SU1458791A1

SU1458791A1 - Apparatus for measuring moisture content of soil

Info

Publication number: SU1458791A1
Application number: SU874289981A
Authority: SU
Inventors: Ivan I Sudnitsyn; Yurij V Egorov; Valerij G Gusev; Vasilij S Starovojtov
Original assignee: Univ Moskovsk
Priority date: 1987-07-27
Filing date: 1987-07-27
Publication date: 1989-02-15

Description

The invention relates to agriculture and can be used to determine soil moisture in irrigated agriculture. With the aim of

increasing the accuracy of measurements by improving the contact with the soil; the electrodes are made in the form of two wires - insulated and non-insulated; the latter is wound over the insulation of the first wire; the insulation has a hydrophobic surface. The wires of the electrodes are connected to a high-frequency capacitance meter. For a better averaging of the spatial variations in the moisture content of the wire, the wires are coiled in a spiral 4–10 m long. The spiral can shrink 1.3-1.5 times during soil shrinkage. The device is cheap and simple in design, allows for long-term stationary monitoring of soil moisture. 4 il.

FIG. 2

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2

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The invention relates to the soil layers measured above with another

technology and can be used to determine soil moisture in irrigated agriculture. $

The purpose of the invention is to improve the accuracy of determining soil moisture by improving the contact of the soil with the electrodes.

The essence of the method lies in the fact that the insulation of a high-potential wire - an electrode is made of a material with a hydrophobic sliding surface, and a low-potential uninsulated wire - an electrode is pressed over a high-potential insulation with a step that ensures a significant predominance of the capacitive resistance of the sensor over the inductive one. At the same time, the sensor is curled into a flexible helix 4-10 m long, capable of elongating by 25% when stretched.

The length of the sensor is 2--3 times the size of the microcomponents of the soil cover and the width of the capture of the soil-cultivating tool. This contributes to the averaging of spatial inhomogeneities of humidity.

Due to the flexibility of the sensor there is no gaps between 30

electrodes and soil swelling. In the longitudinal direction, the sensor can slip along the soil due to the slight friction. The moisture absorption of the specified insulation 35 is negligible (less than 0.01%). Due to this, in the proposed sensor there are no inertia and hysteresis inherent in the known devices. Under natural conditions, the soil moisture 49 is usually higher than 3-5%, so the absorption of moisture by insulation does not reduce the measurement accuracy.

FIG. 1 shows the design of the sensor; in fig. 2 - the same _g in an enlarged form; in fig. 3 is a section A-A in FIG. 2; in fig. 4 - sensor output with a deep tab.

The core of the stranded wire 1 in polyethylene insulation 2 is insulated at the end by welding over polyethylene 3. A bare copper conductor 4 is wound on the wire. The sensor is coiled and laid in the soil across the processing direction of agricultural machines. With a deep tab of the sensor, the output from it can be made with shielded wire 5 to eliminate the influence of humidity (Fig. 4). To the sensor output, contact plates 6 are soldered for connection to a portable capacitance meter. The pin is attached to the peg 7.

The device works as follows.

The sensor is inserted into the soil through a slit made from the surface manually or with the help of some mechanism, for example, a cable layer, a donor layer can be used, which forms a channel deep in the soil and feeds a sensor wire from the surface. After laying the sensor is watering. After the soil shrinks and a stable contact of the soil with the sensor surface is formed, the sensor capacitance is measured by a serial capacitance meter (for example, type E7-9). In field conditions, the device is powered by an 18 KN-3 battery.

The proposed sensor can be represented as two series-connected capacitors - constant and variable.

The dielectric of the permanent capacitor is the insulation of the wire, the dielectric of the variable is the soil.

When the pore space is filled with water, the dielectric constant (E) of the soil increases, since the air pressure equals 1 and the water value equals 80. As a result, when the soil is moistened, the sensor capacity increases.

Sensor calibration, i.e. finding the relationship between capacitance C and soil moisture V is performed by comparing the results of capacitance measurement with moisture obtained by the thermostatist-weight method with multiple repetitions.

Example. For the manufacture of the proposed sensor, a piece of stranded wire is taken in polyethylene insulation of the PZA brand with a cross section of 1 mmH core. At one end of the wire, the insulation is pulled off the core by 3-4 mm and melted in the burner flame until the channel disappears. Uninsulated copper wire with a cross section of 0.3 mm ^{2 is} wound onto a rod with a diameter of 4 mm. The resulting helix is put on insulated wire and stretched, and the ends of the helix are fixed. Prepared by1458791

In this way, the wire is wound on a mandrel with a diameter of 15 mm.

Claims

Claim

A device for measuring soil moisture, containing two interconnected electrode-wires connected to a high-frequency capacitance meter, characterized by

ten

that, in order to improve measurement accuracy by improving the contact of electrodes with the soil, the electrode-wires are made in the form of an isolated high-potential and non-isolated low-potential, spiral-wound over high-potential insulation with a pitch ensuring that the capacitance of the sensor exceeds the inductive one by an order of magnitude, while the sensor is twisted into a spiral 4-10 m long with possibility of extension 1.3-1.5 times.

FIG. four

FIG. 3