JPH0926481A - Loop detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent mutual interference between adjacent loop detectors by dividing frequency detected with a detection means into every specific range and indicating with numerals for the divisions. SOLUTION: A loop coil 1 is connected to the detector D side and to an oscillation circuit 2. An oscillation frequency detection circuit 3 can divide and output the oscillation frequency of the circuit into 10 levels. A detection circuit 4 performs a processing such as detection for the frequency variation for the output from a circuit 3 and the produced detection signal is used as driving signal of gate G. A display 5 consists of 7 segments and indicates any numeral among 0 to 9 based on the detection signal from the circuit 3. If there is a difference in oscillation frequency of ca. 10kHz between adjacent loop detectors, erroneous detections due to mutual induction action caused by the adjacent loop coils 1 can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a loop detector for detecting the presence or absence of a metal object such as an automobile using a loop coil buried in a road surface or the like.

[0002]

2. Description of the Related Art Conventionally, the basic structure of this type of loop detector has, for example, a loop coil, a capacitor, an oscillating circuit, and a detecting circuit which are buried in a passageway at an entrance of a parking lot.

The oscillation frequency of the oscillation circuit is determined by the inductance of the loop coil and the constant (capacitance) of the capacitor. In this state, when a metal object of the automobile (vehicle) approaches the loop coil, the inductance of the loop coil changes, The oscillation frequency changes according to this change. Therefore, the presence or absence of the vehicle on the loop coil can be detected by the change in the oscillation frequency.

[0004]

The loop detector is
If there is noise near the embedded loop coil with a frequency close to the oscillation frequency used by the loop detector, the inductance of the loop coil will change and cause erroneous detection.Therefore, install or add a loop detector. When determining the oscillating frequency when setting the oscillating frequency or resetting the oscillating frequency, it was necessary to carefully consider the ambient noise.

That is, the setting of the oscillation frequency of the conventional loop detector has been troublesome because the oscillation frequency must be measured by using a special measuring instrument in order to avoid the mutual interference described above.

Further, knowing the detection sensitivity of the loop detector is an important factor for maintenance and management, and therefore, it has been desired that the detection sensitivity can be easily measured.

Therefore, the present invention has been made in order to solve the above-mentioned drawbacks and to meet the above-mentioned demands, and its purpose is to easily set an oscillation frequency and to easily detect a detection loop. It is to provide a detector.

[0008]

In order to achieve the above object, a loop detector according to the present invention comprises an oscillation circuit having a predetermined oscillation frequency determined by the inductance of a loop coil and the constant of a capacitor, and its loop. In a loop detector for detecting the presence or absence of a metal object from a change in the oscillation frequency of the oscillation circuit due to a change in the inductance when a metal object approaches the coil, a detection means for detecting the frequency of the oscillation circuit and the detection means The divided frequencies are divided into predetermined ranges and corresponding to the divisions,
Alternatively, it has a display means for displaying the frequency as it is as a numeral. Further, the display means is
It is characterized by a display consisting of segments.

The loop detector according to the present invention comprises an oscillation circuit having a predetermined oscillation frequency determined by the inductance of the loop coil and the constant of the capacitor, and the loop detector changes its inductance when a metal object approaches the loop coil. In a loop detector that detects the presence or absence of a metal object from a change in the oscillation frequency of an oscillation circuit, a frequency change detection unit that detects a frequency change ratio of the oscillation circuit when a metal object approaches and does not approach the loop coil, It is characterized by further comprising display means for dividing the frequency change ratio detected by the frequency change detecting means into predetermined ranges and displaying a number corresponding to the division. Further, the display means is a display device composed of 7 segments.

[0010]

In the above construction, the display means divides the frequencies detected by the detection means into predetermined ranges and displays the numbers corresponding to the divisions. In addition, the frequency change ratio detected by the frequency change detecting means is divided into predetermined ranges, and numbers are displayed corresponding to the divisions.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a schematic configuration of a loop detector according to an embodiment, and an example installed in a passage P at an entrance of a parking lot is shown.

The loop coil 1 is embedded in a passage P in front of a gate G provided at the entrance of a parking lot.

Although not shown in FIG. 1, a loop coil for a detector D'which will be described later is embedded in the passage P on the left side of the loop coil 1 with a predetermined distance. In addition, the loop coil, for example, in the case of a two-story parking lot,
There are cases where the coils are arranged in an up-down relationship, but here an example of two loop coils adjacent to each other on the left and right will be described.

The loop coil 1 is connected to the detector D side, and is connected to the oscillation circuit 2 like a well-known loop detector. Then, a plurality (3 in the illustrated example)
A capacitor C consisting of individual capacitors C0 to C2 is connected in parallel.

Of the capacitors C, the capacitor C0 is
The other two capacitors C1 and C2 are fixedly connected and are connected via switches S and S. Therefore, these switches S, S are turned on and off
The constant of the capacitor C can be changed by a combination of the above, and therefore, the oscillation circuit 2 uses the constant of the capacitor C and the inductance of the loop coil 1 which are set by combining ON and OFF of the switches S and S. It will be driven at the determined oscillation frequency.

The oscillating frequency detecting circuit 3 is arranged so that the oscillating frequency of the oscillating circuit 2 can be divided and output in a plurality of steps, for example, 26 to 30 kHz, 31 to 35 kHz, 36 to 40 kHz ... It is configured. The output signal is configured to be output to the display 5 described later (see the solid arrow from the oscillation frequency detection circuit 3 in FIG. 1 to the display 5).

The oscillation frequency detecting circuit 3 does not approach when the loop detector 1 is set to the sensitivity mode, when the vehicle (automobile) B approaches the loop coil 1, that is, when the metal object approaches. The sensitivity output, which is an output corresponding to the frequency change rate at this time, is configured to be output to the display device 5 described later (see the dashed line arrow from the oscillation frequency detection circuit 3 to the display device 5 in FIG. 1).

To further explain the above-mentioned sensitivity output, the oscillation frequency f of the oscillation circuit 2 is f = 1 / (2π (root LC)) (where L is the inductance of the loop coil 1 and C is the constant of the capacitor C). However, “=” is represented by grin.

By the way, the inductance of the loop coil 1 is ΔL when the vehicle is present and when it is not present.
Assuming a change, the change rate ΔL / L can be expressed by the following equation, where f is the frequency of the oscillation frequency of the oscillation circuit 2 and Δf is the change. ΔL / L = 2 × Δf / f (however, Δf << f) (however,
(= Is a grin)

As is clear from the above equation, the rate of change of the inductance is the rate of change of the frequency, and therefore the sensitivity of the loop detector can be detected by detecting the rate of change of the frequency. Therefore, in the present invention, the term "frequency change rate" is used in the same meaning as the inductance change rate.

In the loop detector according to the present embodiment, the inductance change rate ΔL / L is, for example, 0.
When the sensitivity is 01%, the sensitivity is "7", when it is 0.02%, the sensitivity is "6", when it is 0.04%, the sensitivity is "5".
The zero-stage sensitivity display is configured to be displayed on the display unit 5.

The detection circuit 4 processes the output from the oscillation frequency detection circuit 3 to detect the amount of frequency change, and generates a detection signal. The generated detection signal is used as a drive signal for the gate G. Is configured.

The detection signal is generated in the detection circuit 4 in the same manner as in the conventional loop detector. That is, when the vehicle B enters the passage P and approaches the loop coil 1, the inductance of the loop coil 1 changes, so that the oscillation frequency of the oscillation circuit 2 changes. This frequency change is input to the detection circuit 4 via the oscillation frequency detection circuit 3, and when the frequency change is equal to or more than a predetermined value, a detection signal indicating the presence or absence of the vehicle a is output. In the illustrated example, the detection circuit 4 is the oscillation frequency detection circuit 3
Although the signal is input from the oscillation circuit 2 via the, the signal may be input directly from the oscillation circuit 2.

The display 5 is composed of one 7-segment and is constructed so that it can display any one of numbers 0 to 9 based on the detection signal from the oscillation frequency detection circuit 3.

The number "3" shown indicates the current oscillation frequency range of the loop detector. As described above, when a number is assigned every 5 KHz, by the combination of the switches S and S of the capacitor C,
It shows that the oscillation frequency of the oscillation circuit 2 is in the range of 36 to 40 KHz.

The numeral "1" on the display 5'of the adjacent detector D'is not shown, but the oscillation frequency of the oscillation circuit 2 is 26 due to the combination of the switches S and S of the capacitor C.
It shows that it is set to -30KHz.

By the way, if there is a difference of about 10 KHz in oscillation frequency between the adjacent loop detectors,
It is possible to prevent erroneous detection due to the mutual induction effect caused by the adjacent loop coils. Therefore, the selection of ON or OFF of the switches S, S of the capacitor C is made so that the number is one or more than the number of the display 5'of the adjacent detector D '.

In the loop detector according to the present embodiment, the switches S and S of the capacitor C are arranged so that the numerical indications of the respective indicators 5 and 5'have a predetermined interval not only when newly installing but also when adding. False detection can be effectively prevented only by operating.

When the detector D is set to the sensitivity detection mode by a switch (not shown), the presence of the vehicle A on the loop coil 1 with respect to the indicator 5 from the oscillation frequency detection circuit 3 as described above. The number corresponding to the frequency change rate when not performing, that is, the detection sensitivity of the loop detector is displayed. Therefore, based on this detection sensitivity,
Furthermore, it is possible to adjust the device so that the desired detection sensitivity is obtained.

In the above example, the detected frequency is divided and displayed in one digit, but a plurality of seven segments may be provided and the detected frequency may be displayed as it is. Alternatively, the number of the 7 segments may be one, and a switch for selecting the digit of the numeral may be provided to display the detected frequencies one digit at a time.

[0031]

As described above, the loop detector according to the present invention has a detecting means for detecting the frequency of the oscillating circuit, and the frequency detected by the detecting means is divided into predetermined ranges and corresponding to the division, or the frequency thereof. Since it is composed of display means for displaying the numbers as they are, it can be easily distinguished from the frequencies used by the adjacent loop detectors, and erroneous detection can be effectively prevented. Further, when the display means is a display device composed of 7 segments, it can be manufactured at low cost.

Further, the loop detector according to the present invention is
Frequency change detecting means for detecting the frequency change rate of the oscillation circuit when the metal object approaches and does not approach the loop coil, and the frequency change rate detected by the frequency change detecting means is divided into predetermined ranges. , And the display means for displaying the numbers corresponding to the sections, the sensitivity can be easily adjusted.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a loop detector according to an embodiment of the present invention.

[Explanation of symbols]

 1 Loop coil 2 Oscillation circuit 3 Oscillation frequency detection circuit 4 Detection circuit 5 Display C Capacitor S switch P Passage G Gatey Vehicle (metal object)

Claims (4)

[Claims] 1. An oscillation circuit having a predetermined oscillation frequency determined by an inductance of a loop coil and a constant of a capacitor, the oscillation frequency of the oscillation circuit according to an inductance change when a metal object approaches the loop coil. In a loop detector that detects the presence or absence of a metal object from a change, detecting means for detecting the frequency of the oscillation circuit, and dividing the frequency detected by the detecting means into predetermined ranges and corresponding to the division, or A loop detector characterized by having a display means for displaying the frequency as it is in numerical form. 2. The loop detector according to claim 1, wherein the display means is a display consisting of 7 segments. 3. An oscillation circuit having a predetermined oscillation frequency determined by the inductance of the loop coil and the constant of the capacitor, the oscillation frequency of the oscillation circuit being accompanied by a change in inductance when a metal object approaches the loop coil. In a loop detector for detecting the presence or absence of a metal object from a change, frequency change detecting means for detecting a frequency change ratio of the oscillation circuit when the metal object approaches the loop coil and when the metal object does not approach, and the frequency change detecting means. A loop detector, comprising: a display unit that divides the frequency change rate detected in step 3 into predetermined ranges and displays a number corresponding to the section. 4. The loop detector according to claim 3, wherein the display means is a display consisting of 7 segments.