SU911282A1 - Thermal converter of soil moisture potential - Google Patents

Description

(54) HEAT POTENTIAL CONVERTER

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The invention is related to measuring equipment, namely, moisture measurement and can be used in. devices designed to measure the moisture potential in soils

Thermal converters of the soil moisture potential are known, which contain a thermistor with a wire surrounding it. When a thermal converter is placed in the soil as a result of the free moisture exchange of the porous block, the block is watered with moisture, and after a while the moisture potentials develop in the surrounding and surrounding soil. When current is passed through a heating element, the temperature of the thermostatic element grows. The rate of dew temperature depends on the dssy yy heat in the block, and, hardly, from the moisture content and the corresponding moisture potential inside the porous block. The indicated rate is the temperature increase and is taken as a measure of the potential of the soil moisture. The difference in the rate of growth of temperature with a change in the value of the moisture content of the porous block from moisture-saturated to air-dry soil moisture.

characterizes the sensitivity of the thermal converter and depends mainly on the material from which porous block 1 is made.

The disadvantages of such a converter, in addition to its low sensitivity, are low stability of the Characteristics due to the gradual destruction of the gypsum block under the action of moisture and its low mechanical strength.

A heat converter is known in which a porous ceramic block is used, in the center of which there is a thermistor serving as a heater and a temperature-sensitive element at the same time; Mechanical strength is the stability of xa, the characteristics of this converter

20 significantly higher 2

However, the sensitivity of this converter does not exceed 1.5. In addition, the use of a thermistor

25 leads to the dependence of the tester transducer on the temperature of the soil,

Claims (2)

The closest technical solution to the invention is a heat converter comprising a semi-conductor diode with a heating coil located in a porous block. When the heating current passes through the spiral, the heat wave propagates into the porous block, changing the temperature of the semiconductor diode, which serves as a temperature-sensitive element 3. However, the sensitivity of the known converter is small and does not exceed 2. The aim of the invention is to lower the sensitivity of the thermal potential of the soil moisture potential. This goal is achieved by the fact that a porous transducer block containing a semiconductor diode with a heater is made of a powdered abrasive material (filler) with high thermal conductivity, enclosed in a moisture-permeable shell. The moisture permeable shell is necessary for ensuring the mechanical strength of the converter and is made in the form of a cylindrical cup made of porous ceramics. The filler is an abrasive powder made from any one type of material: electrocorundum, quartz, boron carbide or diamond with particle sizes from a few to hundreds of microns, i.e. sizes that correspond to the natural dispersion of most soils. . In the drawing, a schematic representation of the proposed converter is shown. The moisture permeable shell 1, made of porous ceramics, is filled with quartz powder 2. In the price of the re block, nickel wire is placed between the sensing element 3 and the heating coil 4 of nichrome. The heat converter is introduced into the soil before measurements. To measure the potential of moisture through the heating element 4 of the converter, a current is passed and the rate of temperature rise of the thermosensitive element 3 is determined, for example, by the magnitude of the change in its resistance. In dry soil, the heat dissipation from the heating element is small due to the large contact heat resistance between quartz particles In this case, the rate of temperature rise, and consequently, the change in resistance of the thermosensitive element is large. In wet soil, under the action of soil moisture filling the pores between the particles, the powder is saturated to an equilibrium moisture content, the thermal contact between the particles improves, the heat from the heating element increases and, accordingly, the temperature of the temperature sensitive element increases. The stability of the characteristics of the converter is achieved due to the high hardness of the particles, ensuring the stability of the contacts between the particles, and hence the contact heat resistance. The sensitivity of the proposed converter, characterized by the ratio of the growth rates of the temperature of the temperature-sensitive element for the dry and fully moisture-saturated state, reaches 10-15, which is 5-10 times greater than that of the known thermal converters. Claims of the invention A soil moisture potential thermal converter comprising a semiconductor diode with a heating coil placed in a porous block, characterized in that, in order to increase the sensitivity, the porous block is made of an abrasive powder material with high thermal conductivity. Sources of information taken into account in the examination 1.Globus A.M. Experimental soil hydrophysics. L., Gidrrmeteoizdat, 1969, p. 190. 2.B oodworth ME and Page EB Soif sci soc. Amer Proc ,, 1957, vof. 21, 1, p. 11 - 15. Z. Pepe S. Oe,, Hoffman, G.3,, Rau6ins S.L. Soif sci, soc.Amer. Proc., 1971, vpt. 35, p. 27 - 33 (prototype).