JPS61173118A - Acoustic type volume measuring instrument - Google Patents

Abstract

PURPOSE:To make possible the exact detection of a resonance frequency by detecting the temp. of an electroacoustic apparatus, comparing the same with a reference value and controlling a heater provided to an electroacoustic converter according to the result of the comparison. CONSTITUTION:The temp. by the heat generated from a movable coil 15 of the electroacoustic converter 17 is directly detected. More specifically, a temp. resistance element such as thermistor is coupled to the coil 15 and is connected to a temp. detector 37 from which the voltage corresponding to the temp. of the coil 15 is outputted. The detection voltage has a proportional relation with the temp. of the converter 17 when the detection output is set near the voltage level at the frequency substantially lower than the resonance frequency. The voltage and the reference voltage are thereupon compared by a comparator 33 and the result of the comparison is applied to a temp. control circuit 34, which controls a heater 35. The temp. control is thus executed.

Description

[Detailed Description of the Invention] [Industrial Application Field] 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.

[Conventional technology]

An acoustic signal is applied to the inside of the container to be measured, such as a fuel meter for an automobile fuel tank. A device has been proposed that measures fuel and determines the amount of fuel present in the container.

Conventionally, such a device is constructed as shown in FIG. In this Fig. 3, 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 closed container 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 closed container 11, and therefore the volume of the liquid 14 is measured by measuring the volume inside the closed container 11, that is, the volume V of the space other than the one filled with the liquid 14. I can do it.

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 generator 18 generates a sawtooth voltage sweep signal 19 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. 4B. 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. 4C, 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. As shown in FIG. 4A, the sweep signal 19 varies in the range of voltage E, ~Ez in a sawtooth wave manner, and accordingly, the oscillation frequency f changes in the period f, ~ft in a sawtooth wave manner. However, when the frequency f becomes the resonant frequency fm, the amplitude of the signal on the input side of the electroacoustic transducer 17 becomes significantly large.
Peak 25 appears.

Therefore, in the output of the peak detector 24, a pulse 26 is generated at a portion corresponding to the peak 25 as shown in the fourth diagram. The level Em of the sweep signal 19 when this pulse 26 is obtained
is sampled and held in the sampling holding circuit 27 as shown in FIG. 4E. This level E is the resonance signal generator f of VCO21.
The sampled holding voltage Em is converted into a digital signal by the A/D converters 2 and 8 and displayed on the display 29.

In this case, the resonance frequency fm is determined by the internal volume V of the container 11 and the constant of the converter 17 as described above, and since the constant of the converter 17 is constant, it corresponds to the volume V. Follow
By calibrating in advance the voltage Em corresponding to the detected frequency fm and the container V, the container 11 is displayed on the display 29.
The internal volumes V and B can display the remaining amount of the liquid 14.

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 fm of the VCO at the peak 25 and the volume (2) in the sealed container 11 have a linear relationship. good.

[Problem that the invention seeks to solve]

In such conventional acoustic volume measuring devices, 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 stable temperature characteristics of the electroacoustic transducer itself, and also maintains the temperature characteristics of the liquid in the container to be measured. Another object of the present invention is to provide an acoustic volume measuring device that reduces the influence of temperature changes on adhesion, keeps the electroacoustic transducer in a stable region, and thereby accurately measures the resonant frequency and the volume inside the sealed container. do.

The measuring device of the present invention detects the temperature of an electroacoustic transducer, compares it with a reference value, and controls a heating device provided in the electroacoustic transducer based on the comparison result.

[Embodiments of the invention]

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

FIG. 1 shows a first embodiment of the present invention. In the figure, the same parts as in FIG. 3 are denoted by the same reference numerals, and since the operation thereof is the same as that in FIG. 3, a description thereof will be omitted.

The VCO 21 oscillates as shown in FIG. 4B by the sawtooth wave shown in FIG. 4A generated by the sweep signal generator 18. The oscillation signal whose frequency changes like a sawtooth wave is transmitted to the amplifier 22.
It is also input to the AC/DC converter 31 through the amplifier 22.

The A C/DC converter 31 envelope-detects 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 fourth diagram.

Therefore, the output signal of the peak detection circuit 24 may be used without requiring the AC/CD 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 fourth diagram, the voltage level V 1evel at a frequency fs sufficiently lower than the resonance frequency fm is the same as the voltage when the DC signal is applied to the electroacoustic transducer 17. Therefore, the voltage V aIlp obtained by amplifying this voltage level Vlevel
The temperature characteristic of is shown in FIG. 5A. That is, the resistance value of the movable coil of the electroacoustic transducer 17 increases as the temperature increases. Therefore, among the oscillation signals output from the VCO 21, the voltage V amp after DC conversion at a frequency fs sufficiently lower than the resonance frequency fm
is almost proportional to temperature.

Therefore, the DC voltage at the low frequency fs is detected, and as shown in FIG. By controlling the heating device 35, temperature control as shown in the drawings is performed. That is,
When the voltage V amp is lower than the reference voltage V ref, the heating device 35 is activated to heat the electroacoustic transducer 17, and when the voltage V amp is no longer higher than the reference voltage V ref, the heating device 35 is deactivated and does not heat.

In FIGS. 5A and 5B, 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.

Further, as a means for obtaining the DC voltage Vlevel shown in the fourth 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 converted into a DC signal by the AC/DC converter 31. reading,
By inputting this to the averaging circuit 32 and repeating this several times, the average value of the DC level is calculated. 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.

FIG. 2 shows a second embodiment of the present invention, in which the temperature due to heat generated from the movable wire ring 15 of the electroacoustic transducer 17 is directly detected.

That is, a temperature resistance element such as a thermistor (
(not shown) is connected to the temperature sensor 37 to output a voltage VaB corresponding to the temperature of the movable wire ring 15.

This detection output is set to a frequency fs sufficiently lower than the resonance frequency fm.
When the voltage V is set in the vicinity of 1evel, the fifth
As shown in FIG. A, the detected voltage V amp is proportional to the temperature of the movable wire ring 15, that is, the temperature of the electroacoustic transducer 17.

Therefore, this voltage V atsp and the reference voltage V ref are compared by a comparator 33 as shown in FIG. 5B, and the comparison result is applied to the temperature control circuit 34 to control the heating device 35 to perform temperature control.

At this time, if the reference voltage V ref is set to a certain level by keeping the temperature of the electroacoustic transducer 17 high as described above, even if the liquid 14 adheres to the diaphragm 36, it can be evaporated.

〔Effect 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 even if liquid adheres to the movable part of the electroacoustic transducer, it is possible to detect the resonance frequency accurately. It can be evaporated by the device, and changes in the mass of the movable parts can also be prevented.

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]

1 and 2 are block diagrams showing an embodiment of the acoustic volume measuring device according to the present invention, FIG. 3 is a block diagram showing a conventional acoustic volume measuring device, and FIGS. 4 A to E are respectively FIG. 5A is a waveform diagram of each part in the apparatus according to FIGS. 1, 2, and 3. B is a characteristic diagram for explaining the operation of the apparatus according to FIG. 1 and FIG. 2, respectively. DESCRIPTION OF SYMBOLS 11... Airtight container, 14... Liquid, 15... Movable wire ring, 17... Electro-acoustic transducer, 21... VCO1
31... AC/DC converter, 32... averaging circuit,
33... converter, 34... temperature control circuit, 35
... Heating device, 37... Temperature detector. Patent applicant Yazaki Sogyo Co., Ltd. Figure 3 Figure 4

Claims (1)

[Claims] an electroacoustic transducer installed in a sealed container to be measured and for changing the volume inside the sealed container; a driving means for driving the electroacoustic transducer with an electric signal of a substantially continuous frequency; and a volume inside the sealed container to be measured. and a detection means for detecting a resonant frequency determined by a constant of the electroacoustic transducer, the acoustic volume measuring device for determining the volume inside the sealed container by the detection means, the acoustic volume measuring device detecting the temperature of the electroacoustic transducer. a comparator that compares the temperature detected by the temperature detection means with a reference value; and a temperature control means that operates based on the comparison result from the comparator.
An acoustic volume measuring device characterized in that temperature characteristics of the electroacoustic transducer are stabilized by a heating device that is controlled by the temperature control means and heats a movable part of the electroacoustic transducer.