A Laplace-domain method for in situ temperature calibration in sensor networks

The deployment of sensor networks in recent times has increased the need for metrological evaluation of them. Conventional calibration methods are not suitable for calibration of sensors in such systems due to the dynamic surroundings and inability of transporting the sensors to calibration facilities, hence the need for in situ calibration methods traceable to the International System of Units (SI) is evident. This paper proposes a calibration method based on the Laplace transform of the sensor signals to obtain calibration coefficients by distinguishing the medium effect present in the network and separating it from the signals. The method works in a non-steady state and to introduce the traceability, only one sensor needs to be calibrated in advance to act as the network reference. Validation in a laboratory sensor network demonstrates that, with any sensor acting as the externally calibrated network reference, the calibration coefficients obtained for all sensors agree with those from conventional laboratory calibration within their expanded uncertainties (k = 2), with a maximum deviation of 1.3%. Sensors located in the interior of the measurement domain show improved agreement with conventional calibration, with relative deviations of the order of 0.2%. Calibration of sensors in a real-world sensor network was also carried out with results showing that the method can be used in such a case.