High-sensitivity shock accelerometer

Abstract

FIELD: measurement technology.SUBSTANCE: invention is intended for use in seismology and vibration diagnostics in cases where the operation of an accelerometer is associated with large shock loads. The accelerometer consists of a rod-type piezoelectric element, installed with one end in the accelerometer housing by means of a holder made of an elastic compound. The second end of the piezoelectric element is connected to the housing by the same compound.EFFECT: increased resistance of the accelerometer to external shock loads and increased conversion factor.2 cl, 2 dwg

Description

[0001] The invention relates to measuring equipment, namely to highly sensitive piezoelectric accelerometers, which during operation experience large impacts and must maintain their main characteristics: the value of the conversion coefficient and its amplitude-frequency characteristic (AFC).

[0002] The invention can be used in seismology, acoustics, vibration diagnostics and other fields of technology.

[0003] A known accelerometer design operates on the compression-tension deformation of a piezoelectric element and consists of a housing, on the base of which this piezoelectric element is fixed, equipped with an inertial mass (Yu.A. Iorish "Vibrometry", M., Mashinostroenie, 1963, p. 568, fig. 14.53, b). Using this scheme, a wide class of accelerometers has been developed, which, due to the low inertial mass, can withstand high shock accelerations (of the order of 10 5 m / s 2) and have a high-frequency resonance in the tens of kHz range. However, such accelerometers have a low conversion coefficient, typically no more than 0.3 mV / (m / s). 2 ).

[0004] There are technical challenges that require an accelerometer to have acceptable shock resistance in all directions with a higher transducer gain, reaching several tens of mV / (m / s). This approach also allows for a low resonant frequency. The challenge lies in combining a high transducer gain with acceptable shock resistance.

[0005] A known accelerometer design consists of a housing and a piezoelectric element (UK Patent, GB No. 89923 5A class G 1 N / 1968), in which the mass of the piezoelectric element performs the function of the inertial mass, however, such an accelerometer has insufficient shock resistance under external influences.

[0006] The use of the invention makes it possible to create accelerometers that are resistant to external shock effects (shock accelerations of the order of 10 5 m / s 2 in all directions) and having a conversion coefficient an order of magnitude higher than that of existing impact accelerometers.

[0007] The essence of the invention is that in a known highly sensitive impact accelerometer, comprising a housing and a piezoelectric element, the latter is designed as a rod with electrodes at its ends. The height of the rod must satisfy the condition:

[0008] ,

[0009] where - height of the piezo element;

[0010] - mechanical stress of destruction of piezoceramics;

[0011] - density of piezoceramics;

[0012] - safety factor (2÷5);

[0013] - maximum impact acceleration.

[0014] The rod is mounted in the housing by adhesion of the holder material, which is made of an elastic compound with a dynamic modulus of elasticity of E = (5÷10) MPa. The parameters of the piezoelectric element, compound, and holder must satisfy the following condition:

[0015] ,

[0016] where - area of ​​the piezoelectric element;

[0017] - the distance between the lower end of the piezoelectric element and the housing;

[0018] - holder height;

[0019] - distance from the piezoelectric element to the side surface of the housing;

[0020] - Poisson's ratio of the compound;

[0021] - the perimeter of the horizontal section of the piezoelectric element;

[0022] - compound adhesion index;

[0023] - mechanical stress of destruction of piezoelectric ceramics.

[0024] The proposed accelerometer combines high conversion efficiency with shock resistance through the following factors:

[0025] - the piezoelectric element is made in the form of a rod, which reduces its capacitance, and this increases the voltage conversion coefficient;

[0026] - limitation of the height of the piezoelectric element, associated with the fact that the piezoelectric element’s own mass does not destroy it under impact;

[0027] - selection of the holder parameters and its adhesion, in which the piezoelectric element is held in the holder without being torn out or damaged by impact;

[0028] - the use of an elastic material to form a holder that hides the unevenness of the base of the housing and changes the hard nature of its impact interaction with the piezoelectric element to a soft one, protecting the piezoelectric element from chipping and cracking, typical with hard impacts.

[0029] To prevent the upper part of the piezoelectric element from striking the housing wall during lateral impacts, the same compound, at least p high, is introduced between it and the piezoelectric element. This makes it possible to make the permissible impact forces comparable in both the longitudinal and transverse directions.

[0030] Figure 1 shows the design diagram of the proposed accelerometer, which consists of a housing 1, a piezoelectric element 2 and a holder 3 with the main parameters of the holder indicated on it.

[0031] Fig. 2 shows the design diagram of the proposed accelerometer with elastic limiters 4.

[0032] A pilot batch of the proposed accelerometer with a K-68 vixint holder was manufactured. The holder dimensions were achieved by casting the housing and piezoelectric element in appropriate fixtures. The accelerometers with a built-in repeater for various models ranged in diameter from 9 to 17 mm and height from 22 to 35 mm. The conversion factor was in the range of 25-40 mV / m / s. 2 at an accelerometer resonant frequency of 8-16 kHz. The accelerometers withstood impacts exceeding 10 5 m / s 2 both in the longitudinal and transverse directions.

Claims

1. A highly sensitive shock accelerometer comprising a housing and a piezoelectric element, characterized in that the piezoelectric element is made in the form of a rod with electrodes at the ends and a height selected from the condition , where H is the height of the piezoelectric element; σ к - mechanical stress of destruction of piezoceramics; ρ is the density of piezoelectric ceramics; N - safety factor (2÷5); x'' is the maximum impact acceleration, while the rod is fixed in the housing at one end by adhesion of the holder material made of elastic compound, and the parameters of the piezoelectric element, compound and holder satisfy the condition where S is the area of ​​the piezoelectric element; h0 - distance between the lower end of the piezoelectric element and the housing; h - height of the holder; δ is the distance from the piezoelectric element to the side surface of the housing; μ is the Poisson's ratio of the compound; P is the perimeter of the horizontal section of the piezoelectric element; σ ад - compound adhesion index; σ к - mechanical stress of destruction of piezoelectric ceramics.

2. A highly sensitive impact accelerometer according to claim 1, characterized in that the side surface of the piezoelectric element on the second end is connected to the wall of the housing by means of an elastic compound.

Images