SU1765773A1 - Accelerometer - Google Patents

Abstract

Use: measuring technique. SUMMARY OF THE INVENTION: An accelerometer comprises a housing and a cantilever sensing element, on the surfaces of which metallized areas are applied. The converter is made on the basis of surface acoustic wave generators, each generator is formed by an amplifier connected between the corresponding input and output interdigital transducers arranged in pairs on both sides of the cantilever sensing element. At the same time, one of the delay lines on each side is located opposite the metallized area on the body at a certain distance from it. 5 il.

Description

The invention relates to the field of measurement technology and can be used in accelerometers for measuring the acceleration of moving objects.

An accelerometer with a transducer of surface acoustic waves (SAW) is known, on a sensitive element of which a delay line is formed with input and output counter-pin transducers (IDT), a SAW generator is formed on the delay line by turning on an amplifier between the input and output IDT.

Such an accelerometer provides a low conversion factor.

To increase the conversion coefficient, delay lines are formed on two sides of the sensing element (SE). Such an accelerometer, taken as a prototype, has a body, a sensitive element, delay lines behind two sides of the SE, including input and output IDT, contains surfactants - generators on delay lines formed by turning on the amplifier between the input and output IDT, frequency mixer, frequency meter.

The disadvantages of the accelerometer are the lack of information on the direction of acceleration and temperature error caused by various changes in the frequencies of SAW-generators due to the temperature difference between the opposite surfaces of SE.

The aim of the invention is to eliminate the temperature error and determine the direction of acceleration.

The goal is achieved in an accelerometer comprising a housing, a cantilever sensing element, a frequency meter, a transducer of surface acoustic waves, including delay lines with input and output anti-pin converters, SAW generators on delay lines formed by the XI

ABOUT

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An amplifier between the input and output IDTs, in that the delay lines are located on the housing on two surfaces parallel to the main surfaces of the SE, on each surface there are two delay lines formed symmetrically with respect to the longitudinal axis of the SE, with the direction of the acoustic path the longitudinal axis of the SE is perpendicular to the axis of bending of the SE, the SE is equipped with metallized areas corresponding to the location of one of the delay lines on each surface of the housing, the metallized areas of the SE are located delay lines at a distance d + fMHH,

where I is the surfactant wavelength, fMHH is the deflection of the sensitive element at the lower limit of the accelerometer measurement, the outputs of the surfactant generators are connected to the input pulse shapers, the outputs of which are a pair of delay lines on each surface of the housing are connected to the introduced frequency deductors, the outputs of which are connected frequency meters.

The distinguishing features of the claimed accelerometer are that the delay lines are located on the body on two surfaces parallel to the main surfaces of the SE, on each surface on the body two delay lines are formed, located symmetrically relative to the longitudinal axis of the SE, with the direction of the acoustic path along the longitudinal axes of ChE perpendicular to axis of bending of ChE, ChE equipped with metallized sections corresponding to the location of one of the delay lines on each surface of the body, metallized areas and SE are located on the delay lines rassto-

nii d -3 + fwMH, where I - the wavelength of the surfactant,

fwHH is the deflection of the sensing element at the lower limit of the accelerometer measurement, the outputs of the SAW-generators are connected to the input of pulse generators, the outputs of which for a pair of delay lines on each surface of the housing are connected to the introduced frequency subtractors whose outputs are connected to frequency meters.

FIG. 1 shows a general view of the accelerometer; in fig. 2-4 - types of the case and a sensitive element of the accelerometer; in fig. 5 is a block diagram of an accelerometer.

The accelerometer (Fig. 1) has a housing 1, a cantilever sensing element 2. On the housing 1 on one of the surfaces parallel to the main planes of ČE 2, the input IDT 3 and output IDT 4 are located

one delay line, input IDT 5 and output IDT 6 of the second delay line (FIGS. 1, 2). On the second surface of the housing, the input IDT 3 and output IDT 4 of one delay line, input IDP 5 and output IDP b of the second delay line are located (Fig. 1.3). On the sensing element 2 are metallized areas 7, 7, corresponding to the location of one of the delay lines on each surface of the housing 1 (Fig. 1, 4).

FIG. 2 IDTs 3, 4 of one delay line and IDP 5, 6 of the second delay line are located symmetrically relative to the longitudinal axis of the FE 2, ensuring the direction of the acoustic path along the longitudinal axis of the FE 2 perpendicular to the axis of the bend of the FE 2. Metallized surfaces 7, 7 are located relative to the BSB 3, 4 and 3, 4

at a distance of d d + fmin (Fig. 1).

From the piezoelectric material can be made either the whole body 1 or its parts with surfaces on which delay lines are formed. If the body 1 is made of a piezoelectric material, a substrate made of a piezoelectric material is applied on the surface of the body 1 parallel to the main surfaces of the SE 2 to form delay lines.

The sensing element 2 is made of non-piezoelectric non-conductive material. Obtaining the necessary deflection of the SE 2 is provided either by its corresponding rigidity or by making a jumper at the junction of the FE 2 with the housing 1.

In FIG. 3, switching on amplifier 8 between input transducer 3 and output transducer 4 of one delay line on one of the surfaces on housing 1 forms a SAW generator, the signal of which through pulse shaper 10 enters a frequency subtractor 12. Turning on amplifier 9 between input transducer 5 and a second SAW generator is formed by the output of the IDT 6 of the second delay line, the signal of which through the pulse shaper 11 is fed to the second input of the frequency subtraction device 12. From the frequency subtraction device 12, the signal is fed to the frequency meter 13.

Turning on the amplifier 8 between the input IDT 3 and output IDT 4 of one of the delay lines on the second surface on the housing 1 forms an SAW generator, the signal from which through the pulse shaper 10 is fed to the input of the frequency subtraction device 12. Turning on the amplifier 9 between the input IDT 51 and the output IDT 6; the second delay line forms the second SAW-generator, the signal from which through the pulse shaper 11; is fed to a second input of a frequency generator 12, connected by its output to a frequency meter 13.

In the absence of acceleration, the SE 2 is in an average position relative to the surfaces of the housing 1. Since, in this case, the distance between the metallized sections 7, T and the IDTs 3, 4 and 3 opposite to them, the delay lines is equal to the sum of a quarter of the wavelength of the surfactant and deflection sensing element 2 on the bottom

accelerometer measurement limit (d d +

+ fMHH), the metallized sections 7, 7 do not have a shunting effect on the electric field of the piezoelectric, which occurs when the SAW generator is operating.

This means that the frequency of the SAW generator is affected only by the phase incursion, which is proportional to the length of the delay line and the velocity of the SAW propagation in the sound drive. Therefore, the frequencies of all four SAW-generators are, in principle, equal to zero signals from devices that subtract frequencies 12, 12 and frequency meters 13, 13,

If there is acceleration perpendicular to the main surfaces of the FE and directed, for example, so that the FE 2 moves in the direction of the housing 1 from the IDT 3, 4, 5, b, when the distance between the metallized section 7 and the IDT 3, 4 becomes equal to a quarter SAW wavelength

(d 2). the metallized section 7 begins to have a shunting effect on the electric field in the piezoelectric delay line at IDT 3,4. This will cause a change in the frequency of the first SAW generator on the delay line from IDT 3,4. and 5, 6, do not change, since these delay lines are located outside the zones of the metallized sections 7, 7. The frequency of the SAW generator on the delay line with IDT 3,4 also does not change, since the metallized section 7 is removed from the IDT 3,4, and the distance between the section 7 and IDP 3,4 becomes even greater than the sum of a quarter of the SAW wavelength and SE deflection (d

2 h fMi / m).

Due to the fact that the frequency of only the first SAW generator on the transducer 3, 4 varies, and the other three SAW generators do not change the frequency, then at this acceleration direction, the frequency difference between the output of the frequency subtraction device 12 and the output signal the accelerometer will be at the output of the frequency meter 13.

With the opposite acceleration direction, the frequency of only the SAW generator on the delay line with IDT 3, 4 changes, and the frequencies of the other three SAW generators do not change. Therefore, the frequency difference will be only at the output of the frequency subtraction device 12, and the output signal of the accelerometer will come from the output of the frequency meter 13.

Pulse shapers 10, 10, 11, 11 convert a sine wave signal

SAW-generators with the central frequency fo in the pulse signal with the pulse frequency fo. Schmitt triggers can be used as pulse shapers.

The devices for subtracting frequencies 12, 12 subtract the frequencies of the pulses arriving at their inputs. Such devices can be reversible counters or special devices.

Thus, the accelerometer measures the acceleration and determines its direction, i.e. depending on the acceleration direction, a signal comes from one or another frequency meter.

Since the pairs of delay lines are located on the same surface, they are in closer temperature conditions, thus eliminating the effect of temperature on the frequencies of SAW generators.

and, therefore, to the output signal of the accelerometer.

Elimination of the temperature error of the accelerometer increases its accuracy. The ability to determine the direction of acceleration extends the functionality of the accelerometer application.

Claims (1)

Invention Formula An accelerometer comprising a housing in which a cantilever sensing element, a frequency meter and a transducer on surface acoustic waves based on generators, formed by switching an amplifier between the input and output counter-pin transducers of delay lines, is fixed, in order to reduce the temperature error and expanding functional capabilities by providing a definition of the acceleration direction, pulse shapers and frequency subtraction blocks are inserted into it, to the inputs of each th outputs of which are connected two pulse shaping, the output Each frequency subtraction unit is connected to the input of the corresponding frequency meter, and the delay lines are arranged in pairs on two surfaces of the housing parallel to the main surfaces of the sensing element, which are opposite to one of the delay lines at a distance d L / 4 + iMm zt  L metallized areas are located from it, with the output of each of the generators connected to the input of the corresponding pulse former, where I is the wavelength, and iwnH is the deflection of the sensitive element at the lower limit of the accelerometer measurement. 56 I And f T t t 3 h Fig.Z eight Phage. 2 FIG. four