Digital loop detector system

• US 3,868,626 A
• Filed: 07/09/1973
• Issued: 02/25/1975
• Est. Priority Date: 07/09/1973
• Status: Expired due to Term

• Current Assignee: Eagle Signal Controls Corp.
• Original Assignee: Dale P. Masher
• Inventors: Masher, Dale P.
• Primary Examiner(s): Cooper, William C.
• Application Number:
  US05/377,544
• Time in Patent Office: 596 Days
• Field of Search: 340/38C,38R,258R,258B,258C
• 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 detecting system for creating an output signal when an electrically conductive object, such as a vehicle, comes within the field of effect of a loop. The system includes means for creating a pulse train having a frequency controlled primarily by the inductance of the loop, means for counting the pulses of the pulse train for a selected time interval to produce a count generally representative of the inductance of the loop during the time interval, means for creating a reference count, means for comparing the representative count with the reference count, and means for creating an output signal when the representative count differs from the reference count by at least a given amount in a given numerical direction, either above or below the reference count.

Claims

1. A digital detecting system for generating an output signal when an electrically conductive mass comes within the field of effect of a loop, said system comprising:

means for creating a pulse train, the number of pulses in said train being controlled primarily by the presence of said mass in the field of effect of said loop;

means for generating a first signal representative of the average of the number of pulses in said pulse train;

means for generating a second signal representative of a reference count;

means for comparing said first and second signals; and

, means for creating an output signal when said first signal differs from said second signal.

2. A digital detecting system for creating an output signal when an electrically conductive object comes within the field of effect of a loop, said system comprising;

means for creating a pulse train having a frequency controlled primarily by the inductance of said loop;

means for counting the pulses of said pulse train for a selected time interval to produce a count generally representative of the average frequency of said pulse train during said time interval;

means for creating a reference count;

means for comparing said representative count with said reference count; and

means for creating said output signal when said representative count differs from said reference count by at least a given amount in a selected numerical direction.

3. A system as defined in claim 2 including means for changing said given amount.

4. A system as defined in claim 2 including means for changing said time interval.

5. A system as defined in claim 2 including means for creating a succession of said time intervals and means for controlling said output signal as long as said representative count exceeds said reference count by at least said given amount during such successive time interval.

6. A system as defined in claim 5 including means for maintaining said output signal and means for increasing said reference counts while said output signal is being maintained.

7. A system as defined in claim 6 wherein said increasing means includes means for incrementing said reference count periodically while said output signal is being maintained.

8. A system as defined in claim 7 including means for creating a succession of time intervals at a given rate and wherein said incrementing means includes means for creating incrementing pulses at a rate substantially less than said given rate.

9. A system as defined in claim 6 wherein said means for creating a reference count includes means for making said reference count correspond to a representative count when a representative count fails to exceed a reference count during a time interval and while said output is being maintained.

10. A system as defined in claim 2 including means for creating a succession of said time intervals.

11. A system as defined in claim 10 wherein said means for counting said pulses of said pulse train includes an accumulator counter and said means for creating a reference count includes a count register.

12. A system as defined in claim 11 wherein said comparing means includes a means for comparing the count in said register and the count created in said accumulator during a time interval.

13. A system as defined in claim 12 including means for inserting the count of said accumulator during a given time interval into said reference register after said given time interval.

14. A system as defined in claim 13 including means for actuating said inserting means in response to said representative count differing from said reference count during a time interval in the numerical direction opposite to said selected numerical direction.

15. A system as defined in claim 13 including means for actuating said inserting meanS in response to said representative count equalling said reference count.

16. A system as defined in claim 13 including means for actuating said inserting means in response to said representative count differing from said reference count in said selected numerical direction by an amount less than said given amount.

17. A system as defined in claim 16 including a time delay means for delaying actuation of said inserting means for more than one time interval.

18. A system as defined in claim 10 wherein said reference count creating means includes a memory unit and means for inserting a representative count during one time interval into said memory unit for use as a reference count during a successive time interval.

19. A system as defined in claim 18 including means responsive to creation of said output signal for inhibiting said inserting means for a period of time, and means for controlling said period of time.

20. A system as defined in claim 10 wherein said output creating means includes a timer having means for starting and a signal when a selected time has been reached;

means for creating said output signal in response to said timer signal;

means for actuating said starting means when said representative count reaches said reference count in a given time interval and means for deactuating said timer starting means when said given time interval is completed whereby said output signal will be created when said timer is operated for a time exceeding said selected time.

21. A system as defined in claim 10 wherein said pulse counting means includes a down counter;

means for setting said down counter to a known count prior to a given time interval;

said reference count creating means includes a means for receiving a count and means for inserting a new count from said down counter into said count receiving means after a time interval prior to said given time interval; and

, said comparator means including means for comparing the count of said down counter to said new count during said given time interval.

22. A system as defined in claim 1 wherein said output creating means includes means for creating an output signal when said reference count exceeds said representative count by at least a selected number of counts.

23. A digital detecting system for creating an output signal when an electrically conductive object comes within the field of effect of a loop, said system comprising:

means for creating a pulse train having a frequency controlled primarily by the inductance of said loop;

means for creating a reference count;

a down counter means responsive to input pulses for counting down from a number loaded into said down counter means;

means for loading said reference count into said down counter;

means for directing said pulse train as an input pulse to said down counter means for a selected time interval; and

means active after said time interval for creating said output signal when said down counter has counted down from said reference count to a number exceeding said reference count.

24. A digital detecting system for creating an output signal when an electrically conductive mass comes within the field of effect of a loop, said system comprising:

means for creating a reference count;

means for creating a binary count representative of the inductance of said loop during a selected time interval after creation of said reference count; and

means for creating said output signal when said representative count during said selected time interval differs from said previously created reference count by at least a selected number.

25. A digital detecting system as defined in claim 24 including means for creating a succession of said time intervals and said means for creating a reference count includes:

means for creating a count insertion signal when said representative count does not exceed said reference count by at least said selected number and means responsive to said count insertion signal for setting said reference count to said representative coUnt of one time interval for use in the next time interval.

26. A digital detecting system as defined in claim 25 wherein said count insertion signal creating means includes a flip-flop having a first state corresponding to insertion signal when said representative count fails to exceed said reference count during a given time interval.

27. A digital detecting system as defined in claim 25 including a time delay means for delaying creation of said count insertion signal when said representative count exceeds said reference count by less than said selected number in a succession of said time intervals.

28. A digital detecting system as defined in claim 27 wherein said time delay means includes a counter having a timed out output after a time greater than at least two of said time intervals and means responsive to said timed out output for allowing creation of said count insertion signal.

29. A digital detecting system as defined in claim 28 including means for enabling said counter when said representative count exceeds said reference count by less than said selected number.

30. A digital detecting system as defined in claim 24 including means for creating a succession of said time intervals and means for incrementing said reference count when said representative count exceeds said reference count in a time interval.

31. A digital detecting system for creating an output signal when an electrically conductive mass comes within the field of effect of a loop, said system comprising:

an oscillator circuit having a pulse train output with a frequency which is controlled by the inductance of said loop and wherein said output pulse train has a frequency that increases at least a given amount when one of said objects enters the field of effect of said loop;

means for counting the pulses of said pulse train over a selected time interval to obtain a count representative of the inductance of said loop;

means for creating a reference count; and

means for creating said output signal when said representative count exceeds said reference count by at least a selected number.

32. A digital detecting system for creating an output signal when an electrically conductive object comes within the field of effect of a loop, said system comprising:

means for creating a succession of closely spaced, uniform time intervals;

means for creating a pulse train having a frequency controlled primarily by the inductance of said loop;

means for counting the pulses of said pulse train during each of said time intervals to produce a count generally representative of the inductance of said loop, said count having a first general range when at least one of said objects is within said field of effect of said loop and a second general range when no object is in said field of effect of said loop; and

means for creating said output signal when said representative count is in said first range.

33. A digital detecting system for creating an output signal when an electrically conductive object comes within the field of effect of a loop, said system comprising:

means for creating a succession of closely spaced, uniform time intervals;

means for creating a pulse train having a frequency controlled primarily by the inductance of said loop;

means for counting the pulses of said pulse train during each time interval to produce a count generally representative of the inductance of said loop;

means for creating a reference count;

means for comparing said representative count and said reference count;

a first device having first and second conditions;

means for shifting said first device into said first condition when said representative count differs from said representative count in a given interval by a given number of counts; and

means responsive to said first condition of said first device for creating said output signal.

34. A system as defined in claim 33 wherein said reference count creating means includes means for storing a count and means for inserting a representative count of a time interval into said storing means for use in subsequent time intervals.

35. A system as defined in claim 34 including means for inhibiting said inserting means for a time exceeding one of said time intervals when said output signal is created.

36. A system as defined in claim 34 including a second device having first and second conditions, and means for shifting said second device into its first condition when said representative count exceeds said reference count during said given time interval.

37. A system as defined in claim 36 including means for causing said storage means to store a representative count upon receipt of a storage signal and means responsive to said first device being in its second condition and said second device being in its first condition for creating said storage signal.

38. A system as defined in claim 37 including means for delaying said storage signal for a delay time at least more than one time interval, and overriding means for allowing said storage signal in response to shift of said second device into said second condition during delay time.

39. A system as defined in claim 36 including means for causing said storage means to store a representative count upon receipt of a storage signal and means responsive to said first device being in its second condition and said second device being in said second condition for creating said storage signal.

40. A digital detecting system for creating an output signal when an object comes within a detection field, said system includes:

means for creating a series of closely spaced counting intervals;

means for creating a pulse train having pulses occurring at a frequency which changes when one of said objects comes within said detection field;

means for counting said pulses during each of said counting intervals to provide a count representative of the average frequency during each counting interval;

means for creating a reference count prior to each counting interval;

means for comparing said representative count during a given interval with said reference count existing during said given interval;

means for creating a control signal when said representative count differs from said reference count during said given interval by a given amount; and

, means for creating said output signal in response to said control signal.

41. A system as defined in claim 40 wherein said means for creating a reference count includes means for storing said reference count and means for inserting a representative count into said storing means for use during said given interval.

42. A system as defined in claim 41 including means creating a first signal when said output signal is created;

and inhibiting means responsive to said first signal for inhibiting said inserting means.

43. A system as defined in claim 42 including means for controlling the time during which said inhibiting means inhibits said inserting means.

44. A system as defined in claim 43 including means for changing said reference count while said inhibiting means is inhibiting said inserting means.

45. A method of detecting a vehicle and creating an output signal when said vehicle comes within a detection field, said method comprising the steps of:

a. creating a series of closely spaced counting intervals;

b. creating a pulse train having pulses occurring at a frequency which changes when one of said vehicles comes within said detection field;

c. counting said pulses during each of said counting intervals to provide a count representative of the average frequency during each counting interval;

d. establishing a reference count for a given counting interval by using a representative count from a prior interval;

e. determining the amount by which said representative count differs from said reference count in said given interval; and

, f. creating said output signal when said amount reaches a given level.

46. A method as defined in claim 45 including the additional step of:

g. inhibiting said establishing step For a succession of counting intervals when said output signal is created so that said reference count during said successive intervals remains at a controlled level.

47. A method as defined in claim 46 including the additional step of:

h. changing said controlled level in incremental steps during said successive intervals.

48. A method as defined in claim 46 including the additional step of:

h. discontinuing said inhibiting step after a preselected time.

49. A method as defined in claim 48 including the additional step of:

i. changing said controlled level in incremental steps during said preselected time.

50. A digital detecting system for creating an output signal when an object comes within a detection field, said system including:

means for creating a series of closely spaced, counting intervals;

means for creating a pulse train having pulses occurring at a frequency which changes when one of said objects comes within said detection field;

means for counting said pulses during each of said counting intervals to provide a count representative of the average frequency during each count interval;

means for creating a reference count prior to each counting interval;

means for comparing said representative count during a given interval with said reference count existing during said given interval;

means for creating a control signal when said representative count differs from said reference count during said given interval by a given amount;

means for creating said output signal in response to said control signal;

said means for creating a reference count including means for converting a prior representative count into a reference count for subsequent use.

51. A system as defined in claim 50 including means for retaining said reference count constant for a number of successive intervals, and means responsive to said representative count differing from said reference count by less than said given amount for actuating said retaining means.

52. A digital detecting system for creating an output signal when an object comes within a detection field, said system including:

means for creating a pulse train having pulses occurring at a frequency which changes when one of said objects comes within said detection field;

means for determining the frequency of said pulse train at successive intervals;

means for establishing a reference frequency prior to each interval;

means for comparing said determined frequency during a given interval with said reference frequency during said given interval;

means for creating a control signal when said representative frequency differs from said reference frequency during said given interval by a given amount; and

, means for creating said output signal in response to said control signal.

53. A digital detecting system for creating an output signal when an electrically conductive object comes within the field of effect of a loop, said system comprising:

means for creating a pulse train having a frequency controlled primarily by the inductance of said loop;

means for counting the pulses of said pulse train for a selected time interval to produce a count generally representative of the average frequency of said pulse train during said time interval;

means for creating a reference count;

means for comparing said representative count with said reference count;

means for creating said output signal when said representative count differs from said reference count by at least a given amount in a selected numerical direction;

meansd for creating a succession of time intervals; and

means for maintaining said output signal as long as said representative count differs from said reference count by said given amount.

54. A system as defined in claim 53 including means for increasing said reference count while said output signal is maintained.

55. A digital detecting system for creating an output signal when an electrically conductive object comes within the field of effect of a loop, said system comprising:

means for creating a pulse train having a frequency controlled primarily by the inductance of said loop;

means for creating a count representative of the average frequency of said pulse train during a counting interval;

means for creating a reference count;

means for comparing said representative count with said reference count; and

, means for creating said output signal when saisd representative count differs from said reference count by a given amount.

56. A system as defined in claim 55 wherein said representative count creating means includes a means for counting a fixed frequency for said counting interval and means for varying the time of said counting interval by the frequency of said pulse train.

57. A digital detector system for creating an output signal when an electrically conductive vehicle comes within the field of effect of a loop mounted adjacent a roadway, said system comprising:

a loop oscillator for creating an output pulse train having a frequency controlled by the inductance of said loop;

digital means for creating digital representation of the frequency of said pulse train;

means for comparing said digital representation with a digital reference; and

means for creating said output signal when said digital representation differs from said digital reference by a given digital amount.

58. A digital system as defined in claim 57 wherein said digital representation is a representative count, said digital reference is a reference count and said digital amount is a number.

59. A digital detecting system for creating an output signal when an electrically conductive object comes within the field of effect of a loop, said system comprising;

means for creating a pulse train having a frequency controlled primarily by the inductance of said loop;

means for counting the pulses of said pulse train for a selected time interval to produce a count generally representative of the average frequency of said pulse train during said time interval;

means for creating a reference count;

means for comparing said representative count with said reference count; and

means for creating said output signal when said representative count differs from said reference count a given amount in a selected numerical direction.

60. A digital detecting system for generating an output signal in response to the presence of an electrically conductive mass within the field of effect of a loop, said system comprising:

means for generating a first signal having a frequency controlled by the presence of said mass in the field of effect of said loop;

means controlled by said first signal for creating a first count signal representative of the time base average of the frequency of said first signal;

means for generating a second count signal representative of a reference count;

means for comparing said first and second count signals; and

, means for generating an output signal when said first count signal differs from said second count signal.

61. A digital detecting system as defined in claim 60 wherein said output signal generating means generates said output signal when said first count signal differs from said second count signal by at least a selected value.

62. A digital detecting system as defined in claim 60 wherein said output signal generating means generates said output signal when said first count signal exceeds said second count signal by at least a selected value.