SOIL MOISTURE SENSOR

• US 20150330932A1
• Filed: 05/18/2015
• Published: 11/19/2015
• Est. Priority Date: 05/19/2014
• Status: Active Grant

• Current Assignee: Fiskars Oyj Abp
• Original Assignee: Fiskars Oyj Abp
• Inventors: Kumaran, Hari Hara, Tomar, Vibha
• Granted Patent: US 9,804,113 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: A01G 25/167 Control by humidity of the soil itself or of devices simulating soil or of the atmosphere; Soil humidity sensors
• CPC Class Codes: G01N 27/221 by investigating the dielectric properties using microwaves G01N22/00; measuring loss factors or dielectric constants per se G01R27/26
• CPC Class Codes: G01N 27/223 for determining moisture content, e.g. humidity rain detectors on vehicle windows B60S1/0825

Abstract

A soil moisture sensor includes a capacitive probe configured to be inserted into soil, a series RLC circuit electrically coupled to the capacitive probe, a microcontroller configured to determine the capacitance value of the soil and determine the moisture content of the soil from the capacitance value of the soil.

Claims

1. A soil moisture sensor, comprising:

a capacitive probe configured to be inserted into soil;

a series RLC circuit electrically coupled to the capacitive probe;

a microcontroller configured to;

determine the capacitance value of the soil; and

determine the moisture content of the soil from the capacitance value of the soil.

2. The soil moisture sensor of claim 1, wherein the capacitive probe comprises two electrodes.

3. The soil moisture sensor of claim 2, wherein each electrode comprises a pointed tip configured for insertion into soil.

4. The soil moisture sensor of claim 2, wherein the two electrodes form a parallel plate capacitor.

5. The soil moisture sensor of claim 2, wherein the microcontroller is configured to provide a drive signal to the series RLC circuit.

6. The soil moisture sensor of claim 5, wherein the drive signal frequency is selected with reference to a resonance curve of the series RLC circuit.

7. The soil moisture sensor of claim 6, where the drive signal frequency is selected to fall on the falling edge of the resonance curve of the series RLC circuit.

8. The soil moisture sensor of claim 7, wherein the drive signal frequency is less than 1 MHz.

9. The soil moisture sensor of claim 8, wherein the drive signal frequency is between 50 kHz and 500 kHz.

10. The soil moisture sensor of claim 9, wherein the drive signal frequency is between 100 kHz and 300 kHz.

11. The soil moisture sensor of claim 7, wherein the microcontroller comprises a pulse-width modulated signal generator and the pulse width modulated signal generator provides the drive signal to the series RLC circuit.

12. The soil moisture sensor of claim 5, wherein the series RLC circuit provides an input signal to the capacitive probe.

13. The soil moisture sensor of claim 12, wherein the capacitive probe provides an output signal to the microcontroller, wherein the output signal is dependent on the capacitance of the soil between the two electrodes.

14. The soil moisture sensor of claim 13, further comprising:

a current-to-voltage converter electrically coupled to the microprocessor, wherein the output signal of the capacitive probe is received by the analog-to digital converter, which converts the output signal to a proportional output voltage provided to the microcontroller as an input to determine the capacitance value of the soil.

15. The soil moisture sensor of claim 1, wherein the capacitive probe, the series RLC circuit, and the microcontroller are located in a single unit.

16. The soil moisture sensor of claim 1, wherein the capacitive probe and the series RLC circuit are located in a portable unit and the microcontroller is located in a processing unit.

17. The soil moisture sensor of claim 16, wherein the portable unit and the processing unit are configured to communicate wirelessly.

18. The soil moisture sensor of claim 16, wherein the portable unit and the processing unit are configured to communicate via a wired connection.

20. The soil moisture sensor of claim 1, wherein the capacitive probe, the series RLC circuit, the microcontroller, and the current-to-voltage converter are located in a single unit.

19. A soil moisture sensor, comprising:

a capacitive probe comprising two electrodes configured to be inserted into soil;

a series RLC circuit electrically coupled to the capacitive probe;

a microcontroller comprising a pulse-width modulated signal generator and an analog-to-digital converter; and

a current-to-voltage converter electrically coupled to the microprocessor, wherein the pulse-width modulated signal generator provides a drive signal to the series RLC circuit and the drive signal frequency is selected with reference to a resonance curve of the series RLC circuit;

wherein the series RLC circuit provides an input signal to the capacitive probe;

wherein an output signal dependent on the capacitance of the soil between the two electrodes is induced by the input signal and the output signal is provided to the current-to-voltage converter;

wherein the current-to-voltage converter converts the output signal to a proportional output voltage and the proportional output voltage is provided to the analog-to-digital converter;

wherein the analog-to-digital converter converts the proportional output voltage to a digital signal;

wherein the microcontroller determines the capacitance value of the soil based on the digital signal; and

wherein the microcontroller determines the moisture content of the soil in view of the capacitance value of the soil and the dielectric constant of the soil.