JPS6118237B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a glass plate breakage detection device that detects vibrations of a glass plate that occur when a glass plate is damaged or broken, and can notify that a glass plate has been broken. It is. In more detail, we analyzed the vibration of a glass plate caused by the impact of an object, and analyzed the combination of high-frequency vibrations of 100KHz or more and low-frequency vibrations of 50KHz or less that are characteristic of glass plates being damaged or broken. The object of the present invention is to provide a device that operates as a result of non-destructive vibration caused by other non-destructive causes, such as collisions with sand, pebbles, metal objects, etc. Hereinafter, the present invention will be explained based on illustrated embodiments. FIG. 1 is a block diagram of this embodiment. In the figure, 1 is a detector for detecting vibrations of the glass plate to detect breakage. 2 is a resonant circuit that resonates at a predetermined high frequency of 100 KHz or more from the detector 1. Reference numeral 3 denotes an amplifier circuit that detects and amplifies the high frequency alternating current signal of a predetermined level or higher from the resonant circuit 2. Reference numeral 4 denotes a signal holding circuit that holds the level of the output signal of the amplifier circuit 3 for a predetermined period of time, and has the function of keeping the signal close to the same level for a certain period of time even after the input signal has ceased. 5 is a low-pass filter that allows vibration components of 50 KHz or less from the detector 1 to pass through. 6 is an AND circuit that generates an output signal by logically multiplying the output signal from the signal holding circuit 4 and the output signal from the low-pass filter 5 at a predetermined level or higher;
This output generation circuit is driven by the output signal of the AND circuit 6 and generates a signal for operating an alarm device 8 such as a lamp, buzzer, or bell. In addition,
9 is a protection circuit, and 10 is a power supply.

FIG. 2 shows a specific embodiment of the present invention in which each block of FIG. 1 is embodied. In the same figure,
P is a piezoelectric element for converting the mechanical vibration of the glass plate into an electric signal, and in actual use, it is attached to the glass plate via, for example, a metal plate base.

A capacitor C ₁ and a fixed inductor L ₁ are connected in series to the piezoelectric element to cut out low frequency components and form a series resonant circuit. The NPN transistor _Q1 detects and amplifies the resonance signal at both ends of the fixed inductor _L1 , and its amplification degree and input impedance are adjusted by the feedback resistor _R2 . resistance
R ₃ , R ₄ , R ₅ , a capacitor C ₂ , and a PNP type transistor Q ₂ constitute a signal holding circuit 4, and one end of the capacitor C ₂ is connected to the + power supply line, and the collector of the transistor Q ₁ It is charged in a short time by a pulsed conductive signal from the
Furthermore, since this charging voltage is applied to the base of transistor _Q2 , the emitter and collector become conductive, and current flows through resistor _R5 . In this case, when the current amplification factor of transistor Q ₂ is large enough and in saturation, resistor R ₅
The voltage across the capacitor C is approximately equal to the voltage across the capacitor _C2 . Therefore, the base input impedance of transistor Q ₂ becomes very high, and the collector current of transistor Q ₂ corresponding to the voltage of capacitor C ₂ can be maintained for a sufficiently long time.
The AND circuit 6 uses a junction field effect transistor (hereinafter referred to as FET) Q ₃ , the source electrode S is grounded, and this is realized by the presence or absence of drain current and gate voltage. That is, when the gate voltage is zero or positive, the drain current from the signal holding circuit 4 is characteristically in a conductive state, and no voltage appears at the drain electrode D. However, when a negative voltage is applied to the gate electrode G, the cut-off state occurs, and the output signal of the signal holding circuit 4 is transferred to a silicon-controlled rectifying element (hereinafter referred to as a thyristor) constituting the output generating circuit 7 at the next stage. It is guided to the gate electrode and conducts between the anode electrode and the cathode electrode.

The reason for using FETQ ₃ in the AND circuit 6 is as follows.

The signal component of 50KHz or less obtained at the same time when the glass plate is broken, that is, when the element resonates, has a voltage level of about 1V to 2V, but in addition to having a very high output impedance, there is a roll pass due to R ₁ and R ₄ . Since a filter is inserted, an FET is inevitably set as a voltage control element.

Next, the low-pass filter 5 includes a level adjustment variable resistor VR ₁ and a resistor R ₁ connected to both ends of the piezoelectric element P.
and capacitor C ₄ , R ₁ and C ₄
The cutoff frequency is 50KHz.

In this device, whether or not to operate the alarm 8 depends on whether the thyristor _Q4 is conductive or non-conductive.

The power consumed by this device is almost zero in a no-signal state, and can be designed to have a very small value even in an operating state. This is because a thyristor (silicon-controlled rectifier) is used as the output generation circuit, and since the thyristor _Q4 is used, it has a self-holding characteristic that allows the output to continue.

A piezoelectric element for detecting vibrations in a glass plate is
A material with a large electromechanical coupling coefficient K _p and a large dielectric constant is desirable, and in this example, "PCM-80" manufactured by Matsushita Electronic Components Co., Ltd. was used. Also,
The characteristics of this piezoelectric element are closely related to the resonant circuit 2 and have a large influence on the performance of the resonant circuit 2. That is, the resonant frequency of the resonant circuit 2, which is set to a predetermined high-frequency vibration frequency, is also made to match the resonant frequency of the piezoelectric element itself (in the case of a disc-shaped element, the contour resonant frequency in the radial direction).

The reason why the resonant frequency of the resonant circuit is made to match the resonant frequency of the piezoelectric element in this way is as follows. Transistor Q ₁ must be operated in an unbiased state using only the energy of the piezoelectric element itself. In other words, the base voltage at which transistor _Q1 turns on is approximately 0.7V, and it is necessary to raise the output voltage to this voltage without an active amplifier. This is because the detector itself is a switch and power cannot be wasted.

The equivalent circuit of a piezoelectric element when it resonates is basically a series resonant circuit of reactance L, capacitance C, and resistance R, and the output impedance is extremely small, so the energy that can be extracted can reach its maximum at this frequency. . Therefore, if the resonant frequency of the series resonant circuit of the resonant circuit consisting of C ₁ and L ₁ matches this frequency, the voltage across L ₁ will be maximum.

In fact, if you do not configure it like this, the diameter will be 10 mm.
It is difficult to operate a transistor with a signal of 100KHz or higher using a piezoelectric element of about 100KHz.

Here, if the above resonant frequency is r, then r
is given by r=N _p /D [where N _p is the frequency constant of the piezoelectric element (Hz・m) and D is the diameter of the piezoelectric element (m)], but since one side of the piezoelectric element is bonded, the above The electromechanical coupling coefficient K _p changes somewhat,
The actual resonant frequency will increase by several percent.

A piezoelectric element characteristically has a very small equivalent impedance at this resonant frequency. Therefore, at this time, the Q of the resonant circuit 2 becomes very large, and as a result, a large output is obtained at both ends of the fixed inductor _L1 , and high frequency selectivity is obtained. However, there are various other types of high gain filters that have the resonance characteristics of these piezoelectric elements and are composed of L and C, and are not necessarily limited to the circuit configuration described above. Furthermore, if the piezoelectric element has a large interelectrode capacitance and a sufficiently small impedance at high frequencies, there is no need to use resonance. The properties of a piezoelectric element at sufficiently low frequencies depend on the value of the load impedance across it. That is, the output impedance of the piezoelectric element at low frequencies is almost only the capacitance between its electrodes, and the load resistor connected thereto constitutes a high-pass filter. Therefore, in the circuit configuration of this embodiment, the roll pass filter 5 of 50 KHz or less consisting of VR ₁ , R ₁ , and C ₄ has a function as a band pass filter.

In the circuit configuration of this embodiment, if the signal detected by the piezoelectric element P contains a high frequency component of 100 KHz or more that is characteristic of a destructive signal, the L ₁ ,
It is separated by the resonant circuit 2 consisting of C ₁ and amplified to a required level by the transistor Q ₁ at the same time as detection, and then held as the collector current of the transistor Q ₂ for a certain period of time. This is to prevent a synchronization error between the two signals in the AND circuit 6 due to a time difference due to a difference in the propagation speed of the low-frequency vibration and high-frequency vibration propagating through the glass plate, and a difference in duration between the two. That is, this is due to the phenomenon that high frequency components due to general destruction are detected faster than low frequency components and are very short in time. On the other hand, a level adjusting device including a piezoelectric element P
A low frequency signal (1KHz to 50KHz in the example) passed through a band pass filter which is finally constituted by a roll pass filter 5 consisting of VR ₁ , R ₁ and C ₄ .
is applied to the gate electrode G of FET Q ₃ , and a negative voltage signal higher than the gate cutoff voltage value of Q ₃ causes a cut-off state between the drain electrode D and the source electrode S, and the holding current flows to the gate electrode of thyristor Q ₄ . be guided. Therefore, if this is at a level above the sensitive value, thyristor _Q4 becomes conductive;
Activate the alarm 8.

In this case, if the signal detected by the piezoelectric element P does not contain the above-mentioned high frequency components, or if the low frequency components are weak, the logic in the AND circuit will not hold, and therefore the thyristor
Q ₄ , so it is clear that the alarm 8 is not activated.

Note that the negative voltage signal applied to FETQ ₃ is not a DC signal but an AC signal directly output from the piezoelectric element, and the negative voltage signal applied to FETQ 3 is a negative half cycle of a level that can operate FETQ ₃ . There is an instantaneous cut-off between the current and the source, and the output current of the signal holding circuit is applied in pulses to the gate of thyristor _Q4 .

The resistor R ₁ and capacitor C ₄ are unrelated to this effect and function as a pure roll-pass filter.

As described above, the detection section is a combination of a resonant circuit and a roll-pass filter, and this is for the following reasons.

From the principle of destructive detection, the purpose is achieved when a signal component of 100 KHz or higher and a signal component of 50 KHz or lower are simultaneously established.

Therefore, instead of the resonant circuit, a circuit having a roll-pass filter function of 100 KHz or more may be used.

However, as described above, it is not practical to use these circuits because they are non-power consuming.

Therefore, the result is limited to a series resonant circuit made up of L ₁ and C ₁ . Also, the resonant circuit referred to here is a series resonant circuit. That is, this is because the resonant circuit operates and low frequency output is also required at the same time. C ₁ is useful for cutting low frequency components.

Note that the diode D ₁ connected in parallel to the thyristor Q ₄ is intended to protect the circuit against reverse polarity connection, and the capacitor C ₃ can serve as a high frequency power source for the noise limiter and the circuit. The holding current (minimum current value to maintain the turned-on state) of thyristor _Q4 in its operating state is:
It is desirable that the value be sufficiently small in relation to the load impedance of connected external alarms, etc.
For this, the gate electrode of thyristor _Q4 and the FET
It is effective to insert a resistor between the thyristor Q4 and the drain electrode D to limit the current flowing out from the gate electrode when the thyristor _Q4 is in a conductive state.

As explained in detail above, the glass plate breakage detection device of the present invention operates only when the glass plate is damaged or broken, can issue an alarm, has high sensitivity, and is highly reliable against malfunctions. Because of its high resistance, it is suitable for various security devices such as crime prevention. In addition, especially when the present invention is configured as illustrated in Fig. 2, the power supply circuit can also be used as a circuit for feeding power to the alarm, making it possible to centrally manage a large number of devices connected in parallel. It is also advantageous in that it is easy to wire, does not require special cables such as shielded wires, and saves power.

[Brief explanation of the drawing]

FIG. 1 is a basic block diagram of one embodiment of the invention, and FIG. 2 is a circuit diagram showing a specific embodiment of the invention. 1...Detector, 2...Resonance circuit, 3...Amplification circuit, 4...Signal holding circuit, 5...Roll pass filter, 6...AND circuit, 7...Output generation circuit, 8...Alarm device , 10...power supply, P...piezoelectric element.

Claims (1)

[Claims] 1. A detector including a piezoelectric element attached to a glass plate to detect breakage, and connected to the detector so that the output signal of the detector is input, and
A resonant circuit that resonates at a predetermined frequency of 100KHz or more, an amplifier circuit that amplifies a signal of a predetermined level or higher from the resonant circuit, a signal holding circuit that holds the output signal of the amplification circuit for a predetermined time, and the output of the detector. a low-pass filter connected to the detector so that the signal is input and extracts a signal of a predetermined frequency component of 50 KHz or less; an output signal of a predetermined level or higher from the low-pass filter; and a held output signal of the signal holding circuit. and an output generating circuit that generates a signal for operating an alarm means in response to the output signal of the AND circuit, and the resonant circuit includes: The resonant frequency is configured to match the resonant frequency of the piezoelectric element of the detector,
The AND circuit includes a field effect transistor whose drain electrode and source electrode are connected between the output end of the signal holding circuit and one power supply line, and whose gate electrode is connected to the output end of the low-pass filter, The output generating circuit includes a silicon-controlled rectifier whose anode electrode and cathode electrode are connected between the feed lines and whose gate electrode is connected to the drain electrode of the field-effect transistor, and the anode of the silicon-controlled rectifier A glass plate breakage detection device characterized in that an alarm means is connected between an electrode and a cathode electrode.