GB2069206A - Intrusion warning systems - Google Patents
Intrusion warning systems Download PDFInfo
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- GB2069206A GB2069206A GB8101157A GB8101157A GB2069206A GB 2069206 A GB2069206 A GB 2069206A GB 8101157 A GB8101157 A GB 8101157A GB 8101157 A GB8101157 A GB 8101157A GB 2069206 A GB2069206 A GB 2069206A
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- 238000001514 detection method Methods 0.000 claims description 31
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- 238000010586 diagram Methods 0.000 claims description 20
- 230000010354 integration Effects 0.000 claims description 11
- 230000004044 response Effects 0.000 claims description 9
- 230000035945 sensitivity Effects 0.000 claims description 5
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- 230000009471 action Effects 0.000 claims description 4
- 238000000926 separation method Methods 0.000 claims 1
- 230000035559 beat frequency Effects 0.000 description 4
- 239000004020 conductor Substances 0.000 description 4
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- 238000003379 elimination reaction Methods 0.000 description 1
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Classifications
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- G—PHYSICS
- G08—SIGNALLING
- G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
- G08B13/00—Burglar, theft or intruder alarms
- G08B13/22—Electrical actuation
- G08B13/26—Electrical actuation by proximity of an intruder causing variation in capacitance or inductance of a circuit
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Abstract
An intrusion warning system for indicating the presence of an intruder in a given area comprises a single antenna wire (4) encircling said area and insulated from the ground, a high frequency (e.g.1 kHz to 10 kHz) oscillator (1) for feeding a high frequency signal to the antenna (4), a coupling impedance (2), for example a capacitor, connected between an output terminal of the oscillator (1) and the antenna (4), and a signal processing means (5) which produces an alarm upon detecting a change to beyond a predetermined level of the voltage on the antenna (4), as induced by the proximity of an intruder. <IMAGE>
Description
SPECIFICATION
Intrusion warning systems
The present invention relates to intrusion warning systems utilising an antenna to which, in use, an A.C.
signal isfed.
Figure 1 (a) of the accompanying drawings is a block diagram of an example of a conventional intrusion detection and warning system utilising an electric field, such as shown in US Patent No. 4 064 499. In the system of Figure 1(a), a voltage of a high frequency, for example about 9750 Hz, shown at (E) in Figure 2 and generated by a signal generating circuit 1, is applied between a field wire Sand the ground and a voltage change induced on an antenna wire A disposed such that there is a substantially uniform distance gap g between it and the field wire S is detected and processed to produce an intruder detection signal.The voltage change due to the intruder is detected as follows:
Provided that a resistance between the antenna A and the ground, i.e. an input impedance of an amplifier, is sufficiently large, then by considering the equivalent circuit of Figure 1 (b) the induced voltage V, in the case where there is no intruder, is given by:
V- Ci,CC'0 .e ..... (1)
C1 + CO where; C,' is the capacitance between the field wire Sand the antenna A; CO is the capacitance between the antenna A and the ground; and
e is the voltage of the high frequency signal applied to the field wire S.
Then, if an intruder is present, if the intruder's body is considered as an electric conductor, and the capacitance between the intruder's body and the antenna A is CM, the induced voltage Vla becomes as given by the following equation (2): V'5 = C1) e ..... (2)
C1 + C0 + CM The induced voltage is amplified by an amplifier 7, then detected by a detector circuit 8 and, after passing through a bandpass filter 9, is led to a threshold circuit 10 where its input value V5 is compared with a predetermined threshold value Vth.
When an intruder passes through the electric field of the antenna A, as shown in Figure 1(c), the induced voltage Vla changes as shown at (V'5) in Figure 2 by virtue of changing of the capacitance CM. Therefore, the input voltage V5 to the threshold circuit 10 changes as shown at (V5) in Figure 2 and in Figure 1(d). Therefore, when the input voltage V5 becomes lower than a predetermined threshold value VthL as shown in Figure 1 (d), at a time t1 as shown at (V5) in Figure 2, the threshold circuit 10 sends an output signal to an alarm or warning circuit 6 which issues a warning signal (Vs) at the time t1, as shown by (Vs) in Figure 2, to light a lamp or ring a buzzer.
When a strong wind blows, the gap or spacing between the two wires Sand A of the above-described conventional intruder detection system is likely to change considerably, thereby producing an undesirable change of the capacitance Ci between the two wires, whereby false alarms are likely to be issued.
Furthermore, when the area to be protected is broad, it is expensive to install two wires with a uniform gap, which is sometimes also difficult due to the particular lie of the land.
Furthermore, the sensitivity of detection is largely influenced by changes of the capacitance CO between the antenna wire A and the ground, which is dependent on the length of the antenna wire A and the height of the antenna wire A above the ground. The conventional system thus suffers from the disadvantage that it does not necessarily have a sensitivity as designed, since the design is carried out for an average antenna wire of average height and length or, in other words, the apparatus can be used only for a limited range of height and length of the antenna. Moreover, to provide a pair of wires may give rise to difficulty in actual practice because of surrounding conditions.
A further disadvantage of the conventional system is that a false warning is likely to be caused by generation of a beat between the high frequency signal fed to the antenna and a high harmonic of the frequency of the AC power existing in the protected area. Such beat produces a signal of a very low frequency, such as 0.1 to 2 Hz, and such low frequency signal passes through the bandpass filter 9 and causes the alarm circuit 6 to produce a false alarm. In order to avoid such false warning, in the system of US
Patent No 4 064 499 the oscillation frequency of the high frequency to be fed to the antenna is locked by a complicated frequency lock circuit or the alarm output is disabled by utilising an output of a beat frequency detector circuit (BFD) when the AC power frequency is of such a frequency as to produce the above-mentioned undesirable beat.However, to take the first measure of using the frequency lock circuit (FLC) is very complicated, resulting in an increase in the cost of the system, and the second measure of disabling the alarm gives rise to the danger that intruder detection is often ceased.
According to the present invention there is provided an intrusion warning system for indicating the presence of an intruder in a given area, the system comprising:
an antenna provided around said area and insulated from the ground;
an oscillatorforfeeding an AC signal to the antenna;
a coupling impedance means connected between an output terminal of the oscillator and the antenna; and
a signal processing means for producing an output signal in response to a change to beyond a predetermined level of the voltage of the AC signal on the antenna.
Systems embodying the present invention can enable a reduction in the number of wires to be positioned around the protected area to a single line thereby reducing the cost of the system, can reduce false warnings, can provide an intrusion alarm with high sensitivity regardless of variations of the length or height of an antenna wire, and can provide reliable protection without periodically disabling the system, regardless of variations of the power source frequency, without complicated circuitry.
The invention will now be further described, by way of illustrative and non-limiting example, with reference to the accompanying drawings, in which:
Figure 1aha) is a block diagram of an example of a conventional intrusion warning system;
Figure l Fb) is an equivalent circuit of the system of Figure 1 (a);
Figure 1(c) is a schematic view illustrating the passing of an intruder under an antenna of the system of
Figure 1(a);
Figure 1(d) is a graph showing the change of input signal (Va) to an amplifier 7 of the system of Figure 1 (a) in relation to positions (P, to P5) of the intruder shown in Figure 1(c); Figure 2 is a waveform chart showing waveforms of electric signals at various parts of the system of Figure 1(a);; Figure 31awl is a block diagram of an intrusion warning system embodying the present invention;
Figures 3(b), (c) and (d) are circuit diagrams showing examples of a coupling impedance 2 of the system of
Figure 3(a);
Figures 3we), Ifl and (g) are circuit diagrams showing examples of an input impedance 3 of the system of
Figure 3(a);
Figure 4(a) is a waveform chart showing waveforms of electric signals at various parts of the system of
Figure 3(a);
Figure 4(b) is a schematic view illustrating the passing of an intruder under an antenna of the system of
Figure 3(a);;
Figure 4(c) is a graph showing the change of input signal to an amplifier 7 of the system of Figure 3(a) in relation to positions (P1 to Pg) of the intruder shown in Figure 4(b);
Figure 5 is a block diagram of a system corresponding to that of Figure 3(a), showing an exemplary form of the oscillator 1 in detail, with relevant parts shown in dotted lines;
Figure 6 is a more detailed circuit diagram of the system shown in Figure 5;
Figure 7 is a waveform chart showing waveforms of electric signals at various parts of the system of Figure 6, for illustrating a beat-eliminating action thereof;
Figure 8 is a frequency spectrum chart for illustrating the beat;
Figure 9 is a block diagram of a modified embodiment of the present invention for eliminating false warnings caused by the beat;;
Figure 70 is a frequency spectrum chart for illustrating the beat-elimination action of the system of
Figure 9;
Figure 11 is a block diagram of a modified embodiment of the present invention for detection of the direction of intruders crossing antennae thereof;
Figures 12(a) and 12(b) are waveform charts of signals at various parts of the system of Figure 11;
Figure 13 is a detailed circuit diagram of a direction detection circuit 30 shown in Figure 11;
Figure 14 is a block diagram of another modified embodiment of the present invention for detection of the direction of an intruder moving parallel to an antenna thereof;
Figures 15(a) and 15(b) are waveform charts of signals at various parts of the circuit of Figure 14;;
Figure 16 is a detailed circuit diagram of a differentiator 31, an integrator 32 and a level detector 33 of the system of Figure 14;
Figure 17(a) is a perspective view of an example of an antenna pole cap designed for eliminating false warnings caused by rain drops on an antenna pole;
Figure 17(b) is a sectional elevation view of the antenna cap of Figure 17(a);
Figure 18 is a sectional elevation view of another antenna cap;
Figure 19(a) is a chart showing the relationship between a detection voltage AV and the capacitance C, of a coupling capacitor that can be used as a coupling impedance 2 in a system embodying the present invention; ;
Figure 19rub) is a chart showing the relationship between a detection voltage AV and the resistance R, of a coupling resistor that can be used as a coupling impedance 2 in a system embodying the present invention;
Figure 19(c) is a block diagram of a coupling impedance 2 that can be used in a system embodying the present invention;
Figure 19fed) is a detailed circuit diagram of an example of a coupling resistance that can be used in a system embodying the present invention; and
Figure 19we) is a detailed circuit diagram of an example of a coupling capacitance that can be used in a system embodying the present invention.
Figure 3(a) shows a block diagram of a first intrusion warning system embodying the present invention.
An antenna 4 is connected through a coupling impedance 2 to a high frequency (e.g. 1 to 10 kHz) oscillator 1 so that high frequency current is fed from the oscillator to the antenna 4 through the coupling impedance 2.
An input impedance 3 is connected between the antenna 4 and the ground, and the high frequency voltage across the input impedance 3 is supplied as an input signal to a signal processing part 5, which comprises an amplifier 7, a detector 8, a bandpass filter 9 having a very low passband such as 0.08 to 0.3 Hz, and a threshold value detection circuit 10. The circuit 10 is connected to an alarm or warning circuit 6.
The coupling impedance 2 is, for example, a capacitor, as shown in Figure 3(b), or an inductance or a resistance as is explained in more detail below. The input impedance 3 comprises a high resistance or a high impedance circuit such as a parallel-connected LC resonant circuit which has a resonance frequency substantially equal to the frequency of the oscillator 1 and thus has a very high impedance at that frequency.
Provided that the impedance between the antenna 4 and the ground is sufficiently large, the induced voltage V in the case where there is no intruder is given by V- C1 . e ..... (3),
C1 + CO where:
C1 is the capacitance of the coupling impedance 2; CO is the capacitance between the antenna 4 and the ground; and
e is the voltage of the high frequency signal fed from the oscillator 1.
Then, if an intruder is present, if the intruder's body is considered as an electric conductor, and the capacitance between the intruder's body and the antenna 4 is CM, the induced voltage V'5 becomes as given bythefollowing equation (4):
C1 C1 + CO t- C, + CM The induced voltage Vla is amplified by the amplifier 7, then detected by the detection circuit 8 and, after passing through the bandpass filter 9, is led to the threshold circuit 10 where its input value V5 is compared with a predetermined threshold value VthL.
When an intruder passes through the electric field of the antenna 4, as shown in Figure 4(b), the induced voltage changes as shown at (Vla) in Figure 4(a), by virtue of changing of the capacitance CM. Therefore, the input voltage V5 to the threshold circuit 10 changes as shown at (V5) in Figure 4(a) and in Figure 4(c).
Therefore, when the input voltage V5 becomes lower than the predetermined threshold value VthL at the time t1 as shown at (V5) in Figure 4(a), the threshold circuit 10 sends an output signal to the warning circuit 6 which issues a warning signal (V5) at the time t1, as shown at (Vs) in Figure 4(a), to light a lamp or ring a buzzer.
Equations (3) and (4) are substantially the same as Equations (1 ) and (2), as can easily be understood.
Therefore, it is evident that, in the same way as in the conventional system of Figure 1(a), it is possible in the system of Figure 3(a) to detect an intruder by means of a voltage change in the antenna 4, which is a single field wire. Since only a single antenna wire is used, there is no problem arising from the possibility of a strong wind causing an undesirable variation of the gap or spacing between parallel wires, and the cost of construction of the system is reduced. The only requirement of the wire construction is to keep the wire at a uniform height above the ground. Further, the single wire antenna system is less sensitive to undesirable vibration caused by the wind than the conventional two-wire system, and accordingly there is a smaller possibility of false alarms.
Some other impedance can be used for the coupling impedance 2, such as an inductance as shown in
Figure 3(c), a resistance as shown in Figure 3(d), or a composite impedance formed by connecting the capacitance, inductance and resistance.
A high resistance as shown in Figure 3(e) is ordinarily used for the input impedance. However, other input impedances, for example a parallel resonant circuit as shown in Figure 3(f) or an inductance as shown in
Figure 3(g), can be used. If the input impedance of Figure 3(f) is used, its resonant frequency is preferably selected to be close to or substantially the same as that of the oscillation frequency of the high frequency oscillator 1, so that the change of the input signal to the amplifier upon the detection of an intruder is very sharp by virtue of the sharp gradient of the resonance curve, thereby providing high sensitivity.
It is also possible to provide (an) additional antenna wire(s) 4" which is (are) connected in series with (an) additional coupling impedance(s) connected to a single common high frequency oscillator 1 and connected to (an) additional signal processing part(s).
Figure 5 shows a first example of the oscillator 1 with which the intrusion alarm system can attain high stability against electric fields of harmonics of the commercial A.C. power source, so that the system does not issue false alarms due to a beat produced between the higher harmonics and the oscillating signal. A feature of the structure of the oscillator of Figure 5 is that it comprises an oscillation circuit 15 capable of oscillating at two different frequencies between which it is switched by means of a frequency switching control signal voltage applied thereto, and a beat detector block 19 which detects the occurrence of a beat of low frequency and issues the control signal to be applied to the oscillation circuit 15.
The beat detector block 19 comprises a mixer 11, a beat detector circuit 12 including a bandpass filter, a threshold circuit 13 and a frequency switching control circuit 14, connected in that order, and applies the frequency switching control signal to the oscillation circuit 15. The mixer circuit 11 mixes the commercial
A.C. power current and the high frequency output signal of the oscillation circuit 15 and issues a mixed signal, i.e. a reference beat signal between the harmonics of the A.C. power current and the high frequency output signal. The detector circuit 12 including the bandpass filter rectifies the mixed signal, i.e. the reference beat signal from the mixer circuit 11. The beat threshold circuit 13 issues an output signal when the beat frequency becomes low and the output signal of the detector circuit 12 then becomes larger than a predetermined level.The frequency switching control circuit 14 is operative to issue an output signal of high (H) or low (L) level and comprises, for example, a T-type flip-flop circuit driven by the output signal of the beat threshold circuit 13 and a comparator which supplies the frequency switching control signal to the oscillation circuit 15.
The operation of the circuit of Figure 5 is as follows: When the frequency of the commercial A.C. power source drifts and the beat frequency is gradually lowered, the amplitude of the beat output is gradually increased as shown in the left half part of Figure 7(G). The output of the beat detector 12 which is an integration of a half-wave-rectified signal shown in Figure 7(H), then gradually increases as shown in Figure 7(1). Then, at the time when the beat detector output shown in Figure 7(1) exceeds a predtermined threshold level VBth, the threshold circuit 13 issues a pulse signal as shown in Figure 7(J), which switches the flip-flop cicuit in the frequency switching circuit 14 and makes the output voltage of the circuit 14 change. Therefore, the frequency switching control circuit 14thereafter issues a signal to the oscillation circuit 15.The detailed circuit construction of the system of Figure 5 is shown in Figure 6. As shown in Figure 6, the output (L) of the comparator of the frequency switching control circuit 14 having the waveform shown in Figure 7(K) is applied to the gate of a field effect trnsistor FET 2 of the oscillation circuit 15, which is an RC oscillator and changes its output frequency signal to be applied to the antenna 4 in response to a change of the voltage applied to the gate. By means of the frequency switching, the frequency of the high frequency signal provided by the oscillation circuit 15 is switched from a previous frequency f01 to another frequency f02, as shown in Figure 7(A) and in a frequency spectrum chart shown in Figure 8, wherein harmonics of the A.C.
commercial power frequency which line up on the frequency spectrum chart are shown by h,h,h..... The frequencies f01 and f02 are selected to have a relationship defined by the following equation and shown in FigureS: I fo2 - f01 = nfAC + Af ..... (5).
where:
n is an arbitrary positive integer;
fAc is the frequency of the commercial A.C. power supply; and
Af is a frequency smaller than fAC, for example a frequency 0.4 to 0.6 times as large as fAc.
According to the abovementioned selection of f01 and f02, when either one of the oscillation frequencies f01 or f02 forms an undesirable beat of a low frequency with a harmonic of the A.C. power supply the other of them does not produce a noticeably strong beat of a low frequency. By means of switching from the frequency f01 to the frequency f02, the amplitude of the beat becomes small and the beat frequency becomes very high, so that the possibility of a false warning disappears or is at least greatly reduced. At the same time, the output of the beat detector 12 becomes small, and thus the output of the threshold circuit 13 becomes small, but the flip-flop retains the same state until another output is supplied to the threshold circuit 13.That is to say, the system of Figures 5 and 6 prevents the generation of an undesirable false warning due to a beat produced by interference between the A.C. power supply harmonics and the oscillation frequency, by means of switching the oscillation frequency from that which is producing a beat to that which does not produce a beat. When the frequencyf02 comes to produce another beat with the harmonics of the A.C. frequency, then another pulse is applied to the frequency switching control circuit 14 and the oscillation circuit 15 is thus controlled to switch its frequency to the other frequency fowl.
As already explained, the voltage at an output terminal of the amplifier 7 is applied to the detector 8 of the signal processing circuit 5. The amplitudes of the output of the detector 8 and thus the output of the bandpass filter 9 increase, as shown in Figures 7(C) and 7(D), as the level of the beat becomes high. However, such level change due to the beat does not make the threshold circuit 10 produce an output, since the threshold levels VthH and VthL of the threshold circuit 10 are selected not to react with such output from the bandpass filter for the beat. The preferred passband of the bandpass filter is empirically found to be 0.08 Hz to 0.3 Hz, whereby an intruder who is about 1 .5m from the antenna 4 can be detected.
Though the frequency switching arrangement is provided in the system of Figures 5 and 6, the intruder detection function is the same as that of the system of Figure 3(a), which function has been described above with reference to Figure 4. That is, the intruder causes a change of voltage on the antenna 4 and the change is processed by the signal processing circuit 5, wherein when the output of the bandpass filter 9 goes below the predetermined level VthL the threshold circuit 10 triggers the alarm circuit 6.
Figure 9 shows a block diagram of another system embodying the present invention, wherein to avoid undesirable false alarms or warnings due to the low frequency beat phenomenon a pair of different frequencies f01 and f02 are each continuously generated by two oscillation circuits 15' and 15" in the oscillator 1.
The oscillator 1 of Figure 9 comprises, as well as the two oscillation circuits 15' and 15" providing the oscillation frequencies f01 and f02, a mixer 152 which adds the two signals of the frequencies f01 and f02 and feeds them, through the coupling impedance 2, to the antenna 4. The signal processing circuit 5 of this embodiment has a pair of tuned amplifiers 7 and 7' tuned to the frequencies f01 and f02, followed respectively by detectors 8 and 8', bandpass filters 9 and 9', and threshold circuits 10 and 10'. The output terminals of the threshold circuits 10 and 10' are connected to respective input terminals of an AND-gate 28, which is followed by an alarm circuit 6.The frequencies f01 and f02 are selected to have a relationship defined by the following equation and shown in Figure 10: I f02 - f01 I = nfAc + Af .. - (6), where:
n is an arbitrary positive integer;
fAc is the frequency of the commercial A.C. power supply; and
Af is a frequency smaller than fAC, for example a frequency 0.4 to 0.6 times as large as fAC According to the abovementioned selection off01 and f02, when either one of the oscillation frequencies f01 and f02 forms an undesirable beat of a low frequency with a harmonic of the A.C. power supply the other of them does not produce a noticeably strong beat of a low frequency.Therefore, even in the event of a frequency drift which produces a beat of low frequency with either frequency, only one of the threshold circuits 10 or 10' will produce an output and, therefore, the AND-gate 28 will not activate the alarm circuit 6.
On the other hand, when an intruder is present, both the bandpass filters 9 and 9' issue output signals to activate both the threshold circuits 10 and 10', whereby the AND-gate 28 issues an output to the alarm circuit 6 thereby activating it to issue an intruder alarm.
Figures 11, 12(a), 12(b) and 13 show another intrusion warning system embodying the invention, the system being capable of detecting the direction of passing of an intruder through a protected zone by providing two parallel antennae along the zone. The system shown in Figure 11 has two parallel antennae 4 and 4' with a predetermined gap between them. When an intruder arrives in the direction shown by a dotted arrow a, the antenna 4 changes its voltage first and the other antenna 4' changes its voltage later. Therefore, as shown in Figure 1 2(a), the first detector 22 produces a voltage change v1 and the second detector produces a voltage v2 thereafter. Therefore, a differential amplifier 29, which produces an output of v-v2, produces a signal shown asv1-v2 in Figure 12(a).Accordingly, in a direction detection circuit 30, the detailed circuit of which is shown in Figure 13, when the output voltage v1-v2 from the differential amplifier 29 is higher than a reference voltage VH as shown in Figure 12(a) a comparator Ca issues an output pulse Vp shown in Figure 12(a), and, on the other hand, when the output voltage v1-v2 from the differential amplifier 29 is lower than a reference voltage VL as shown in Figure 12(b) a comparator Cb issues an output pulse Vo as shown in Figure 12(b). When the pulse Vp falls, an RS flip-flop circuit FF is set and issues an output pulse Q, and at the same time monostable multivibrator M1 is triggered to issue a pulse M1 of a predetermined duration or length, as shown in Figure 12(a).On the other hand, when the pulse V0 falls, the RS flip-flop circuit FF is reset and issues an output pulse Q and at the same time a monostable multivibrator M2 is triggered to issue a pulse M2 of a predetermined duration or length, as shown in Figure 12(b). The durations or lengths of the pulses M1 and M2 of the multivibrators M1 and M2 are selected to be sufficiently longer than the time required for an intruder to pass the parallel antennae 4, 4'. An AND-gate G1 produces an AND signal of the Q output of the flip-flop FF and the M1 and M2 outputs of the multivibrators M1 and M2. An AND-gate
G2 produces an AND signal of the8output of the flipflop FF and the M1 and M2 outputs of the multivibrators
M1 and M2.Therefore, when the intruder passes the parallel lines (antennae) in the a-direction of Figure 11, the pulse Vp is issued prior to the pulse Vo and only the gate G1 issues an output to indicate a-direction intrusion. On the other hand, when the intruder passes the parallel antennae in the ss-direction of Figure 11, the pulse V0 is issued prior to the pulse Vp and only the gate G2 issues an output to indicate ss-direction intrusion. This system is very useful since the direction of a man passing the antenna can be detected. By generalising the idea of this embodiment, by providing a number of pairs of substantially parallel antennae in a protected area, the motion of an intruder in such field can be detected.
Figure 14 shows another system embodyng the invention, the system being capable of detecting motion of an intruder with respect to the lengthwise direction of the antenna. The antenna 4"' is shaped like an saw-tooth waveform. The saw-tooth wave shape is preferably formed in a substantially vertical plane and the bottom line of the antenna is preferably formed parallel to the ground. Other parts are substantially the same as in any of the foregoing embodiments, except that a direction detection circuit 34 is connected between the detector 8 and the alarm circuit 6. The direction detection circuit 34 comprises a differentiator 31, an integrator 32 and a level detector 33.Since the antenna 4"' is saw-tooth shaped, as shown in Figure 14, the capacitance Cm between the antenna 4"' and a human body passing under the antenna is as shown in
Figures 15(a) and 15(b) with respect to lengthwise movement in directions X1 and X2 along the antenna 4"' represented by the position on the abscissa. Therefore, when the human body moves along the lengthwise directions Xq and X2 of the antenna 4"', the voltage V4"' of the antenna and the differentiated output dV/dt thereof are as shown by the waveforms V4 and dVidt of Figures 15(a) and 15(b), respectively.Therefore by integrating the outputs of the differentiator 31 by the integrator 32 and applying the integrated output to the level detector 33, the level detector 33 provides a first output or a second output, when the integrated output goes beyond a predetermined threshold level VH or VL of Figure 15(a) or 15(b), respectively. Therefore, by means of the polarity of the outputs of the level detector 33, the direction of the motion of the human body can be detected.
Figure 16 shows a circuit diagram of an example of the direction detection circuit 34 of Figure 14, output terminals Vpa and Vp2 being output terminals for indication X1-direction movement and X2-direction movement, respectively, of a human body under the antenna 4"'.
If only the detection of movement along the lengthwise direction of the antenna, irrespective of the direction of such movement, is all that is required, it is sufficient to employ an antenna having symmetrically shaped teeth along its length. For example, a symmetrical saw-tooth wave or a square wave shape antenna can be used for such detection.
Figure 17(a) is a perspective view of an example of an antenna pole cap 200 of a conductive substance which covers a top part of a pole 100 of an insulative substance which supports the antenna 4. Figure 17(b) is a sectional elevational view of the pole cap 200 of Figure 17(a). The pole cap 200 is made of a conductive substance such as a stainless steel and is shaped substantially in the form of a cone without a bottom face.
The top part of the cone-shaped cap 200 has a wire holder 201 for holding the antenna 4 therethrough or thereby. The cone-shaped cap 200 has a vacant open sapce 202 within it which affords a long insulation length for the top part of the pole 100. Since the cap 200 is made of a conductive material and is connected to the antenna 4 and protects a considerable length of the top part of the pole 100 against the attachment of water drops, even heavy rain does not materially change the capacitance CO between the antenna 4 and the ground. Therefore, false alarms hitherto likely to be caused by rain drops becoming attached to the antenna pole to form a conductor to increase the capacitance between the antenna pole and the ground, can be effectively eliminated.The shape of the cap is preferably, as mentioned, conical, since this causes rain drops to fall down away from the pole. Figure 18 is a sectional elevational view of a modification of the cap 200 wherein a horizontal disc 102 is formed on the pole 100 at the part in the space 202 enclosed by the conical cap. The disc 102 effectively prevents rain drops from being blown upwardly and reaching the top part of the pole 100. By using the above-described pole caps on the antenna pole, the possibility of false alarms being caused by an undesirable change of the antenna to ground capacitance due to rain drops is effectively eliminated or at least greatly reduced.
The inventors examined the relationship between the value of the coupling impedance 2 and the impedance of the antenna 4. Figure 19(a) shows a relationship between the capacitance C, of the coupling impedance 2 and the amount of voltage change AV of the antenna 4 for a 1 pF change of the capacitance CO (between the antenna 4 and the ground).The parameters are different values of the capacitance CO This graph shows that the voltage change AV, that is the detection output, has a maximum value with respect to change of the capacitance value C, of the coupling capacitor, and that the optimum conditions are for the cases when the coupling capacitance C, is almost equal to the capacitance CO From the abovementioned fact, it is deduced that the coupling capacitance C, should preferably have a value substantially equal to the capacitance CO The inventors further examined the relationship between the value of a coupling resistance R, acting as the coupling impedance 2 and the amount of voltage change AV of the antenna 4 for a 1 pF change of the capacitance CO between the antenna 4 and the ground, as shown in Figure 19(b). The parameters are different values of the capacitance CO The frequency of the oscillator is about 10 kHz.This graph shows that the voltage change AV, that is the detection output, has a maximum value with respect to change of the resistance value R, of the coupling resistor, and that the optimum conditions are for the cases where the impedance Z, is almost equal to the impedance of the capacitor CO From the abovementioned consideration, in order to obtain maximum detection output, it is ideal for the coupling impedance to be such that the value of the coupling impedance 2 is substantially equal to the value of the impedance between the antenna 4 and the ground, or, in other words, that one voltage between the antenna 4 and the ground is substantially equal to one half of the voltage fed to the input side of the coupling impedance 2. Furthermore, from a comparison of Figures 19(a) and 19(b), in the case of an input resistance Rin = 1 megohm, for the condition that Co > 50pF the use of a resistor as the coupling impedance 2 gives a higher output voltage, and for Co < 50pF the use of a capacitor as the coupling impedance 2 gives a higher output voltage.
Figure 19(c) shows an example of a circuit which enables the abovementioned ideal control of the coupling impedance. The coupling impedance 2 includes a variable impedance 18 whose impedance value is controlled by a signal from an impedance control circuit 16. For example, the variable impedance 18 can be a variable capacitance diode which changes its capacitance in accordance with a D.C. control voltage applied thereto. The circuit 2 also comprises an integration circuit 17 or a low pass filter of a very low cut-off frequency which integrates the output voltage of the detector circuit 8, that is the voltage on an output terminal 81 of the detector circuit 8, and supplies its integrated or low-passed output to the impedance control circuit 16. The abovementioned circuits form a feedback loop together with the input impedance 3, the input amplifier 7 and the detector 8.The feedback loop functions as follows. When the output signal on the output terminal 81 is lowered from a predetermined level, and therefore the output of the integration circuit 17 becomes low, the lowered voltage is applied to the gate electrode of an FET which constitutes a variable impedance circuit 18. Therefore, the effective source-drain resistance of the FET of the variable impedance circuit 18 is lowered. By means of such change of the source-drain resistance, the coupling impedance 2 is controlled so that the output on the output terminal 81 rises to the predetermined value. By means of such feedback operation, the voltage of the antenna 4 is adjusted to the voltage of the input side of the coupling impedance 2.In this circuit, the integration circuit or the low pass filter circuit 17 is provided in order that the controlling, i.e. changing of the coupling impedance 2, is not carried out when a relatively quick change of the voltage is produced at the antenna 4 by means of detection of an intruder. Therefore, the integration circuit or the low pass filter circuit 17 is designed in such a manner as not to issue an output signal when the change of voltage is so quick that it is caused by motion of the human body. That is, the loop responds only very slowly, so that intrusion detection signals are not extinguished by the feedback action.
Figure 19(d) is a circuit diagram showing in more detail the coupling impedance shown in Figure 19(c). The circuit of Figure 19(d) corresponds to the coupling impedance 2 of Figure 8, which is connected between the oscillator 1 and the antenna 4 of Figure 8. The integraton circuit 17 comprises a known operational amplifier, and the variable impedance element 18 comprises an FET (FET 1). The impedance control circuit 16 has a variable resistor VR18 for manual adjustment of the optimum point of the impedance control.
Figure 19(e) shows another example of a coupling impedance 2 having an automatic adjusting function.
This example has several capacitors Ca, Cb, Cc, Cd, Ce, Cf, Cg and Ch connected in common at one end thereof and connected at their other ends to an analog switch (multiplexer) 181, which is connected to the oscillator 1. The analog switch 181 is connected to a 8-bitA/D converter 180. The circuit also comprises an integration circuit 17, an impedance control circuit 16 and an amplifier 182 which applies an output to the 8-bit A/D converter 180. In this example, the analog swich 181 switches the capacitors in 28 = 256 steps of capacitance by means of combination of the capacitors and adjusts the coupling capacitance to such a suitable vaue that the antenna voltage is about half of the voltage produced by the oscillator 1.
By means of the above-mentioned feedback circuit loop containing the variable impedance 2, the high frequency voltage fed from the oscillator 1 to the antenna 4 is adjusted to a highest value irrespective of variation of the capacitance CO of the antenna to ground, that is, irrespective of variations of the length, height and number of the antenna to be connected to the coupling impedance. Therefore, it is very easy to install the system.
CLAIIS 1. An intrusion warning system for indicating the presence of an intruder in a given area, the system comprising:
an antenna provided around said area and insulated from the ground;
an oscillator for feeding an AC signal to the antenna;
a coupling impedance means connected between an output terminal of the oscillator and the antenna; and
a signal processing means for producing an output signal in response to a change to beyond a predetermined level of the voltage of the AC signal on the antenna.
2. An intrusion warning system according to claim 1, wherein the oscillator comprises
a frequency-switchable oscillation circuit which switches its oscillation frequency in response to a control signal applied thereto, and
a beat detection cicuit operative to detect a beat between the output frequency of the oscillator and harmonics of an A.C. power supply for producing said control signal to cause switching of the oscillation frequency in response to the occurence of a beat signal of an amplitude in excess of a predetermined level.
3. An intrusion warning system according to claim 2, wherein the frequency-switchable oscillation circuit is switchable to oscillate at a first frequency f01 or at a second frequency fo2, f01 and f02 having the relationship I f02 - fro11 = nfAc + Af, where:
n is an arbitrary positive integer,
fAc is the frequency of an A.C. signal which produces a beat with the signal of the oscillator, and
Af is a frequency smaller than fAc.
4. An intrusion warning system according to claim 1, wherein:
**WARNING** end of DESC field may overlap start of CLMS **.
Claims (12)
1. An intrusion warning system for indicating the presence of an intruder in a given area, the system comprising:
an antenna provided around said area and insulated from the ground;
an oscillator for feeding an AC signal to the antenna;
a coupling impedance means connected between an output terminal of the oscillator and the antenna; and
a signal processing means for producing an output signal in response to a change to beyond a predetermined level of the voltage of the AC signal on the antenna.
2. An intrusion warning system according to claim 1, wherein the oscillator comprises
a frequency-switchable oscillation circuit which switches its oscillation frequency in response to a control signal applied thereto, and
a beat detection cicuit operative to detect a beat between the output frequency of the oscillator and harmonics of an A.C. power supply for producing said control signal to cause switching of the oscillation frequency in response to the occurence of a beat signal of an amplitude in excess of a predetermined level.
3. An intrusion warning system according to claim 2, wherein the frequency-switchable oscillation circuit is switchable to oscillate at a first frequency f01 or at a second frequency fo2, f01 and f02 having the relationship I f02 - fro11 = nfAc + Af, where:
n is an arbitrary positive integer,
fAc is the frequency of an A.C. signal which produces a beat with the signal of the oscillator, and
Af is a frequency smaller than fAc.
4. An intrusion warning system according to claim 1, wherein:
the oscillator comprises a first oscillation circuit of a frequency f01 and a second oscillation circuit of a frequency f02, f01 and f02 having the relationship If02 - f01 = nfc + Af, where
n is an arbitrary positive integer,
fAc is the frequency of an AC signal which produces a beat with the signal of the oscillator, and
Af is a frequency smaller than fAC; and
the signal processing means comprises
a signal separation means for separating a first signal of the frequency f01 and a second signal of the frequency fo2, a first signal processing part and a second signal processing part, and
an output circuit which issues an output signal only when both the first and second signal processing parts issue their output signals.
5. An intrusion warning system according to any one of the preceding claims, which comprises
a second antenna disposed parallel with the said antenna and connected to be fed by the oscillator with the AC signal,
a second coupling impedance means connected between the output terminal of the oscillator and the second antenna, and
an order detection circuit for detecting the order of occurrence of voltage changes on the first-mentioned and the second antennae.
6. An intrusion warning system according to any of the preceding claims, where
the antenna is shaped in a saw-tooth waveform, and
the signal processing means comprises a differentiator for differentiating said change of voltage of the antenna thereby to produce a direction signal in response to the polarity of an output signal of the differentiator.
7. An intrusion warning system according to any one of the preceding claims, which comprises an antenna holder pole of an insulative substance and having a cap, the cap being shaped as a bottomless cone,
made of a conductive substance, having an antenna holding means at the top and being mounted on the
pole by fixing the top of the pole inside a top end part of the cap.
8. An intrusion warning system according to claim 7, wherein the pole has a substantially horizontal disc in a space enclosed by the cap.
9. An intrusion warning system according to any one of the preceding claims, wherein the coupling impedance means comprises means to vary the impedance for an optimum detection sensitivity.
10. An intrusion warning system according to claim 9, wherein the coupling impedance means is a voltage-controlled impedance circuit arranged to be controlled by the output signal of the signal processing
means.
11. An intrusion warning system according to claim 10, wherein the coupling impedance is arranged to
be controlled to such a value that the voltage fed to the antenna is substantially equal to 50% of the voltage fed from the oscillator to the coupling impedance means.
12. An intrusion warning system substantially as herein described with reference to Figures 3(a) to 4(c),
Figures 5 to 8, Figures 9 and 10, Figures 11 to 13, Figures 14 to 16, Figures 17(a) and 17(b), Figure 18, Figures
19(c) and 19(d) or Figure 19(e) of the accompanying drawings.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP333080A JPS56101294A (en) | 1980-01-15 | 1980-01-15 | Electric field type human body detector |
| JP4232480A JPS56140487A (en) | 1980-03-31 | 1980-03-31 | Electric field type human body detector |
| JP55168918A JPS603625B2 (en) | 1980-11-28 | 1980-11-28 | Electric field human body detector |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB2069206A true GB2069206A (en) | 1981-08-19 |
| GB2069206B GB2069206B (en) | 1984-07-11 |
Family
ID=27275768
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8101157A Expired GB2069206B (en) | 1980-01-15 | 1981-01-15 | Instrusion warning systems |
Country Status (6)
| Country | Link |
|---|---|
| AU (1) | AU542678B2 (en) |
| DE (2) | DE3152533C2 (en) |
| FR (1) | FR2473764B1 (en) |
| GB (1) | GB2069206B (en) |
| IT (1) | IT1210603B (en) |
| SE (1) | SE450673B (en) |
Cited By (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4382252A (en) * | 1980-03-31 | 1983-05-03 | Matsushita Electric Works, Ltd. | Intrusion warning system |
| US4621258A (en) * | 1983-08-22 | 1986-11-04 | Campman James P | Proximity detecting apparatus |
| US4792804A (en) * | 1986-05-02 | 1988-12-20 | Dei-Dispositivi Elettronici Industriali Di Rubechini Roberto | Apparatus for detecting a body in motion on the ground of a protected area |
| GB2279757A (en) * | 1990-11-16 | 1995-01-11 | Moonstone Technology Ltd | Device for determining the presence and/or characteristics of an object or a substance |
| WO1995012185A1 (en) * | 1993-10-29 | 1995-05-04 | Hansson Goeran | Capacitive detector device and alarm system |
| WO1997012174A1 (en) * | 1995-09-25 | 1997-04-03 | Soerensen Joern | A method and a device for sensing the distance between a first object and a second object |
| GB2368176A (en) * | 2000-08-03 | 2002-04-24 | John Christopher Rees | Proximity sensor employing a flexible capacitive sensing element |
| WO2005022174A1 (en) * | 2003-08-27 | 2005-03-10 | Martec Serpe-Iesm (Sa) | System for detecting and locating faults in an electric fence |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3439015A1 (en) * | 1984-10-25 | 1986-04-30 | Horizont Gerätewerk GmbH, 3540 Korbach | ELECTRIC FENCE |
| ITTO980452A1 (en) * | 1998-05-26 | 1999-11-26 | Elvis Sas Di Zannier Gian Carl | DEVICE AND METHOD OF DETECTION OF THE PRESENCE OF THE HUMAN BODY. |
| AT512650B1 (en) * | 2012-07-06 | 2013-10-15 | Abatec Group Ag | Truck anti-theft device by means of a tariff line |
| DE102018124389A1 (en) * | 2018-10-02 | 2020-04-02 | Livisi Gmbh | Method and device for recognizing a person in a room |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2421771A (en) * | 1942-07-17 | 1947-06-10 | Glenn H Browning | Approach protective system |
| US3230518A (en) * | 1961-03-20 | 1966-01-18 | American District Telegraph Co | Method of detecting intruders and intruder detection apparatus of the capacity-type utilizing balanced asymmetric fields |
| US3462755A (en) * | 1966-04-26 | 1969-08-19 | Mosler Research Products Inc | Capacity alarm |
| GB1320153A (en) * | 1969-06-26 | 1973-06-13 | Brown Y | Alarm systems |
| US3697971A (en) * | 1970-12-30 | 1972-10-10 | Siegfried Domin | Alarm system |
| US3829850A (en) * | 1971-12-17 | 1974-08-13 | Tyco Laboratories Inc | Proximity detector |
| US4064499A (en) * | 1975-09-12 | 1977-12-20 | Stellar Systems, Inc. | Intrusion warning system utilizing an electric field |
-
1981
- 1981-01-14 DE DE3152533A patent/DE3152533C2/en not_active Expired
- 1981-01-14 FR FR8100556A patent/FR2473764B1/en not_active Expired
- 1981-01-14 DE DE3100936A patent/DE3100936C2/en not_active Expired
- 1981-01-14 SE SE8100184A patent/SE450673B/en not_active IP Right Cessation
- 1981-01-14 IT IT8167033A patent/IT1210603B/en active
- 1981-01-15 AU AU66240/81A patent/AU542678B2/en not_active Ceased
- 1981-01-15 GB GB8101157A patent/GB2069206B/en not_active Expired
Cited By (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4382252A (en) * | 1980-03-31 | 1983-05-03 | Matsushita Electric Works, Ltd. | Intrusion warning system |
| US4621258A (en) * | 1983-08-22 | 1986-11-04 | Campman James P | Proximity detecting apparatus |
| US4792804A (en) * | 1986-05-02 | 1988-12-20 | Dei-Dispositivi Elettronici Industriali Di Rubechini Roberto | Apparatus for detecting a body in motion on the ground of a protected area |
| GB2279757A (en) * | 1990-11-16 | 1995-01-11 | Moonstone Technology Ltd | Device for determining the presence and/or characteristics of an object or a substance |
| GB2279757B (en) * | 1990-11-16 | 1995-06-07 | Moonstone Technology Ltd | Device for determining the presence and/or characteristics of an object or a substance |
| WO1995012185A1 (en) * | 1993-10-29 | 1995-05-04 | Hansson Goeran | Capacitive detector device and alarm system |
| US5764145A (en) * | 1993-10-29 | 1998-06-09 | Hansson; Goran | Capacitive detector device and alarm system |
| WO1997012174A1 (en) * | 1995-09-25 | 1997-04-03 | Soerensen Joern | A method and a device for sensing the distance between a first object and a second object |
| GB2368176A (en) * | 2000-08-03 | 2002-04-24 | John Christopher Rees | Proximity sensor employing a flexible capacitive sensing element |
| WO2005022174A1 (en) * | 2003-08-27 | 2005-03-10 | Martec Serpe-Iesm (Sa) | System for detecting and locating faults in an electric fence |
Also Published As
| Publication number | Publication date |
|---|---|
| IT1210603B (en) | 1989-09-14 |
| SE450673B (en) | 1987-07-13 |
| DE3100936C2 (en) | 1985-10-31 |
| SE8100184L (en) | 1981-07-16 |
| FR2473764B1 (en) | 1985-08-09 |
| IT8167033A0 (en) | 1981-01-14 |
| GB2069206B (en) | 1984-07-11 |
| AU6624081A (en) | 1981-07-30 |
| DE3100936A1 (en) | 1981-12-03 |
| DE3152533C2 (en) | 1984-06-07 |
| FR2473764A1 (en) | 1981-07-17 |
| AU542678B2 (en) | 1985-03-07 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| 746 | Register noted 'licences of right' (sect. 46/1977) |
Effective date: 19950619 |
|
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 19970115 |