## 7 Conclusions  
Through the description of the design concept, the structure and sub-systems of a probe-moving calibration facility for hot-wire anemometers in extremely low speed regime,  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**E (V)**} & \multirow{2}{*}{\(H\)} & \multicolumn{2}{c}{**20\%RH**} & \multicolumn{2}{c}{**60\%RH**} & \multicolumn{2}{c}{**80\%RH**} \\ \cline{2-9}  & & \(\Delta U\) **(m/s)** & **\(\Delta U\) (m/s)** & **\(\Delta U\) (m/s)** & **\(\Delta U\) (m/s)** & **\(\Delta U\) (m/s)** & **\(\Delta U\) (m/s)** & **\(\Delta U\) (m/s)** \\ \hline
1.30 & \(-\)0.125 & 0.105 & 0.02 & 19.048 & 0.071  
and via the analysis of the results of the facility adjustment tests and the calibration results of a hot-wire anemometer in the facility, the following conclusions can be drawn:  
1. The air velocity of the calibration facility can vary from 0.10 m/s to 1.0 m/s, the air temperature can be controlled to a specified value within a range of ambient atmospheric temperature to 60 \({}^{\circ}\)C, and the air humidity can be adjusted to a set value within an interval of 20%RH to 80%RH (at a constant temperature from ambient value to 40 \({}^{\circ}\)C);
2. The velocity control accuracy of the calibration facility in this paper is 0.000989 m/s and 0.241%, which satisfy the design target \(\pm\)0.003 m/s and \(\pm\)0.4%, respectively;
3. The maximum error of the temperature control of the facility is 0.9 \({}^{\circ}\)C, meeting the design target \(\pm\)1 \({}^{\circ}\)C; The maximum error of the humidity control is 2.9%RH, satisfying the design target 4%RH;
4. The errors of the fitting curves of calibration using modified King's law and [PERSON]'s formula in the present facility are 0.02236 m/s, and 0.023217 m/s, respectively, satisfying the calibration accuracy design target of 0.03 m/s. The corresponding relative fitting errors with the two formulas are 5.214% and 8.527%, respectively. It appears that the modified King's law yields better results;
5. The difference in humidity or temperature between the calibration environment and the application environment may bring certain or noticeable errors in measured velocity. Under the same temperature, if the fitting curve of one humidity value is used to predict the measured velocity of a flow with another humidity value, the maximum error in measured velocity may reach an order of magnitude of 1.267% per percentage point of relative humidity discrepancy. Under the same humidity if the fitting curve of one temperature is used to obtain the measured velocity of a flow with another temperature, the maximum error per degree Celsius of temperature discrepancy may reach an order of magnitude of 5.672%. Conceptualization, T.Z., Z.Z., G.Z. and Z.X. ; methodology, T.Z., Z.Z. and Z.X. ; software, Y.T., X.D. and W.L. ; validation, Y.T., X.D. and W.L. ; formal analysis, Z.Z., Y.T., T.Z. and Z.X. ; investigation, Z.Z., Z.X., Y.T., X.D. and W.L. ; resources, T.Z., G.Z. and C.G. ; data curation, Y.T., X.D. and W.L. ; writing--original draft preparation, Z.Z. ; writing--review and editing, Z.Z. ; visualization, Z.Z., Y.T., X.D., W.L. and Z.X. ; supervision, T.Z., Z.Z., G.Z. and C.G. ; project administration, T.Z. and Z.Z. ; funding acquisition, T.Z., G.Z. and C.G. All authors have read and agreed to the published version of the manuscript. This research received no external funding. Not applicable. Data Availability Statement: Data are contained within the article. The authors are grateful to Huxian (a county) Qinxing Environmental Protection Equipment Factory for manufacturing the steel frame structure of the outer wall of the enclosed chamber (e.g., welding), and rough machining on the mounting platform, the guide track pedestal, etc., Xi'an Pulisen Machine Tools Co., Ltd. for the finish machining on the mounting platform and the guide track pedestal, and Shaanxi Zhongke Rubber and Plastic Product Co., Ltd. for developing and producing the sealing blocks used in the enclosed chamber bottom wall.