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Determination of Optimal Measurement Points for Calibration Equations—Examples by RH Sensors

Department of Materials Science and Engineering, University of California, San Diego, CA 92093, USA
Department of Bio-Industrial Mechatronics Engineering, National ChungHsing University, Taichung 40227, Taiwan
Author to whom correspondence should be addressed.
Sensors 2019, 19(5), 1213;
Received: 26 February 2019 / Revised: 6 March 2019 / Accepted: 6 March 2019 / Published: 9 March 2019
PDF [2022 KB, uploaded 12 March 2019]


The calibration points for sensors must be selected carefully. This study uses accuracy and precision as the criteria to evaluate the required numbers of calibration points required. Two types of electric relative humidity (RH) sensors were used to illustrate the method and the standard RH environments were maintained using different saturated salt solutions. The best calibration equation is determined according to the t-value for the highest-order parameter and using the residual plots. Then, the estimated standard errors for the regression equation are used to determine the accuracy of the sensors. The combined uncertainties from the calibration equations for different calibration points for the different saturated salt solutions were then used to evaluate the precision of the sensors. The accuracy of the calibration equations is 0.8% RH for a resistive humidity sensor using 7 calibration points and 0.7% RH for a capacitance humidity sensor using 5 calibration points. The precision is less than 1.0% RH for a resistive sensor and less than 0.9% RH for a capacitive sensor. The method that this study proposed for the selection of calibration points can be applied to other sensors. View Full-Text
Keywords: calibration points; saturated salt solutions; humidity sensors; measurement uncertainty calibration points; saturated salt solutions; humidity sensors; measurement uncertainty

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Chen, H.-Y.; Chen, C. Determination of Optimal Measurement Points for Calibration Equations—Examples by RH Sensors. Sensors 2019, 19, 1213.

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