초록 ▼

A moisture sensor having an oscillator circuit with its output frequency directly proportional to moisture percentage present in the substance of interest, such as soil. The oscillator circuit includes two spaced plates in the substance which function as a capacitor. The frequency of the oscillation

A moisture sensor having an oscillator circuit with its output frequency directly proportional to moisture percentage present in the substance of interest, such as soil. The oscillator circuit includes two spaced plates in the substance which function as a capacitor. The frequency of the oscillations changes as the capacitance between the plates changes due to the moisture present between the plates. The sensor is particularly adapted for use as a soil moisture detector and provides indications of moisture percentage or end points such as wet or dry conditions.

대표청구항 ▼

A moisture sensor for detecting percentage moisture in a substance, said sensor being adapted to be coupled to an indication means and comprising: a source of electrical power; a variable frequency oscillator coupled to said power source and having a pulsed output, said oscillator comprising: a firs

A moisture sensor for detecting percentage moisture in a substance, said sensor being adapted to be coupled to an indication means and comprising: a source of electrical power; a variable frequency oscillator coupled to said power source and having a pulsed output, said oscillator comprising: a first transistor having an emitter and a first base; and a first variable resistor coupled between said power source and said emitter, the charging current to said capacitance means being governed by said first variable resistor; capacitance means in said oscillator, said capacitance means having electrodes of fixed size and spacing, the capacitance value of said capacitance means being responsive to the dielectric constant between said electrodes, said dielectric constant being a function of the percentage moisture between said electrodes, the pulse-to-pulse interval of the output pulses of said oscillator being linearly related to the capacitance value of said capacitance means; a constant current generator connected to said oscillator and providing a constant charging current to said capacitance means, said constant current generator comprising: a second transistor having a base, a collector and an emitter; and a second variable resistor connecting said base to ground, said base being coupled to said power source; means for coupling the output of said oscillator to said indication means to indicate relative moisture content of the substance; whereby said first variable resistor controls oscillation rate and said second variable resister is adapted to be set to establish linearity between moisture percentage and the capacitance of said capacitance means.