Patent US3917979A successfully refreshed from Google Patents.
US3917979A
Expired / Lapsed
US
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Protection circuit for an adjustable motorized hospital bed
Assignee: B-W HEALTH PRODUCTS INC A CORP OF MO
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Filing: 1974-03-18
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Granted: 1975-11-04
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Expires: 1994-03-18
Abstract
Abstract The electrical control system for a motor operated adjustable hospital bed is energized by AC voltage from a grounded AC power supply. A separate ground connection between the bed frame or chassis and the power supply ground establishes the bed chassis at earth ground potential during normal operating conditions. The patient is protected against shock hazards in the event that he contacts an AC voltage (from the bed''s control system or from any external electrical apparatus) at the same time that he touches the bed chassis, thereby causing ground leakage current to flow through his body. This protection is achieved by constantly monitoring the ground leakage current flowing through the ground connection and opening that connection anytime the leakage current exceeds a predetermined threshold level, such as around 9 microamperes. In addition, the AC power supplied to the bed is interrupted.
Inventors
- 👤 Jr Joseph A Volk
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-07 23:06
CPC Classifications
H; H02; H02H; H02H3/00; H02H3/16; H02H3/162
Claims Analysis
Total Claims: 9
Claim 1
Independent Claim
108 words
A protection circuit for an adjustable motorized hospital bed wherein a grounded AC power supply is coupled to the bed''s electrical control system for applying AC operating voltage thereto, and wherein a ground connection couples the bed chassis to the power supply ground, comprising: means, including a series-connected resistor in the ground connection, for monitoring any ground leakage current flowing through said ground connection; switching means responsive to said monitoring means for interrupting the ground connection anytime the ground leakage current exceeds a predetermined threshold level; and a pair of oppositely poled diodes, each connected in shunt with said resistor, for limiting the voltage developed across said resistor.
Claim 2
Dependent Claim
108 words
A protection circuit for an adjustable motorized hospital bed wherein a grounded AC power supply is coupled to the bed''s electrical control system for applying AC operating voltage thereto, and wherein a ground connection couples the bed chassis to the power supply ground, comprising: means, including a series-connected resistor in the ground connection, for monitoring any ground leakage current flowing through said ground connection; switching means responsive to said monitoring means for interrupting the ground connection anytime the ground leakage current exceeds a predetermined threshold level; and a pair of oppositely poled diodes, each connected in shunt with said resistor, for limiting the voltage developed across said resistor.
Claim 3
Dependent Claim
34 words
A protection circuit according to claim 1 in which said switching means also decouples the bed''s electrical control system from the AC power supply when the ground leakage current exceeds said predetermined threshold level.
Claim 4
Dependent Claim
57 words
A protection circuit according to claim 2 wherein the AC operating voltage is applied to the bed''s electrical control system over a pair of line conductors, and including means for actuating said switching means to decouple the control system from the AC power supply anytime either one of the line conductors becomes grounded to the bed chassis.
Claim 5
Dependent Claim
50 words
A protection circuit according to claim 2 wherein the AC power supply is coupled to the bed''s electrical control system via an isolation transformer, the primary winding of which is disconnected from the AC power supply by said switching means when the ground leakage current exceeds said predetermined threshold level.
Claim 6
Dependent Claim
84 words
A protection circuit according to claim 4 and including a pair of series-connected, oppositely poled diodes in shunt with the secondary winding of said transformer, the junction of said diodes being coupled to said ground connection, wherein said monitoring means monitors any fault current flowing between said junction and said ground connection, and in which said switching means responds to said monitoring means to decouple the bed''s electrical control system from the AC power supply anytime the fault current exceeds a given threshold level.
Claim 7
Dependent Claim
59 words
A protection circuit according to claim 4 wherein the primary winding of said isolation transformer is coupled to the AC power supply via hot and neutral leads, and wherein a pair of solid state switches in series with the hot lead and the ground connection, respectively, are rendered non-conductive when the ground leakage current exceeds said predetermined threshold level.
Claim 8
Dependent Claim
32 words
A protection circuit according to claim 1 in which said switching means is actuated by said monitoring means to interrupt the ground connection when the ground leakage current exceeds approximately 9 microamperes.
Claim 9
Dependent Claim
102 words
A protection circuit according to claim 1 in which said switching means includes a solid state switch in series with the ground connection, a bistable device for controlling said solid state switch and having set and reset operating conditions, and means for establishing said bistable device normally in its reset operating condition to render said solid state switch conductive, thereby maintaining the ground connection continuous; and in which said monitoring means actuates said bistable device to its set condition, when the ground leakage current exceeds said predetermined threshold level, to render said solid state switch non-conductive and to interrupT the ground connection.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1978-11-03 | 1979-05-05 | 1979-11-04 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1982-11-03 | 1983-05-05 | 1983-11-04 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1986-11-03 | 1987-05-05 | 1987-11-04 | $7700.00 | Window Closed / Lapsed |