US3706980A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Rf system for measuring the level of materials
Assignee: Drexelbrook Controls Inc
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Filing: 1970-04-27
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Granted: 1972-12-19
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Expires: 1990-04-27
Abstract
Abstract In an RF system which measures the level of materials, the probe includes a measuring electrode and a guard shield. The guard shield is interposed between the electrode and a conductive member, commonly the container for the material, throughout the body of the probe. The variable capacitance between the measuring electrode and the conductive member is a measurement of the level of the material. This variable capacitance is connected in a capacitance bridge. An operational amplifier has its input connected to the junction of two fixed adjacent arms of the bridge and has its output connected to the guard shield to maintain the guard shield at the same potential as the measuring electrode. This prevents deposits of foreign material on the probe from affecting the measurement. An output amplifier is connected between the output of the first amplifier and a junction of two opposite adjacent arms of the bridge. Connection of the output amplifier in this manner prevents changes in the input impedance of the output amplifier from changing the zero point of the bridge.
Inventors
- 👤 Frederick L Maltby
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-27 04:20
CPC Classifications
G; G01; G01F; G01F23/00; G01F23/22; G01F23/26; G01F23/263; G01F23/266; G01F23/268
Claims Analysis
Total Claims: 11
Claim 1
Independent Claim
200 words
A system responsive to the level of materials comprising: a conductive electrode, a conductive member, the variable impedance between said electrode and said conductive member being determined by the level of said materials, a guard shield interposed between said electrode and said conductive member, a source of alternating voltage having first, second and third terminals, said source generating a low amplitude alternating voltage between said first and said second terminals and a high amplitude alternating voltage between said first and said third terminals, means for coupling said second terminal to said guard shield so as to apply said low amplitude alternating voltage to said guard shield, another impedance, said variable impedance and said other impedance forming a voltage divider across said source between said first and third terminals, said low amplitude alternating voltage applied to said guard shield and the voltage across said variable impedance being substantially equal for a preDetermined level of materials, and a detector means responsive to the difference between said low amplitude voltage and the voltage at the junction of said variable impedance and said other impedance of said divider so to indicate the level of materials in a range about said predetermined level of materials.
Claim 2
Independent Claim
200 words
A system responsive to the level of materials comprising: a conductive electrode, a conductive member, the variable impedance between said electrode and said conductive member being determined by the level of said materials, a guard shield interposed between said electrode and said conductive member, a source of alternating voltage having first, second and third terminals, said source generating a low amplitude alternating voltage between said first and said second terminals and a high amplitude alternating voltage between said first and said third terminals, means for coupling said second terminal to said guard shield so as to apply said low amplitude alternating voltage to said guard shield, another impedance, said variable impedance and said other impedance forming a voltage divider across said source between said first and third terminals, said low amplitude alternating voltage applied to said guard shield and the voltage across said variable impedance being substantially equal for a preDetermined level of materials, and a detector means responsive to the difference between said low amplitude voltage and the voltage at the junction of said variable impedance and said other impedance of said divider so to indicate the level of materials in a range about said predetermined level of materials.
Claim 3
Dependent Claim
41 words
The system of claim 1 wherein said source of alternating voltage and said coupling means provide sufficient drive for said low amplitude voltage applied to said guard shield to maintain said low amplitude voltage applied to said guard shield substantially constant.
Claim 4
Dependent Claim
38 words
The system of claim 2 wherein said means for coupling said second terminal to said guard shield comprises a substantially 100 percent feedback amplifier to provide sufficient drive so as to maintain said low amplitude voltage substantially constant.
Claim 5
Dependent Claim
41 words
The system of claim 3 including fail safe means coupled between the input and the output of said feedback amplifier for sensing and indicating when the difference between said input and said output of said feedback amplifier exceeds a predetermined level.
Claim 6
Dependent Claim
48 words
The system of claim 1 comprising a probe including said conductive electrode and said guard shield, said probe further including insulation between said conductive electrode and said guard shield, said guard shield being interposed between said conductive electrode and said conductive member throughout the body of said probe.
Claim 7
Dependent Claim
59 words
The system of claim 5 wherein said conductive member comprises the wall of a container and said probe comprises a flush sensor positioned on the wall of said container, said guard shield comprising a hollow cup of conductive material completely surrounding said conductive electrode except on a detecting surface thereof, said guard shield being insulated from said conductive electrode.
Claim 8
Dependent Claim
81 words
The system of claim 5 wherein said conductive electrode comprises a flat surface opposed to the surface of said materials, said probe further comprising insulation separating said conductive electrode from said guard shield, said guard shield extending perpendicularly away from the surface of said conductive electrode, said guard shield being substantially the only support of said conductive electrode so that foreign materials splashed on said probe will not affect the capacitance between said first electrode and the surface of said materials.
Claim 9
Independent Claim
204 words
A system responsive to the level of materials comprising: a conductive electrode, a conductive member, the variable impedance between said electrode and said conductive member being determined by the level of said materials, a guard shield interposed between said electrode and said conductive member, a capacitance bridge having first and second capacitors as two adjacent arms of said bridge and having as the opposite adjacent arms a manually adjustable capacitor and said variable impedance. a third capacitor connected between the junction of said two adjacent arms and the junction of said opposite adjacent arms, an operational amplifier having its input connected to the junction of said two adjacent arms and having its output connected to said guard shield, said operational amplifier having feedback which maintains said guard shield at the same potential as said electrode when said bridge is balanced, and an output amplifier having one input connected to the junction of said two opposite adjacent arms of said bridge and having the other input connected to the output of said operational amplifier so that changes in impedance of said output amplifier do not change the zero point of said bridge, the output signal of said output amplifier representing the level of said material.
Claim 10
Independent Claim
204 words
A system responsive to the level of materials comprising: a conductive electrode, a conductive member, the variable impedance between said electrode and said conductive member being determined by the level of said materials, a guard shield interposed between said electrode and said conductive member, a capacitance bridge having first and second capacitors as two adjacent arms of said bridge and having as the opposite adjacent arms a manually adjustable capacitor and said variable impedance. a third capacitor connected between the junction of said two adjacent arms and the junction of said opposite adjacent arms, an operational amplifier having its input connected to the junction of said two adjacent arms and having its output connected to said guard shield, said operational amplifier having feedback which maintains said guard shield at the same potential as said electrode when said bridge is balanced, and an output amplifier having one input connected to the junction of said two opposite adjacent arms of said bridge and having the other input connected to the output of said operational amplifier so that changes in impedance of said output amplifier do not change the zero point of said bridge, the output signal of said output amplifier representing the level of said material.
Claim 11
Dependent Claim
72 words
The system recited in claim 8 further comprising a guard shield monitor including: a guard shield amplifier having one input connected to the junction of said first arms of said bridge and a second input connected to the output of said operational amplifier, and alarm means connected to the ouTput of said monitor amplifier when the two inputs to said monitor amplifier have a difference in voltage which exceeds a predetermined amount.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1975-12-19 | 1976-06-19 | 1976-12-19 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1979-12-19 | 1980-06-19 | 1980-12-19 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1983-12-19 | 1984-06-19 | 1984-12-19 | $7700.00 | Window Closed / Lapsed |