US4386342A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Intrusion alarm system
Assignee: Individual
•
Filing: 1981-03-31
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Granted: 1983-05-31
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Expires: 2001-03-31
Abstract
Abstract An alarm system comprises a blower driven by an electric motor, the blower being fitted to the premises to be protected and serving to blow air into the premises. With all doors and windows shut the blower supplies a steady flow of air, the flow rate depending on the nature of the blower and how fast air can leak out of the premises around doors and windows, through air vents etc. The current drawn by the motor is constant in these circumstances and is monitored. When entry is made to the premises, by opening a door or window, the air flow rate increases and the load on the motor changes. This is reflected in a change in the current drawn by the motor and the blower can blow air from the premises, air entering around doors and windows etc.
Inventors
- 👤 Alexander T. McKinley
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-28 05:46
CPC Classifications
G; G08; G08B; G08B13/00; G08B13/20; G08B13/02; G08B13/08
Claims Analysis
Total Claims: 6
Claim 1
Independent Claim
164 words
An alarm system for indicating that entry has been made into closed premises, the alarm system comprising a blower, an electric motor for driving the blower, means for monitoring the current being drawn by the motor and for producing an output signal which varies with changes in motor current, means connected to the monitoring means for detecting a change in said output signal and hence for detecting the change in motor current which occurs upon there being a change in the load on the motor, an alarm activated by the detecting means, means operable by the user to arm the system, means for activating the alarm in response to a change in the condition of the arming means to the disarmed condition, timing means for delaying activation of the alarm for a predetermined period after such change in the condition of the arming means to the disarmed condition, and manually operable means for operation during the delay period for preventing the alarm being activated.
Claim 2
Dependent Claim
164 words
An alarm system for indicating that entry has been made into closed premises, the alarm system comprising a blower, an electric motor for driving the blower, means for monitoring the current being drawn by the motor and for producing an output signal which varies with changes in motor current, means connected to the monitoring means for detecting a change in said output signal and hence for detecting the change in motor current which occurs upon there being a change in the load on the motor, an alarm activated by the detecting means, means operable by the user to arm the system, means for activating the alarm in response to a change in the condition of the arming means to the disarmed condition, timing means for delaying activation of the alarm for a predetermined period after such change in the condition of the arming means to the disarmed condition, and manually operable means for operation during the delay period for preventing the alarm being activated.
Claim 3
Dependent Claim
37 words
An alarm system according to claim 1, in which said monitoring means generates an electric field, and the change in the strength of the field which occurs upon there being a change in motor current is detected.
Claim 4
Dependent Claim
56 words
An alarm system according to claim 1, in which said monitoring means includes means for generating a voltage proportional to the current being drawn by the motor, and said detecting means includes means for generating two reference voltages and comparator means for determining if said proportional voltage lies within the limits represented by said reference voltages.
Claim 5
Dependent Claim
29 words
An alarm system according to claim 1, and including timing means for delaying activation of said alarm for a predetermined period after a change in motor current is detected.
Claim 6
Dependent Claim
38 words
An alarm system according to claim 1, and which includes means operable by the user to arm the system, and timing means for delaying arming of the system for a predetermined time after operation of the arming means.
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) | 1986-05-30 | 1986-11-29 | 1987-05-31 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1990-05-30 | 1990-11-29 | 1991-05-31 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1994-05-30 | 1994-11-29 | 1995-05-31 | $7700.00 | Window Closed / Lapsed |