JPS61173119A - Acoustic type volume measuring instrument - Google Patents

Abstract

PURPOSE:To make possible the exact detection of a resonance frequency by taking out the amplitude of a transmission signal to be supplied to an electroacoustic converter at a DC level, comparing the same with a reference value and controlling a heater provided to the electroacoustic converter according to the result of the comparison. CONSTITUTION:The AC transmission signal of VCO21 is envelope-detected and converted to a DC signal like a full-wave rectifier 23 and a peak detecting circuit 24 in an AC/DC converter 31. The signal converted to the DC is supplied to an averaging circuit 32 from which the DC signal is read out repeatedly several times. The average value thereof is compared with the preset reference value by a comparator 33. The temp. control circuit 34 is controlled according to the result of the comparison. The operation of the heater 35 attached to the fixing part at the circumferential edge of a cone oscillation diaphragm 36 of the electroacoustic converter 17 is controlled in the circuit 34. The fluctuation of the resonance frequency by a temp. change is thereby eliminated and the exact detection of the resonance frequency is made possible.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a device for measuring the volume inside a closed container such as a fuel tank for an automobile, and particularly to a device for measuring the volume by supplying an acoustic signal into the container. The present invention relates to an acoustic volume measuring device.

(Prior art) An acoustic signal is applied to a container to be measured, such as a fuel meter for an automobile fuel tank, and the measured object is determined from a resonant frequency determined by the constant of an electroacoustic transducer for providing this acoustic signal and the volume of the part to be measured. A device has been proposed that measures the volume inside a container and determines the amount of fuel, etc., present in the container.

Conventionally, such a device is constructed as shown in FIG. In this figure 2, the sealed container to be measured 1
1 has an opening 16 formed in its upper surface, and an electroacoustic transducer 17 is attached to the sealed capacity 11 so as to close this opening 16. The electroacoustic transducer 17 can be, for example, a moving coil type speaker, and the periphery of the cone diaphragm is connected to the inner periphery of the opening 16 so that the opening 16 is closed. There is. Therefore, by driving this electroacoustic transducer 17 with an alternating current signal, the airtight container 1
The internal volume within 1 can be changed. That is, the liquid 14 is filled in the sealed container 11, and the volume of the liquid 14 is measured by measuring the volume inside the sealed container 11, that is, the volume of the space other than the one filled with the liquid 14. be able to.

Then, an electrical signal with a substantially continuous frequency is supplied to the electroacoustic transducer 17 to drive it. As a means for supplying an electric signal, first, a sweep signal 19 of a sawtooth wave voltage shown in FIG.
21, an oscillation output is obtained from the VCO 21 in which the frequency repeatedly increases with time as shown in FIG. This oscillation output is supplied to the electroacoustic transducer 17 through the amplifier 22 to drive it.

In order to detect the resonant frequency determined by the volume V inside the sealed container 11 and the constant of the electroacoustic transducer 17, a full-wave rectifier 23 is connected to the input side of the electroacoustic transducer 17,
The peak value of this full-wave rectified output is detected by a peak detection circuit 24.

When the driving frequency for the electroacoustic transducer 17 matches the resonance frequency fm determined by the constant of the electroacoustic transducer 17 and the volume V of the container 11, the acoustic impedance becomes maximum and the signal on the input side of the electroacoustic transducer 17 The amplitude increases significantly. Therefore, as shown in FIG. 3C, the signal level at the input side of the electroacoustic transducer 17 has a peak 25 when the drive signal frequency f reaches the resonant frequency fm. The sweep signal 19 has a voltage E l-E 2 as shown in FIG. 3A.
The range of oscillation frequency f changes in a sawtooth wave manner, and accordingly, the oscillation frequency f changes in a sawtooth wave manner during the period f1 to f2. The amplitude of the signal at the input side becomes significantly larger and a peak 25 appears. Therefore, the output of the peak detector 24 generates a pulse 26 at a portion corresponding to the peak 25 as shown in the third diagram. The level Em of the sweep signal 19 when this pulse 26 is obtained is determined by the sampling and holding circuit 27.
Sample and hold as shown in Figure E. This level E is VC
The sampling holding voltage Em is converted into a digital signal by the A/D converter 28 and displayed on the display 29.

In this case, the resonant frequency fIll is determined by the container 11 as described above.
It is determined by the internal volume V of the converter 17 and the constant of the converter 17, and since the constant of the converter 17 is constant, it corresponds to the volume ■.

Therefore, the detected frequency fm, the corresponding voltage Em and the container V
By calibrating in advance, the container 1 is displayed on the display 29.
1, that is, the remaining amount of the liquid 14 can be displayed.

Note that the correction circuit 30 may be provided between the sampling and holding circuit 27 and the A/D converter 28 so that the oscillation frequency fvg of vCO at the peak 25 and the volume V inside the sealed container 11 have a linear relationship. good.

(Problems to be Solved by the Invention) In such a conventional acoustic volume measuring device, the temperature characteristics of the electroacoustic transducer itself are poor especially at low temperatures, and the detected peak oscillation frequency fluctuates.

That is, in a movable wire ring type electroacoustic transducer, for example, a temperature change causes a change in the DC resistance value of the movable wire ring, resulting in a fluctuation in the resonance frequency, which disrupts the relationship with the volume of the container to be measured.

Additionally, if liquid such as gasoline adheres to the movable part (cone diaphragm) of the electroacoustic transducer due to vapor pressure, the mass of the diaphragm will change, and the oscillation frequency at the peak will similarly fluctuate. Stable capacity measurement becomes difficult.

(Means for Solving the Problems) The present invention was made in view of the problems of the conventional devices, and it maintains the temperature characteristics of the electroacoustic transducer itself stably, and also maintains the temperature characteristics of the liquid in the container to be measured. The purpose of the present invention is to provide an acoustic volume measuring device that reduces the influence of temperature changes on adhesion, maintains an electroacoustic transducer in a stable region, and thereby accurately measures the resonant frequency and the volume inside a sealed container. do.

The measuring device of the present invention extracts the amplitude of the oscillation signal supplied to the electroacoustic transducer at a DC level, compares it with a reference value, and controls the heating device provided in the electroacoustic transducer based on the comparison result. This is what I did.

(Example of the invention) Embodiments of the present invention will be described below with reference to the drawings.

In the embodiment shown in FIG. 1, the same parts as in FIG. 2 are given the same reference numerals, and since their operations are the same as in FIG. 2, their explanation will be omitted.

The VCO 21 oscillates as shown in FIG. 3B by the sawtooth wave shown in FIG. 3A generated by the sweep signal generator 18. The oscillation signal whose frequency changes like a sawtooth wave is transmitted to the amplifier 22.
The signal is input to the AC70C converter 31 through the amplifier 22.

The AC70C converter 31 performs envelope detection on the AC oscillation signal of the VCO 21 in the same way as the full-wave rectifier 23 and the peak detection circuit 24, and converts it into a DC signal as shown in the third diagram.

Therefore, the output signal of the peak detection circuit 24 may be used without using the AC70C converter 31 separately.

This DC-converted signal is supplied to the averaging circuit 32, the DC signal is read out several times, and the average value is calculated. The calculated average value is compared with a preset reference value by a comparator 33, and the temperature control circuit 34 is controlled based on the comparison result.

The temperature control circuit 34 controls the operation of a heating device 35 attached to the peripheral fixed portion of the cone diaphragm 36 of the electroacoustic transducer 17.

Next, the operation of the above configuration will be explained.

In the DC signal having the resonance frequency fm shown in the third diagram, the voltage level Vlevel at a frequency fs sufficiently lower than the resonance frequency flI+ is the same as the voltage when the DC signal is applied to the electroacoustic transducer 17.

Therefore, the voltage V which is amplified from this voltage level Vleel
The temperature characteristics of amp are as shown in FIG. 4A. That is,
The resistance value of the movable coil of the electroacoustic transducer 17 increases as the temperature increases. Therefore, the VCO
Among the oscillation signals output from 21, the voltage Va after DC conversion at a frequency fs sufficiently lower than the resonance frequency fm
mp is approximately proportional to temperature.

Therefore, the DC voltage at this low frequency fs is detected, and as shown in FIG. 4B, this DC voltage Vamp and the reference voltage V
ref by a comparator 33, and controls a heating device 35 that applies the comparison result to a temperature control circuit 34, thereby performing temperature control as shown in the drawings. That is, when the voltage Vamp is lower than the reference voltage Vref, the heating device 35 is operated to heat the electroacoustic transducer 17, and when the voltage Vamp is no longer higher than the reference voltage Vref, the heating device 35 is inactive and does not heat.

In FIGS. 4A and 4B, a DC voltage at a temperature of 60° C. is set as the reference voltage Vref. Set to the value of In this case, by setting the reference voltage Vref high to a certain extent, the control temperature range becomes high, and the liquid 14 reaches the cone diaphragm 36.
Even if it adheres to the electroacoustic transducer 17, it can be evaporated and changes in the characteristics of the electroacoustic transducer 17 can be prevented.

In addition, as a means to obtain the DC voltage Vleel shown in the third diagram, the VCO 21 is oscillated at a low frequency of about 300 Hz for a certain period of time (for example, 2 seconds), and the signal amplitude at that time is read out as a DC signal by the AC70C converter 31. , this is input to the averaging circuit 32 and this is repeated several times to calculate the average value of the DC level. Alternatively, a low frequency to be extracted is set in advance, and when the oscillation frequency of the VCO 21 by the sawtooth wave from the sweep signal generator 18 matches the set low frequency, a trigger signal is applied and the DC signal at that time is read out.

(Effects of the Invention) As described above, according to the present invention, it is possible to accurately detect the resonance frequency by eliminating fluctuations in the resonance frequency due to temperature changes of the electroacoustic transducer, and to prevent liquid from adhering to the movable part of the electroacoustic transducer. Even if it is, it can be evaporated by a heating device, and changes in the mass of the movable parts can also be prevented.

Furthermore, according to the present invention, the temperature characteristics of the electroacoustic transducer itself are used to detect temperature.
Temperature detection can be easily performed without the need to separately provide a temperature sensor.

Furthermore, by attaching a heating device to a location where the movable part of the electroacoustic transducer is fixed, it is possible to heat the electroacoustic transducer and raise its temperature with low power.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the acoustic volume measuring device according to the present invention, FIG. 2 is a block diagram showing a conventional acoustic volume measuring device, and FIG. 3 A8 to E are respectively similar to FIG. 1 and FIG. Waveform diagrams of various parts in the apparatus according to FIG. 2, and FIGS. 4A and 4B are characteristic diagrams for explaining the operation of the apparatus according to FIG. 2, respectively. 11... Airtight container 14... Liquid 17... Electroacoustic transducer 21... vCo 31... A C/DC converter 32... Averaging circuit 33... Comparator 34...・Temperature control circuit 35...Heating device patent applicant Yazaki Corporation Figure 2 Figure 3

Claims (1)

[Claims] an electro-acoustic-acoustic transducer that is installed in a sealed container to be measured and changes the volume inside the sealed container; a driving means that drives the electro-acoustic transducer with an electrical signal of a substantially continuous frequency;
an acoustic volume measuring device comprising: a detection means for detecting a resonance frequency determined by a volume within the sealed container to be measured and a constant of the electroacoustic transducer; DC conversion means for converting a signal from the driving means using the electric signal having a frequency sufficiently lower than the resonance frequency into a DC signal, a comparator for comparing the DC signal of the DC conversion means with a reference value, and a comparison result from the comparator. The temperature characteristics of the electroacoustic transducer are stabilized by a temperature control means operated by the temperature control means, and a heating device that is controlled by the temperature control means and heats the movable part of the electroacoustic transducer. Acoustic volume measuring device.