US4568937A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Induction loop vehicle detector
Assignee: Microsense Systems Ltd
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Filing: 1983-06-02
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Granted: 1986-02-04
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Expires: 2003-06-02
Abstract
Abstract An induction loop vehicle detector comprises an oscillator circuit having a plurality of capacitors switchable in circuit with a road loop under the control of a microcomputer to determine the oscillator frequency. The microcomputer monitors the oscillator frequency and controls the switching of the capacitors to periodically return the frequency to a predetermined value. A counter counts a predetermined number of oscillator cycles and gates of h.f. clock into a second counter whereby the count of the counter represents the oscillator period. A "vehicle detected" output is given when the monitored frequency alters by more than a predetermined amount, representing a decrease in the inductance of the loop. On detecting an increase in the inductance above a predetermined threshold the detector is inhibited for a predetermined time, e.g. about 1 second, to avoid errors caused by magnetic effects.
Inventors
- 👤 Michael A. G. Clark
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-02 02:34
CPC Classifications
G; G08; G08G; G08G1/00; G08G1/01; G08G1/042; G01; G01V; G01V3/00; G01V3/08; G01V3/10; G01V3/101
Claims Analysis
Total Claims: 12
Claim 1
Independent Claim
145 words
A vehicle detector comprising: an oscillator circuit having capacitance means arranged to be connected to a road loop for determining the frequency of the oscillator circuit; means for monitoring the frequency of said oscillator circuit; a control processor arranged to control the capacitance of the capacitance means so as to periodically return the frequency to a predetermined value; detector means for producing an output signal indicative of a detected vehicle when the monitored frequency alters by more than a predetermined amount, said detector means detecting a decrease in the inductance of the road loop and in response thereto for providing a signal indicative of the presence of a vehicle; means for detecting an increase in the inductance above a predetermined threshold; and means, responsive to said means for detecting, for inhibiting the detector means for a predetermined time after detecting said increase in the inductance.
Claim 2
Dependent Claim
145 words
A vehicle detector comprising: an oscillator circuit having capacitance means arranged to be connected to a road loop for determining the frequency of the oscillator circuit; means for monitoring the frequency of said oscillator circuit; a control processor arranged to control the capacitance of the capacitance means so as to periodically return the frequency to a predetermined value; detector means for producing an output signal indicative of a detected vehicle when the monitored frequency alters by more than a predetermined amount, said detector means detecting a decrease in the inductance of the road loop and in response thereto for providing a signal indicative of the presence of a vehicle; means for detecting an increase in the inductance above a predetermined threshold; and means, responsive to said means for detecting, for inhibiting the detector means for a predetermined time after detecting said increase in the inductance.
Claim 3
Dependent Claim
40 words
A vehicle detector as claimed in claim 1 wherein the control processor is a microprocessor and the capacitance means comprises a plurality of capacitors arranged to be switched in and out of circuit with the road loop by the microprocessor.
Claim 4
Dependent Claim
25 words
A vehicle detector as claimed in claim 1 wherein a plurality of capacitors are arranged to be selectively switchable in parallel with the road loop.
Claim 5
Dependent Claim
38 words
A vehicle detector as claimed in claim 1 wherein a plurality of capacitors are arranged to be selectively connectable to taps in one winding of a transformer, the other winding of which is connected to the road loop.
Claim 6
Dependent Claim
32 words
A vehicle detector as claimed in claim 1 wherein the road loop is selectively connectable to taps in a transformer winding whereby the loop inductance may be effectively multiplied under program control.
Claim 7
Dependent Claim
36 words
A vehicle detector as claimed in claim 1 wherein the detector means produces an output on the basis of a count representing the alteration in the frequency before said frequency is returned to the predetermined value.
Claim 8
Dependent Claim
37 words
A vehicle detector as claimed in claim 1 wherein the detector means produces an output on the basis of the change in the value of the capacitance means required to return the frequency to the predetermined value.
Claim 9
Dependent Claim
65 words
A vehicle detector as claimed in claim 1 wherein the detector means detects an increase in the inductance of said road loop and is arranged to produce a signal when said inductance exceeds an average or quiescent value by more than a predetermined amount and said signal starts a timer or stops the repeated resetting of a timer allowing it to complete its timing operation.
Claim 10
Dependent Claim
60 words
An induction loop vehicle detector comprising means for detecting a decrease in the inductance of an induction loop and in response thereto for providing a signal indicative of the presence of a vehicle, and means for detecting an increase in the inductance above a predetermined threshold and means for inhibiting the detector for a predetermined time after detecting said increase.
Claim 11
Dependent Claim
60 words
An induction loop vehicle detector comprising means for detecting a decrease in the inductance of an induction loop and in response thereto for providing a signal indicative of the presence of a vehicle, and means for detecting an increase in the inductance above a predetermined threshold and means for inhibiting the detector for a predetermined time after detecting said increase.
Claim 12
Dependent Claim
60 words
A vehicle detector as claimed in claim 9 wherein the means for detecting an increase in the inductance is arranged to produce a signal when the inductance exceeds an average or quiescent value by more than a predetermined amount and said signal starts a timer or stops the repeated resetting of a timer allowing it to complete its timing operation.
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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) | 1989-02-03 | 1989-08-05 | 1990-02-04 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1993-02-03 | 1993-08-05 | 1994-02-04 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1997-02-03 | 1997-08-05 | 1998-02-04 | $7700.00 | Window Closed / Lapsed |