JPH0113523B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a liquid meter that detects the amount of liquid in a container from the capacitance of a pair of electrodes provided in the container, and particularly to a liquid amount measuring circuit.

An example of this type of conventional liquid meter is the one shown in FIG. Figure A shows the installation state of the dielectric constant measurement electrode pair 2 and liquid volume measurement electrode pair 3 installed inside the container 1, and Figure B shows the capacity of the container from the capacitance of each of the electrode pairs 2 and 3. 1 shows an arithmetic circuit that calculates the amount of liquid in 1. The electrode pair 2 is installed at the bottom of the container 1 so as to be constantly immersed in the liquid 4, and the electrode pair 3 is installed in the depth direction of the liquid in the container. The purpose of the electrode pair 2 is to detect a standard capacitance determined by the dielectric constant of the liquid 4 filling between the electrodes, and the purpose of the electrode pair 3 is to detect the capacitance determined by the ratio of the liquid 4 filling the gap between the electrodes and air. Then, the arithmetic circuit shown in FIG. 1B calculates the liquid amount from the capacitance of the electrode pair 3 with the capacitance of the electrode pair 2 as a reference. This liquid amount detection will be explained below.

In FIG. 1A, the container 1 is a cube, and the area S of the liquid surface is constant and the height (depth direction) is L,
Area S ₂ of electrode pair 2 for dielectric constant measurement, distance d ₂ between electrode plates,
Assuming that the area of the electrode pair 3 for measuring liquid volume is S ₃ , the distance between the electrode plates is d ₃ , and there is a liquid 4 with a relative dielectric constant ε _r at a depth l in a melter with a height L, the electrostatic charge of the electrode pair 3 is Capacity C _M is below
It becomes equation (1). However, ε ₀ is the dielectric constant of air.

C _M = ε _r・ε ₀・S ₃ ×l/L/d ₃ +ε ₀・S ₃ ×L−1/
L/d ₃ = S ₃・ε ₀ /L・d ₃ (l・ε _r +L−l) ...(1) Here, S ₃ , ε ₀ , L, and d ₃ are constants, and these are called constants. Transforming equation (1) as A(=S ₃ ε ₀ /Ld ₃ ), we get l=C _M −A・L/A(ε _r −1)=C _M −C ₀ /A(ε _r
-1)...(2). However, since AL=(S ₃ ·ε ₀ )/d ₃ is the capacity when there is no liquid 4, this is indicated as C ₀ .

From the above equation (2), the liquid volume V in the container is determined as V=l·S=S/A· _CM −C ₀ /ε _r −1 (3). That is, the liquid volume V can be determined by measuring the capacitance C _M of the liquid volume measuring electrode pair 3.

In the above formula (3), the relative dielectric constant ε _r is determined by the liquid 4, but if the liquid 4 is gasoline for automobiles, the relative dielectric constant changes depending on the temperature, and furthermore, the dielectric constant changes depending on the temperature, and the addition of gasoline additives or the use of gasohol, etc. The dielectric constant changes significantly. Therefore, in order to measure the liquid volume of a liquid whose relative dielectric constant varies or is unknown, the capacitance detected by the dielectric constant measuring electrode pair 2 is used as a value proportional to the relative permittivity ε _r of the liquid.

The capacitance C _S of the dielectric constant measurement electrode pair 2 is C _S =ε ₀ ·ε _r ·S ₂ /d ₂ , and the relative permittivity ε _r is expressed by the following equation (4).

ε _r =C _S ·d ₂ /ε ₀ ·S ₂ ...(4) From these equations (4) and (3), the liquid volume V is transformed into the following equation (5).

V=A ₀・C _M −C ₀ /KC _S −C ₀ …(5) However, A ₀ =S・L, K=(d ₂・S ₃ )/(d ₃・
S ₂ ) is a constant.

Therefore, the amount of liquid in the container 1 can be measured by measuring the capacitances C _M and C _S of the electrode pair 2 and 3 and calculating the equation (5). The calculation circuit for equation (5) above is shown in Figure 1B.
The configuration is shown in .

In Figure 1B, the capacitance of electrode pair 2 and 3
C _M and C _S are coupled as capacitances for setting the oscillation frequency of the oscillation circuits 5 and 6, respectively, and pulses T _M (=C _M・B _M ) and T with periods proportional to the capacitances C _M and C _{S S} (=
_{The oscillation circuits 5 and 6 output (B M , B S}
is a proportionality constant).

These pulse periods T _M and T _S are converted into binary count values by period measuring circuits 7 and 8, respectively, and the period measuring circuit 7
The constant B _M ·C ₀ is subtracted from the output by the subtraction circuit 9 to obtain B _M (C _M -C ₀ ), and a value proportional to CM - _{C 0} in the above equation (5) is obtained. On the other hand, the output of the period measurement circuit 8 is multiplied by a constant K (K・_TS ) in a multiplication circuit 10, and the constants B _S and C ₀ are subtracted in a subtraction circuit 11.
B _S (KC _S −C ₀ ), and a value proportional to KC _S −C ₀ in the above equation (5) is obtained.

The numerical value calculated in this way is divided by the division circuit 12, and further by the multiplication circuit 13 by the constant A ₀ · B _S /
B _M is multiplied and a value proportional to the liquid volume V ₀ is obtained from the output of the multiplication circuit 13 as a result of the calculation of the above equation (5). This liquid level detection value is input to a liquid level indicator or used as calculation data for other calculation circuits such as a remaining travel distance meter.

These conventional liquid level meters have two oscillation circuits and a period measurement circuit in their liquid level calculation circuit.
Since it requires one division circuit, two subtraction circuits, and two multiplication circuits based on binary value calculation, there is a problem in that it requires a complicated and expensive hardware configuration or an expensive microcomputer.

SUMMARY OF THE INVENTION An object of the present invention is to provide a liquid amount measuring circuit that can ensure measurement accuracy equivalent to that of the conventional method by configuring an arithmetic circuit using simple circuit hardware.

The arithmetic circuit according to the present invention includes two oscillation circuits and four
It is characterized by being configured with two frequency dividing circuits, two monostable multivibrators, two gate circuits, and two counter circuits.

FIG. 2 is a circuit diagram showing one embodiment of the present invention. Oscillation circuits 5 and 6 generate pulses with periods T _M and T _S proportional to the respective capacitances C _M and C _S at the electrode pair 3 for liquid volume measurement and the electrode pair 2 for dielectric constant measurement, as in the conventional circuit. do. These pulses are transmitted through frequency dividing circuits 14 and 15, respectively.
Frequency division is performed by frequency division ratios N ₁ and N ₂ , and the pulses are converted into pulses with periods T _M ×N ₁ and T _S ×N ₂ , respectively. Output pulses with division periods 14 and 15 are used as trigger pulses for monostable multivigulators 16 and 17, respectively.
Pulse period T _M ×N ₁ , T _S ×N ₂ pulse width T ₁ ,
Has T ₂ .

Gate circuit 18 is monostable multivibrator 1
The remaining period T _M・N ₁ excluding the output pulse width T ₁ of 6
The output pulse (period T _S ) of the oscillation circuit 6 is extracted by −T ₁ . Similarly, the gate circuit 19 extracts the output pulse (period T _M ) of the oscillation circuit 5 for the remaining period T _S ·N ₂ −T ₂ excluding the output pulse width T ₂ of the monostable multivibrator 17 . These gate circuits 18,1
The output pulses of 9 are divided by frequency division ratios N ₄ and N ₃ by frequency dividers 20 and 21, respectively.

The counter circuit 22 counts the number of output pulses of the frequency divider 20 for each output pulse period of the frequency divider 21, and the counted value is stored and held in the latch circuit 23, and the content of the latch circuit 23 is a value proportional to the liquid amount. is extracted as

3 and 4 show the time chart of FIG. 2, and the operation of FIG. 2 will be explained below with reference to this time chart.

Output pulses of oscillation circuits 5 and 6 (Fig. 3 a, b)
are the capacitances C _M and C _S of the electrode pairs 3 and 2, respectively, and the period T _M ,
T _S becomes a proportional pulse train whose proportionality constant is
Set B _M and B _S. The outputs of the frequency dividers 14 and 15, which divide these pulses with the frequency division ratio of N ₁ and N ₂ , have a period
This results in a pulse train of T _M ×N ₁ and T _S ×N ₂ (Fig. 3c, d). The monostable multivibrators 16 and 17 triggered by these pulses produce pulses with output widths T ₁ and T ₂ (Fig. 3 e and g), respectively, and this pulse width
Periods excluding T ₁ and T ₂ T _M ×N ₁ −T ₁ , T _M ×N ₁ −T ₂
Gate circuit 1 that only allows pulse trains T _S and T _M to pass through
The outputs of 8 and 19 are shown in Figure 3 f and h.

Therefore, the average periods T _MO and T _SO of the output pulses of the gate circuits 18 and 19 are expressed by the following equations (6) and (7).

T _MO = T _S・N ₁・T _M /N ₁・T _M −T ₁ …(6) T _SO =T _M・N ₂・T _S /N ₂・T _S −T ₂ …(7) Furthermore, the average periods T _MO1 and T _SO1 of the output pulses of the frequency dividers 20 and 21, which divide the outputs of the gate circuits 18 and 19 by frequency division ratios N ₄ and N ₃ respectively, are calculated by the following equations (8) and (9). become.

T _MO1 =N ₄ ×T _MO =N ₄・T _S・N ₂・T _S /N ₁ T _M −T ₂ ……(8) T _SO1 =N ₃ ×T _SO =N ₃・T _M・N ₂ -T _S /N ₂ T _S −T ₂ (9) Then, the counter circuit 22 counts the pulse train of the average period T _MO1 for each average period T _SO1 . The pulse train with this average period T _MO1 and T _SO1 is shown in Fig. 4 i, j
(The time scale in FIG. 4 is smaller than that in FIG. 3.) The count value N of the counter circuit 22 changes as shown in FIG. 4 k, and the following (10)
It becomes a ceremony.

N=T _MO1 ×T _SO1 =N ₂ /N ₄・N ₃ /N ₁ ×N ₁・T _M −T ₁ /N ₂・T _S −T ₂ =N ₃ /N ₄・1/B _M・C _M −T ₁ / (B _M・N ₁ ) / B _S・C _S −T ₂
/N ₂ ...(10) In the above formula (10), from the relationship with the above formula (5), N ₃ /N ₄・1/B _M = A _O (container volume) B _M・T ₁ /N ₁ = The frequency division ratios N ₁ to _{N 4} of the frequency dividers 14, 15, 20, and 21, the oscillator proportionality constant B _M・_{B S , and the monostable multivibrator 16, so as to satisfy T 2 /N 2 = C O B S =} K, 17 pulse widths T ₁ , T ₂
By setting , the contents of the counter circuit 22 (FIG. 4l) can obtain a numerical value proportional to the liquid amount.

Here, the frequency divider 20 has a frequency division ratio N ₄ =1, that is, the frequency divider 20 can be omitted, but the capacitance
Since C _M is small, the period of the pulse passing through the gate circuit 19 becomes small, and when applied to a gasoline tank of an automobile, the capacitance of the electrode pair 3 constantly fluctuates due to vibration, making the display unstable. I end up. For this purpose, it is better to provide the frequency divider 20 and increase its frequency division ratio, and accordingly increase the frequency division ratio of the frequency divider 21 for display.

As described above, the liquid amount measuring circuit according to the present invention has the following features:
In addition to two oscillation circuits that obtain pulses with a period proportional to the capacitance of the dielectric constant measurement electrode pair 2 and the liquid volume measurement electrode pair 3, there are two frequency dividers 14 and 15 and two monostable multivibrators. 16, 17, gate circuits 18, 19, frequency divider 21, and counter circuit 22 are prepared, the gate circuits 18 and 19 subtract the pulse width, the frequency dividers 14 and 15 multiply the pulse width, and the counter circuit calculates the number of pulses. Since the structure is configured to perform division of , it is possible to measure the liquid amount with high precision at a low cost with a smaller number of logic circuit elements than in the conventional liquid amount measuring circuit.

[Brief explanation of drawings]

FIG. 1A is a schematic diagram showing the arrangement of electrode pairs of a liquid meter;
Fig. 1B is an arithmetic circuit diagram of a conventional liquid meter, Fig. 2 is an arithmetic circuit diagram showing an embodiment of the present invention, and Figs. 3 and 4 are timing diagrams for explaining the operation of Fig. 2. It's a chat. 1... Container, 2... Electrode pair for dielectric constant measurement, 3...
... Electrode pair for liquid volume measurement, 5, 6 ... Oscillation circuit, 1
4, 15... Frequency divider, 16, 17... Monostable multivibrator, 18, 19... Gate circuit, 2
0, 21... Frequency divider, 22... Counter circuit, 2
3...Latch circuit.

Claims (1)

[Claims] 1. A container having a container volume V ₀ into which a liquid to be measured is placed, and a pair of electrodes having an area S ₃ and an inter-electrode distance d ₃ in the container according to the amount of the liquid to be measured. Provided at a position where the capacitance C _M of the pair of electrodes changes,
When the liquid volume is zero, the capacitance C becomes ₀ , and there is a proportional constant to the capacitance C _M according to the target liquid volume.
a first pulse generating means that generates a pulse signal with a period T _{M determined} by multiplying by B _{M ;} a second pulse generating means for generating a pulse signal with a period T _S determined by multiplying a capacitance C _S corresponding to the target liquid by a proportionality constant B _S by a pair of electrodes; The pulse width is changed in synchronization with the pulse that is obtained by dividing the pulse signal by the frequency division ratio N ₁ .
A third pulse generating means outputs a pulse signal with a pulse width T ₁ , and a pulse signal with a pulse width T ₂ is generated in synchronization with a pulse obtained by dividing the pulse signal from the second pulse generating means by a frequency division ratio N ₂ . A fourth pulse generating means to output, and a pulse width T ₁ from the third pulse generating means.
a first passing means for passing a pulse signal with a period T _S from the second pulse generating means from the falling edge of the pulse signal until the next rising edge; and a pulse width T from the fourth pulse generating means. ₂
a second passing means for passing the pulse signal with a period T _M from the first pulse generating means from the falling edge of the pulse signal until the next falling edge; and a pulse signal passed through the second passing means. A pulse signal having an average period of a pulse signal obtained by dividing a pulse signal that has passed through the first passing means by a frequency division ratio N ₄ for each pulse interval of an _average period of a pulse signal obtained by dividing the frequency by a frequency division ratio N 3. N ₃ /B _M・N ₄ =V ₀ T ₁ /B _M・N ₁ =T ₂ /N ₂ =C ₀ B _S =d ₂・S ₃ /d ₃・S 2. A liquid amount measuring circuit characterized in that the counting means obtains a count value proportional to the amount of liquid in the container by satisfying the relationship ( ₂ ).