Solid State Humidity Sensors

A variety of humidity sensors have been developed to address the problem of humidity measurement in instrumentation, agriculture and systems which are automatic. Various types of humidity sensors have been reviewed along with their mechanisms of humidity detection. Thin and thick film preparation processes are quite flexible. This flexibility provides advantages over other technologies. After comparing all the aspects of different humidity sensors, it has been observed that there are still some shortcomings left, which need to be removed to enhance the humidity sensing capability, recovery and response times of the sensor elements.

PLC-based lumber humidity measurement method

Purpose or research. The paper considers the solution of the scientific and practical problem of measuring the humidity content of lumber on the basis of a programmable logic controller (PLC), which makes it possible to implement control systems for drying lumber on inexpensive controllers of wide application with the advantages of modern SCADA systems.Methods. To achieve this goal, modern methods for assessing the humidity content of lumber by electrical resistance have been investigated. We have provided a review and analysis of the known dependences of the electrical resistance of lumber on moisture. It is noted the need to measure resistance in the range of 2.5 KΩ to 25 MΩ. The schematic solution for matching a high-resistance measurement bridge with an additional voltage source with a PLC is described here. We have proposed a method for calculating the matching scheme. Expressions are obtained for calculating humidity according to the data of an analog-to-digital converter. The procedure for setting up the measurement channel according to the readings of two reference measurements is presented.Results. The estimation of the measurement error of humidity and resistance is carried out. It is shown that a resistance measurement error of up to 20% leads to a humidity measurement error of up to 1%, provided that the parameters are correctly configured. To set it up, it is enough to take two reference measurements to complete the procedure for setting the humidity measurement parameters.Conclusion. In the process of designing modern systems for drying lumber, you can use the algorithms and programs of the technological process available and well presented in the literature for implementation on the PLC. The article offers a solution to the main problem of measuring the humidity content of lumber, which is necessary for these algorithms and programs. The material can be useful for researching technological stages of the drying process and developing industrial control systems based on inexpensive controllers.

New Electronic Interface Circuits for Humidity Measurement Based on the Current Processing Technique

The paper describes a new electronic conditioning circuit based on the current-processing technique for accurate and reliable humidity measurement, without post-processing requirements. Pseudobrookite nanocrystalline (Fe2TiO5) thick film was used as capacitive humidity transducer in the proposed design. The interface integrated circuit was realized in TSMC 0.18 μm CMOS technology, but commercial devices were used for practical realization. The sensing principle of the sensor was obtained by converting the information on environment humidity into a frequency variable square-wave electric current signal. The proposed solution features high linearity, insensitivity to temperature, as well as low power consumption. The sensor has a linear function with relative humidity in the range of Relative Humidity (RH) 30-90 %, error below 1.5 %, and sensitivity 8.3 x 1014 Hz/F evaluated over the full range of changes. A fast recovery without the need of any refreshing methods was observed with a change in RH. The total power dissipation of readout circuitry was 1 mW.