Airport loop detector system

• US 3,900,829 A
• Filed: 10/17/1973
• Issued: 08/19/1975
• Est. Priority Date: 10/17/1973
• Status: Expired due to Term

• Current Assignee: Lennart Ernst Long
• Original Assignee: Lennart Ernst Long
• Inventors: Long, Lennart Ernst
• Primary Examiner(s): Yusko, Donald J.
• Application Number:
  US05/407,213
• Time in Patent Office: 671 Days
• Field of Search: 340/38R,38L,258C 331/65,8
• US Class Current: 340/941
• CPC Class Codes: G08G 1/042 using inductive or magnetic detectors

Abstract

An airport loop detector system which includes demand tracking for stabilization. The system comprises a detector for detection of vehicles such as aircraft which enter the loop, and initiates action to automatically return the detector to its normal operating procedure if it should deviate therefrom.

Claims

1. An object detector system to detect the entry of metallic objects into a defined loop comprising:

an oscillator;

a tank circuit connected to the oscillator to generate an electromagnetic field to define the loop, the inductance of the tank circuit varying in response to the entry of a metallic object into the loop;

first incremental voltage frequency tuning means to derive a signal indicative of the change in inductance of the tank circuit;

amplifier means to amplify said signal indicative of the change in inductance of the tank circuit;

output means connected to the amplifier to provide an indication as to the '"'"''"'"''"'"''"'"'presence'"'"''"'"''"'"''"'"' or '"'"''"'"''"'"''"'"'no presence'"'"''"'"''"'"''"'"' of an object within the loop;

second means connected to the amplifier to determine if the amplifier is operating in its most sensitive range; and

frequency retuning means connected to the second means to cause a correction signal to be fed to the oscillator to drive the amplifier to operate in its most sensitive range.

2. The loop detector system recited in claim 1 wherein the retuning means comprises:

range window means to derive a digital signal when the amplifier is operating out of its most sensitive range window;

gating means;

a digital-to-analog converter; and

third analog means selectively operable to cause said gating means to gate the digital signal through to the digital-to-analog converter, the latter being connected to the oscillator, to apply thereto a signal to frequency tune the oscillator.

3. The loop detector system recited in claim 2 further comprising inhibit means to generate an inhibit signal to open circuit the gating means when the '"'"''"'"''"'"''"'"'presence'"'"''"'"''"'"''"'"' of an object within the loop is detected, to prevent retuning.

4. The loop detector system recited in claim 3 further comprising means to inhibit the output means during the retuning procedure and to mute undesired signal excursions to prevent a false '"'"''"'"''"'"''"'"'presence'"'"''"'"''"'"''"'"' signal from appearing at the output means.

5. The loop detector system recited in claim 4 further comprising means to produce a signal indicative of the retuning procedure taking place.

6. The loop detector system recited in claim 1 further comprising means to deactivate the retuning means when the '"'"''"'"''"'"''"'"'presence'"'"''"'"''"'"''"'"' of an object within the loop is detected to prevent retuning.

7. The loop detector system recited in claim 6 further comprising means to inhibit the output means during the retuning procedure to prevent a false '"'"''"'"''"'"''"'"'presence'"'"''"'"''"'"''"'"' signal from appearing at the output means.

8. The loop detector system recited in claim 7 further comprising means to produce a signal indicative of the retuning procedure taking place.