture, in the conservative approach, the expanded uncertainties of 2.0 \({}^{\circ}\)C, cell I2, and 1% of the full scale (300 to 3000 psig), cell I3, were considered as input data for dew point temperature and pressure, respectively,  
\begin{table}
\begin{tabular}{c c c c} \hline \hline ASTM D1142 Test Method, Approach 1 & ASTM D1142 Test Method, Approach 2 & Portable Moisture Analyzer—PM880 \\
342.8 lbs H\({}_{2}\)O/MMSCF NG & 346.1 lbs H\({}_{2}\)O/MMSCF NG & 345.6 lbs H\({}_{2}\)O/MMSCF NG \\ \hline \hline \end{tabular}
\end{table}
Table 1: Comparing the approaches from Sections 2.1–2.3.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Dew Point** & **Pressure** & **Moisture Calculated** & **Moisture Calculated** & **Moisture Expanded Uncertainty** \\ (\({}^{\circ}\)**C**) & **(psig)** & **by PM880 \({}^{\ast}\)** & **by the Spreadsheet \({}^{\ast}\)** & **Calculated by the Spreadsheet \({}^{\ast}\)** \\ \hline \(-\)27.4 & 1165.91 & 0.70 & 0.70 & 0.14 \\ \(-\)38.0 & 455.37 & 0.41 & 0.42 & 0.08 \\ \(-\)47.5 & 436.37 & 0.17 & 0.16 & 0.04 \\ \(-\)32.1 & 555.30 & 0.64 & 0.65 & 0.12 \\ \(-\)23.1 & 1129.80 & 1.01 & 1.02 & 0.19 \\ \(-\)25.3 & 1121.384 & 0.84 & 0.85 & 0.16 \\ \(-\)24.5 & 1113.99 & 0.91 & 0.91 & 0.17 \\ \(-\)30.9 & 888.31 & 0.57 & 0.58 & 0.11 \\ \(-\)41.0 & 443.62 & 0.31 & 0.31 & 0.06 \\ \(-\)39.8 & 848.28 & 0.26 & 0.26 & 0.06 \\ \hline \hline \end{tabular} \({}^{\ast}\) lbs H\({}_{2}\)O/MMSCF NG = pounds of H\({}_{2}\)O/million standard cubic feet of natural gas.  
\end{table}
Table 2: Moisture results and their respective expanded uncertainties in lbs H\({}_{2}\)O/MMSCF NG.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Dew Point** & **Pressure** & **Moisture Calculated** & **Moisture Calculated** & **Moisture Expanded Uncertainty** \\ (\({}^{\circ}\)**C**) & **(psig)** & **by PM880 \({}^{\ast}\)** & **by the Spreadsheet \({}^{\ast}\)** & **Calculated by the Spreadsheet \({}^{\ast}\)** \\ \hline \(-\)27.4 & 1165.91 & 6.08 & 6.1 & 1.3 \\ \(-\)38.0 & 455.37 & 2.40 & 5.0 & 1.1 \\ \(-\)47.5 & 436.37 & 1.64 & 1.7 & 0.40 \\ \(-\)32.1 & 555.30 & 7.47 & 7.8 & 1.7 \\ \(-\)23.1 & 1129.80 & 9.42 & 9.7 & 1.9 \\ \(-\)25.3 & 1121.384 & 7.63 & 7.8 & 1.6 \\ \(-\)24.5 & 1113.99 & 8.32 & 8.5 & 1.7 \\ \(-\)30.9 & 888.31 considering a coverage factor, k = 2. These conservative values of uncertainty sources already encompass other contributing factors, such as fluctuations in ambient temperature and moisture and long-term sensor drift.  
The moisture results calculated by the developed spreadsheet are compatible with those generated by the portable moisture analyzer PM880 regarding the unit in Ibs H\({}_{2}\)O/MMSCF NG; however, it presents some discrepancies regarding the ppmv H\({}_{2}\)O unit. The expanded uncertainty results, k = 2, with a confidence level of 95.45%, are in the range of 20%.  
Therefore, a significant advantage is that the manuscript explicitly presents the algorithms, whereas commercial software operates as a \"black box\" without demonstrating the steps, calculating measurement uncertainty, or assessing compliance.