Oscillator circuit

Claim 2

An oscillator circuit for a moisture content measuring system wherein radiofrequency energy in a tank circuit is coupled to materials containing moisture through fringe-field capacitance electrodes, the Q of said tank circuit being reduced as a measure of moisture content, said oscillator circuit comprising: a field effect transistor having a source, a drain, and a gate, said transistor being connected to said tank circuit in a Class C oscillator configuration; stabilization means for stabilizing said oscillator circuit as the Q of said tank circuit is reduced, said stabilization means including a diode connected in the gate circuit of said transistor in a rectifying configuration for a portion of the radiofrequency energy in said tank circuit whereby self-bias is provided for said oscillator circuit which is proportional to the reduction in the Q of said tank circuit.

Claim 3

The oscillator circuit of claim 1 wherein: said stabilization means further includes a diode connected in the source circuit of said transistor for cooperation with said diode connected in the gate circuit of said transistor to provide for temperature stabilization of the operating point of said transistor.

Claim 4

The oscillator circuit of claim 1 wherein: said stabilization means further includes a thermistor connected in the drain circuit of said transistor for cooperation with said diode connected in the gate circuit of said transistor to provide temperature stabilization of the sensitivity of the oscillator to tank circuit loading.

Claim 5

The oscillator of claim 3 wherein: said stabilization means further includes a diode connected in the source circuit of said transistor for cooperation with said diode connected in the gate circuit and said thermistor connected in the drain circuit of said transistor to provide for temperature stabilization of the operating point of said transistor.

Claim 6

The oscillator circuit of claim 1 including: means for dissipating transient voltage pulses appearing on said fringe-field capacitance electrodes due to operation of said moisture content measuring system in the vicinity of static electric fields, said dissipating means having a back-biased diode connected in the gate circuit of said transistor whereby negative high voltage transients are shunted through said back-biased diode.

Claim 7

The oscillator circuit of claim 5 wherein: said dissipating means includes a zener diode connected in the drain circuit of said transistor for preventing the voltage at the drain from exceeding the avalanche voltage of said zener diode.

Claim 8

The oscillator circuit of claim 1 including coupling means for coupling each of said fringe-field capacitance electrodes to said tank said coupling means allowing radiofrequency energy to pass to and froM said tank to said electrodes but preventing the pasing of high-voltage transients appearing on said electrodes due to operation of said moisture content measuring system in the vicinity of static electric fields, said coupling means comprising: a first gas discharge tube connected across each of said electrodes, said discharge tube being ionized when high-voltage transients appear on said electrodes; a pi-section low-pass filter connected between each electrode and said tank circuit, said low-pass filter passing the radiofrequencies generated by said oscillator circuit and substantially attenuating the radiofrequencies associated with high-voltage transient pulses; and a second gas discharge tube connected across the junction of said low-pass filter and said tank circuit, said second discharge tube being ionized when remaining high-voltage transient pulses appear at said junction to effectively shunt said transients through said discharge tube.

Claim 9

The oscillator circuit of claim 7 including: a back-biased diode connected in the gate circuit of said transistor for dissipating negative high-voltage transients in the gate circuit.

Claim 10

The oscillator circuit of claim 8 including: a thermistor in the drain circuit of said transistor for temperature stabilization of the sensitivity of the oscillator to tank circuit loading.