JPS6063471A - Resonance impedance measuring device - Google Patents

Abstract

PURPOSE:To measure efficiently the resonance impedance of a resonator such as a piezoelectric element or the like with a high precision by providing a self-oscillating circuit constituted with an object to be measured and two phase inverting amplifiers. CONSTITUTION:A sine wave self-oscillating circuit is constituted of a loop passing a piezoelectric element 13 as the object to be measured, phase inverting amplifier 7, phase inverting amplifier 9, and a low-pass filter 10. The amplitude of oscillation appearing at a point Q in the output side of the phase inverting amplifier 7 is detected by a detector 15 and is compared with an amplitude reference voltage of an amplitude reference voltage source 16 by a voltage comparator 17, and the amplification factor of the phase inverting amplifier 9 is so controlled that the amplitude of oscillation at the point Q is constant. The resonance impedance of the piezoelectric element 13 is detected by the indicated value of an AC voltmeter 14 connected to a point S. Because of measurement based on an accurate constant current, the measurement error is reduced, and the reproducibility is improved considerably.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a resonant impedance measuring device used to measure the resonant impedance of a resonator such as a piezoelectric element.

Prior art For example, a piezoelectric element generally exhibits a frequency-impedance characteristic as shown in FIG. In FIG. 1, fr is the resonant frequency and Zr is the resonant impedance. When measuring this 1y4th resonance impedance, conventionally,
It was measured by resistance displacement measurement using an external oscillator. Fig. 2 is an electric circuit connection diagram of a conventional resonant impedance measuring device using this resistance replacement method. 6 is a circuit switcher, and 6 is a piezoelectric vibrator which is an object to be measured. With this measuring device, the piezoelectric element 6
To measure the resonance impedance of , first, measure the reference resistance of reference resistor 4.

At the same time, the oscillation frequency of the external oscillator l is set to a pure resistance value close to the resonant frequency fr of the piezoelectric element 6.
Adjust to a value that approximates the resonant frequency of. Further, the range resistor 3 is selected to have a value approximately ten times that of the reference resistor 4. Then, move the movable contact 51 of the circuit switch 5 from the contact 52 side.
After adjusting the voltage to the 3 side, adjust the output of the oscillator 1 so that the AC voltmeter 2 shows an appropriate value, and note down the indicated value. Next, switch the movable contact 51 of the circuit switch 5 from the contact 52 to the contact 53 side, connect the piezoelectric element 6 to the measurement terminal, and set the oscillator l so that the indicated value of the AC voltmeter 2 becomes the minimum.
The oscillation frequency of the AC voltmeter 2 is variably adjusted, and the resonance impedance Zr is calculated by comparing the indicated value of the AC voltmeter 2 at that time with the indicated value recorded previously. From the second one onwards, this procedure is repeated to measure each resonance impedance Zr.

Disadvantages of the Prior Art However, the conventional resonant impedance measuring device shown in FIG. 2 has the following drawbacks.

(a) Since the alternating current signal of the oscillator l is not constant with respect to the resonance impedance Zr of each object to be measured, measurement conditions vary and measurement errors occur.

(b) The operation of the frequency adjustment dial for setting the oscillation frequency of the oscillator 1 is critical and is inefficient unless it is done by an experienced person.

(c) Since manual work that is directly involved in the measurement results is added, human measurement errors are likely to occur.

OBJECTS OF THE INVENTION It is an object of the present invention to provide a resonant impedance measuring device that can eliminate the above-mentioned conventional drawbacks and measure the resonant impedance of a resonator such as a piezoelectric element with high precision and high efficiency.

Structure of the Present Invention In order to achieve the above objects, the present invention provides a first phase inversion layer amplifier having a range resistor constituting a feedback resistor, and a first phase inversion layer amplifier that positively feeds back the output of the phase inversion layer amplifier of the tlS1 to its input side. an automatic oscillation circuit configured to include two phase inversion layer amplifiers, a terminal for connecting a device under test provided in series with the input of the first phase inversion layer amplifier, and an automatic oscillation circuit configured to include two phase inversion layer amplifiers; The device is characterized by comprising a control circuit that controls the circuit so that its oscillation amplitude is constant, and a measuring device that measures an alternating current voltage applied to the object to be measured connected to the terminal.

Embodiment FIG. 3 is an electrical circuit connection diagram of the resonant impedance measuring device according to the present invention. In FIG. An inversion layer amplifier 7, a range resistor 8 constituting its feedback resistance, a second phase inversion layer amplifier 9 that positively feeds back the output of the phase inversion layer amplifier 7 to its input side, and an output of this phase inversion layer amplifier 9. The low-pass filter 101 removes distortion contained in the phase shift layer amplifier 7 and provides positive feedback to the input side of the phase inversion layer amplifier 7. The low-pass filter 101 is provided with measurement terminals 11 and 12 to which the piezoelectric element 13-, which is the object to be measured, is connected. 14 is an AC voltmeter.

Further, the circuit below the chain line 15 is compared with a reference voltage provided from an amplitude reference voltage source 16, and the voltage comparator 17 controls the amplification factor of the phase inversion layer amplifier 9 based on the comparison output. Reference numeral 18 denotes an amplitude alarm indicator composed of, for example, a light emitting diode.

In the above circuit configuration, when the piezoelectric element 13 as the object to be measured is connected between the measurement terminals 11 and 12, the phase inversion amplifier 7 - the phase inversion amplifier 9 - the low-pass filter l - the piezoelectric element 13 - the phase inversion amplifier A sine wave automatic oscillation circuit is constructed by the loop of 7.

On the other hand, the oscillation amplitude appearing at point Q on the output side of the phase inversion layer amplifier 7 due to the self-help oscillation operation of the self-help oscillation circuit is detected by the detector 15, and the detected output is sent to the voltage comparator 1.
7, it is compared with an amplitude reference voltage provided from an amplitude reference voltage source 16. Based on the comparison output of the voltage comparator 17, the amplification factor of the phase inversion layer amplifier 9 is controlled so that the oscillation amplitude at point Q is constant. Distortion accompanying this control of the amplification factor is removed by the low current filter IO.

Here, if we pay attention to the phase inversion layer amplifier 7, the human power impedance is extremely high as a general characteristic of a single phase inversion type amplifier, and □ also has a human power terminal A on the (-) side and an input terminal B on the (+) side. The potential difference between them is very small and almost no current flows. For this reason, there is almost no potential difference between point P and the ground, and almost no current flows, so the electric current passes through the range resistor 8 that constitutes the feedback resistor, as shown by the dotted line (A).
flows in a loop.

As described above, since the potential at point P is substantially equal to the ground potential and is zero, the following equation holds true in the present invention where the amplitude at point Q is controlled to be constant.

I=V, Q, /R, , , , , (1) However, ■ is the current flowing through the loop (A) (A) Vq is the AC amplitude voltage value at point Q (V) R is the range resistance Here, since the resistance value R (Ω) of the range resistor 8 and the amplitude voltage value Vq (V) at point Q are constant, the current I (A) is constant. This current I (A) flows through the loop shown by the dotted line (A) as described above, and all of it flows from point S through the piezoelectric element 13, which is the object to be measured, and reaches point P. Therefore, the voltage at point S is set to Vs. Then, the resonance impedance Zr of the piezoelectric element 13 is expressed by the following equation.

Zr=Vs/I , , : , , , (2) Above (2)
Substituting equation (1) into the equation, Z r = V s/ (
V q/R)=Vs/, (3) where K is a constant.

As is clear from this equation (3), the AC voltage value V at point S
If s is detected, the resonance impedance Z of the piezoelectric element 13
We can know r. In this embodiment, an AC voltmeter 14 is connected to point S, and therefore, this AC voltmeter 14
The resonance impedance Zr of the piezoelectric element 13 can be known from the indicated value.

As described above, since the resonant impedance measurement device according to the present invention performs measurement using an accurate constant current, measurement errors are reduced and reproducibility is significantly improved. Furthermore, there is no need to operate the frequency adjustment dial of the oscillator, which was conventionally necessary, and it is possible to completely eliminate artificial measurement errors caused by the operation of the measuring instrument. In addition, little skill is required for operation, making the measurement work simple and improving measurement efficiency.

The amplitude alarm indicator 18 is used to indicate when amplitude control cannot be performed sufficiently, and is intended to prevent erroneous readings. In addition, the AC signal is divided into the piezoelectric element 13 and the AC voltmeter 14 at point S, but the amplitude control of oscillation only works on the current flowing into the piezoelectric element 13 side, which is the object to be measured, and it actually affects the low frequency range. Since the AC signal flowing out from the filter 10 is the sum of the measurement current flowing from point S to point P and the current flowing to the AC voltmeter 14, no measurement error occurs.

Effects of the Present Invention As described above, the resonant impedance measuring device according to the present invention includes a first phase inverting amplifier having a range resistor constituting a feedback resistor, and an output of the first phase inverting amplifier as its input. a self-excited oscillation circuit configured with a second phase-inversion type amplifier that provides positive feedback to the phase-inversion layer amplifier; A terminal for connecting the object to be measured and the self-Tm
Controlling the oscillation circuit so that its oscillation amplitude is constant1
1j control circuit and a measuring device that measures the alternating current voltage applied to the object 111 connected to the terminal, eliminating manual operation and human error, and eliminating the need for piezoelectric elements etc. It is possible to provide a resonant impedance measurement device that can measure the resonant impedance of a resonator with high precision and high efficiency.

[Brief explanation of drawings]

FIG. 1 is a frequency-impedance characteristic diagram of a piezoelectric element, FIG. 2 is an electric circuit diagram of a conventional resonant impedance measuring device, and FIG. 3 is an electric circuit diagram of a resonant impedance measuring device according to the present invention. 7...First phase inversion amplifier 81111-range resistor 9...Second phase inversion amplifier 10...Low pass filter 13...Object to be measured 14.e.AC voltmeter 15...・Detector 16... Amplitude reference voltage source 17... Fist voltage comparator Patent applicant TDC Co., Ltd. Figure 1 Figure 2 Otori

Claims (1)

[Claims] (1) A first phase-inverting amplifier having a range resistor constituting a feedback resistor, and a second phase-inverting amplifier that positively feeds back the output of the first phase-inverting amplifier to its input side. an automatic oscillation circuit, and the first automatic oscillation circuit.
a terminal for connecting an object to be measured, which is provided in series with the input of the phase-inverting amplifier, and a control circuit that controls the automatic oscillation circuit so that its oscillation amplitude is constant;
A resonant impedance measuring device comprising: a measuring device that measures an alternating current voltage applied to the object to be measured connected to the terminal.