US3701138A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Fluid level sensor and system
Assignee: CLARK ENGINEERING INC
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Filing: 1971-03-25
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Granted: 1972-10-24
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Expires: 1991-03-25
Abstract
Abstract A sensor and system for sensing the level of fluid in a vessel above and below a predetermined level. The sensor comprises a base for mounting on a wall of the vessel with control and reference resistors on a support member extending from the base into the vessel. The resistors form legs of a normally balanced bridge circuit having an indicator connected to its output. A hollow housing having fluid inlet, outlet, and meniscus breaking means surrounds the resistors and support member to insure that the resistors are covered by fluid when fluid in the vessel is at or above the predetermined level and to rapidly drain and expose the control resistor when the fluid drops below the predetermined level to unbalance the bridge circuit and produce an indication at the indicator.
Inventors
- 👤 Joseph H Pulliam
- 👤 Thomas W Mccurnin
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-27 15:29
CPC Classifications
G; G01; G01F; G01F23/00; G01F23/22; G01F23/24; G01F23/246; G01F23/247
Claims Analysis
Total Claims: 12
Claim 1
Independent Claim
209 words
A sensor for sensing the level of a fluid in a vessel above and below a predetermined level, comprising: a base for mounting on a wall of said vessel about said predetermined level; a support member of nonconductive material for extending from said base into said vessel; a control resistor on said support member; a reference resistor on said support member spaced from said control resistor; a layer of heat transmissive, electrically and chemically inert material over and sealing said control resistor and said reference resistor on said support member; hollow housing means including fluid inlet and outlet means and extending from said base for surrounding said support member and control and reference resistors with fluid when fluid in said vessel is at or above said predetermined level, and for draining at least a portion of said housing including said control resistor when fluid drops below said predetermined level; and means for electrically connecting said control and reference resistors in a normally balanced bridge circuit connected to a voltage source and an indicator means such that a drop in fluid below said predetermined level results in an immediate unbalance of said bridge circuit and indication at said indicator means as said control resistor heats relative to said reference resistor.
Claim 2
Dependent Claim
209 words
A sensor for sensing the level of a fluid in a vessel above and below a predetermined level, comprising: a base for mounting on a wall of said vessel about said predetermined level; a support member of nonconductive material for extending from said base into said vessel; a control resistor on said support member; a reference resistor on said support member spaced from said control resistor; a layer of heat transmissive, electrically and chemically inert material over and sealing said control resistor and said reference resistor on said support member; hollow housing means including fluid inlet and outlet means and extending from said base for surrounding said support member and control and reference resistors with fluid when fluid in said vessel is at or above said predetermined level, and for draining at least a portion of said housing including said control resistor when fluid drops below said predetermined level; and means for electrically connecting said control and reference resistors in a normally balanced bridge circuit connected to a voltage source and an indicator means such that a drop in fluid below said predetermined level results in an immediate unbalance of said bridge circuit and indication at said indicator means as said control resistor heats relative to said reference resistor.
Claim 3
Dependent Claim
25 words
The sensor of claim 1 including meniscus breaking means adjacent said fluid outlet means for breaking any meniscus formed during draining of said housing means.
Claim 4
Dependent Claim
34 words
The sensor of claim 2 wherein said meniscus breaking means comprises a slot in said housing means leading from said fluid outlet means and a hole in said housing means communicating with said slot.
Claim 5
Dependent Claim
150 words
The sensor of claim 1 wherein: said control and reference resistors are like, low resistance, self-heating resistors electrically connected in series across said voltage source in said bridge circuit; and said sensor further includes a partition dividing said housing means into a first compartment including said reference resistor and a second compartment including said control resistor and said fluid inlet and outlet means, and a top opening in said housing means into said first compartment whereby when fluid in said vessel is at or above said predetermined level, said control and reference resistors are covered with fluid and said bridge circuit is balanced and when fluid in said vessel drops below said predetermined level, fluid rapidly flows from said second compartment and said control resistor heats rapidly to change its resistance value relative to said reference resistor thereby unbalancing said bridge circuit and producing said indication at said indicator means.
Claim 6
Dependent Claim
56 words
The sensor of claim 4 wherein said housing means comprises a sleeve extending from said base to axially receive said support member, said sleeve being open at an outer end remote from said base to define said fluid inlet and outlet means and including meniscus breaking means extending from said open outer end of said sleeve.
Claim 7
Dependent Claim
49 words
The sensor of claim 5 wherein said meniscus breaking means comprises upper and lower meniscus breakers each including a slot and a hole in said sleeve, each slot being open to said outer end and each hole being spaced from said outer end and communicating with its associated slot.
Claim 8
Dependent Claim
98 words
The sensor of claim 1 wherein said reference resistor is a relatively high resistance resistor and said control resistor is a relatively low resistance self-heating resistor connected in different legs of said bridge circuit whereby when fluid in said vessel is at or above said predetermined level, said control and reference resistors are covered by fluid and when fluid in said vessel drops below said predetermined level, fluid rapidly drains from said housing means and said control resistor rapidly heats to change its resistance value thereby unbalancing said bridge circuit and producing said indication at said indicator means.
Claim 9
Dependent Claim
56 words
The sensor of claim 7 wherein said housing means comprises a sleeve extending from said base to axially receive said support member, said sleeve being open at an outer end remote from said base to define said fluid inlet and outlet means and including meniscus breaking means extending from said open outer end of said sleeve.
Claim 10
Dependent Claim
49 words
The sensor of claim 8 wherein said meniscus breaking means comprises upper and lower meniscus breakers each including a slot and a hole in said sleeve, each slot being open to said outer end and each hole being spaced from said outer end and communicating with its associated slot.
Claim 11
Independent Claim
240 words
A system for detecting the level of a fluid in a vessel above and below a predetermined level, comprising: a base for mounting on a wall of said vessel about said predetermined level; a support member of nonconductive material for extending outwardly from said base into said vessel; a control resistor on said support member; a reference resistor on said support member and spaced from said control resistor; a layer of heat transmissive, electrically and chemically inert material over and sealing said control resistor and said reference resistor on said support members; hollow housing means including fluid inlet and outlet means and extendIng from said base for surrounding said support member and control and reference resistors with fluid when fluid in said vessel is at or above said predetermined level, and for draining at least a portion of said housing including said control resistor when fluid drops below said predetermined level; first and second balancing resistors external to said vessel; indicator means; and circuit means connecting said reference and control resistors to said first and second balancing resistors as a normally balanced bridge circuit having an input connected to a voltage source and an output connected to said indicator means whereby a drop in the level of fluid in said vessel below said predetermined level results in an immediate unbalance of said bridge circuit and indication at said indicator means as said control resistor heats relative to said reference resistor.
Claim 12
Independent Claim
240 words
A system for detecting the level of a fluid in a vessel above and below a predetermined level, comprising: a base for mounting on a wall of said vessel about said predetermined level; a support member of nonconductive material for extending outwardly from said base into said vessel; a control resistor on said support member; a reference resistor on said support member and spaced from said control resistor; a layer of heat transmissive, electrically and chemically inert material over and sealing said control resistor and said reference resistor on said support members; hollow housing means including fluid inlet and outlet means and extendIng from said base for surrounding said support member and control and reference resistors with fluid when fluid in said vessel is at or above said predetermined level, and for draining at least a portion of said housing including said control resistor when fluid drops below said predetermined level; first and second balancing resistors external to said vessel; indicator means; and circuit means connecting said reference and control resistors to said first and second balancing resistors as a normally balanced bridge circuit having an input connected to a voltage source and an output connected to said indicator means whereby a drop in the level of fluid in said vessel below said predetermined level results in an immediate unbalance of said bridge circuit and indication at said indicator means as said control resistor heats relative to said reference resistor.
References Cited (Backward Citations)
US2824278A
Cited
US3461446A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1975-10-24 | 1976-04-24 | 1976-10-24 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1979-10-24 | 1980-04-24 | 1980-10-24 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1983-10-24 | 1984-04-24 | 1984-10-24 | $7700.00 | Window Closed / Lapsed |