JP4210004B2 - Capacitance type alarm device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
TECHNICAL FIELD The present invention relates to a capacitive alarm device that issues an alarm by detecting the approach or contact of a person or animal to a protection target made of a conductor such as a window frame or door of a building, or a car body, and in particular theft. The present invention relates to a device that is useful as a prevention device.
[0002]
[Prior art]
Conventionally, various devices for preventing theft of buildings and vehicles have been proposed. For example, an anti-theft device for automobiles is known that is equipped with an ultrasonic Doppler radar in a vehicle, detects a smashing of a window glass or a vehicle body, and issues an alarm. This device detects a Doppler signal that appears in the output signal of an ultrasonic Doppler radar mounted in the vehicle when the window glass or the vehicle body of the vehicle is struck, and the Doppler signal continues for a longer time than a predetermined time. An alarm signal is generated to activate an alarm device such as a buzzer.
[0003]
However, such an anti-theft device for automobiles detects a Doppler signal that is generated when the window glass or the vehicle body is smashed, so that when the theft occurs, the window glass is broken or the vehicle body is It is hurt. In addition, there is a problem that it is impossible to prevent theft of tires and theft of articles in the engine room and trunk. Furthermore, it is necessary to newly install an ultrasonic wave generation part and an ultrasonic wave reception part, and there also exists a problem on cost. Such a problem is common to any antitheft device using the Doppler effect.
[0004]
[Problems to be solved by the invention]
The present invention has been proposed in order to solve these problems, and an object of the present invention is to provide a capacitance type alarm device that detects a capacitance according to the distance to a detection target and issues an alarm. There is to do.
[0005]
[Means for Solving the Problems]
In order to achieve the above-mentioned object, the present invention is electrically connected to a sensor electrode made of a conductor, detects a capacitance between the sensor electrode and a detection object, and detects the detected capacitance. There is provided a capacitance type alarm device comprising capacitance detection means for generating a corresponding signal and alarm means for generating an alarm upon detecting that the signal exceeds a predetermined threshold.
[0006]
The capacitance detection means has an inverting input terminal, a non-inverting input terminal, and an output terminal, and the output terminal and the inverting input terminal are connected by a feedback resistor, and the inverting input terminal and the non-inverting input An operational amplifier having an imaginary short between the terminals is provided. The inverting input terminal and the sensor electrode are connected by a conducting wire, and at least a part of the conducting wire is surrounded by a shield wire connected to the non-inverting input terminal. By applying an AC signal to the non-inverting input terminal, the operational amplifier outputs a voltage corresponding to the distance between the sensor electrode and the detection target.
[0007]
The alarm means includes a signal processing means and an alarm device. The signal processing means detects a holding unit that holds a peak value of the voltage, and detects that the peak value exceeds a predetermined threshold value. And a detector for operating the alarm device.
[0008]
As the sensor electrode, for example, a conductor such as a car body of a car or a window frame of a building can be used. Furthermore, it is convenient to use the electrostatic capacity type alarm device provided with a power source that is turned on and off by remote control.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a block diagram schematically showing the configuration of one embodiment of a capacitance detection device according to the present invention. In FIG. 1, the electrostatic capacity type crime prevention apparatus is an electrostatic capacity electrically connected to a sensor electrode S made of a conductor such as a window frame or door of a building to be protected and a car body of a car via a conductor. A detection unit 1 is provided. The sensor electrode S is provided to generate a capacitance having a magnitude corresponding to the distance from the detection target D such as a human being, an animal, or a tool. As will be described later, the capacitance detection unit 1 detects the size of the capacitance in the sensor electrode S using the imaginary short state of the operational amplifier, and outputs a voltage corresponding to the capacitance. This voltage is applied to the signal processing unit 2. In other words, the capacitance detection unit 1 converts the physical quantity detected by the sensor electrode S into an electrical signal that can be processed by the signal processing unit 2 at the subsequent stage.
[0010]
The signal processing unit 2 has a function of processing the voltage received from the capacitance detection unit 1 and determining whether or not the magnitude of the voltage is within a preset range. Can be used. Thereby, it is determined whether or not the capacitance of the sensor electrode S is in a normal state, that is, whether or not the distance between the sensor electrode S and the detection target D such as a person or animal is within a predetermined value. be able to. The signal processing unit 2 generates an alarm signal when it determines that the voltage output from the capacitance detection unit 1 has deviated from a preset range, and supplies the alarm signal to an alarm device 3 such as a buzzer. Actuator 3 is activated.
[0011]
The sensor electrode S may be of any material and shape as long as it is a conductor. If the object to be protected is an automobile, the sensor electrode S is a conductive body 5 of the automobile as shown in FIG. Yes, when the object to be protected is a building, the conductive window frame 6 can be used as the sensor electrode S as shown in FIG. In FIG. 2A, an appropriate position of the vehicle body 5 of the vehicle is connected to the input terminal of the capacitance detection unit 1 to detect when a detection object D such as a person or an animal approaches the vehicle. Since the distance between the detection object D and the vehicle body can be detected using the capacitance generated between the object D and the vehicle body which is the sensor electrode S, the anti-theft device and the pedestrian's automobile can be detected. It is possible to configure a contact prevention device that warns of an abnormal approach. In the case of (b) in FIG. 2, a crime prevention device is configured to warn contact or approach to the window frame by connecting an appropriate position of the window frame 6 to the input terminal of the capacitance detection unit 1. Can do.
[0012]
FIG. 3 shows an example of the configuration of the capacitance detection unit 1. The capacitance detection unit 1 includes a capacitance detection circuit 11 and a signal line 12 that connects the capacitance detection circuit 11 to the sensor electrode S. The capacitance detection circuit 11 includes an operational amplifier 13, and the voltage gain of the operational amplifier is much larger than the closed loop gain. A feedback resistor 14 is connected between the output terminal and the inverting input terminal (−) of the operational amplifier 13, and negative feedback is applied to the operational amplifier 13. Further, one end of the signal line 12 is connected to the inverting input terminal (−) of the operational amplifier 13, and the sensor electrode S is connected to the other end of the signal line 12. On the other hand, the non-inverting input terminal (+) of the operational amplifier 13 is connected to an output terminal of the oscillation circuit 15 that generates an AC signal and a shield line 16 that surrounds at least a part of the periphery of the signal line 12.
[0013]
The reason why at least a part of the signal line 12 is surrounded by the shield line 16 is to prevent unnecessary signals such as noise from the outside from being induced to the signal line 12 by the shield line 16, and the shield line 16 is grounded. Not.
[0014]
Thus, negative feedback is applied to the operational amplifier 13 via the feedback resistor 14, and the voltage gain of the operational amplifier 13 is much larger than the closed loop gain. Imaginary short. That is, the voltage difference between the inverting input terminal (−) and the non-inverting input terminal (+) of the operational amplifier 13 is substantially zero. Therefore, the signal line 12 and the shield line 16 are at the same potential, and the stray capacitance generated between the signal line 12 and the shield line 16 can be canceled. This is true regardless of the length of the signal line 12, and is true regardless of the movement, bending, folding, etc. of the signal line 12.
[0015]
Now, assuming that the voltage output from the operational amplifier 13 when the sine wave signal is generated from the oscillation circuit 15 is Vout,
[0016]
[Expression 1]
Vout = (1 + jωCs · Rf) · Vin (1)
Is established. Where Vin is the amplitude of the sine wave signal generated from the oscillation circuit 15, ω is the angular frequency of the sine wave signal, Rf is the resistance value of the feedback resistor 14, and Cs is the sensor electrode S and the detection target. It is the value of the capacity formed between the object D. At this time, when the distance between the sensor electrode S and the detection object D is d, the distance between Cs and d is
[Expression 2]
Cs = ε · A / d (2)
The relationship becomes true. However, (epsilon) is a dielectric constant between the sensor electrode S and the detection target D, A is an area of the part which opposes the detection target D of the sensor electrode S. FIG.
[0018]
Substituting equation (2) into equation (1), equation (1) becomes
[Equation 3]
Vout = (1 + jωRf · ε · A / d) · Vin (3)
Can be rewritten. This equation indicates that the voltage Vout output from the capacitance detection circuit 11 has a value corresponding to the distance d between the sensor electrode S and the detection object D, in other words, the output of the capacitance detection circuit 11. Indicates that a voltage Vout corresponding to the distance between the sensor electrode S and the detection object D appears.
[0020]
If a conductor is present near the sensor electrode S, this conductor also forms a stray capacitance with the sensor electrode S. Therefore, the influence of such stray capacitance is removed as much as possible to detect the capacitance. In order to accurately operate 11 based on the capacitance Cs between the sensor electrode S and the detection object D, a conductor existing around the sensor electrode S is electrically connected to the shield wire 16. It is desirable. In this way, the conductor around the sensor electrode S has the same potential as the sensor electrode S and does not affect the operation of the capacitance detection circuit 11.
[0021]
FIG. 4 shows a capacitance value Cs (unit femtofarad) formed between the sensor electrode S and the detection target when Rf = 10 MΩ, Vin = 0.5 V, ω = 2π × 10 kHz, and ε = 1. ) Is a graph showing how the voltage Vout (unit volt) output from the capacitance detection circuit 11 changes with respect to the change in. From this graph, it can be seen that Vout increases almost linearly as the distance d between the sensor electrode S and the detection object D decreases as Cs increases.
[0022]
FIG. 5 shows the voltage Vout (unit volt) with respect to the distance d (unit millimeter) between the sensor electrode S and the detection target when the sensor electrode S is circular and the diameter φ is 15 mm, 30 mm, and 45 mm. It is a graph which shows a change. However, in either case, ε is the dielectric constant of air. From this graph, if d is in a range smaller than a certain value, Vout decreases as d increases, and this range depends on the size of the area A where the sensor electrode S and the detection object D face each other. I understand that.
[0023]
FIG. 6 is a block diagram illustrating an example of the configuration of the signal processing unit 2. The signal processing unit 2 determines that an abnormal state has occurred when the voltage Vout output from the capacitance detection unit 1 exceeds a preset threshold value, generates an alarm signal, and generates an alarm device 3 such as a buzzer. It operates and includes a peak holding unit 21 and a comparison detection unit 22. The peak holding unit 21 receives the voltage Vout from the capacitance detection unit 1, extracts and holds the peak value of the voltage Vout at a predetermined timing, and adds the held peak value to the comparison detection unit 22. The comparison detection unit 22 compares the received peak value with a predetermined threshold value, and when the peak value exceeds the threshold value, generates an alarm signal and gives it to the alarm device.
[0024]
The threshold value set in the comparison detection unit 22 depends on what kind of device, such as an automobile contact prevention device or an anti-theft device, is used for the electrostatic capacity alarm device according to the present invention. Can be determined according to the minimum distance that the detection object D can approach to the sensor electrode S, including the case where the sensor electrode S comes into contact.
[0025]
As mentioned above, although one embodiment of the capacitance type alarm device according to the present invention has been described, the present invention is not limited to such an embodiment. For example, it may be possible to remotely control on / off of the power supply of the capacitive alarm device as necessary. In addition, if there is a conductor such as a metal fitting, a detection device can be configured without newly providing a sensor element, and an alarm device, an entrance / exit sensor, etc. can be made at low cost.
[0026]
【The invention's effect】
As described above, as understood from the description of the present invention with reference to the illustrated embodiment, the invention of claim 1 is based on the fact that the detection object has approached the sensor electrode up to a predetermined distance or the sensor electrode. It is possible to detect the contact without a blind spot and activate an alarm.
[0027]
The invention of claim 2 can obtain a voltage that accurately corresponds to the capacitance formed between the sensor electrode and the detection object, and is, for example, in the order of femtofarad (1/1000 of picofarad). Even if it is a minute one, it is possible to convert the capacitance to voltage with high accuracy, so that an alarm can be accurately issued according to the distance between the sensor electrode and the detection target. Play.
[0028]
According to the third aspect of the present invention, an alarm can be issued when a predetermined capacitance is detected, so that it is possible to prevent malfunction.
If these are used in the body of an automobile, there is an effect that it is possible to provide an automobile antitheft device without a blind spot. Moreover, if it is used for a window frame, a door, etc. of a building, there exists an effect that the crime prevention apparatus for buildings without a blind spot can be provided.
[0029]
According to the fourth aspect of the present invention, it is possible to control the start and end of the operation of the apparatus from a remote location.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of a capacitive alarm device according to the present invention.
2A shows a configuration of a capacitive alarm device when a vehicle body is used as the sensor electrode of FIG. 1, and FIG. 2B shows a configuration of a capacitive alarm device when a window frame is used as the sensor electrode of FIG. FIG.
FIG. 3 is a diagram illustrating an example of the configuration of the capacitance detection unit 1 in FIG. 1;
4 is a graph showing the relationship between the output voltage Vout of the capacitance detection circuit 11 of FIG. 3 and the capacitance Cs generated at the sensor electrode S. FIG.
5 is a graph showing how the output voltage Vout of the capacitance detection circuit 11 of FIG. 3 changes according to the distance between the sensor electrode S and the detection object D according to the shape of the sensor electrode S. FIG. .
6 is a block diagram illustrating an example of a configuration of a signal processing unit 2 in FIG.
[Explanation of symbols]
S: sensor electrode, D: object to be detected, 1: capacitance detection unit,
2: signal processing unit, 3: alarm, 5: vehicle body, 6: window frame,
12: signal line, 13: operational amplifier, 14: feedback resistor, 15: oscillation circuit,
21: Peak holding unit, 22: Comparison detection unit,

Claims (3)

A capacitance detecting means that is electrically connected to a sensor electrode made of a conductor, detects a capacitance between the sensor electrode and a detection object, and generates a signal corresponding to the detected capacitance; Alarm means for detecting that the signal exceeds a predetermined threshold and issuing an alarm;
A capacitive alarm device comprising :
The capacitance detection means has (A) an inverting input terminal, a non-inverting input terminal and an output terminal, and the output terminal and the inverting input terminal are connected by a feedback resistor, and the inverting input terminal and the inverting input terminal An operational amplifier that is in an imaginary short state with respect to the non-inverting input terminal; (B) a conducting wire having one end connected to the inverting input terminal and the other end connected to the sensor electrode; and (C) the conducting wire. And a shield wire connected to the non-inverting input terminal, and (D) an oscillation circuit that applies an AC signal to the non-inverting input terminal,
The capacitive alarm device , wherein the operational amplifier outputs a voltage corresponding to a distance between the sensor electrode and the detection target and a frequency of the AC signal . The alarm means comprises a signal processing means and an alarm device,
The signal processing means includes a holding unit that holds the peak value of the voltage, and a detection unit that detects that the peak value has exceeded a predetermined threshold and activates the alarm device, The electrostatic capacity type alarm device according to claim 1.   The electrostatic capacity type alarm device according to claim 1, further comprising a power source that is turned on and off by a remote control.

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