Transient processes of oscillating method of wood drying control for synthesis of algorithms for adjustment of parameters of resistive humidity sensors

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Abstract

Relevance. The use of resistive lumber humidity sensors allows increasing the level of automation. However, the reliability of readings of such sensors should be checked, since the fault tolerance of resistive sensors is quite low. The paper deals with the urgent task of monitoring the operation, response to failures and setting up the parameters of lumber moisture sensors for the transient process of the oscillatory drying method about the occurrence of events of more reliable and fault-tolerant temperature sensors. This method generates a set of transient processes that may contain useful information, the analysis of which allows evaluating the quality of drying and the main indicators of the technological process. Aim. Development of an algorithm for assessing the moisture content of lumber based on the analysis of transient processes of temperature sensors to assess the correct operation of resistive sensors and adjust calibration parameters. Methods. Analysis of transient processes from the archive database of technological processes obtained during one and a half years of operation of the dispatching system of the main parameters for 28 complete cycles of drying of sawn timber. The analysis is based on identifying the correlation of the time of cooling and heating of air when opening and closing the dampers. Under conditions of closed dampers, the possibility of determining the moisture content of sawn timber is studied based on the approximation of the dependence on the equilibrium moisture content. Results. The authors have developed the algorithms for automated adjustment of calibration parameters of resistive sensors relying on approximation of calculation of lumber moisture content derived from equilibrium air humidity, automatic control of lumber drying mode depending on readings of resistive humidity sensors. Conclusions. The analysis of the dependence of the transient cooling and heating time of the wet sensor has a weak correlation with the moisture content of the lumber and cannot provide an adequate assessment of the moisture content. Under conditions when the dampers are closed for 30–40 minutes, it is possible to observe the equilibrium moisture content of the lumber with an error of up to 2%, which allows adjusting the resistive sensors for continuous monitoring of the moisture content of the lumber. The study may be of interest to engineers and technical workers in the forestry industry involved in the creation of modern automation systems and the improvement of existing methods for controlling wood drying processes. The work can serve as a basis for developing new methods and algorithms for controlling the technological process using transient analysis to extract additional parameters.

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