Views: 20 Author: Site Editor Publish Time: 2020-03-09 Origin: Site
This design uses a single-chip microcomputer as the control and parameter calculation circuit. The signal generator outputs a continuous analog excitation frequency sweep signal, which is applied to the piezoelectric ceramics ,which detects the voltage and current amplitude of the analog signal, converts it into a digital signal, and sends it to the microcontroller. The measuring voltage The current system, frequency-resonant and anti-resonant frequency parameters are calculated to obtain the system function program, including external data acquisition, excitation signal acquisition, resonance and anti-resonant frequency calculation, d33 parameter calculation, fault status processing and alarm, etc. The excitation signal and detection circuit output by the signal generator. The frequency of the excitation signal is from 35 to 45kHz. Resonant fr and anti-resonant frequency fa of piezoceramic cylinder transducer are obtained through the frequency sweeping program. The relationship between resistance R, inductance L, capacitance C and voltage and current can be used to obtain d33 of piezoelectric ceramics according to the formula.
Structural diagram of the pressure adjustment part.The system hardware consists of single-chip pressure detection and adjustment, frequency sweep signal output and resonance frequency calculation.The pressure adjustment section compares with the pressure signal with the set value to determine the forward and reverse running status of the motor.
The working process is as follows a single-chip computer unit pressure detection and adjustment-frequency sweep signal output and resonance frequency detection calculation, so as to achieve the calculation of d33. In order to improve the measurement accuracy, selecting the frequency 35 ~ 45kHz output by the signal generator for data measurement, conversion, and recording, and finally calculate d33. Three unknowns R, L, and C in the equation can be obtained (mainly C parameters) The specific value of d33 is calculated to obtain the piezoelectric strain constant d33.
The test circuit uses the transmission line method. Because the capacitance of the stock piezoelectric ceramicitself is small, the ratio of the distributed capacitance to the free capacitance Cr of the fixture and the test system should not be greater than 1/10, otherwise, the test results must be corrected. The method requires d33 to test the geometrical dimensions of the sample as follows: the ratio of the length L to the width W of the plate-shaped ceramic sheet, that is, L / W> 5, in order to ensure a single longitudinal length of the plate-shaped piezo ceramic sheet in a mode of stretching vibration and avoiding other .The interference of the vibration mode on the test results; otherwise, parasitic peaks will appear in the resonance curve, making it difficult to determine the resonance frequency. Known sample material bulk density ρ (kg / m3), free capacitance CT (F) (including the total static and dynamic capacitance values of the plate-like piezo ceramic plate measured at low frequency C ,, C, and C, which is C. + C₁.), Length L (mm), thickness d (mm), width W (mm), sample electrode area S (mm²), the series resonance frequency fs (Hz) of the sample is detected by adding a sweeping excitation signal, and the parallel Resonant frequency fp (Hz) in order to calculate the d33 value. In the calculation of d33, time and frequency are required to be accurate. Due to accurate measurement of fs and fp. It is difficult, so you can refer to the V-shaped network transmission method to measure the maximum resonance frequency and anti-resonance frequency. Here, fs and fp can be replaced by fr and fa.
Test experiment and analysis
Two groups of L * W * d with 5 H each of 20 mm x 5 mm x 1 mm and 60 mm x 5 mm x 1 mm piezoelectric ceramics to be tested were applied with a given pressure of 0.5 N for testing experiments , The corresponding d33 is obtained by detecting and calculating the parameters (R, L, C) of the piezoelectric ceramic sheet. The test frequency (35 ~ 45 kHz) signal applied in the detection process is adjusted for signal frequency every lo s, which is (40 ± 0.5 × n) kHz. The single-chip microcomputer samples and obtains the current and voltage values of the excitation signals of different frequencies, and detects and calculates R, L, C, and d33.
The d33 parameter test calculation of the sample to be tested is compared with the test using a standard d33 parameter measuring instrument. The results show that the range between the maximum and minimum values of the test results is stable within an acceptable range, and the error is less than 5% comparing with the value obtained by the standard tester. The parameters (R, L, C) of the piezoceramic chip obtained from the actual detection are in good agreement with the parameters measured by the standard measuring instrument, which effectively improves the test efficiency and provides conditions for the subsequent online measurement algorithm and device design.
