RU99158U1 - REMOTE MEASUREMENT DEVICE FOR PIEZOELECTRIC ACCELEROMETER CONVERSION - Google Patents

Abstract

 A device for remote measurement of the conversion coefficient of a piezoelectric accelerometer, comprising a measurement and control unit, a switch connected to a control body, and a test voltage source, characterized in that it further comprises a piezoelectric accelerometer connector, a charge amplifier, an analog-to-digital converter, a controlled delay line, a key , adder, block for detecting extremes, block for calculating the parameters of free oscillations, block for correcting the transmission coefficient, block for determining reference and an interface unit, with the charge amplifier connected to the piezoelectric accelerometer connector through the first switch contact, the test voltage source connected to the piezoelectric accelerometer connector through the second switch contact, the piezoelectrometer connector terminals are connected to each other, an analog-to-digital converter is connected to the output of the charge amplifier , the controlled delay line and the summing adder input are connected in parallel to the output of the analog-to-digital converter, the output is the delay line being drawn through the key is connected to the subtracting input of the adder, the inputs of the measurement and control unit and the extrema detection unit are connected in parallel to the adder output, the extrema detection unit output is connected to the input of the unit for calculating the parameters of free oscillations, and the output of the unit for calculating the parameters of free oscillations is connected in parallel to the correction unit the transmission coefficient and the health determination unit, the output of the transmission coefficient correction unit is connected to the input of the measurement and control unit, interface

Description

The utility model relates to the field of measurement technology and is intended for periodic remote measurement of the conversion coefficient of a piezoelectric accelerometer (hereinafter referred to as the piezo accelerometer) by exciting resonant vibrations of its sensitive element and determining their parameters without dismantling the piezo accelerometer from the operation object and without removing the operation object from the operating mode.

A device is known that implements a method of electrical excitation of resonant oscillations of a piezoelectric accelerometer [Patent of the Russian Federation No. 2150708, cl. G01P 21/00, G01P 15/09, 1999], comprising an excitation voltage source, a switch, connectors for connecting an accelerometer and a recorder, a control signal generator, first and second normally open keys and a delay element, and a source is used as an excitation voltage source constant voltage.

The disadvantage of this device is that it allows you to evaluate only the health of the piezo-accelerometer. Small changes in the conversion coefficient, affecting the accuracy of measuring vibration parameters and caused, for example, by temperature fluctuations, this device does not detect. In addition, it is functional only in the absence of external mechanical influences on the piezo-accelerometer from the side of the measurement object. In the presence of such influences, the vibrations of the sensitive element of the piezo-accelerometer caused by them are summed up with free vibrations, which makes it impossible to directly determine the parameters of free vibrations. This feature significantly limits the scope of this device. In fact, the parameters of free oscillations of the sensitive element of the piezo-accelerometer can be measured only during a planned or emergency stop of the measurement object, that is, when the dismantling of the piezo-accelerometer is often not difficult, and there is the possibility of using traditional monitoring methods.

Closest to the technical nature of the proposed utility model (prototype) is a vibration control system [Patent of the Russian Federation No. 2226676, cl. G01H 17/00, 2003], comprising a vibration sensor with an input for supplying a test voltage thereto, a measurement and control unit, a switch connected to the control body, a test voltage source, a comparison element, a reference signal source, and a vibration sensor malfunction indicator.

The disadvantage of the system is the need to use a sensor of a special design that has not only a signal output proportional to acceleration, but also an input for supplying a test voltage to it. Most of the piezoelectric accelerometers currently manufactured and operated do not have such an input, which significantly limits the scope of the system.

The objective of the proposed utility model is to provide the ability to determine the conversion coefficient of the piezoelectric accelerometer in the process of functioning of the measurement object. The technical result consists in increasing the accuracy of measuring vibration parameters by quickly correcting the overall transmission coefficient of the measurement channel, taking into account the periodically measured conversion coefficient of the piezo accelerometer.

The technical result is achieved by the fact that the device for remote measurement of the conversion coefficient of the piezoelectric accelerometer contains a measurement and control unit, a switch, a control, a test voltage source, a connector for connecting a piezo accelerometer, a charge amplifier, an analog-to-digital converter, a controlled delay line, a key, an adder, a block detecting extrema, a unit for calculating the parameters of free oscillations, a block for correcting the transmission coefficient, a unit for determining health and interface the unit, the charge amplifier being connected to the piezoelectric accelerometer connector through the first switch contact, the test voltage source is connected to the piezoelectric accelerometer connector through the second switch contact, the terminals of the piezoelectric accelerometer connector are connected to each other through the third contact of the switch, an analog-to-digital converter is connected to the output of the charge amplifier, to the output of the analog-to-digital converter is connected in parallel with a controlled delay line and a summing input of the adder, the output of the controlled line is delayed the ki is connected through a key to the subtracting input of the adder, the inputs of the measurement and control unit and the extrema detection unit are connected in parallel to the adder output, the extrema detection unit output is connected to the input of the free vibration parameter calculation unit, the transmission coefficient correction block is connected in parallel to the output of the free vibration parameter calculation unit and a health determination unit, the output of the transmission coefficient correction unit is connected to the input of the measurement and control unit, the interface unit is connected to the output in measurement and control unit and to determine the serviceability of the unit; the control is connected to the interface unit, the measuring and control unit, the extremum detection unit, the key, the controlled delay line and the switch are connected to the control unit outputs.

Figure 1 presents a functional diagram of a device for remote measurement of the conversion coefficient of a piezoelectric accelerometer, and figure 2 is a timing diagram explaining its operation, and figure 2a shows the waveform at the terminals of the piezoelectric accelerometer, figure 2b, the waveform at the output a charge amplifier (before processing), and in FIG. 2c, a waveform corresponding to resonant vibrations of a sensitive element of a piezo accelerometer at the output of the adder.

The device contains a connector 1 for connecting a piezo-accelerometer 2, a switch 3, a test voltage source (ITN) 4, a charge amplifier (US) 5, an analog-to-digital converter (ADC) 6, a controlled delay line 7, a key 8, an adder 9, a measurement unit, and control (BIC) 10, the transmission coefficient correction block (BKKP) 11, the control element (OS) 12, the interface unit (IB) 13, the unit for detecting extrema (BVE) 14, the unit for calculating the parameters of free oscillations (BVSK) 15 and the health determination unit (BOI) 16, and UZ 5 is connected to the connector 1 of the piezo-accelerometer 2 black Without the first contact of the switch 3, the ITN 4 is connected to the connector 1 of the piezo-accelerometer 2 through the second contact of the switch 3, through the third contact of the switch 3 the conclusions of the connector 1 of the piezo-accelerometer 2 are connected to each other, the ADC 6 is connected to the output of the UZ 5, and the controlled ADC 6 is connected in parallel delay line 7 and the summing input of the adder 9, the output of the controlled delay line 7 through a key 8 is connected to the subtracting input of the adder 9, the inputs of the BIC 10 and BVE 14 are connected to the output of the adder 9, the output of the BVE 14 is connected to the input of BVSK 15, to the output FAC 15 are connected in parallel BKKP 11 and the BOI 16 BKKP outlet 11 is connected to the input of the BIC 10, the IB 13 is connected to the output of the BIC 10 and 16 to the BOI; OS 12 is connected to IB 13, to the outputs of OS 12 are connected BIK 10, BVE 14, key 8, a controlled delay line 7, and switch 3.

The device operates as follows. In normal mode, the op-amp 12 switches the switch 3 to the upper position, opens the key 8, allows the BIC 10 to work, and blocks the operation of the BEC 14. The charge is proportional to the acceleration of the sensitive element of the piezo-accelerometer 2 due to the vibration of the object, from the terminals of the piezo-accelerometer 2 through connector 1 to the ultrasound 5, and then to the ADC 6, where it is converted to digital form. The code from the output of the ADC 6, proportional to the instantaneous value of the charge, goes to the summing input of the adder 9. Since the key 8 is open, this code goes to the input of the BIC 10 without changes, where it is analyzed and converted into controlled vibration indicators (frequency of the fundamental harmonic vibration, instantaneous and current values of vibration acceleration, vibration velocity and some others). At the same time, BIC 10 normalizes the calculated parameters using the current value K of the conversion coefficient of the piezo accelerometer 2 obtained from BKKP 11. The obtained parameter values are periodically or upon request transmitted through IB 13 to the next level of the monitoring and diagnostic system. Simultaneously with the described actions, the code from the output of the ADC 6 is constantly accumulated in the controlled delay line 7; as it is filled, the oldest codes are lost and replaced with new ones. The value of the delay T _{ZAD is} regulated by OA 12 depending on the frequency of the fundamental harmonic of the vibration of the object and must be equal to an integer N of periods of this harmonic. In addition, the delay should exceed the total duration of the intervals T1 ... T4 (figure 2).

Calibration of the described device is carried out during commissioning, and if possible, planned preventive maintenance at the facility of operation of the piezo-accelerometer 2. At the same time, the piezo-accelerometer 2 is dismantled from the object, and its conversion coefficient K ₀ is measured directly (for example, using a vibrating stand). Then the piezoelectric accelerometer 2 is mounted on the object, and the described device is turned on in normal mode and after some time it is transferred to the mode of determining model parameters. It is assumed that during the time elapsed between the measurement of the coefficient K ₀ and the inclusion of the mode for determining the model parameters, the state of the piezo accelerometer 2 and its operating conditions have not changed significantly.

In the mode of determining the model parameters, the OS 12 closes the key 8, as a result of which the values accumulated in the controlled delay line 7, delayed for several periods, are subtracted from the current values received from the ADC 6. If there is no noticeable change in the vibration of the operation object during the delay time, the sequence codes at the output of the adder 9 will contain only a random component due to the noise of the measurement channel and non-harmonic components of vibration (pigv, interval T1). BIC 10 evaluates the parameters of this sequence of codes, which will subsequently be used in calculating the parameters of the natural oscillations of the sensitive element of the piezo accelerometer 2.

After some time Tl (4 ... 5 periods of the fundamental harmonic of vibration), the op-amp 12 puts switch 3 in the middle position. In this case, the sensitive element of the piezoelectric accelerometer 2 as a result of the inverse piezoelectric effect is deformed under the influence of the excitation voltage coming from ITN 4 (figa, interval T2). After some time T2, when the deformation reaches a steady-state value, OS 12 switches the switch 3 to the lower position, thus closing the terminals of the piezoelectric accelerometer 2. The charge at the terminals caused by the connection of ITN 4 decreases to zero within a very short period of time (Fig. 2a, TK interval), and the deformation of the sensitive element of the piezoelectric accelerometer 2 begins to change in the form of damped oscillations with a resonant frequency. To these vibrations is added a component caused by the vibration of the object of operation (figa, interval T4). At the end of the time interval, the OA 12 switches the switch 3 to the upper position, reconnecting the UZ 5 to the terminals of the piezoelectric accelerometer 2. At the same time, the OA 12 blocks the operation of the BIC 10 and enables the operation of the BEE 14. As a result of the operation of the controlled delay line 7, the output of the adder 9 a sequence of codes proportional to the instantaneous values of the charge at the terminals of the piezoelectric accelerometer 2, corresponding to the resonant vibrations of the sensitive element of the piezoelectric accelerometer 2 (pigv, interval T4). With the exception of the initial section, where the signal may be limited by the input nodes of the described device (US 5 and ADC 6), the obtained sequence of codes is rather accurately described by the expression:

where y (i) is the i-e value of the sequence;

i - reference number (0 ... n);

Y is the initial value of the function at i = 0 (at the time of switching off the test voltage source);

t ₀ - time quantization period;

τ is the transient decay time constant;

ω is the circular frequency of the resonant oscillations of the sensitive element of the piezoelectric accelerometer 2;

To determine the value of Y, the BEE 14 detects local extrema of the code sequence (Fig.2c, the interval T4 except for the signal limited section), and the BESC 15 determines the parameters of the exponential envelope of the transition process Y and τ, as well as the frequency of resonant oscillations ω . In this case, the detection of extrema is performed until the level of the useful signal (FIG. 2B, interval T4) becomes comparable with the level of interference (FIG. 2B, interval T1).

The values of Y, τ and ω (Y ₀ , τ ₀ , ω ₀ ) obtained in the process of determining the model parameters are stored in the BKKP11 memory. There, through IB 13, at the command of the operator of the monitoring and diagnostic system, the reference value of the conversion coefficient of the piezo accelerometer 2 K ₀ , measured directly, as well as the maximum permissible deviations of the parameters τ ω and the conversion coefficient from the nominal value, is recorded.

At the end of the calculations, the OS 12 transfers the device from the mode of determining the model parameters to the normal mode by opening the key 8, enabling the BIC 10 and blocking the BVE 14.

The described device switches to the mode of measuring the current value of the conversion coefficient of the piezo-accelerometer 2 either automatically at a predetermined frequency, or at the command of the operator through IB 13. The operation of the device in this mode is largely similar to the operation in the mode of determining model parameters. The device in the same way excites the resonant vibrations of the sensitive element of the piezo-accelerometer 2, selects the sequence of codes corresponding to these vibrations, and determines the parameters Y and τ of the exponential envelope of the function describing it, as well as the frequency of the resonant oscillations ω.

Since over time and depending on the operating conditions of the piezo-accelerometer 2, its characteristics can change, the values of the parameters Y, τ, and ω calculated in the measurement mode (Y ₁ , τ ₁ ω ₁ ) generally differ from similar values of Y ₀ , τ ₀ , ω ₀ calculated in the mode of determining the model parameters.

After calculating the parameters Y ₁ , τ ₁ , ω ₁ BKPP11 calculates the current value of the conversion coefficient of the piezo accelerometer 2 K by the formula:

BOI 16 compares the obtained values of K, τ ₁ , ω ₁ with the specified maximum permissible values and, on the basis of the comparison results, forms a sign of serviceability of the piezo-accelerometer 2, which is transmitted through IB 13 to the next level of the monitoring and diagnostic system.

At the end of the calculations, the device goes into normal operation. Moreover, to calculate the controlled vibration parameters, the BIK 10 uses the new value of the conversion coefficient K obtained in the mode of measuring the current value of the conversion coefficient of the piezo accelerometer 2.

The described algorithm for the operation of the device for remote measurement of the conversion coefficient of the piezoelectric accelerometer is justified as follows. The conversion coefficient of a 2 K piezo-accelerometer is, by definition, described by the expression

where q is the charge arising in the sensitive element of the piezoelectric accelerometer 2.

a - vibration acceleration;

Given the second law of Newton and the well-known expression 4, connecting the charge with the force acting on the sensitive element of the piezo-accelerometer 2, we obtain:

Where d ₃₃ is a longitudinal piezoelectric module of the material of the sensitive element of the piezoelectric accelerometer 2;

F is the force acting on the sensitive element of the piezo-accelerometer 2 from the side of the inertial element of the piezo-accelerometer 2;

M is the mass of the inertial element of the piezoelectric accelerometer 2.

Thus, the conversion coefficient of the piezoelectric accelerometer 2 varies in proportion to the change in the piezoelectric module:

Where K ₁ is the conversion coefficient corresponding to the piezoelectric module d ₃₃ ¹ .

d ₃₃ ¹ - longitudinal piezoelectric module at time t ₁ ;

d ₃₃ ⁰ - longitudinal piezoelectric module at time t ₀ ;

To ₀ is the conversion coefficient corresponding to the piezoelectric module d ₃₃ ⁰ ;

The measurement of the value of the piezoelectric module during operation of the piezoelectric accelerometer 2 is difficult, however, the ratio can be obtained as follows.

When ITN4 is connected to the terminals of the piezoelectric accelerometer 2, its sensitive element receives a deformation, the value of which is calculated in accordance with the known expression

Where  Δh is the change in the height of the sensitive element of the piezoelectric accelerometer 2;

U is the voltage applied to the terminals.

At the time of disconnection of ITN 4, the sensitive element of the piezoelectric accelerometer 2 will be in a deformed state, which is equivalent to the action of the force F ₀ on the inertial element of the piezoelectric accelerometer 2, defined by the following well-known expression:

Where  h is the height of the sensitive element of the piezoelectric accelerometer 2;

A is the cross-sectional area of the sensitive element of the piezoelectric accelerometer 2, perpendicular to the direction of action of the force.

S is the elasticity of the material of the sensitive element of the piezoelectric accelerometer 2.

Given expression 7 we get:

When this force is applied, a charge will arise on the electrodes of the sensitive element of the piezo-accelerometer 2, the value of which, taking into account expressions 4 and 9, can be determined by the formula:

If the values of Q ₀ at the time t ₀ and Q ₁ at the time t _{1 are} known, then the ratio of the values of the piezoelectric modules at the same time instants taking into account expression 10 can be defined as

At the same time, we believe that the test voltage U, as well as the geometric dimensions of the sensitive element of the piezoelectric accelerometer 2 (A, h) and the elasticity of the material S are constant (see, for example: MV Bogush, Effect of temperature on the conversion coefficient of piezoelectric sensors. Devices and systems Management, control, diagnostics - 2008. - No. 2. - p. 36-39.).

Thus, directly measuring at some point t ₀ of time (for example, during commissioning) conversion coefficient K ₀ and determining by means of the described device a corresponding value Q _0, it is possible by measuring the current value of Q _1, the current value K ₁ conversion factor (s taking into account expressions 6, 11):

The direct measurement of the Q value is complicated by the need to close the terminals of the piezoelectric accelerometer 2 immediately after shutting down the ITN 4. However, the mechanical oscillatory process that occurs in the sensitive element of the piezo accelerometer 2 leads to a change in the charge, which is quite accurately described by the expression

where q (t) is the value of the charge at time t;

t is the time;

Q - the value of the charge at the time of shutdown ITN 4;

τ is the transient decay time constant;

ω is the circular frequency of the resonant oscillations of the sensitive element of the piezoelectric accelerometer 2.

Thus, knowing a certain number of q (t) values, we can determine the value of Q.

The considered device allows one to measure the conversion coefficient of piezo-accelerometers that control the vibration parameters of rotary machines (turbine units of electric stations, compressors of gas pumping stations and the like), that is, those in which the vibration has a clearly pronounced periodic character.

The technical result consists in the fact that the conversion coefficient of piezo-accelerometers is controlled by the device in the operating mode of the operation object, which allows monitoring at the required frequency and timely correcting the transmission coefficient of the entire measuring channel, thereby increasing the accuracy of vibration parameter measurements. In addition, significant deviations of the conversion coefficient and the resonant frequency from the initial value can be used as a sign of a malfunction of the piezo-accelerometer, which will allow to detect failures at the earliest stages of their occurrence.

Claims (1)

A device for remote measurement of the conversion coefficient of a piezoelectric accelerometer, comprising a measurement and control unit, a switch connected to a control body, and a test voltage source, characterized in that it further comprises a piezoelectric accelerometer connector, a charge amplifier, an analog-to-digital converter, a controlled delay line, a key , adder, block for detecting extremes, block for calculating the parameters of free oscillations, block for correcting the transmission coefficient, block for determining reference and an interface unit, with the charge amplifier connected to the piezoelectric accelerometer connector through the first switch contact, the test voltage source connected to the piezoelectric accelerometer connector through the second switch contact, the piezoelectrometer connector terminals are connected to each other, the analog-to-digital converter is connected to the output of the charge amplifier , the controlled delay line and the summing adder input are connected in parallel to the output of the analog-to-digital converter, the output is the delay line being drawn through the key is connected to the subtracting input of the adder, the inputs of the measurement and control unit and the extrema detection unit are connected in parallel to the adder output, the extrema detection unit output is connected to the input of the unit for calculating the parameters of free oscillations, and the output of the unit for calculating the parameters of free oscillations is connected in parallel to the correction unit the transmission coefficient and the health determination unit, the output of the transmission coefficient correction unit is connected to the input of the measurement and control unit, interface unit is connected to the output of the measurement unit and the control unit and to determine the proper operation; the control is connected to the interface unit, the measuring and control unit, the extremum detection unit, the key and the controlled delay line are connected to the control unit outputs.