Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Patent
1988-08-25
1990-04-03
Eisenzopf, Reinhard J.
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
73 1H, 73304C, 324675, G01R 2726
Patent
active
049143778
ABSTRACT:
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.
REFERENCES:
patent: 4347741 (1982-09-01), Geiger
patent: 4499767 (1985-02-01), Fathauer et al.
patent: 4589281 (1986-05-01), Aldrich
patent: 4624139 (1986-11-01), Collins
patent: 4723122 (1988-02-01), Maltby
Eisenzopf Reinhard J.
Ludlow Industries, Inc.
Mueller Robert W.
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