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Mechanical vibrations of electrical machines occur during operation and start-up. Their magnitude and frequency are due to the uneven distribution of the rotor mass by volume, and when the machine is operated for a long time, the wear of the bearing bearings continues. To prevent accidents of machines and bearing foundations, it is necessary to control the amplitude and frequency of vibrations by means of sensors that convert mechanical vibrations into electrical signals that can be registered and, if necessary, build on them a protection that, when vibrations exceed a specified norm, disconnects from the energy source.
In the article two types of sensors are considered: magnetoelectric, working on the basis of the law of electromagnetic induction and direct piezoelectric effect. In the first sensor inside the hollow coil with a large number of turns, a cylindrical permanent magnet is suspended on the damping springs, which under the action of vibrations moves along the turns, finding in them an e.d.s. to , where W – is the number of turns of the coil; linear velocity of magnet motion; B – is the magnitude of the magnetic induction; S is the cross-sectional area of the coil; and the angles between the normal of the plane of the coil winding and the lines of the vector of magnetic induction.
The other sensor uses a piezoceramic plate rigidly fixed on the base of the plate. On the other hand, the plate is connected to the console. At one end of the console is suspended a load of mass m. Mechanical vibrations force the load to move up and down. The other end of the console is connected to the back of the piezoceramic plate. This design allows you to act on the plate by squeezing and stretching, resulting in an electrical signal. The signal power is very low, so an amplifier with a large input resistance is installed at its output.
The sensor inputs are connected to the DA1 operational amplifier with a frequency-dependent negative feedback with a gain of 100. The amplified signal from the DA1 output through the capacitor C3 is applied to the detector VD2, VD3 operating in the voltage doubling mode. The rectified and filtered signal is fed to the comparator input DA2 and compared with the reference signal taken from the divider R10, R11, R12.
If the amplitude of the signal proportional to the magnitude of the vibration is such that condition is fulfilled, then the output of DA2 will have a high potential, therefore, the transistor VT1 will be closed and relay K1 will be off. There will be no alarm. Excessive vibration increase leads to the fact that , which leads to the unlocking of VT1, and consequently to the activation of protection.
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