Joe F Aldrich, 64Stephen Creek, TX

4589281, May 20, 1986

Sep 20, 1984

6/653028

Joe L. Aldrich - Kingwood TX

Keystone International, Inc. - Houston TX

G01F 2326

73290R

Disclosed is a monitoring system and method for detecting the presence or absence of material at a location. The apparatus may generally be constructed to include a sensing unit, including an antenna probe for positioning at the location wherein material is to be detected, and a control unit for responding to signals from the sensing unit indicating the presence of material at the antenna probe. The control unit may include an indicator to inform an operator of the presence or absence of material at the antenna probe, and also an output which enables peripheral equipment to operate only under selected conditions at the antenna probe. The sensing signal from the sensing unit is dc, with fluctuations indicating the presence of material at the antenna probe. The sensing signal may be communicated a considerable distance to the control unit over ordinary electrical lead lines without electrical shielding, and the control unit responds to a break in such communication lines by not permitting enabling of such peripheral equipment.

4222267, Sep 16, 1980

Feb 10, 1978

5/877028

Joe L. Aldrich - Kingwood TX

Keystone International, Inc. - Houston TX

G01F 2326

73304C

Disclosed are apparatus and methods for detecting the presence, or absence, of material at a predetermined location. An oscillator generates a constant-frequency, constant-amplitude signal which is fed through a load resistor to an antenna probe positioned at the sensing location. The amplitude of the signal fed to the antenna probe varies as the impedance of the antenna probe is affected by material in its environment, or lack thereof. The signal amplitude is converted into a d-c voltage level, and is transmitted to a switching circuit which provides an output signal depending on a comparison between the d-c voltage level and a reference voltage level. The sensitivity of the switching circuit is adjustable to accommodate the degree to which the particular material, whose presence or absence is to be detected, affects the impedance of the antenna probe. The output from the switching circuit may be used to operate one or more devices indicative of the environment of the antenna probe and/or affecting the environment by adding to and/or removing therefrom material affecting the impedance of the antenna probe.

4226118, Oct 7, 1980

Jul 28, 1978

5/928820

Joe L. Aldrich - Kingwood TX

Keystone International, Inc. - Houston TX

G01F 2328

73290V

Disclosed are apparatus and methods for detecting the extent to which material is present at a predetermined sensing area. An antenna probe is extended throughout the sensing area, and is loaded with a signal from an oscillator. A reference oscillator provides a constant-frequency signal of the same base frequency as the antenna oscillator signal. The presence of impedance-affecting material in the sensing area reduces the impedance load of the antenna and, therefore, the frequency of the output signal of the antenna oscillator in proportion to the extent of immersion of the antenna probe in such material. The output signals from both oscillators are compared in a frequency differencer circuit which produces output signals whose frequency, equal to the difference in frequencies of the two oscillator output signals, is an indication of the amount of material present in the sensing area. A testing circuit provides an indication of the frequency of the differencer output signal, and is used in adjusting the sensitivity of the detector circuitry with the antenna probe free of impedance-affecting material. With the oscillator sensitivities adjusted, the detector circuitry is zeroed, again with reliance on the testing circuit to indicate when both oscillators are generating the same output frequency.