SU1397814A1 - Apparatus for measuring the humidity of soil - Google Patents

Abstract

The invention relates to a measurement technique and is aimed at improving the accuracy of measuring soil moisture by preventing the breakdown of its structure, as well as expanding the range of moisture measurement. A device for measuring soil moisture contains a stabilized source of current and a two-port network formed by a series-induced induction coil 2 and a capacitive humidity sensor that contains a low

Description

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potential cylindrical electrode 4 and a high-potential electrode 5 made as a blunt cone embedded in a dielectric substrate 3 with a base 3. In parallel with a capacitive sensor, a resistance modulator 6 connected as a key diode and two varicaps 7 and 8 controlled by voltages U are connected and Ug respectively. A matching amplifier 9 and a demodulator 10 are connected to the coil 2 of the inductance. When the sensor is unfilled with soil, the voltage change and (Ug is fixed) while the modulator 6 is running, no demodulation of the output signal of the demodulator 10 is obtained. humidity sensor. Then the sensor edges of the electrode 4 crashes into the soil, the capacity of the sensor increases. By decreasing the voltage and the sensor is again balanced. Based on the difference in U values, the capacity is determined, which is uniquely related to soil moisture. 2 Il.

The invention relates to a measurement technique and can be used to measure soil moisture.

The purpose of the invention is to improve the measurement accuracy by preventing the disturbance of the soil structure and expanding the measurement range.

Fig. 1 is a schematic diagram of the device; Fig. 2 shows time diagrams of voltages; the sun shows the operation of the device.

The device for measuring soil moisture contains a high-frequency stabilized current source 1 and serially connected inductance catupzha 2 and a capacitive sensor connected to it in the form of a low-potential cylindrical electrode 4 and a high-potential electrode 5 mounted on a dielectric substrate 3, which is buried by the base in the dielectric substrate 3. A resistor modulator 6 is connected in parallel to the capacitive sensor. in the form of a key diode, as well as two varicaps 7 and 8. A matching amplifier 9 and a voltage demodulator 10 on the inductance coil are connected to the inductor 2.

The device works as follows.

The source 1 provides the power supply with a stable current in series to the connected coil 2 of the inductance and

capacitive sensor. In this case, a resistance modulator 6 containing a source of control signals (not shown) periodically shunts a capacitive sensor. The nature of the change in the resistance Rj of the modulator is presented in FIG. The resulting signal Uy at the high potential electrode 5 of the capacitive sensor is also shown in FIG. 2.

Due to the operation of the modulator 6, an amplitude-modulated voltage appears on the inductance coil 2 and is fed to the input of the matching amplifier 9 and then to the demodulator 10, the output of which receives the signal and, ". Further, from time t, by varying the magnitude of the control voltage U, the capacity of varicap 7 is set such that the voltage on the inductor 2 does not change when the capacitor sensor is bypassed. The voltage Ug on the varicap 8 is kept constant. 3TONry correspond to the graphics Uj and

after time t,

The total capacitance of an empty capacitive sensor (without a soil sample) and two varicaps determines the initial

JQ is the capacitance of the device, and the voltage U is its initial output voltage. When measuring humidity, the capacitive sensor is immersed in the soil with a cylindrical electrode 4 to the level at which the electrode

5 5 will be in full contact with the soil. At the same time, the capacitance of the sensor is increased and a signal appears again on the inductor 2. By increasing the voltage U, the capacity of varicap 7

reduce to the disappearance of this signal

which corresponds to the achievement

initial capacity. Since the voltage is in a certain functional dependence on the capacity of varicap 7, by its value it is possible to determine the change in the capacity of the sensor and the soil moisture uniquely associated with the capacity of the sensor. Balancing the circuit, i.e. voltage adjustment and, can be done manually or using an appropriate automatic adjustment system.

The use of a high potential electrode, made in the form of a blunt cone, minimizes the possible disruption of the structure of the controlled soil, while ensuring reliable contact with it.

The use of two parallel-connected varicaps not only allows the measurement range to be expanded, but also provides an increase in sensitivity, since the range of variation of the control voltage U on one varicap with a fixed control voltage Ug on the second varicap increases significantly, which allows do not improve measurement accuracy

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Claims (1)

Invention Formula A device for measuring soil moisture, containing a high-frequency stabilized power source, connected in series with an inductor and a capacitive sensor, filled in the form of low-potential and high-potential electrodes attached to a dielectric substrate, a resistance modulator and a varicap connected in parallel with a capacitive sensor, and a demodule voltage torus on an inductance coil, characterized in that, in order to increase accuracy by preventing structures from breaking soil and expanding the range of measurements, it is equipped with a second varicap, connected in parallel to the first, and a matching amplifier connected between the coil, inductance and the demodulator input, the power source is designed as a current source, the low-potential electrode is cylindrical, and the high-potential electrode is conical obtuse angle at the apex, located inside the cylindrical electrode and recessed by the base into the dielectric substrate. / ygsh / 1mshmta