A high sensitivity single-probe heat pulse soil moisture sensor based on a single npn junction transistor

Dias, Pedro Carvalhaes; Roque, Wellington; Ferreira, Elnatan Chagas; Dias, José Antonio Siqueira

doi:10.1016/j.compag.2013.05.003

Cited by 26 publications

(22 citation statements)

References 6 publications

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“…It is important to observe that, for θ v = 40%, the value of ∆T in this sensor (with an energy heat pulse E = 0.745 J) was ∆T ≈ 3.1 • C, while in [13], where the transistor was in direct contact with the soil and the energy heat pulse was 100% higher, the value of ∆T was ∆T = 4.5 • C, which is only 45% higher.…”

Section: Measurement With the Sensor Not Inserted In The Soilmentioning

confidence: 85%

“…The signal conditioning system presented in [13] is a complex laboratory equipment that uses relatively high voltages (+25 V and −5 V) to work and is not adequate to be integrated in an autonomous irrigation management system powered by energy harvesters [19].…”

Section: Power Management Circuitsmentioning

confidence: 99%

“…Recently, we presented a novel technique for the fabrication of SHPP sensors, where the metal cylinder with the heating element (resistor) and the temperature-sensing element (thermistor or thermocouple) were replaced by a single bipolar transistor, which acts both as the heating and temperature-sensing element [13]. Although there are many advantages in using such a sensor, because it is very low cost and the fabrication is extremely simple (the sensor is actually a commercial transistor), it suffers from the soil contact problem.…”

Section: Introductionmentioning

confidence: 99%

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Autonomous Soil Water Content Sensors Based on Bipolar Transistors Encapsulated in Porous Ceramic Blocks

et al. 2019

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We present an autonomous sensor to measure soil water content that uses a single heat pulse probe based on a transistor encapsulated in a porous block. The sensor uses a bipolar junction transistor, which performs as both a heating and temperature-sensing element. Since the sensor depends on a porous block to measure the matric potential of the soil, it does not suffer from accuracy problems if the contact between the probe and the soil is not perfect. A prototype of the sensor showed a temperature variation of Δ T = 2.9 ∘ C when the porous ceramic was saturated with water. The sensor presented an almost linear behavior for small changes in the matric potential of a red latosol when tested in the 1-kPa and 35-kPa pressure range, showing a sensitivity of S = 0.015 ∘ C/kPa. The ultra-low power signal conditioning circuit can read the sensor’s temperature with a resolution of approximately 0.02 ∘ C, so the matric potential can be read in increments of at least 1.33 kPa. When powered only by a 2-F supercapacitor from the energy-harvesting system, the interrogation circuit is able to take one soil water content measurement per day, for eleven days.

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Section: Measurement With the Sensor Not Inserted In The Soilmentioning

confidence: 85%

Section: Power Management Circuitsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Autonomous Soil Water Content Sensors Based on Bipolar Transistors Encapsulated in Porous Ceramic Blocks

et al. 2019

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“…Furthermore, the thermal properties of water are only slightly influenced by salt concentration and temperature . Most of these thermal‐based moisture measurement methods rely on the difference in thermal conductivity between wet and dry material . So far these methods are only applicable for bulk materials or if the ambient influence is well defined.…”

Section: Introductionmentioning

confidence: 99%

New Type of Thermal Moisture Sensor for in‐Textile Measurements

Schönfisch

Göddel

Blinn

et al. 2019

Physica Status Solidi (a)

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The measurement of moisture in textile materials worn on or near the skin can be performed for a variety of reasons, for example, to analyze the amount of perspiration in clothing, wound fluid in bandages or even urine in diapers or bed sheets. Conventional moisture measurement methods, such as electrical resistance or capacitance measurement, can be susceptible to cross sensitivities to electrical fields or ionic impurities, often occurring in measurements close to the human body. The very reliable gravimetric methods are too bulky and difficult to be integrated in portable and online measurements. In this paper, the authors present a “transient heat moisture sensor” (THMS) which is small and comparatively easy to integrate into textiles. The authors describe the measurement principle and present a sensor element manufactured with thin film technologies. The analytical description of the sensor fits to both, experimental data and the result of first numerical analysis (COMSOL Multiphysics). The authors demonstrate how to limit the sensors spatial sensitivity to a thin layer of textile without being influenced by the adjacent environment by proper timing of the signal readout.

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“…The energy required to measure soil water content using capacitive sensors is typically three orders of magnitude lower than with sensors based on the heat dissipation principle [9,10,11,12,13,14], making them an excellent choice to be used with cost-effective low-power energy harvesting modules.…”

Section: Introductionmentioning

confidence: 99%

A Self-Powered and Autonomous Fringing Field Capacitive Sensor Integrated into a Micro Sprinkler Spinner to Measure Soil Water Content

Costa

Oliveira

Morais

et al. 2017

Sensors

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We present here the design and fabrication of a self-powered and autonomous fringing field capacitive sensor to measure soil water content. The sensor is manufactured using a conventional printed circuit board and includes a porous ceramic. To read the sensor, we use a circuit that includes a 10 kHz triangle wave generator, an AC amplifier, a precision rectifier and a microcontroller. In terms of performance, the sensor’s capacitance (measured in a laboratory prototype) increases up to 5% when the volumetric water content of the porous ceramic changed from 3% to 36%, resulting in a sensitivity of S=15.5 pF per unity change. Repeatability tests for capacitance measurement showed that the θv sensor’s root mean square error is 0.13%. The average current consumption of the system (sensor and signal conditioning circuit) is less than 1.5 μA, which demonstrates its suitability for being powered by energy harvesting systems. We developed a complete irrigation control system that integrates the sensor, an energy harvesting module composed of a microgenerator installed on the top of a micro sprinkler spinner, and a DC/DC converter circuit that charges a 1 F supercapacitor. The energy harvesting module operates only when the micro sprinkler spinner is irrigating the soil, and the supercapacitor is fully charged to 5 V in about 3 h during the first irrigation. After the first irrigation, with the supercap fully charged, the system can operate powered only by the supercapacitor for approximately 23 days, without any energy being harvested.

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A high sensitivity single-probe heat pulse soil moisture sensor based on a single npn junction transistor

Cited by 26 publications

References 6 publications

Autonomous Soil Water Content Sensors Based on Bipolar Transistors Encapsulated in Porous Ceramic Blocks

Autonomous Soil Water Content Sensors Based on Bipolar Transistors Encapsulated in Porous Ceramic Blocks

New Type of Thermal Moisture Sensor for in‐Textile Measurements

A Self-Powered and Autonomous Fringing Field Capacitive Sensor Integrated into a Micro Sprinkler Spinner to Measure Soil Water Content

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