DE3243960A1 - Circuit arrangement for indicating breakage of a glass pane - Google Patents

Abstract

In order to prevent false alarms, caused by the impact of solid objects against the glass pane, and/or environmentally-dependent attenuation effects which lead to an unacceptable reduction in the monitoring voltage in active glass-breakage reporting systems, the voltage level is monitored at two points in time after a disturbance or the breakage of a glass pane for the presence of a new level value, and the unacceptable reduction in the monitoring voltage resulting from environmentally-dependent pane attenuations which occur is prevented by the frequency change of the monitoring voltage below a predetermined voltage value.

Description

Circuit arrangement for displaying broken glass

The invention relates to a circuit arrangement for indicating broken glass for a glass pane monitoring device with the help of (active) in the pane introduced ultrasonic waves, which are taken back from the disc by a receiver and converted into alternating voltages.

There are already (active) methods known, which with the help an ultrasound transducer to form elasticity of the glass pane starting from one point Excite vibrations (bending waves) and in an ultrasonic receiver - mostly diametrically to the encoder arranged on the disc - these oscillations in alternating voltages are more appropriate Reshape frequency. The voltage level at the receiver is monitored and its Change in the event of a broken pane evaluated for alarm display, as on the transmission ge from the transmitter to the receiver, the ultrasonic vibrations are exposed to numerous influences that are noticeable in changes in the reception voltage, not only the Disk brews displayed. So-called false alarms are e.g. due to mechanical stress, Contact, wetting, coating, change in frame influences. But hits against the window can also lead to false alarms.

To eliminate these disadvantages, solutions have become known which require several criteria to sound an alarm in the event of glass breakage.

In such processes, e.g. the ultrasonic vibrations are amplitude and monitored in terms of frequency. Another method evaluates the alarm in the event of a broken pane In addition to the change in voltage level, the occurrence of sound and ultrasonic frequencies that are typical of breakage the end. With this method, interference triggers can largely be eliminated The security of breakage detection depends on the generation of sufficiently high breakage sound capacities dependent, if e.g.

a trigger criterion is not on the active transmission path from the receiver is removed.

In the case of environmental ultrasc @ all level vaporization in the glass pane receive voltage fluctuations occur that lead to an alarm, if specified The minimum voltage values are not reached.

The cause of this phenomenon is the formation of standing waves connected to the disc when the receiver is temporarily in a trough of waves with a very low voltage level. In order to raise the alarm in such cases avoid, a process has become belannt, which two ultrasonic receivers used, the BEZW at a distance of a quarter of the ultrasonic wavelength. one odd multiples thereof are arranged on the disk.

If the receivers are combined in a housing with a fixed distance, so this method can only be effective with a certain glass thickness of the pane, because the wavelength of the bending waves forming on the disk is the square root is proportional to the thickness of the pane divided by the ultrasonic frequency. For example, the wavelength of the flexible wave in a 10 mm thick pane of glass is 1.6 times larger than in a 4 mm thick pane of glass with the same transmission frequency.

Object of the invention. is to display circuitry von Glascheibenbru (h to indicate what the stated causes of false alarms excludes the reporting criteria from the active transmission path and an easy one Verifiability of the functional reliability of the arrangement enables.

The circuit arrangement according to the invention eliminates the causes mentioned for a false positive. As is known, the ultrasonic oscillation generated by the encoder arrives on direct goat and varied @ at the edges of the disc reflected to the receiver. The receiving voltage is made up of a direct component and the reflection components together and is constant for stable conditions of the arrangement on the disk. Every global disturbance leads to changes in the receiving voltage via phase changes in the components. The circuit arrangement admittedly absorbs all changes in the received voltage, giving an alarm but only takes place if the receiving voltage changes gradually and the changed Value still maintains. This evaluation corresponds to a change in contour (Breakage) of the glass pane.

According to the invention, only the high-frequency voltage level is used as the triggering criterion is used, the absolute value and change behavior of which are controlled. Environmental disturbances, which are in slow Receiving voltage will act already regulated in the high-frequency amplifier. Cause blows to the disc rapid voltage changes, which are called alternating changes eventually in the old Skip voltage value.

To avoid standing waves on the pane of glass, as at the beginning described to avoid a Feiilalarm is advantageous in further training of the invention, the circuit arrangement is provided with a device that when Falling below a specified voltage level that has not yet led to the alarm, linear with the voltage value that is undershot that which is introduced into the glass egg pane Frequency of the ultrasonic wave changes. Frequency and voltage changes are in one Control loop linked so that the occurrence is smaller, below the specified minimum voltage decreasing input level is avoided.

In a further development of the invention, there is a voltage level jump in the encoder, triggered from a central point, to check the functionality used, in that a test alarm can be generated with this measure.

The circuit arrangement according to the invention is described below, The following block diagram has been expanded to include schematic circuit details is when it is necessary to understand the functional relationships.

The ultrasonic transmitter (2) and the receiver are on the glass pane (1) (4), usually arranged diagonally opposite one another. The circuit of the ultrasonic transducer (2) is shown schematically in block (3), the circuit of the receiver (4) in Block (5) drawn in simplified form. The ultrasonic frequency of the encoder is after two viewpoints selected. The wavelength associated with the frequency should be as small as possible in order to avoid significant phase changes in the received voltage To obtain breakage of the disc, which result in changes in stress. on the other hand a significant proportion of flexural waves should develop in thick panes, as the thickness of the pane increases, the sound is transmitted more and more in longitudinal shape. With a frequency of 180 kHz, slices up to Monitor 10 mm thickness. Since only the carrier frequency is evaluated, the receiver can be designed to be very narrow-band, in the present case e.g. with a bandwidth of 30 kHz (3 db).

The hole frequency voltage emitted by the receiver (4) (5) arrives to the cone amplifier (6), which has a peak voltage of about 1.5 to 3 V at the output, which is fed to the rectifier (7). Arises at the emitter of the rectifier the DC voltage proportional to the AC voltage with a residual ripple on RC element (7.1) of less than 1% of the HF voltage. This DC voltage is called the control voltage, Delayed in time by the RC element (6.1), fed to the amplifier (6). The time constant of the RC element (6.1) is about T = 30 seconds, which means that long-term changes (temperature and aging).

With this measure, the circuit arrangement can also be connected to the The pane sizes and glass that occur in practice are strengthened without any need for adjustment adjust.

The voltage is also taken from the emitter of the rectifier (7), which increases the on-resistance of the transistor (7.2) at level values below 1 volt can be larger, so that the capacitance diode (3.1) in the ultrasonic transducer (2) (3) receives higher bias values and thus changes the encoder frequency when the Receiver (4) gets into a voltage sink with extremely low receiving voltages.

The DC voltage of the rectifier (7) is present for evaluation two timers (8.1) and (11.1) with different time constants. Timer (8.1) is based on the time constant T = 0.1 sec., Time element (11.1) is based on the constant T = 1 sec. Line voltage change occurring at the timing element (8.1) amplified about 200 times in the amplifier (8) and solves the monostable multivibrator (9) which supplies a voltage pulse for 75 nilliseconds in an unstable state, the trailing edge of which transistor (9.1) is briefly switched to the conductive state. The resulting otromimpuls via the diode (9.2) can be the monostable multivibrator (10) only switch to the unstable state when the transistor (8.2) is in Amplifier (8) has a high forward resistance. The tilting stage (10) switches then for 1 second in the unstable state, whereby the diode (10.2) is connected to the collector of the transistor (10.1) operating voltage applied to the timing element (11.2) during this time can not take effect. In the stable state of the flip-flop (10) is the forward resistance of the transistor (10.1) is very small and thus the capacitor of the timing element (11.2) short-circuited via the diode (10.2), thereby also the switching step (12) is blocked.

A voltage change occurring at the output of the rectifier stage (7) is also effective at the timing element (11.1) and about 200 times in the push-pull amplifier (11) reinforced. This voltage change can affect the capacitor of the timing element (11.2), as previously described, only charge when the tilting stage (10) is on for 1 second is in the unstable state. During this time I had a voltage integration on Timing element (11.2) has taken place up to the switching threshold of Stufc (12), then an alarm is triggered, the alarm relay (13) de-energized, the alarm contact (13.1) opens the Line of the plant.

The output voltage of the rectifier (7) will eventually also to the minimum and maximum value monitoring (14), which for level values below 0.3 volts and over 4 volts via the switching stage (12) triggers the alarm because either Sabotage measures led to the voltage dropping below the permissible range, or there is a component failure.

So that the circuit after switching on the operating voltage as a result the starting control process in the amplifier (6) cannot switch to alarm, an auxiliary switch-on stage (15) is provided which the switching stage for about 20 seconds (12) blocks until the control processes run at slow rates of change.

The function of the circuit arrangement is based on the voltage diagram understandable. The rectifier (7) provides a voltage in fault-free operation which corresponds to the level Uo. In the event of a malfunction, e.g. by a blow against the disk, the level Uo is a low-frequency, time-strongly damped alternating voltage Ust superimposed on both timing elements (8.1) and (11.1), these but cannot charge to the necessary threshold voltages for further switching operations initiate. With the voltage jump Ust, the flip-flop (9) was also in the unstable state and after 75 milliseconds over the pulse trailing edge the transistor (9.1) conducting, but the trigger stage (10) could not be triggered, because the transistor (8.2) in the amplifier (8) due to the missing £> storage voltage blocked the input of the flip-flop (10).

In the event of a broken pane, a different condition (! Given. Jumps in in such a case, the voltage level at the rectifier (7) at time to from Value Uo to value U1, then both timing elements (8.1) and 411.1) are in different Time lapses charged to full voltage values. The jump in tension from Uo to U1 pushes the stage (9) into the unstable state via the amplifier (8) and after 75 milliseconds the transistor (9.1) opens. The current can in this Trap via the diode (9.2) to the input of the trigger stage (10) because the transistor (8.2) as a result of the storage voltage present in the amplifier (8), in the not conductive state. As long as the flip-flop (10) is in the unstable state remains (1 second from time t1), the memory element (11.1) that is present, in the amplifier (11) about 200 times amplified voltage, the capacitor in the timing element (11.2) to the threshold voltage of stage (12), whereupon stage (12) the Alarm relay (13) drops out.

The described procedure of the glass breakage notification and interference blanking allows the functionality of the system to be checked very easily. This is the purpose of the '2ransSstor (3.2) in the ultrasonic transducer (3) (2). How schematic shown is the piezoelectric transducer in the transmitter (3) (2) to the output splitter of the transistor (3.3) connected. The transistor (3.2) can with positive control the base short-circuit a dune resistor, which is expediently done with a springso holder (3.4), which supplies the operating voltage to the base via a series resistor.

When you press the switch (3.4), the piezoelectric Ultrasonic frequency fed to the transducer by changing the resistance divider abruptly changed in the voltage value and thus the level behavior of a broken glass simulated. The switch (3.4) can, for example, be arranged at a central point (system center) will.

Claims (8)

Circuit arrangement for the display of glass pane breakage claims 1. Circuit arrangement for displaying broken glass with one on each Ultrasonic transmitter and ultrasonic receiver arranged on the monitoring disc, which the ultrasonic oscillation picked up from the disk in the receiver in alternating voltages converts and oversees its amplitude to identify a glass break, d a d u r c h. g e k e n n z C i c h n e t that a broken pane in the Receiver caused a change in the receiving voltage at least two time intervals t1 and t2 after the change time for the presence of the new voltage level is controlled, whereby an alarm is only given if at the time of change tl a timing element (8.1) with a small time constant that has the full storage voltage, which initiates the control time i) point t2 via a monostable multivibrator (10) and at this point in time t2 at a timing element (11.2) with a large time constant the full Memory voltage is available. 2. Circuit arrangement according to claim 1, d a d u r c h g e k e n n z e i c h n c -t that to rectify the output of the receiver, amplified High frequency voltage a transistor emitter rectifier with a low source resistance is used. 3. Circuit arrangement according to claim 1 and 2, d a d u r c h g e k e n n z e e c h n e t, since the monitoring voltage present at the rectifier (7) two timing elements are supplied, (8.1) and (11.1) with different time constants, where the term with the smaller constant (8.1) is the first control point in time t1 initiates regardless of the level of its storage voltage. 4. Circuit arrangement according to the preceding claims, d a d u r c h e k e n n n z e i c h n e t that the timing element (11.1) with the larger time constant charges a timing element (11.2) with the same time constant via an amplifier (11), whose charging process can only begin at time t1 when the timer (8.1) with the smaller time constant has the full charge voltage 5. Circuit arrangement according to the preceding claims, d a d u r c h g e n n n z e i c ii n e t, that when the monitoring voltage at the rectifier falls below a predetermined level (7) the frequency of the monitoring voltage is automatically changed to the extent that the predetermined level value can at least be maintained. 6. Circuit arrangement na.ch the preceding claims, d a d u r c h zur e k e n n z c i c h 1l e t that the frequency change by a varactor diode takes place, the bias of which a. Transistor (7.2) delivers. 7. Circuit arrangement according to the preceding claims, d a d u r c h g e k e n n z e 1 c h n e t that the bandwidth of the amplifier in the receiver (4) (5) and in the control amplifier (6) is narrow, preferably 30 kHz with a 3 db interval at the maximum value. 8. Circuit arrangement according to the preceding claims, d a d u Noted that the triggering of a test alarm for the evaluation the functionality of the circuit arrangement in the ultrasonic transducer (2) (3) Sound level jump achieved by short-circuiting a partial resistance in the output stage will.