US3573783A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Proximity sensor
Assignee: R F CONTROLS Inc
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Filing: 1967-09-13
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Granted: 1971-04-06
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Expires: 1987-09-13
Abstract
Abstract The proximity sensor detects persons or objects moving into or out of the field of an antenna energized by a low frequency signal. More particularly, a bridge circuit is coupled between a source of low frequency, an antenna, and a detector. The bridge is balanced to divide the energy from the source between the antenna and the detector. A switch is connected to cause a control function responsive to the detection of unbalances which occur in the bridge when the field of the antenna is upset. By changing the efficiency of the bridge, the depth of the antenna field may be varied without affecting the operating threshold of the detector.
Inventors
- 👤 Solly L Fudaley
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-28 10:00
CPC Classifications
G; G08; G08B; G08B13/00; G08B13/22; G08B13/26; H; H03; H03K; H03K17/00; H03K17/94; H03K17/96; H03K2017/9602; H03K2017/9604; H03K2017/9606
Claims Analysis
Total Claims: 13
Claim 1
Independent Claim
246 words
An alarm giving proximity sensor comprising a source of a low frequency signal having a fixed phase angle, a bridge circuit having an antenna in one arm thereof, isolation amplifier means for coupling said source to energize said bridge and establish a quiescent electromagnetic field of predetermined phase angle in the vicinity of said antenna, detector means, feedback tuned amplifier means having a narrow band-pass characteristic coupled between said detector and points on said bridge having a predetermined potential difference when said bridge is energized during said quiescent field condition, adjustable impedance means in another arm of said bridge for causing a predetermined adjusted level of current to pass from said source through said bridge and said narrow band-pass amplifier means to said detector during said quiescent field condition, said bridge means being responsive to changes in said electromagnetic field for causing a shifting of said predetermined phase angle in said field without appreciably changing either the low frequency or the phase of said signal from said source, said shift of said predetermined phase angle in said field causing a change of said level of current transmitted from said source through said bridge and, said feedback tuned amplifier, to said detector means, switching means operated to an intermediate state responsive to said predetermined level of current to said detector, and means responsive to changes of said level of current for selectively performing a control function depending upon whether said level of current goes up or down.
Claim 2
Dependent Claim
246 words
An alarm giving proximity sensor comprising a source of a low frequency signal having a fixed phase angle, a bridge circuit having an antenna in one arm thereof, isolation amplifier means for coupling said source to energize said bridge and establish a quiescent electromagnetic field of predetermined phase angle in the vicinity of said antenna, detector means, feedback tuned amplifier means having a narrow band-pass characteristic coupled between said detector and points on said bridge having a predetermined potential difference when said bridge is energized during said quiescent field condition, adjustable impedance means in another arm of said bridge for causing a predetermined adjusted level of current to pass from said source through said bridge and said narrow band-pass amplifier means to said detector during said quiescent field condition, said bridge means being responsive to changes in said electromagnetic field for causing a shifting of said predetermined phase angle in said field without appreciably changing either the low frequency or the phase of said signal from said source, said shift of said predetermined phase angle in said field causing a change of said level of current transmitted from said source through said bridge and, said feedback tuned amplifier, to said detector means, switching means operated to an intermediate state responsive to said predetermined level of current to said detector, and means responsive to changes of said level of current for selectively performing a control function depending upon whether said level of current goes up or down.
Claim 3
Dependent Claim
82 words
The sensor of claim 1 wherein said switching means comprises a pair of relays, one of said relays being biased to be operated and the other of said relays being biased to be unoperated responsive to said predetermined level of current in said bridge, said one relay releasing when said current falls below said predetermined level and said other relay operating when said current rises above said predetermined level, and indicator means for selectively indicating the operation and release of said relays.
Claim 4
Dependent Claim
31 words
The sensor of claim 2 and means for stabilizing said switching means against changes in ambient temperature conditions to enable a reduction in the difference between said high and low levels.
Claim 5
Dependent Claim
35 words
The sensor of claim 1 wherein said antenna is mounted adjacent the perimeter of a dangerous area, and means responsive to the detection of said change in current level bridge for signalling a danger condition.
Claim 6
Dependent Claim
30 words
The sensor of claim 1 and an automatic machine tool, said antenna being mounted adjacent said machine, and means whereby said control function is an emergency stopping of said machine.
Claim 7
Dependent Claim
48 words
The sensor of claim 1 wherein said isolation means interposed between said source and said bridge provides for efficiently transmitting the output of said source to said bridge while precluding any changes in the output of said source responsive to changes in the current flow in said bridge.
Claim 8
Dependent Claim
30 words
The sensor of claim 1 and means responsive to changes in the level of current flow, of said bridge for giving a snap-action like response to actuate an alarm indicator.
Claim 9
Dependent Claim
14 words
The sensor of claim 1 wherein said low frequency is in the audiofrequency range.
Claim 10
Dependent Claim
42 words
The sensor of claim 1 wherein said narrow band-pass means comprises an amplifier having a plurality of cascaded stages, each of said stages including a negative feedback circuit having a noise bypass and degenerative feedback tuned to provide a narrow band-pass filter.
Claim 11
Dependent Claim
24 words
The sensor of claim 1 and control means for selectively controlling the depth of said electromagnetic field without changing said predetErmined level of current.
Claim 12
Dependent Claim
42 words
The sensor of claim 10 wherein said control means comprises a bridge circuit for dividing the energy of said predetermined frequency between said antenna and said detecting means, and means for changing said division of said energy without changing said threshold level.
Claim 13
Dependent Claim
28 words
The sensor of claim 11 wherein said control means comprises a transformer coupled between said source and said detector, and means for varying the Q of said transformer.
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) | 1974-04-05 | 1974-10-05 | 1975-04-06 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1978-04-05 | 1978-10-05 | 1979-04-06 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1982-04-05 | 1982-10-05 | 1983-04-06 | $7700.00 | Window Closed / Lapsed |