JPH0362204B2 - - Google Patents

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. measure,
A device has been proposed that uses this information to determine the fuel and other information present in the container.

Conventionally, such a device is constructed as shown in FIG. In FIG. 3, the sealed container 11 to be measured has an opening 16 formed on the top surface.
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 internal volume within the closed container 11 can be changed. In other words, the liquid 14 is filled in the closed container 11, and therefore the volume inside the closed container 11, that is, the volume of the space other than that filled with the liquid 14 is V.
The volume of the liquid 14 can be measured by measuring .

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. As shown in FIG. 4B, an oscillation output is obtained from the VCO 21 in which the frequency repeatedly increases with time. 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 this 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, and this full-wave rectifier 23 is connected to the input side of the electroacoustic transducer 17. A peak value of the output is detected by a peak detection circuit 24.

When the driving frequency for the electroacoustic transducer 17 matches the resonance frequency m determined by the constant of the electroacoustic transducer 17 and the volume V of the container 11, the acoustic impedance becomes maximum and the electroacoustic transducer 17
The signal amplitude on the input side becomes significantly large. 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 reaches the resonance frequency m. The sweep signal 19 is a voltage E ₁ -E ₂ as shown in FIG. 4A.
Accordingly, the oscillation frequency changes in a sawtooth wave manner over a period of ₁ to ₂ , but when that frequency reaches the resonance frequency m,
The amplitude of the signal at the input side of the electroacoustic transducer 17 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 FIG. 4D. Sweep signal 1 when this pulse 26 is obtained
The level Em of 9 is sampled and held by the circuit 27 as shown in Fig. 4E.
Sample and hold as shown in . This level E
It corresponds to the resonance signal generator m of VCO21,
The sampled 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 resonance frequency m 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. Therefore, by calibrating the voltage Em corresponding to the detected frequency m and the container V in advance, the internal volume V of the container 11, that is, the remaining amount of the liquid 14 can be displayed on the display 29.

Furthermore, the oscillation frequency m of the VCO at peak 25
The correction circuit 30 is connected to the sampling holding circuit 27 and the A/
It may also be provided between the D converter 28 and the D converter 28.

[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 type electroacoustic transducer, for example, due to temperature changes, the DC resistance value of the movable wire changes, the resonance frequency fluctuates, and the relationship with the volume of the container to be measured breaks down. .

Also, due to vapor pressure, etc., liquids such as gasoline may cause the moving parts of the electroacoustic transducer (cone diaphragm) to
If it adheres to the diaphragm, the mass of the diaphragm changes, and the oscillation frequency at the peak also fluctuates, making stable capacitance measurement difficult.

Therefore, in view of the above-mentioned conventional problems, the present invention has been made to
Maintains stable temperature characteristics of the electroacoustic transducer itself,
In addition, the temperature characteristics of the electroacoustic transducer itself are maintained stably, and the influence of the adhesion of liquid in the sealed container to the electroacoustic transducer is reduced, making it possible to more accurately measure the volume of the space inside the sealed container. It is an object of the present invention to provide an acoustic volume measuring device as described above.

[Means for solving problems]

In order to achieve the above object, an acoustic volume measuring device according to the present invention is provided so as to close the opening of a closed container containing a liquid therein, and is driven to cover the opening of a closed container containing a liquid. an electroacoustic transducer for changing the volume of an unfilled space; a drive means for driving the electroacoustic transducer with an electrical signal of continuously varying frequency; detection means for detecting a resonant frequency determined by the volume of the space and a constant of the electroacoustic transducer; an acoustic volume measuring device for measuring the temperature of the electroacoustic transducer, comprising: temperature detection means for detecting the temperature of the electroacoustic transducer and outputting a signal having a magnitude corresponding to the detected temperature; and a signal outputted by the temperature detection means. and a reference value corresponding to a predetermined temperature; a temperature control means operated according to the comparison result by the comparator; and a heating means for keeping the temperature of the heating part constant and evaporating the liquid adhering to the movable part, and the temperature control means is configured such that the temperature detected by the temperature detection means is set based on a reference value. The electroacoustic transducer is heated by the heating means when the temperature is lower than the temperature, and the heating of the electroacoustic transducer by the heating means is stopped when the temperature is higher than the temperature.

[Effect]

In the above configuration, the temperature of the electroacoustic transducer is detected by the temperature detection means, the comparator compares the detected temperature with a reference value corresponding to a predetermined temperature, and as a result of this comparison, the detected temperature becomes the reference value. When the temperature is lower than the set temperature, the temperature control means causes the heating means to heat the movable part of the electroacoustic transducer, and when the temperature is higher than the set temperature, the temperature control means causes the heating means to stop heating the movable part of the electroacoustic transducer. This ensures that the temperature of the electroacoustic transducer is maintained at a predetermined temperature determined by the reference value, and that even if liquid adheres to the moving parts of the electroacoustic transducer, it is immediately evaporated and removed. Therefore, the constants of the electroacoustic transducer do not change due to temperature changes or attached liquid.

[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. This oscillation signal whose frequency changes like a sawtooth wave is input to the amplifier 22 and, through the amplifier 22, to the AC/DC converter 31.
The AC/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 FIG. 4D.

Therefore, the output signal of the peak detection circuit 24 may be used without separately providing the AC/DC converter 31.

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.
In the temperature control circuit 34, a heating device 35 is attached to the peripheral fixed portion of the cone diaphragm 36 of the electroacoustic transducer 17.
control the behavior of

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

In the DC signal having the resonance frequency m shown in FIG. 4D, the voltage level Vlevel at a frequency s sufficiently lower than the resonance frequency m is similar to the voltage when the DC signal is applied to the electroacoustic transducer 17. Therefore, the temperature characteristics of the voltage Vamp obtained by amplifying this voltage level Vlevel are as shown in FIG. 5A. That is, the movable ring of the electroacoustic transducer 17 is
As the temperature rises, the resistance value increases almost proportionally. Therefore, among the oscillation signals output from the VCO 21, the DC-converted voltage Vamp at a frequency s sufficiently lower than the resonance frequency m is approximately proportional to the temperature.

Therefore, this DC voltage at the low frequency s is detected, and as shown in FIG. By controlling the temperature, the temperature is controlled as shown in the drawing. That is, the voltage Vamp is the reference voltage Vref
In a lower state, the heating device 35 is activated to heat the electroacoustic transducer 17, and when the voltage is higher than the reference voltage Vref, the heating device 35 is deactivated and does not heat.

In addition, in FIGS. 5A and 5B, the reference voltage Vref
The DC voltage at a temperature of 60℃ was set as
It is set to a desired value depending on the characteristics of the electroacoustic transducer 17, the type of the closed container 11, or the type of liquid 14 to be filled. In this case, by setting the reference voltage Vref high to a certain extent, the control temperature range becomes high, and even if the liquid 14 adheres to the cone diaphragm 36, it can be evaporated, thereby preventing changes in the characteristics of the electroacoustic transducer 17. can.

In addition, as a means to obtain the DC voltage Vlevel shown in FIG. The average value of the DC level is calculated by inputting this into the averaging circuit 32 and repeating this several times. 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 (not shown) such as a thermistor is thermally coupled to the movable wire ring 15, and this is connected to the temperature detector 37 to output a voltage Vamp corresponding to the temperature of the movable wire ring 15.

Therefore, this voltage Vamp and the reference voltage Vref are
Comparing with the comparator 33 as shown in Figure B,
The comparison result is added to the temperature control circuit 34, and the heating device 3
Temperature control is performed by controlling 5.

At this time, if the reference voltage Vref 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, the temperature of the electroacoustic transducer is maintained at a predetermined temperature determined by a reference value, and even if liquid adheres to the electroacoustic transducer, it is immediately evaporated and removed. It became like this,
Since the constant of the electroacoustic transducer does not change due to temperature changes or adhered liquid, it becomes possible to more accurately measure the volume of the space inside the closed container.

[Brief explanation of drawings]

1 and 2 are block diagrams showing an embodiment of the acoustic volume measuring device according to the present invention, and FIG.
The figure is a block diagram showing a conventional acoustic volume measuring device, FIGS. 4A to 4E are waveform diagrams of various parts of the device according to FIGS. 1, 2, and 3, respectively, and FIGS. FIG. 2 is a characteristic diagram for explaining the operation of the apparatus according to FIGS. 1 and 2; 11... airtight container, 14... liquid, 15... movable wire ring, 17... electroacoustic transducer, 21...
VCO, 31...AC/DC converter, 32...Averaging circuit, 33...Comparator, 34...Temperature control circuit, 35...Heating device, 37...Temperature detector.

Claims (1)

[Scope of Claims] 1. Electricity that is provided to close the opening of a closed container containing a liquid therein and that changes the volume of a space not filled with liquid in the closed container by being driven. an acoustic transducer, a driving means for driving the electroacoustic transducer with an electrical signal whose frequency continuously changes, a volume of a space not filled with liquid in the sealed container, and a constant of the electroacoustic transducer. and a detection means for detecting a resonance frequency determined by the detection means, the acoustic volume measuring device measures the volume of a space within the sealed container based on the resonance frequency detected by the detection means, temperature detection means for detecting the temperature of the electroacoustic transducer and outputting a signal of a magnitude corresponding to the detected temperature; and comparing the signal output by the temperature detection means with a reference value corresponding to a predetermined temperature. a comparator that operates according to the comparison result of the comparator; and a temperature control means that is controlled by the temperature control means to heat the movable part of the electroacoustic transducer to keep the temperature of the heating part constant and to control the temperature of the movable part. heating means for evaporating the liquid adhering to the temperature control means, the temperature control means controlling the electroacoustic conversion by the heating means when the temperature detected by the temperature detection means is lower than the temperature set by a reference value. 1. An acoustic volume measuring device, characterized in that the heating of the electroacoustic transducer by the heating means is stopped when the heating temperature is high.