JPH0154645B2 - - Google Patents

Description

[Detailed description of the invention]

This invention drives an electroacoustic transducer that can change the volume inside the sealed container to be measured, detects a resonance state from the electrical output of the electroacoustic transducer, and measures the volume of the sealed container to be measured from the resonance frequency. The present invention relates to an acoustic volume measuring device. <Background> In this type of measuring device, when external vibrations are applied and this vibrates the diaphragm of the electroacoustic transducer, accurate measurements become difficult. This invention solves this problem. First, a proposed acoustic volume measuring device of this type will be explained with reference to FIG. In FIG. 1, a sealed container 11 to be measured has an opening 12 formed in the upper part of the side plate in this example, and an electroacoustic transducer 13 is attached to the sealed container 11 so as to close the opening 12. The electroacoustic transducer 13 can be, for example, a movable ring type speaker, and its cone periphery is connected to the inner periphery of the opening 12 so that the opening 12 is closed. Therefore, by driving this electroacoustic transducer 13 with an alternating current signal, the diaphragm 13a of the electroacoustic transducer 13
can vibrate to change the internal volume within the closed container 11. In this example, the liquid 14 is contained in the closed container 11, and therefore the closed container 11
The volume of the liquid 14 can also be measured by measuring the volume V of the space (gas phase) other than the space filled with the liquid 14. For example, as shown in FIG. 2, a pulse with a steep rise and fall as shown in FIG. 3A is applied from a pulse generator 15 to the electroacoustic transducer 13 through a drive circuit 16. In this way, a large number of frequency components are generated when there is a sudden change in the rise or fall, which matches the resonance frequency _n determined by the volume V inside the container 11 and the constant of the electroacoustic transducer 13. Only the frequency component appears as a large damped vibration as shown in FIG. 3B. In other words, the resonant frequency _n is determined from the volume V of the measurement space, the constant k determined by the spring constant (stiffness) of the transducer 13, and the mass m of the movable part of the transducer 13.

[Formula], and the damped vibration of this resonance frequency _n appears. This is amplified by the amplifier 18 in the waveform shaping circuit 17 connected to the input side of the electroacoustic transducer 13, and
A damped oscillation as shown enlarged in FIG. This square wave is input to the clock terminal ck of the shift register 21,
A high level is applied to the data terminal D of the shift register 21, and the pulse generator 15 is applied to the clear terminal Cl.
A pulse is given, and the clear state is maintained during the high level of the pulse. When the pulse shown in FIG. 3A falls, the first square wave from the comparator 19 causes the _Q1 output of the shift register 21 to go to a high level as shown in FIG. 3E, and the second one causes the _Q2 output to go high. The level becomes high as shown in FIG. 3F. This Q ₂ output is inverted as shown in FIG. 3G by an inverter 22, and this and the Q ₁ output are supplied to an AND gate 23.
Therefore, as shown in FIG. 3H, the AND gate 23 outputs a high level from the first period of the square wave (FIG. 3D). Similarly, the inverted outputs of the Q ₂ and Q ₃ outputs of the shift register 21 are supplied to the AND gate 24, and as shown in FIG. 3I, the square waveform of FIG. 3D is generated immediately after the pulse of FIG. A pulse is obtained that goes high for one period of .
The counter 25 is reset by the pulse shown in FIG. 3H from the AND gate 23. The gate 26 is opened by the output of the AND gate 24 (FIG. 3 I), the clock of the clock generator 27 in the pulse generator 15 passes through the opened gate 26, and the clock is counted by the counter 25. be done.
This count value corresponds to one cycle of the vibration signal shown in FIG. Note that the pulse generator 15 is the clock generator 2.
7 is frequency-divided by a frequency divider circuit 29 to obtain the pulses shown in FIG. 3A. The monostable multivibrator 31 is driven by the fall of the output of the AND gate 24, and the counted value of the counter 25 is latched in a latch circuit in the display 28, and the latch output is displayed on the display 28. Damped vibrations in Figure 3 B and C, that is, the closed container 11
The relationship between the resonance frequency _n determined by the internal volume V and the constant of the transducer 13 and the internal volume V is shown in the curve 32 in FIG. The frequency _n increases, and as the liquid 14 decreases and the internal volume V increases, the resonance frequency _n decreases. By displaying the volume V corresponding to the detected resonance frequency _n on the display 28 using the relationship of this curve 32, it becomes possible to directly read the internal volume V of the closed container 11. However, when vibration is applied from the outside and the entire sealed container 11 vibrates, the electroacoustic transducer 13 also vibrates, and the waveform of the detected damped vibration is disturbed, making it difficult to correctly measure its period, that is, the resonant frequency _n . There is a possibility that it will not be possible. <Summary of the Invention> An object of the present invention is to provide an acoustic volume measuring device that can accurately measure the resonance frequency, that is, the volume, without being affected by external vibrations. According to this invention, two electroacoustic transducers are used, the diaphragms of these electroacoustic transducers are arranged to face each other, and the space created between these diaphragms is the internal space of the sealed container to be measured. be isolated. These electroacoustic transducers are driven synchronously, and the electrical outputs of these electroacoustic transducers are summed in a summing circuit.
The resonant frequency determined by the volume of the sealed container is detected from the added output. <Example> For example, as shown in FIG.
Electroacoustic transducers 13 and 33 with the same characteristics are placed in the upper part of the
are arranged laterally, and the diaphragms 13a, 33a of these electroacoustic transducers are arranged facing each other. A cylindrical body 3 is located between the peripheries of the diaphragms 13a and 33a.
A space 35 created between the diaphragms 13a and 33a by connecting the diaphragms 13a and 33a with each other is isolated from the inside of the closed container 11. The output pulses of the pulse generator 15 are sent to the drive circuits 16 and 3.
6 simultaneously, and these drive circuits 16, 36
The electro-acoustic transducers 13 and 33 are driven synchronously through. The electrical outputs of the electroacoustic transducers 13 and 33 are supplied to an adder circuit 37, and the added output is input to a resonance frequency detector 38. With this configuration, for example, the electroacoustic transducers 13 and 33 are simultaneously driven by the pulses shown in FIG. In this state, it is assumed that a vibrational acceleration directed from the electroacoustic transducer 13 toward the electroacoustic transducer 33 is applied to the closed container 11 as shown by the dotted arrow in FIG. In this case, the electroacoustic transducers 13 and 33 each oscillate at a damped _vibration (FIG. 3B, C) However, since these damped vibrations have the same frequency and the same phase, they are added together in the adding circuit 37, resulting in an amplitude twice that of the case where only the electroacoustic transducer 13 shown in FIG. 1 is used. . On the other hand, the outputs of the electroacoustic transducers 13 and 33 due to external vibrations have opposite phases and equal amplitudes, so they are canceled by the adder circuit 37.
does not appear in the output. For example, as shown in FIG.
When only one unit 3 is used and receives sinusoidal external vibration, the damped vibration of the resonant frequency determined by the volume V and the constant of the converter and the output due to the external vibration are combined, for example, as shown in Figure 6A. The damped vibration 41 becomes disordered, and its period, that is, the resonant frequency _n , cannot be measured correctly. However, in the embodiment shown in FIG. 5, the noise due to external vibrations does not appear in the output of the adder circuit 37 because they cancel each other out, but the damped vibrations are added to each other, resulting in a good waveform as shown in FIG. 6B. A damped vibration 42 with a large amplitude is obtained.
Therefore, the resonance frequency _n of this damped vibration 42 can be accurately measured by the resonance frequency detection section 38 as explained with reference to FIG. 2, for example, and the volume V of the container 11 can therefore be accurately measured. Note that the present invention can also be applied to the case where the volume V is measured by detecting a frequency that resonates only in the volume V, regardless of the constants of the electroacoustic transducer. <Effects> As described above, according to the present invention, the volume of a closed container can be measured without being affected by external vibrations. Moreover, since the amplitude of the damped vibration obtained in the output of the adding circuit is larger than that in the case where only one electroacoustic transducer is used, the period can be measured more accurately from this point as well.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between the container and the electroacoustic transducer of the acoustic volume measuring device before improvement, and FIG. 2 is a diagram showing an example of the electric circuit of the acoustic volume measuring device before improvement.
FIG. 3 is a waveform diagram for explaining the operation in FIG. 4, and FIG. 4 is a diagram showing the relationship between volume V and resonance frequency _n .
FIG. 5 is a diagram showing an example of the acoustic volume measuring device according to the present invention, and FIG. 6 is a diagram showing an example of the output waveform of the electroacoustic transducer and the output waveform of the adder circuit affected by external vibration. 11: sealed container to be measured, 13, 33: electroacoustic transducer, 15: pulse generator, 16, 36: drive circuit, 35: space between diaphragms, 37: addition circuit, 38: resonance frequency detection section.

Claims (1)

[Claims] 1 Electroacoustic transducers having diaphragms are arranged facing each other in the sealed container to be measured, and the space created between the front surfaces of the diaphragms of these electroacoustic transducers is isolated from the inside of the sealed container, and the space between the two The electroacoustic transducers are configured to be driven synchronously by driving means using electrical signals of substantially continuous frequencies to change the volume inside the sealed container. An acoustic volume measuring device in which the output signals are added by an adding circuit, a resonance frequency determined by the volume of the sealed container is detected by a resonance detection means from the output of the adding circuit, and the volume inside the sealed container is determined based on the detected frequency.