Dynamic Properties of Wide-Range Piezosorption Sensors for Humidity in Organic Liquids

Abstract

A design is proposed for a wide-range piezosorption sensor for humidity in organic liquids based on the use of two sorbents on a single quartz plate. The most efficient way of depositing the sorbents on the plate is determined on the basis of an analysis of the dynamic sensitivity characteristics of the sensors.In automatic control systems for engineering processes, a large part of the measurements are analytic, with monitoring of the humidity of substances playing a special role [1]. Moisture must be monitored a low and high concentrations in many gaseous and liquid media. At present, there are no instruments capable of measuring the entire range of humidity (low, medium, and macroconcentrations), which leads to production difficulties. The development of such a device would greatly reduce the number of humidity measurement devices and solve many problems with just one wide-range instrument. In addition, it could serve as the basis for unifying and developing a series of modifications of humidity measurement instruments, thereby reducing expenditures on the development and manufacture of humidity meters and hygrometers [2,3].The operating principle of many sensors is based on the sorption of moisture from the medium being analyzed. Changes in their physicochemical or electrical parameters serve as the measure of the moisture content in the medium [4,5]. Depending on the type of sensor, various sorbents with the most distinctive qualities for a given sensor are used. Depending on the type of measurements, sorption sensors are divided into coulometric, sorption-capacitive, and piezosorption sensors. Figure 1 shows the design of a piezosorption sensor for use in hygrometers that consists of a quartz plate 1 with electrodes 2 attached to both sides. This configuration is a quartz resonator. A thin layer (up to 6 μm) of sorbent 3 is deposited on the electrodes and plate, covering mainly the central part of the quartz resonator, so that the amplitude of the oscillations is highest in this region and, therefore, the dependence of the frequency of the oscillations on the mass of moisture absorbed by the sorbent is more marked. This ultimately determines the sensitivity of the piezosorption sensor.In modern instruments, only one sorbent is deposited on the quartz resonator. The type of sorbent depends on the range of humidity to be measured. The sorbents used in sensors have different parameters. One of the major parameters is the sorption isotherm, which determines the choice of optimal working conditions for the measurement process [6].Sorbents that make it possible to measure humidity in micro-and macro-concentrations are used in existing instruments. In this paper, we propose monitoring the moisture content of organic liquids over a wide range, including micro-and macro-concentrations, using a sensor with two sorbents deposited on one side of the quartz plate.Over the last few decades, in the Russian Federation, the firms Praktik-NTs and NPP OKBA have been actively working on the problems of measuring the moisture co...