Piezoelectric vibration sensor in a seismic detector. Vibrometer - a simple device for measuring vibration Wiring diagram of a digital vibration sensor

vibration detector

Such a device can detect any type of mechanical vibrations, can be used to solve various everyday problems. To achieve this sensor, we used small piezoelectric discs, which are contained in the buzzers. It will find its application in alarm systems or in security systems Service systems. The idea for this meeting was born from the frustration of some of the building's tenants, parking their car in their place, turned out too often in the morning with a body dented and, of course, without any -. or indications of the identity of the offender despite the fact, decided to shame the tenant of an unscrupulous dork purchasing space to perform their clumsy maneuvers at the expense of neighboring vehicles, they decided to install vibration-sensitive circuits on the board. So in the course of several nights they discovered that the dehorner of the unrepentant leaf was none other than the son of the tenant, a young driver, returning in the early hours of the disco, a little tipsy, having lost his sense of late Acquired the geometry of parking lots and especially probably not learned from responsibility to the detriment of others. The original anti-theft THIS vibration sensitive circuit can be used NOT only: To be notified immediately if someone hits your parked car or motorcycle, but if a tramp tries to force the door of your house. we will tell you what we used to service the detector (or sensor) to excite the vibration relay to control the pulpit: a siren or any other element that can be controlled by a relay. The small piezo disk inside the piezo buzzer is a small disk (3 and 4) for transmitting sound when applied to the acoustic frequency terminals. These small discs can also work in reverse, that is, if vibrated mechanically, can, at their terminals, collect a BF SIGNAL of 20 mV approximately. this function, Electrical Signal Receive via Vibration piezoelectric with US Capsules is used in the "pickup" (turntable heads) to control the sounds when their tip scans the groove of the disc. black We assure you in advance about that, : To get this little piezoelectric disc you will have to buy an expensive buzzer and then destroy it to extract the precious little disc: on. is it really available and only cheap? How to vibrate this small disc in THIS small vibrating disc, weld, on its face completely made of brass, hard wire, iron or brass, with a diameter of 2 mm and a length of 70 mm (3 and 4). Thereafter, insert the free end of the wire into a 3-pole terminal block, serving as a "counterweight" to transmit the vibrations detected to the piezoelectric disc. The electrical signal transmitted by this disk is taken from the side where the surface is completely white and, for this, it is necessary to weld the end of the copper wire connected to the inverting input of the operational amplifier IC 1-a through a 10 kΩ resistor R3 (1 and numbers 5). the opposite side, whose surface is made of brass, is connected to the non-inverting + IC1 connector-A, and is powered by a positive 6V voltage across the resistor terminals and R1 R2. Wiring diagram we have already said, the electrical signal generated by the oscillations charged on both sides of the piezoelectric disk is applied to the input contacts of the first operational amplifier IC 1-charge amplify approximately 100 times (Figure 1). The amplified output signal from pin 7 of IC1-A is rectified by the silicon diode DS1 and a DC voltage is used to charge the electrolytic capacitor C5 located at the inverting input of the second operational amplifier IC1-B. The non-inverting input of the same opposite IC1-B is connected through a resistor R8, R6 to a trimmer to control the sensitivity cursor. Whenever the piezoelectric disc receives vibration, the DL1 LED. connected to the output pin 1 of IC1-B lamps Lighting Impulse Between this indicator, through the capacitor C6, in pin 2 of IC2 integrated circuit NE555 mounting single vibrator. each input PIN 2 pulse of IC2 is taken to pin 3 of a positive voltage, the polarizing base of the NPN transistor TR2, puts IT in a conduction state, which energizes the relays connected to its collector. : When the relay is energized, the LED DL2, connected in parallel with the relay coil, lights up. the circuit is composed of resistors R12, R16, R17, C9 electrolytic capacitors and diodes DS2 , DS3, DS4, serves to avoid that whenever the relay releases, mechanical vibrations are detected by the piezoelectric disc, exciting again. the trimmer R14 connected to pins 6 and 7 is used to keep the relay energized from 2 seconds to 2 minutes. Transistor TR1, the collector connects to pin 4 of IC2 to keep reset provides the integrated circuit for about 10 seconds, every time, by us assembly is energized. This is necessary to avoid that the detector has control over before we could leave. and doors Closing the car All Can be powered by stabilized circuit 12 V. Figure 1:. vibration detector circuit on small piezoelectric disks, the signal generated by any mechanical vibration is taken and applied on two input pins of op-amp IC1-A (5 and 6 .) Figure 2: picture of ours. Vibration detector Figure 3: full copper side of a small disc, solder hard wire 2mm in diameter and 70mm in length, approx. Figure 4:. at the end of the wire a counterweight (terminal block) will be fixed. vibration sensor circuit components implementation. The small disk of the piezoelectric capsule is inserted into the slot near R3 soldering then On the "white" area of ​​the smallest disk, solder the end of the copper wire to remove the signal. Figure 5b Dimensional drawings of 1 double-sided printed circuit board with through-hole sensor plating. vibrations. Side Components Figure 5c: Dimensional drawings 1 PCB double sided with galvanized through SENSOR Vibration holes. . solder side PARTS LIST R1=10KW R2=10KW R3=10KW R4=1M R5=1.5KW R6=1KΩ Trimmer R7=2.2KW R8=10KW R9=1M R10=1MΩ R11 = 1 kΩ R12 = 10 kW R13 = 22 kW R14 = 1 M trimmer R15 = 10 kW R16 = 47 Ω R17 = 3.9 kW R18 = 10 kW R19 = 22 kW R20 = 47 kW R21 = 47 kW R22 = 1 kΩ C1 = 100 nF polyester C2 = 10 µF electrolytic C3 = 1.5 nF polyester C4 = 10 µF electrolytic C5 = 2 2 µF electrolytic C6 = 100 nF polyester C7 = 100 µF electrolytic C8 = 10 nF polyester C9 = 100 µF electrolytic C10 = 100 uF electrolytic C11 = 100 nF polyester DS1 = 1N4148 diode DS2 = 1N4148 diode DS3 = 1N4148 diode DS4 = 1N4148 diode DS5 = 1N4148 diode DS6 = 1N4007 diode DL1 = LED diode DL2 = LED diode TR1 = NPN BC547 BC53 TR2 = NPN 85 Integrated = IC2 = Integrated NE555 RELAY1 = Relay 12V 1RT Figure 6:. Photo of a Vibration SENSOR prototype AFTER soldering a small disk into a slot. circuit, we must also fix the end of the counterweight wire and for this we use a 3-pole terminal connector Figure 7: Pin outputs of two integrated circuits and LM358 NE555 if viewed from above and with the U-key left. Pinout of the BC547 transistor seen from below and the LED (long leg of the anode). , but another object will do, for example, a nut or "lead" a seal). practical implementation on PCB double sided plated through holes, it is necessary to mount all components as shown in Figure 5. We recommend starting with integrated circuit carriers IC1 and IC2 and after soldering all the pins, continue with the resistors, controlling their value well. left side of the PCB, insert a 1 kΩ trimmer R6. In the center, place the trimmer R14 to 1 MΩ. Then you can start to put on and weld the diodes DS1 to DS6 by guiding their ring with a wrench, as shown in Figure 5. After these components, mount the polyester capacitors and electrolytic capacitors, observing, of course, the polarity of the latter. insert and solder two transistors TR2 and TR1 without cutting their legs, directing them flat in a good way, always shown in Figure 5. at the end, insert and solder more and two terminals adjacent to it, and then insert two chips in: their sockets with their surcharge keyed U point in the right direction as shown in Figure 5. LM358 (IC1) surcharge keyed to the right and NE555 (IC2) body mark to the left (two-marker locators face) This device can be hidden in the car or in the house, us to go planned No enclosure (but you can provide one). In addition, can be inserted directly on the LEDs from the PCB polarity: their feet to complete the vibration detector, you just have to insert into the socket provided on the PCB near R3 piezoelectric disc and solder on both sides, as shown in Figure 8. on opposite side of the disk, the face of the "white" solder a thin copper wire going to the hole near R3 (Figure 5). When using enamel wire, remember before welding it, scratch the insulating layer of enamel with a knife or sandpaper, otherwise the solder will NOT accept contact and will NOT. do We decided to insert a piezoelectric disc directly into the circuit, but it can also provide also a separate circuit for one disc: you can then place this remote control sensor, for example, in the trunk of a car or in a door by fixing it with stained floors of any complexity. In order to bring the drive signal to the PCB, a small shielded cable can be used when the braid is connected to the trace to the non-inverting input of IC1-a and the core carrying the signal to the track from the input impedance R3. Setup and testing AFTER the installation is completed, it is necessary to adjust the R6 sensitivity trimmer and the trimmer delay, setting the time for the relay,. R14 you don't need any measuring instrument to do this:. a small screwdriver is enough to start, turn halfway CURSOR two and trimmers R6 R14 Complain about then put the vibration sensor on the table and supply power to 12V. the same time, DL2 show the excitement of the relay. If it doesn't, you just have to turn on the R6 trim cursor in such a way as to increase the sensitivity. If, however, the circuit was too sensitive, you must turn the trimmer in reverse. when the desired sensitivity is reached, you only need to adjust, with the slider R14, the excitation time of the alarm relay (for example, a siren is triggered). Therefore, the system is in your working condition.

What is this article about

Vibration sensor (vibrometer) - a device that allows you to determine the parameters of vibration phenomena. Vibrometers are most often used to determine:

1. Vibration velocity
2. vibration acceleration
3. Vibration

Simply put, if a vibrating object is considered a simple oscillator, then the vibrometer allows you to obtain information both about the basic parameters of its oscillations (frequency and amplitude), and, in some cases, to obtain a spectral characteristic of the oscillatory process.

Figure 1. Diagram of the vibration sensor.

The general scheme of the vibration sensor contains two main blocks (Figure 1): a vibration transducer (1) and an electronic processing unit (2). The functional purpose of the first block is the conversion of mechanical vibrations into an electrical signal. There are several conversion mechanisms:

• Piezoelectric
• Optic
• eddy current
• Induction

The conversion mechanism largely determines both the characteristics of the device and its cost.

The second block - an electronic processing unit - serves to "decode" the received signal. As a rule, there is an analog-to-digital converter at the input of such blocks, and the main part of the operations on the signal is already performed in digital form, which expands the functionality of the post-processing process, improves noise immunity and allows information to be output via an external interface.

When used in production, stationary vibrometers can be part of regulatory systems as feedback sensors; for this purpose, some models of vibrometers have an analog output signal (usually voltage).

To obtain a comprehensive characteristic of the vibration process, a spectrum analyzer can be added to the measuring system. If the spectrum analyzer is multichannel, it can serve as the basis for a distributed vibration diagnostics system containing more than one vibration sensor.

Currently, most vibrometers fall into one of two types:

1. Optical vibrometer
2. Piezoelectric vibrometer

Let's take a closer look at each type of sensor.

Optical vibrometer

The operation of an optical vibrometer, like ultrasonic displacement sensors, is based on the Doppler effect. The device usually contains a laser radiation source, a receiving optical circuit, and an electronic processing circuit (Figure 2). When radiation is reflected from a stationary object, the wavelength of the received beam does not differ from the true wavelength of the laser. If an object moves along the radiation axis, the wavelength of the reflected radiation shifts by a certain amount (Doppler effect), the value and sign of which carry information about the speed and direction of the object’s movement, and the interferometric scheme used as part of the receiving optical module makes it possible to determine this value. Thus, vibrations of the reflective surface modulate the frequency shift, and electronic processing of this modulation signal allows you to get the parameters of the vibrational vibrations.

Figure 2. Diagram of an optical vibrometer.

Despite the fact that optical vibrometers include a source of laser radiation, such devices are quite safe, since due to the high sensitivity of the receiving optical system, a very low optical power is sufficient for measurements.

One of the main advantages of optical vibrometers is that diagnostics with their help can be carried out without contact; when they are used in a stationary measuring complex, only a single focusing on the measured surface is required. In addition, devices of this type have high accuracy and speed, since they are devoid of moving parts. The disadvantages include a rather high price.

Piezoelectric vibrometer

As the name implies, the operation of this type of device is based on the piezoelectric effect - the phenomenon of the appearance of a potential difference on a piezocrystal during its mechanical deformation. The body of the vibrometer contains an inert body suspended on elastic elements containing a piezoelectric material (Figure 3). If the body of the device is attached to a vibrating surface, the elastic elements will register vibrations of an inert body that is not attached directly to the body, and therefore tends to maintain its original position. In general, in this configuration, a piezoelectric vibrometer is nothing more than an accelerometer, and it is often quite difficult to distinguish between these types of sensitive devices.

Figure 3. Diagram of a piezoelectric vibrometer.

An electrical signal from a piezocrystal, as a rule, is fed to an analog-to-digital converter, and its processing is carried out in digital form. In general, as in the case of an optical vibrometer, the main purpose of the receiving sensitive unit is to convert vibration into an electrical signal, and the nature of its further processing is determined by the parameters of the digital electronic circuit.

The main disadvantage of this class of devices is the need for the sensitive part to come into contact with the measured object, which is not always appropriate in production conditions. In addition, piezoelectric devices tend to have a narrower range of perceived frequencies, since they have a mechanical vibration transmission path, where the maximum frequency is determined by the inertness of the components.

The advantages of piezoelectric vibrometers include their relatively low cost, as well as a relatively simple device, which ensures reliability and resistance to external influences.

Of course, you can buy a security unit in the store. There are various devices on the market. But what if you don't want to overpay for different options. In addition, your hands grow from where you need. No problems!

You can assemble a completely acceptable option yourself. This car alarm has nothing superfluous: central lock control, remote control. But homemade will protect your car from penetration with the help of door and trunk limit switches. And also with the help of a shock-vibration sensor it will warn the owner about unscrewing, for example, wheels. By the way, did you know that it is much more difficult for an attacker to disable this kind of alarm. He doesn't know what you could put in there. In addition, in the absence of a key fob, the degree of protection increases many times over, since auto-crooks will not be able to read the code (after all, it is known that most hacks occur by this method).

Device diagram

Principle of operation is as follows. The signal from A1 of the vibration sensor goes to the amplifier, which is made on VT1, VT2 and controls the thyristor VS1. The base of the transistor VT2 also receives a signal from the limit switches of the doors, hood, trunk. A timer is assembled on transistors VT3, VT4, which controls the anode of the thyristor VS1. The VT3 base circuit uses a large capacitor C3. Due to this, when armed with a securely hidden toggle switch, C3 starts charging through the car's siren and a circuit of resistors R6, R7. In the process of charging the capacitor, VT3, VT4 will be closed, therefore, the thyristor VS1 is locked. Due to this, the circuit is armed with some delay, giving the driver time to leave the car and close the door.

After 20 seconds, the capacitor C3 gains capacity, VT3 opens and turns on the protection. Suppose there was an impact on the car or the opening of a door. Thyristor VS1 unlocks, starts charging C4 through VS1, VT4, R10. The thyristor is designed in such a way that it remains open during the passage of direct current. When the door is closed (signals stop), the alarm siren will notify the owner of the intrusion. If the sensors were triggered with the appearance of the owner, then during the charge of C4 (20 seconds), he will turn off the disguised toggle switch. If this is not done, then VT5, VT6 will open, relay KV1 will turn on, which in turn will connect the siren. In order not to disturb the neighbors and not to run to the car during false alarms, such as a truck passing by, this car alarm has an alarm time limit function. It operates in the following way. When contacts KV1 are closed and current flows through R6, R7, capacitor C3 is charged. After a short time, VT2, VT3, VS1, VT5, VT6 will close and the KV1 relay will turn off and arm again.

What details can be used to implement the schema. Requirements for them are not critical. Capacitors and resistors of any type, preferably small. Relay KV1 with an operating voltage of 12 volts and a coil current within 100 mA. The power contacts of the relay must withstand a current of 5 A. But it can be reduced to 0.5 A if an intermediate relay is used.

The vibration sensor A1 is not difficult to make yourself. It is made in the form of a coil with a steel core, from which a permanent magnet is fixed at a short distance on a flat spring. At the slightest impact on the car body, vibrations are transmitted through the spring to the magnet. That, in turn, will create an alternating magnetic field, which will induce an EMF in the coil. The latter, Ø10x15 mm in size, is wound on a steel core Ø3 mm. For winding, copper wire 0.06 ... 0.07 mm is used. A magnet with dimensions of 25x10x5 mm must be fixed to the spring with glue and thread. As which you can use the spring from the alarm clock. The length of the latter is selected within 60 - 80 mm. When assembling the shock sensor, care should be taken to ensure that the magnet can be positioned as close as possible to the side of the coil. The finished vibration sensor should be placed in space so that the magnet can oscillate perpendicular to the ground.

Homemade vibration sensor

Now the most important thing remains - to hide the toggle switch through which power is supplied to the circuit. This issue should be approached with no less responsibility. Since you have to use it all the time, well, the attacker should not detect it.

The basis of the sensor is a piezoelectric element from the sound emitter ЗП-2, ЗП-4 or ЗП-5. The general view of the sensor (from the side) is shown in Fig. 1a. The piezoelectric element 2 of one of the plates is soldered to the foil pad of the printed circuit board 1. To the top plate of the piezoelectric element 2 according to the figure, the rack 4 is soldered, bent in the form of the letter L from an elastic steel wire with a diameter of 0.5 mm. View of rack 4 along arrow A is shown in fig. 1.6. The legs and saddle of the rack must be irradiated in advance.

The console 3 is bent from the same wire and a weight 5 weighing 10...15 g of lead or solder is securely fixed at one of its ends. After that, the console is soldered with one end to the board, and approximately in the middle - to the saddle of rack 4.

In order to avoid separation of the upper plate from the piezoelectric element, before soldering the console, it is slightly bent so that, after being put in place, it creates an excessive pressing elastic force on the piezoelectric element. The dimensions of the sensor parts are not fundamental, therefore, they are not given in Fig. 1. It is necessary to solder with low-melting solder.

The sensor outputs are a foil pad, to which a piezoelectric element is soldered, and a console base soldered into the board. The board is fixed on the surface,

vibration to be controlled. When this surface mechanically vibrates, several weak pulses with a duration of 3 ... 15 ms appear at the sensor terminals.

In order to amplify these pulses and give them the shape necessary for further processing, the signal from the sensor is fed to the input of the shaping amplifier (see diagram in Fig. 2). Operating Wuxi

Liter DA1 operates in maximum gain mode, and transistor VT1 - in switching mode. Diode VD1 increases the dead zone of the transistor with its cutoff voltage.

The op-amp, together with a diode and a transistor, form a voltage comparator, characterized by low power consumption. The threshold for the comparator is set by a trimmer resistor R2. If the amplitude of the negative half-wave of the sensor signal is less than the voltage across the resistor R2, the transistor VT1 remains closed, and the output voltage is zero.

Mechanical excitation of the sensor leads to the appearance at the output of the shaper of several rectangular pulses with a duration of 3 ... 15 ms, in amplitude suitable for their direct injection into a digital analyzer made on CMOS microcircuits. The simplest such device capable of isolating a useful signal against the background of false positives is a counter (001 in Fig. 2), periodically reset at the input R by pulses of an electronic clock or a special generator. An alarm signal - a high level voltage - will appear at the output only when the number of pulses at the counter input in the interval between two adjacent zeroing pulses reaches a certain number set by switch SA1 (in Fig. 2 it is set to eight).

If you do not set a solution to the problem of eliminating false signals, then the signal from the collector of the transistor VT1 can be applied directly to the input of the alarm generating unit.

As experience shows, the sensor practically does not respond to acoustic signals propagating in the air. Sensitive primarily to the normal component of vibrations, it also perceives quite well perturbations lying in the plane of the piezoelectric element, apparently due to the occurrence of a reaction at the points of attachment of the rack. Thus, the sensor responds to vibrations of arbitrary orientation. The current consumed by the conditioning amplifier in standby mode at a supply voltage of 9 V does not exceed -18 μA, at 5 V - 10 μA.

Source: RADIO 12/94