Vehicle detection

• US 3,873,964 A
• Filed: 02/19/1974
• Issued: 03/25/1975
• Est. Priority Date: 02/19/1974
• Status: Expired due to Term

• Current Assignee: Display Technologies, Inc. (Rhode Island)
• Original Assignee: Thomas R. Potter
• Inventors: Potter, Thomas R.
• Primary Examiner(s): Habecker, Thomas B.
• Assistant Examiner(s): Groody, James
• Application Number:
  US05/443,299
• Time in Patent Office: 399 Days
• Field of Search: 200/86R,86A 340/38R,38L,258C,272
• US Class Current: 340/939
• CPC Class Codes: G01V 3/101 by measuring the impedance of the search coil; by measuring features of a resonant circuit comprising the search coil measuring impedance or characteristics derived therefrom G01R27/00, e.g. quality factor G01R27/26
• CPC Class Codes: G08G 1/042 using inductive or magnetic detectors

Abstract

A digital vehicle detection system is provided which responds to changes in the inductance of a wire loop embedded in the roadway to sense the presence of a vehicle. The loop and associated leadin connections are used as the frequency-determining network of a Class-C oscillator, and digital circuitry is used to measure the frequency of the oscillator. An automatic tuning circuit is included which generates a reference time frame for the frequency measurement, and vehicle detection is sensed when the cycle count in the reference time frame changes in excess of a particular threshold, from one reference time frame to the next. To compensate for drift which causes the resonant frequency of the loop lead-in network to increase, a low rate signal is generated which serves to impart to the system a tendency to decrease the reference frame time, from one frame time to the next.

Claims

1. A digital vehicle detection system including:

an inductive loop to be placed in position to sense the presence of a vehicle;

a first oscillator circuit connected to the signal loop for generating an output having a frequency controlled by the inductance of the loop;

first counter means connected to the output of the first oscillator circuit for counting the cycles of the output signal generated by the first oscillator circuit;

a second oscillator circuit for generating a reference frequency signal output;

counter means coupled to said second oscillator circuit and responsive to said reference frequency output signal for generating a series of variable time frames;

reset circuit means coupled to said last-named means to reset said first counter means at the end of each such variable time frame so as to establish a series of time frames for the first counter means; and

control circuit means coupled to said first counter means to develop a control signal whenever the count of said first counter means exceeds a particular count during any of said time frames.

2. The vehicle detection system defined in claim 1, in which said control circuit means includes manually operable switching means for setting said particular count to different values depending upon the desired sensitivity of the system.

3. The vehicle detection system defined in claim 1, in which said control circuit means includes a flip-flop and logic circuits for setting the flip-flop when the count of said first counter means exceeds said particular count by a first predetermined number of counts, and for subsequently resetting said flip-flop when the count of said first counter means exceeds said particular number of counts less than said first predetermined number.

4. The vehicle detection system defined in claim 3, in which said control circuit means includes a one-shot multivibrator connected to said flip-flop to be activated each time said flip-flop is set to generate an output pulse.

5. The vehicle detection circuit defined in claim 4, in which said control circuit means includes relay means, and a manually operable switch for selectively connecting said relay means to said multivibrator and to said flip-flop to set the system selectively to a pulse mode and to a presence mode.

6. A digital vehicle detection system including:

an inductive loop to be placed in position to sense the presence of a vehicle;

a first oscillator circuit connected to the loop for generating an output having a freqUency controlled by the inductance of the loop;

first counter means connected to the output of the first oscillator circuit for counting the cycles of said output signal generated by the first oscillator circuit;

a second oscillator circuit for generating an output signal having a reference frequency;

second counter means connected to said second oscillator circuit for counting the cycles of the output signal generated by the second oscillator means;

reset circuit means coupled to said second counter means to reset said first and second counter means each time said second counter means reaches a predetermined count so as to establish a series of time frames for the first counter means; and

detection circuitry coupled to said first counter means to develop a control effect whenever the count of said first counter means exceeds a particular count during any of said reference frames.

7. The vehicle detection system defined in claim 6, and which includes up-down counter means;

comparator means interposed between said second counter means and said up-down counter means for producing an output signal when the counts in said second counter means and said up-down counter means have a predetermined relationship; and

reset circuitry coupled to said comparator means for resetting the first and second counter means each time the comparator develops said output signal to control the duration of the successive time frame of the series.

8. The vehicle detection system defined in claim 7, in which said detection circuitry includes pulse generating means for introducing pulses to said up-down counter means to cause said up-down counter means to count down whenever the durations of the successive reference time frames of the series are greater than the time taken by the first counter means to reach a predetermined count.

9. The vehicle detection system defined in claim 8, and which includes further counter means to delay the application of pulses from said pulse generating means to said up-down counter for a predetermined time interval, and manually operable switching means for connecting said further counter means in circuit with said pulse generating means when the system is set to a presence mode of operation.

10. The vehicle detection system defined in claim 7, in which said detection circuitry includes logic circuitry coupled to the first counter means and to said reset circuit means for introducing pulses to said up-down counter means to count up whenever the first counter means fails to reach a particular count during any of said reference time frames.

11. The vehicle detection system defined in claim 7, and which includes a tuning circuit for setting the up-down counter to a predetermined count, and a manually operable switch for selectively connecting said tuning circuit to said up-down counter.

12. The vehicle detection system defined in claim 6, and which includes manually controllable circuitry connected to said second oscillator for controlling the reference frequency of the output signal generated thereby.

13. The vehicle detection system defined in claim 7, in which said detection circuitry includes logic circuitry coupled to the first counter means and to the comparator means for introducing pulses to said up-down counter means to said up-down counter means to count up whenever the first counter means fails to reach a particular count during any of the reference time periods.

14. The vehicle detection system defined in claim 7, and which includes an automatic tuning circuit coupled to said comparator means and to said first counter means for setting said up-down counter means to a count corresponding to a predetermined count of said first counter means for each of the reference time frames.

15. An inductive type of vehicle detection system including:

an inductive loop to be placed in position to sense the presence of a metallic vehicle;

a first Class-C oscillator connected to the loop and using the loop as a frequency determining element and generating A signal having a frequency corresponding to the frequency of the oscillator;

a second Class-C oscillator circuit for generating a signal having a reference frequency; and

digital logic circuit means connected to said first and second oscillators and responding to the signals generated thereby for indicating the presence of a vehicle in the inductive loop.

16. The inductive type of vehicle detection system defined in claim 15, and which includes a lead-in network connecting the inductive loop to the first oscillator circuit and cooperating with the loop to form a two-terminal frequency determining network for the first oscillator.

17. The vehicle detection system defined in claim 1, in which the first and second oscillator circuits are Class-C oscillators, and which includes a two-terminal network connecting the inductive loop to the first oscillator circuit.

18. The vehicle detection system defined in claim 8, in which said detection circuitry includes pulse generating means for introducing pulses to said up-down counter means to cause said up-down counter means to count down whenever the duration of the successive reference time frames of the series are greater than the time taken by the first counter means to reach a predetermined count;

and control circuitry connected to said pulse generating means and to said up-down counter for selectively setting the rate at which said up-down counter means counts down under such conditions.

19. The vehicle detection system defined in claim 8, and which includes means to delay the application of pulses from said pulse generating means to said up-down counter for a predetermined time interval after the detection of a vehicle.

20. The vehicle detection system defined in claim 8, and which includes a synchronizing circuit connected to said pulse generating means for synchronizing said pulse generating means each time a vehicle is detected by the system.