JP2003344551A - Method and apparatus for detection of specimen - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect also a noise signal with an antenna for detecting whether or not a specimen is present in a measuring region and to make preventable the specimen from being misdetected. <P>SOLUTION: An AC signal is supplied via a switch 10 and an impedance 3 to an antenna electrode 4 installed in the measuring region. In a state that the switch 10 is turned on, the specimen is detected by a change in a current flowing in the antenna electrode. In a state that the switch 10 is turned off, a state that the AC signal is not supplied to the antenna electrode is formed. As a result, the noise signal due to a disturbance generated in the antenna electrode at this time is detected. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to detection of an object to be measured in a predetermined space, and more particularly to a method of detecting an object and a device for detecting an object of measurement capable of detecting noise such as an occupant in a vehicle and external radio waves. .

[0002]

2. Description of the Related Art An occupant detection device is known which detects an approach of a human body or the like by using an antenna electrode arranged around a seat of an automobile. FIG. 7 is a diagram showing the basic configuration and operation principle of a conventional detection device. As shown in FIG. 7A, a signal source 1 having one end connected to the ground and outputting an AC signal such as a sine wave signal, a detection resistor 3 having one end connected to the other end of the signal source 1, An antenna electrode 4 connected to the other end of the detection resistor 3, and a voltmeter 2 for detecting a signal voltage connected between the connection point of the detection resistor 3 and the antenna electrode 4 and ground.
Composed of and. In addition, the impedance 5 shown in FIG.
Is impedance of space (also referred to as space impedance) such as capacitance between the antenna electrode 4 and the ground.

In the detector shown in FIG. 7A, a current flows toward the ground through the resistor 3, the antenna electrode 4 and the space impedance 5 by the signal voltage of the AC signal output from the signal source 1. Therefore, a voltage drop occurs in the detection resistor R3 due to the current, and the voltmeter 2 detects the signal voltage of the AC signal that is reduced by the voltage drop from the output voltage of the AC signal of the signal source 1. Here, since the spatial impedance between the antenna electrode 4 and the ground changes depending on the environment around the antenna electrode 4, the current also changes according to the change, and the voltage value detected by the voltmeter 2 also changes.
It changes depending on the surrounding environment.

As a detection device for detecting an occupant, the antenna electrode 4 is installed in the vicinity of a seat of an automobile, and when the occupant gets on or off, the spatial impedance 5 changes depending on the presence or absence of a human body approaching the antenna electrode, and the like. Is detected, a decrease in signal voltage detected by the voltmeter 2 is detected due to an increase in current flowing from the antenna electrode 4 through the human body and the like.

The operating principle of the detection device will be described with reference to FIG. The AC signal (1) in FIG.
This is a signal input to the voltmeter 2 in the initial state where the human body is not approaching. Since the current flowing through the detection resistor 3 is small, a large signal voltage (V1) close to the output level of the signal source 1 is shown. As indicated by the detected voltage (3) from the voltmeter 2,
A large DC detection voltage corresponding to the amplitude of the AC signal (1) is output. Further, the AC signal (2) in FIG. 7 is a signal input to the voltmeter 2 when the human body is approaching (at the time of detection). The signal voltage (V2) lower than the output level of the signal source 1 due to the increase in the current flowing through the detection resistor 3 is shown. The voltmeter 2 outputs a lowered direct current detection voltage corresponding to the amplitude of the alternating current signal (2), as indicated by the detected voltage (3).

FIG. 8 is a diagram showing an example of a detection device using a plurality of antenna electrodes. As shown in FIG. 8 (a),
A single signal source 1 and a voltmeter 2 and two detection resistors 3a,
3b and two antenna electrodes 4a, 4b, the signal voltage from the signal source 1 is supplied to the detection resistors 3a, 3b via the changeover switch 6, and the signal voltage to the voltmeter 2 is also changed over. , And both changeover switches 6 and 7 are changed over synchronously. As shown in FIG. 8B, the DC signal output from the voltmeter 2 is alternately switched and output like a time-division multiplexed signal by synchronously switching both changeover switches 6 and 7.

With the above configuration, an AC signal for detecting the condition of the occupant or the like is alternately supplied to the antenna electrodes 4a, 4b via the changeover switch 6 and the detection resistor R3, and the signal voltage to be detected is also changed by the changeover switch 7. Since the voltage is alternately supplied to the voltmeter 2 via a plurality of detection channels, it is possible to configure a plurality of detection channels for detecting (sensing) a human body or the like. Channel CHa
When is selected, the AC signal is applied to the spatial impedance 5a through the detection resistor R1 and the antenna electrode 4a, and the voltage is applied via the voltmeter changeover switch 7 by the spatial impedance 5a depending on the environmental condition of the measured space of the channel CHa. In the total 2, the signal CHa shown in FIG. 8B is detected,
When the channel CHb is selected, a similar signal CHb is detected at that timing.

A human body detecting device based on the principle of the detecting device shown in FIG. 7 and using a human body detecting wire as an antenna electrode is described in Japanese Patent Laid-Open No. 9-293179. This is to arrange a noise detection line that detects environmental noise in parallel with the human body detection line, output a noise signal from the noise detection line, and subtract the noise signal from the output component of the detection signal captured by the human body detection line. The output level of the signal is determined.

[0009]

The detection device such as the conventional occupant detection system shown in FIGS. 7 and 8 uses an alternating current signal for measurement to pass a current through an antenna electrode and detects a change in the current as a voltage value. The current value (voltage value)
If an unexpected change occurs due to noise such as disturbance to the detection device, will affect the measurement result and lead to false detection.

FIG. 8C is a diagram showing the state of the signal voltage when the detection device is affected by disturbance. If there is a radio wave with the same frequency component as the AC signal used in the detection device or a frequency component near the detection device, or a strong radio wave radiated from an electronic device or wireless equipment around the detection device, the situation such as the measurement area may change. Amplitude of detection signal (signal level)
The waveform of the AC signal may be distorted due to the influence of the radio wave as shown in the figure, and the presence or absence of an occupant may not be correctly detected.

On the other hand, the above-mentioned conventional example in which a noise signal included in the detection signal in the measurement region is separately detected to cancel the noise component included in the detection signal (Japanese Patent Laid-Open No. 9-2931).
No. 79), it is possible to directly cancel the noise component from the detection signal, but for this purpose, it is necessary to obtain the same noise signal as the noise component included in the detection signal from the noise detection line, There is a problem in that it is necessary to consider the arrangement condition of the noise detection line in addition to the installation of the noise detection line.

(Purpose) An object of the present invention is to solve the above problems, and a method for detecting an object to be measured which makes it possible to detect an external disturbance without laying a dedicated antenna or the like for detecting the external disturbance. And an object detection device.

An object of the present invention is to detect an object to be measured, which is capable of detecting a noise signal by an antenna for detecting the presence or absence of an object to be detected in a measurement area, and preventing erroneous detection of the object to be detected. An object is to provide a device to be measured.

[0014]

A method for detecting an object to be measured according to the present invention is to detect an object to be measured by supplying an AC signal to an antenna electrode installed in a measurement region and detecting a change in current flowing through the antenna electrode. In the object detection method, a disturbance signal of the antenna electrode generated at this time can be detected by creating a state in which the AC signal is not supplied to the antenna electrode. Specifically, by measuring the impedance between the antenna electrode installed in the measurement region and the ground, in the DUT detection method for detecting the presence or absence of the DUT in the measurement region, the impedance to the antenna electrode A step of supplying an alternating current signal through the antenna electrode, and detecting an alternating current signal between the impedance and the antenna electrode in a state where the alternating current signal is supplied to the antenna electrode, and detecting and measuring a change in amplitude of the detected alternating current signal. A step of detecting the presence or absence of the object to be measured in the area, a step of stopping the AC signal supplied to the antenna electrode, and a noise signal of the antenna electrode in a state where the AC signal supplied to the antenna electrode is stopped. And a detecting step.

The object-to-be-measured device of the present invention detects the presence or absence of the object to be measured in the measurement area by measuring the impedance between the antenna electrode installed in the measurement area and the ground. At, a signal source for outputting an AC signal, an antenna electrode arranged in the measurement region,
A changeover switch (for example, 10 in FIG. 1) that supplies or does not supply the AC signal to the antenna electrode from the signal source through the impedance, and a signal between the impedance and the antenna electrode when the AC signal is supplied. A detection circuit (for example, 2 in FIG. 1 and 23 in FIG. 4) that detects the presence or absence of the object to be measured in the measurement region based on the amplitude of the detected signal, and the antenna when the AC signal is not supplied. A disturbance detection circuit (for example, 10 in FIG. 1 and 24 in FIG. 4) that detects a noise signal generated in the electrode is provided.

The antenna electrode comprises a plurality of antenna electrodes (for example, 4a and 4b in FIG. 2), and the changeover switch alternately supplies the AC signal from the signal source to the plurality of antenna electrodes via impedance. Alternatively, it is a non-supplying switch (for example, 6 in FIG. 2).

The object-to-be-measured device of the present invention detects the presence or absence of the object to be measured in the measurement area by measuring the impedance between the antenna electrode installed in the measurement area and the ground. In, a signal source that outputs an AC signal, a plurality of antenna electrodes arranged in the measurement region, a disturbance detection switch that supplies or does not supply the AC signal from the signal source, and from the disturbance detection switch via impedance A change-over switch that alternately supplies or does not supply the AC signal to the plurality of antenna electrodes, and detects a signal between the impedance and the plurality of antenna electrodes when the AC signal is supplied, and detects the amplitude of the detected signal. A detection circuit for detecting the presence or absence of the object to be measured in the measurement region based on the above, and before the disturbance signal is not supplied by the disturbance detection switch. A disturbance detection circuit that detects a noise signal generated in the antenna electrode, and further, the detection circuit includes a comparison circuit that compares the amplitude of the signal with a predetermined threshold value, and the threshold value is controlled by the output of the disturbance detection circuit. It is characterized by

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Next, an embodiment of a detection device of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a configuration of a first embodiment of a detection device of the present invention.
As shown in FIG. 1 (a), one end is connected to ground, and a signal source 1 outputs an AC signal for measuring spatial impedance, such as a high frequency sine wave signal, and one end at the other end of the signal source 1. To the disturbance detection switch 10, the detection resistor 3 having one end connected to the other end of the disturbance detection switch 10, the antenna electrode 4 connected to the other end of the detection resistor 3, and the detection resistor 3. A detection circuit (hereinafter, also referred to as a “voltmeter”) that is connected between a connection point with the antenna electrode 4 and the ground and detects an AC signal or a noise signal at the connection point.
2 and a space impedance 5 such as capacitance is formed between the antenna electrode 4 and the ground. That is,
This embodiment differs from the conventional example in that the disturbance detection switch 10 is provided in the configuration.

The detector of the first embodiment is shown in FIG.
As shown in (b), when the disturbance detection switch 10 is in the conductive state (ON state), the same detection operation as in the conventional example is performed. That is, due to the signal voltage of the AC signal output from the signal source 1, a current flows toward the ground through the disturbance detection switch 10, the detection resistor 3, the antenna electrode 4 and the space impedance 5, and the current flows through the detection resistor R3. As a result, a voltage drop occurs, and the voltmeter 2 detects a signal voltage that is lower than the output voltage of the signal source 1 by the voltage drop. Antenna electrode 4
Since the spatial impedance between the antenna and the ground changes depending on the environment around the antenna electrode 4, the current also changes according to the change, and the voltage value of the AC signal detected by the voltmeter 2 also changes depending on the environment around the antenna electrode 4. However, the presence or absence of a human body or the like can be detected from this change.

Further, in the present embodiment, in order to detect noise due to the influence of disturbance in the detection operation of the human body or the like,
The disturbance detection switch 10 is turned off for a predetermined period (OF
The F state) enables a noise signal detection operation due to a disturbance. For example, the disturbance detection switch 10 is periodically turned off, and the noise signal input from the antenna electrode 4 or the like is measured by the voltmeter 2 in this off state.
The voltage of the detected noise is generated according to the installation environment of the detection device and the like, and provides information on the evaluation standard for the original detection result of the human body or the like.

When the present embodiment is used as a detection device for detecting an occupant, the antenna electrode 4 is installed around the seat of the automobile. Spatial impedance 5 depending on the presence or absence of a human body approaching the antenna electrode when a passenger gets on or off.
Is changed and the human body or the like approaches, a decrease in the signal voltage detected by the voltmeter 2 is detected due to an increase in the current flowing from the antenna electrode 4 through the human body or the like. At that time, the noise detection result according to the noise generation environment due to electromagnetic waves in the vehicle is used.

FIG. 2 is a diagram showing the configuration of the second embodiment using a plurality of antenna electrodes. The second embodiment corresponds to the conventional example shown in FIG. 7, and is different from the conventional example in that a switch 10 connected in series to the changeover switch 6 is provided. That is, as shown in FIG. 2A, a single signal source 1 and a voltmeter 2, two detection resistors 3a and 3b, and two antenna electrodes 4a and 4b.
The signal voltage from the signal source 1 is supplied to the detection resistor 3a via the disturbance detection switch 10 and the changeover switch 6,
3b, and the signal voltage to the voltmeter 2 is supplied to the changeover switch 7
The switching switches 6 and 7 are switched in synchronism with the disturbance detection switch 10 in the ON state at least in each detection channel so that the voltmeter 2 detects the signal voltage. By synchronously switching the two changeover switches 6 and 7, the signal voltage of each detection channel is alternately switched and output like a time division multiplexed signal. Further, when the disturbance detection switch 10 is in the OFF state, noise generated in the antenna electrode 4 selected by the changeover switch 7 is input to the voltmeter 2 and the noise voltage is detected.

FIG. 2B is a diagram showing the detection operation of the detection channels CHa and CHb of the present embodiment. The signal voltages of the detection channels CHa and CHb and the noise are periodically detected in the same time width. The control of each switch in the operation of this example can be realized by the control signal shown in FIG. The disturbance detection switch 10 is controlled by a switching control signal S10 that controls the ON state of each of the detection channels CHa and CHb for two periods and the OFF state of the next disturbance detection for one period, and the switch 6 detects the detection channel CHa. The switch 7 is controlled by the switching control signal S6 for controlling the connection to the antenna electrode 4a side only when the switch 7 is controlled by the switching control signal S7 for controlling the connection to the antenna electrode 4b side only when the detection channel CHb is detected.

In the detection device having a plurality of detection channels of the second embodiment, an example in which the disturbance is detected by using only one antenna electrode (4a) has been described. The configuration example is two antenna electrodes 4
When the environmental conditions of the circuit of each channel are the same because a and 4b are arranged close to each other, such a configuration is advantageous in that the circuit is simplified and the disturbance detection period is shortened. is there. However, when the disturbance of the circuit of each channel is different, it is preferable to perform different disturbance detection for each.

FIG. 3 is a diagram showing an example of control of the detection device capable of detecting disturbances of a plurality of detection channels. Figure 3 (a)
As shown in FIG. 5, the switches 6 and 7 perform a switching operation in synchronization with a signal having a duty of 50% in accordance with the switching control signal Sab, and the disturbance detection switch 10 detects the two detection channels after the switching period of the two detection channels is completed. The switching control signal Se is controlled so as to be in the OFF state for the same period as the switching period of 2), and the disturbance of the two detection channels can be detected.

The voltmeter 2 has a detection channel CH as shown in the measured voltage waveform of FIG.
The presence / absence of a human body or the like and a noise signal due to disturbance are input in a time-division manner for each of a and CHb. In the example of the figure, when the disturbance detection switch Se is in the ON state, a low level AC signal indicating the presence of a human body or the like is input to the channel CHb,
A high-level AC signal indicating the absence of a human body is input to the channel CHa, and the OF of the disturbance detection switch Se is further input.
In the F state, noise signals are input to the respective channels CHa and CHb.

Next, an embodiment configured to prevent erroneous detection of the presence or absence of a human body or the like by utilizing the detection result of a noise signal due to disturbance will be described below. FIG. 4 is a diagram showing a configuration example of a single-channel detection device. Two switches 21 and 22 for inputting the signal voltage at the connection point A between the detection resistor 3 and the antenna electrode and performing ON / OFF operations in synchronization with the disturbance detection switch 10, and the respective switches 2
Two amplitude detection circuits 23 and 24 that detect the outputs of the signals 1 and 22 to detect the amplitude, an adder 25 that adds the output of the amplitude detection circuit 24 to the comparison reference voltage, and an amplitude based on the output of the adder 25. And a comparison circuit 26 for performing a voltage comparison with the output voltage of the detection circuit 23. Switch 2 here
The switch 1 is controlled to be ON while the AC signal of the signal source 1 is applied to the antenna electrode 4, and the switch 22 is controlled to be ON while the AC signal of the signal source 1 is not applied to the antenna electrode 4. Further, as the comparison reference voltage, a set voltage Vref of about an intermediate level in the change range of the amplitude of the AC signal that changes with the presence or absence of a human body when the AC signal is applied to the antenna electrode 4 is given.

According to the detection device of FIG. 4, the amplitude detection circuit 2
Reference numeral 4 outputs the amplitude of the noise signal or its average value, and the adder 25 adds the output to the comparison reference voltage Vref to compare the set voltage at the intermediate level in the change range of the amplitude of the AC signal with noise. The threshold of the circuit 26 can be automatically controlled. Therefore, even if the amplitude of the AC signal output by the amplitude detection circuit 23 changes due to disturbance, the comparison circuit 26 correctly corrects the amplitude of the AC signal at an intermediate level in the range of the amplitude change of the AC signal that changes depending on the presence or absence of a human body. Can be detected, and erroneous detection of a human body or the like due to an increase in noise signal or the like can be avoided.

FIG. 5 is a diagram showing a configuration example of the two-channel detection device shown in FIG. Signals from the switch 7 under the control of the disturbance detection switch 10 and the changeover switches 6 and 7 of the detection device shown in FIG.
An amplitude detection circuit 32 that detects the AC signal of Hb and detects the amplitude, a switch 31 that turns on in synchronization with the OFF state of the disturbance detection switch 10, and the disturbance detection switch 10
Amplitude detection circuit 33 that detects the amplitude of the noise signal of each channel CHa in the OFF state, a holding circuit 34 that holds the output of the amplitude detection circuit 33, and an addition that adds the output of the holding circuit 34 and the comparison reference voltage Vref. And a comparison circuit 36 for comparing the output of the amplitude detection circuit 32 with the output of the adder 35.

According to the detection device of FIG. 5, when the disturbance detection switch 10 shown in FIG. 2 is in the OFF state, the changeover switch 7 is in the ON state and the switch 31 is in the ON state with the channel CHa, so that the noise signal of the channel CHa is output. The amplitude detection circuit 33 detects and the holding circuit 34 holds the output. This held output is added to the comparison reference voltage Vref by the adder 35, and is used to control the detection threshold of the AC signal of each channel CHa and CHb.

FIG. 6 is a diagram showing an example of the structure of a detection device for detecting disturbances in two channels. Channels CHa and CHb while the disturbance detection switch 10 is OFF
Amplitude detection circuit 4 that alternately detects and holds the noise signal of
3, 44 and holding circuits 45, 46. When detecting an AC signal of each channel, the switch 47 switches to output the noise level of the channel to the adder 48, and the comparison circuit 49 controls the amplitude detection circuit 41. Compare with output. When the noise signal level of each channel is different, it is possible to make an appropriate determination according to the noise signal level. (Other Embodiments) In the above embodiments, the example in which the AC signal supplied to the antenna electrode is supplied from the signal source 1 via the disturbance detection switch 10 and the changeover switch 6 and further via impedance is shown. It is obvious that this impedance can be modified so that it is connected either before or after each of the switches in the signal path of the AC signal.

Further, in the embodiment having a plurality of antenna electrodes (detection channels), a dedicated detection circuit for detecting disturbance is provided independently of the detection circuit (voltmeter) for the AC signal to detect the disturbance. Instead of using the switch 10, a noise signal of another channel may be detected and held when an AC signal of a channel is detected and used as a threshold control signal when the AC signal of the channel is detected. It is possible. In this case, the detection device shown in FIG. 6 can be used.

By installing a plurality of antenna electrodes in the above-described embodiments in a seat in a vehicle, for example, in a seat, a backrest, etc., the presence or absence of one occupant of a single seat or a plurality of occupants of a plurality of seats, or seating It is possible to configure an occupant detection device that detects the presence or absence of

[0034]

According to the present invention, since the disturbance is detected by the switching means in the circuit without laying an antenna electrode or the like dedicated to the detection of the disturbance or the like, it is not necessary to use or lay the dedicated antenna. In addition to this, it is possible to correctly detect the noise signal in the antenna electrode itself for detecting disturbance and the circuit itself connected thereto.
Further, by using the detected noise signal for the determination of the original AC signal, it is possible to prevent erroneous detection of the detection target.

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention.

FIG. 2 is a diagram showing a second embodiment of the present invention.

FIG. 3 is a diagram illustrating a control example of a switch according to a second embodiment.

FIG. 4 is a diagram illustrating a configuration example of a detection circuit according to the first embodiment.

FIG. 5 is a diagram showing a configuration example of a detection circuit according to a second embodiment.

FIG. 6 is a diagram showing a configuration example of another detection circuit according to the second embodiment.

FIG. 7 is a diagram showing a conventional example.

FIG. 8 is a diagram showing another conventional example.

[Explanation of symbols]

1 signal source 2 Detection circuit (voltmeter) 3 Detection resistance 4 antenna electrodes 5 Spatial impedance 6 changeover switch 7 Voltmeter switching 10 Disturbance detection switch 21, 22, 31, 42 switch 23, 24, 32, 33, 43, 44 Amplitude detection circuit 25,35 adder 26, 36 Comparison circuit 34, 45, 46 holding circuit

Claims (8)

[Claims] 1. A method for detecting an object, in which an alternating current signal is supplied to an antenna electrode installed in a measurement region and an object to be measured is detected by a change in a current flowing through the antenna electrode, the alternating signal being supplied to the antenna electrode. A method of detecting an object to be measured, characterized in that a disturbance signal of the antenna electrode generated at this time can be detected by creating a state not to do so. 2. A measured object detection method for detecting the presence or absence of an object to be measured in the measurement area by measuring the impedance between an antenna electrode installed in the measurement area and the ground. A step of supplying an alternating current signal through the antenna electrode, and detecting an alternating current signal between the impedance and the antenna electrode in a state where the alternating current signal is supplied to the antenna electrode, and detecting and measuring a change in amplitude of the detected alternating current signal. A step of detecting the presence or absence of the object to be measured in the area, a step of stopping the AC signal supplied to the antenna electrode, and a noise signal of the antenna electrode in a state where the AC signal supplied to the antenna electrode is stopped. And a step of detecting the object to be measured. 3. The method for detecting an object to be measured according to claim 1, wherein the measurement target is an occupant in the vehicle. 4. An object detection device for detecting the presence or absence of the object to be measured in the measurement area by measuring the impedance between an antenna electrode installed in the measurement area and the ground, and a signal for outputting an AC signal. Source, an antenna electrode arranged in the measurement region, a changeover switch that supplies or does not supply the AC signal to the antenna electrode from the signal source via impedance, and the impedance and the antenna electrode when the AC signal is supplied. Between the detection signal for detecting the presence or absence of the measured object in the measurement region based on the amplitude of the detected signal, and the noise signal generated in the antenna electrode when the AC signal is not supplied. An apparatus for detecting an object to be measured, comprising: a disturbance detection circuit for detecting. 5. The antenna electrode comprises a plurality of antenna electrodes, and the changeover switch is a switch for alternately supplying or not supplying the AC signal to the plurality of antenna electrodes from the signal source via an impedance. The device for detecting an object to be measured according to claim 4, wherein 6. An object detection device for detecting the presence or absence of the object to be measured in the measurement area by measuring the impedance between an antenna electrode installed in the measurement area and the ground, and a signal for outputting an AC signal. Source, a plurality of antenna electrodes arranged in the measurement region, a disturbance detection switch that supplies or does not supply the AC signal from the signal source, and the AC to the plurality of antenna electrodes through impedance from the disturbance detection switch. A changeover switch for alternately supplying or not supplying a signal, and a signal between the impedance and the plurality of antenna electrodes when the AC signal is supplied is detected, and the measured area of the measurement region is measured based on the amplitude of the detected signal. A detection circuit for detecting the presence / absence of an object, and a noise generated in the antenna electrode when the disturbance detection switch does not supply an AC signal. DUT detecting apparatus comprising: the disturbance detection circuit for detecting a's signal. 7. The detection circuit comprises a comparison circuit for comparing the amplitude of the signal with a predetermined threshold value, and the threshold value is controlled by the output of the disturbance detection circuit. 6. The object detection device according to 6. 8. The device for detecting an object to be measured according to claim 4, wherein an object to be measured is an occupant in the vehicle.