초록 ▼

A capacitance probe extends into a container for material which increases the capacitance between the probe and the container when the material contacts the probe. A fixed RF voltage is supplied to the base of a transistor in an electronic translator having a capacitor between the probe and the tran

A capacitance probe extends into a container for material which increases the capacitance between the probe and the container when the material contacts the probe. A fixed RF voltage is supplied to the base of a transistor in an electronic translator having a capacitor between the probe and the transistor\s emitter. A first diode conducts between the base and RF ground. A second diode conducts between the emitter and the base. A small-value capacitor is connected between an ungrounded DC supply terminal and the probe. A third diode conducts variable DC to the transistor\s collector from a variable DC signal line supplied with DC for the DC terminal through a resistor. A comparator has a first input connected to the line and a second input connected to a reference voltage. The comparator\s output is adapted to energize an output signal and a relay when the DC signal on the line drops below the reference voltage. Additional DC is supplied to the line by an RF driven calibration transistor functioning as an electronically variable resistance controlled by an electronic stepper, for increasing the DC signal line voltage to compensate for material adhering to the probe. The stepper is reset and started by a switch, and is stopped by a second comparator having a first input connected to the signal line and a second input supplied with a higher adjustable reference voltage affording sensitivity adjustment. The stepper controls a capacitance bank connected to the calibration transistor.

대표청구항 ▼

A radio frequency capacitance probe system for material direction, comprising a capacitance probe adapted to be located in a container where material is to be detected, said probe having a minimum capacitance to the container when the material is absent and a substantially increased capacitance when

A radio frequency capacitance probe system for material direction, comprising a capacitance probe adapted to be located in a container where material is to be detected, said probe having a minimum capacitance to the container when the material is absent and a substantially increased capacitance when the material is present around the probe, a radio frequency (RF) source for producing a fixed RF voltage, a first electronic translating circuit having an RF input connection to said source and an RF output connection to said probe, said first electronic translating circuit having means including a first active electronic element affording a first DC signal path along which a DC signal current is increased while the DC resistance of said path is decreased in response to increasing capacitance of said probe and consequent increasing RF current into said probe, a DC signal line to which said first DC signal path is connected for drawing current from said line, a first signal level detector having an input connected to said signal line for triggering an output when the signal voltage on said line drops below a first reference level, utilization means connected to said first signal level detector and operative to perform at least one control function in response to the output thereof, a second electronic translating circuit having a second RF input connection to said RF source and a second RF output connection, a variable balancing capacitance connected to said second RF output connection, said second electronic translating circuit having means including a second active electronic element affording a second DC signal path connected to said DC signal line for supplying a variable DC balancing current to said line, said second electronic translating circuit being operative to produce an increased balancing current and a decreased resistance along said second DC signal path in response to increasing the value of said variable capacitance and thereby increasing the RF current therein, and calibration means for varying said variable capacitance to adjust and calibrate the initial voltage on said signal line and thereby to compensate for increases in the minimum capacitance of said probe due to adherent material after the material contacts the probe and then recedes therefrom.