JPS603625B2 - Electric field human body detector - Google Patents

Description

[Detailed description of the invention] The present invention relates to an electric field type human body detector.

Figure 1 is a block diagram showing the structure of a conventional electric field type human body detector having an excitation line and a detection line, in which 1' is an oscillator for the excitation mound, 2' is an excitation line, and 3' is a detection line, 4' is an amplifier, 5' is a detection circuit, 6' is a bandpass filter, 7
' is a comparator, 8' is a notification circuit for notifying the passing of the human body in one day, and Rin is a resistor.

Note that Eo is the output voltage of the excitation line 2', and Vo is the output voltage of the detection line 3'.
′ are shown respectively. This electrical equivalent circuit is shown in Figure 2, where Cm is the line capacitance between the excitation line 2' and the detection line 3', Co is the ground capacity between the detection line 3' and the ground, and Ch is the detection line 3' and this detection line 3
′ and indicates the interpersonal capacity between the grounded human body and the grounded human body. To explain the detection operation of the human body day using such an equivalent circuit, as the human body day gradually approaches the detection line 3' as shown in FIG. As the human capacitance Ch changes, the induced voltage Vo of the sensing line 3' changes accordingly, and for example, as shown at a in Fig. 3, the point in time when the human body approaches the sensing line 3' most The induced voltage Vo becomes the smallest at .

This induced voltage Vo is detected by a detection circuit 5' via an amplifier 4', and is applied to a comparator 7' which detects a change level via a bandpass filter 6'.
When the changed electromotive voltage Vo exceeds the set level of the comparator 7', the notification circuit 8' is activated to detect the approach or passage of the human body. In this case, the excitation line 2
′ as a human body detection signal emitted from a single fixed frequency f
When o is used, harmonic noise such as power supply hum noise and switching noise received by the detection line 3' is as shown in Fig. 4.
Power frequency (60Hz or 60Hz) as shown in b.
HZ), and as the power supply frequency changes, the frequency changes as shown in Fig. 4A and 4B.

However, as shown in Figure 4A, if the signal frequency exists at a frequency approximately midway between adjacent harmonic noises, the frequency of the beat generated between the detection signal and the harmonic noise will be 20-odd Hz. Yes, the beat of such a frequency cannot pass through the band pass filter 6' (in this case, the band width of the band pass filter 6' is 0.08Hz to 0.3H).
Z), the alarm circuit 8' does not malfunction without affecting the subsequent comparator 7'.
However, as shown in Figure 4, the frequency of harmonic noise fluctuates with the power supply frequency, and as shown at c in the figure, the signal frequency fo approaches the signal frequency fo.
If a beat with a low frequency (for example, several Hz or less) is generated between the
', which causes the comparator 7' to operate and the notification circuit 8' to operate, resulting in a false alarm.

In order to solve this drawback, circuit configurations as shown in FIGS. 5 and 6 have already been proposed. That is, one method is to connect a frequency fixing circuit 9' to the oscillator 1' in FIG.
o is fixed to a non-integer multiple of the AC power frequency.
In this way, harmonic noise with a frequency that is an integral multiple of the power supply frequency does not approach the signal frequency fo, and the beat frequency also becomes relatively high, and the beat is blocked by the band pass filter 36', causing a false alarm. There is no fear. However, this method has the disadvantage that a frequency fixing circuit 9' etc. must be provided and the circuit becomes complicated. As another method, as shown in FIG. 6, a beat frequency detection circuit 10'
The frequency of the beat that occurs between the signal frequency fo and the harmonic noise is constantly monitored, and if a beat of a low frequency that may cause a false alarm occurs, the notification circuit 8' is connected to 4. There is a method to disable the notification circuit 8' for a long time due to fluctuations in the power frequency.
There is an inconvenience that the operation of the system is stopped and the alarm is missed when the human body day approaches. The present invention has been proposed in view of the above points, and its purpose is to provide a simple configuration that eliminates the possibility of false alarms caused by harmonic noise such as power supply hum noise and switching noise that occur in synchronization with the power supply. To provide an electric field type human body detector.

Embodiments of the present invention will be described in detail below with reference to the drawings.
As shown in Fig. 7, if the detection signal is operating at a frequency fo, due to fluctuations in the power supply frequency, etc.
If the frequency of harmonic noise of the power supply shown by b approaches the signal frequency wa, as shown in c, then the signal frequency f
There is a possibility that a low-frequency beat that can pass through a band-pass filter may be generated between the band-pass filter and the harmonic noise.

In such a case, the present invention is configured to move the frequency of the detection signal to approximately the center frequency of the harmonic noise whose distribution is predetermined by the value of the power supply frequency, for example, fo2 in FIG. 7, Furthermore, these two frequencies,
, fo2 can be freely switched. FIG. 8 is a block diagram showing the circuit configuration, and in the same figure, la is an oscillator, which is configured to select and oscillate one of the two detection signals .

The interval between these frequencies fo, , fo2 needs to be selected so that, for example, when the frequency of harmonic noise approaches the detection signal of wa, fo2 is located approximately at the center of the harmonic noise. The output of the oscillator la is applied to the excitation line 2, and the frequencies fo, , fo2 of the aforementioned detection signals are applied to the excitation line 2.
A beat frequency detection circuit lb is added to the beat frequency detection circuit lb for switching control. As shown in the figure, an AC power frequency is also added to this beat frequency detection circuit lb.
In b, the beat frequency generated between the signal frequency, for example fo, and the harmonic noise of the power supply is constantly monitored, and the oscillation frequency f is set in the oscillator la according to the beat frequency.
A control signal for switching o, , b2 is generated. Further, a detection line 3 is installed at an appropriate interval from the excitation line 2, and one end of the detection line 3 is grounded via a resistor Rin. A non-grounded end of the resistor Rin is connected to an amplifier 4, and a detection circuit 5, a bandpass filter 6, a comparator 7, and a notification circuit 8 are sequentially connected to the output side of the resistor Rin. For example, if the oscillator la generates a detection signal of frequency fo, the beat frequency detection circuit lb detects the beat frequency at this signal frequency fo, and this beat frequency is detected by the bandpass. If the frequency is high enough to be blocked by the filter 6, no control signal is applied to the oscillator la, and the frequency of the detection signal is maintained at a certain level.

At this time, the detection operation of the human body day is performed by changing the induced voltage Vo of the detection line 3 due to the change in the human capacitance Ch due to the approach of the human body day, as in the case of the circuit shown in FIG. It is compared with the set level by a comparator 7 via an amplifier 4, a detection circuit 5, and a bandpass filter 6.
This is done by operating the notification circuit 8. Now, due to fluctuations in the power supply frequency, etc., as shown in FIG. 7, when the frequency of harmonic noise approaches the signal frequency fo, and the beat frequency becomes low enough to pass through the bandpass filter 6, the beat frequency detection circuit lb Detecting this, the detection circuit lb operates to issue a control signal to the oscillator la to switch the oscillation frequency to fo2.

As a result, the signal frequency fo2 is located approximately at the center of the adjacent harmonic noises, and the beat frequency is also relatively high, so this beat is blocked by the band/gas filter 6 and the subsequent comparator 7, Without causing the circuit 8 to malfunction, the above;. Then, it enters a standby state for normal detection operation. In this case, when the frequency of the harmonic noise approaches the signal frequency fo2, the oscillation frequency of the oscillator la is switched from fo2 to fo by the control signal of the beat frequency detection circuit lb, as described above. As described above, according to the present invention, a so-called electric field type human body detector is provided with an oscillator that generates detection signals of two frequencies and a beat frequency detection circuit that switches and controls these detection signals. Since the structure is configured to eliminate the cause of such false alarms by switching the frequency of the detection signal, various noises generated in synchronization with the power supply, such as power supply hum noise, harmonic noise such as switching noise, and There is no risk of false alarms occurring due to fluctuations in the power supply frequency, and the
It has the advantage that accurate human body detection can be performed and its circuit configuration is extremely simple.

Further, since the method does not require stopping the function of the notification circuit for a long period of time to prevent false alarms, there are various effects such as completely preventing false alarms.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the circuit configuration of a conventional electric field type human body detector, Fig. 2 is an equivalent circuit, Fig. 3 is a diagram explaining the operation, and Fig. 4 A and B explain the shortcomings of the conventional example. FIG. 5 and FIG. 6 are block diagrams showing the circuit configuration of other conventional examples, and FIGS. 7 and 8 are diagrams showing the embodiment of the present invention. is an explanatory diagram of the frequency spectrum, and FIG. 8 is a block diagram showing the circuit configuration. la...Oscillator, lb...Beat frequency detection circuit, 2...Excitation line, 3...Detection line, H...Human body, Ch...・Interpersonal capacity, Vo...
...Electromotive voltage. Figure O Figure 2 Figure O 3 Figure Om Figure O 5 Figure O 6 Figure O 7 Figure Spear 8

Claims (1)

[Claims] 1 A detection signal is emitted from the excitation line, the electric field is applied to the detection line, and the induced voltage of the detection line changes due to a change in the interpersonal capacitance between the detection line and a human body in proximity to the detection line. In the human body detector that detects the approach of a human body by detecting the 2 with different frequencies, located approximately in the center of the frequency of harmonic noise
A beat frequency detection circuit is connected to an oscillator that generates one of the two detection signals, and detects a beat frequency generated between the frequency of one of the detection signals as an output of the oscillator and the harmonic noise. , when the beat frequency detection circuit detects a beat frequency that causes a false alarm, a control signal for switching the frequency of the detection signal is applied to the oscillator, so that the oscillator generates a detection signal of the other frequency. An electric field type human body detector characterized by the following configuration.