JPS623891B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention vertically erects a transmitter having concentric cylindrical electrodes in a fuel tank, and detects the volume of fuel in the tank from changes in capacitance due to the fuel that immerses the electrodes. , derives the fuel density signal using a dielectric constant detection capacitor placed at the bottom of the tank,
This relates to a fuel meter that measures the weight of fuel in a tank by multiplying this density signal and the volume signal, and more specifically relates to a capacitive fuel meter that obtains the weight signal purely electronically. It is.

FIG. 1 is a circuit diagram showing a conventional fuel meter using a transformer bridge system. In the figure, 1 is a transformer, and an excitation voltage is applied to a primary winding 101. In addition, the secondary winding 10 whose intermediate point is grounded
Terminal voltages V ₁ and V ₂ are generated at both ends of the terminal 2, respectively, and a voltage V ₃ is generated at the connection point between the ground point and the V ₂ terminal. Note that a sliding resistor 201 is connected between the _V3 voltage terminal and the ground point. 3
is a capacitor with concentric cylindrical electrodes arranged vertically in the fuel tank to detect the volume of fuel, one plate of which is connected to the V ₁ voltage terminal of the secondary winding. 4 is a capacitor connected to the _V2 voltage terminal of the secondary winding 102, and is a comparison capacitor for canceling and balancing the voltage generated through the capacitor 3. 5 is a fixed capacitor for calculation, and 6 is a capacitor for detecting the dielectric constant of the fuel connected in parallel with the capacitor 5, which is always immersed in the fuel in the tank. One end of the parallel circuit consisting of the fixed capacitor 5 and the dielectric constant detection capacitor 6 is connected to the sliding resistor 201 via the slider 202, and the other end is connected to the input side of the servo amplifier 7. In addition, capacitor 3,
4 are commonly connected and connected to the input side of the servo amplifier 7. A servo motor 8 is driven by the output of the servo amplifier 7 and moves the slider 202 so that the input to the servo amplifier 7 becomes zero.

When the servo circuit is balanced with such a configuration, the input to the servo amplifier becomes zero and becomes a virtual ground potential. The composite capacitance of capacitor 3 is the sum of the dry capacitance CM and the increase in capacitance due to immersion in fuel with relative dielectric constant K X(K-1) CM
Since the CM value is CM+X(K-1), the current flowing through capacitor 3 is V ₁ ω{CM+X(K-1)
CM}. The combined capacitance of capacitor 5 and dielectric constant detection capacitor 6 is KC _c +CB, and the applied voltage is MV ₃ , so the combined current is MV ₃ ω
(KC _c + CB). Further, the current flowing through the capacitor 4 is V ₂ ωCF. Therefore, if we take the algebraic sum of these while paying attention to the phase of each voltage, we get V ₁ · ω {CM + X (K-1) CM} - M · V ₃ · ω (K · Cc + CB) - V ₂ · ω · CF=0 ......(1) The following relationship holds true. Here ω is the angular frequency (2π
f), Cc is the dry capacitance of the dielectric constant detection capacitor 6, CF is the capacitance of the comparison capacitor 4, CB is the capacitance of the capacitor 5, K is the dielectric constant of the fuel, and X is the immersion ratio of the capacitor 3 (tank (proportional to the fuel volume within) and M indicate the rotation angle (indication) of the slider 202, respectively.

In the above equation (1), if it is determined in advance that V ₁ CT = V ₂ CF so that the voltage generated through capacitor 3 during drying is canceled by the voltage generated in capacitor 4, then the above equation becomes It can be rewritten as

On the other hand, there is a general basic equation between the fuel density D and the dielectric coefficient K as follows: D=A・(K-1)/B+(K-1) (3). Here, A and B are constants determined for each liquid. Therefore, by appropriately determining the circuit constants, the coefficient of X in the above equation (2) can be made equal to the density of the fuel. Also, X
Since M is proportional to the fuel volume in the tank, M in the above equation (2), that is, the rotation angle of the slider 202 in FIG. 1, is proportional to the weight of the fuel in the tank.

However, the above-mentioned conventional device has the disadvantage that it has a complicated servo mechanism, which increases the cost of the device, and that it has movable parts, which can cause failures due to wear and the like.

The present invention provides a capacitance type fuel meter that eliminates the above-mentioned drawbacks, and the present invention will be explained below with reference to the drawings.

2 and 3 are diagrams showing one embodiment of the present invention, in which FIG. 2 is a circuit configuration diagram and FIG. 3 is an operation explanatory diagram. In FIG. 2, the same symbols as in FIG. 1 indicate the same elements, and their explanations will be omitted to avoid duplication.

In FIG. 2, the other plates of capacitors 3 and 4 are commonly connected through half-wave rectifier elements 9 and 10. Further, one connection point of the fixed capacitor 5 and the dielectric constant detection capacitor 6 which are connected in parallel with each other is connected to the _V2 voltage terminal of the secondary coil, and the other connection point is connected to the sawtooth through the half-wave rectifier element 15. It is connected to the input side of an integrator 12 which generates a waveform output. 11 is a converter, and 13 is a comparator for comparing the outputs of the integrator. The integrator 12 is configured such that a FET switching element 12b is connected in parallel to the return capacitor 12a, and the switching element is controlled by an AC power source 14 having a constant frequency lower than the excitation voltage.

Next, the operation of the present invention will be explained. The output currents from the capacitors 3 and 4 excited by the AC power supply are rectified by half-wave rectifier elements 9 and 10, and the half-wave rectified currents I ₁ and I ₂ flowing through these elements are added by a converter 11 and converted into voltage. be done. That is, I ₁ and I ₂ are I ₁ = −√2・V ₁・ω・{CM+CM・(K
−1)・X} ………(4) I ₂ =√2・V ₂・ω・CF ………(5) It is expressed as follows. Here, if V ₁・CM=V ₂・CF, then Io=I ₁ +I ₂ =−√2V ₁・ω・CM・(K−1)・X (6), and the converter 11 When the gain is -G, the output V ₄ of the converter 11 is V ₄ = -G・Io=√2・G・V ₁・ω・CM・
It is expressed as (K-1)・X......(7).

On the other hand, a half-wave rectified output obtained by rectifying the output currents from the capacitors 5 and 6 by a half-wave rectifying element 15 is applied to an integrator 12. That is, I ₃ is expressed as I ₃ =−√2·V ₂ ·ω·(K·Cc+CB) (8). Also, set the gain of the integrator 12 to −F
Then, the output V ₅ of the integrator 12 is V ₅ = −F・I ₃・t=√2・F・V ₂・ω・
It is expressed as (K・Cc+CB)・t……(9).

Here, the outputs of the converter 11 and the integrator 12 are V ₄ ,
When V ₅ is assumed, V ₄ and V ₅ have the relationship shown in FIG. In this case, it is assumed that the output V ₆ of the comparator 13 is configured to output the power supply voltage Vc when V ₅ ≦V ₄ and to become a zero output when V ₅ >V ₄ . As a result, as shown in Figure 3b, after V ₅ rises from zero,
If the time taken to become equal to V ₄ is t′, then V ₅
(max)>V ₄ (max), so t′ is always T
become smaller. That is, at t=t′, V ₄ =
Since V ₅ , from equations (7) and (9), t'=G・V ₁・CM(K−1)・X/F・V ₂・(K
・Cc+CB)......(10) is obtained. Therefore, the output V ₆ of the comparator 13 is a pulse output corresponding to the time t' that changes in relation to the dielectric constant.

When the output V ₆ of the comparator 13 is taken out as a digital output, the power supply voltage of the comparator 13 is connected to +Vc and -Vc as shown in FIG. Comparator 13
The number of pulses N appearing in the output of is becomes. Therefore, by appropriately determining values other than K in equation (11), the output pulse number N can be made proportional to the fuel weight. Note that a known counter can be used as the pulse measuring means, and in this case, the counter can be reset by detecting the falling edge of the sawtooth wave.

In addition, when taking out the output of the comparator 13 as an analog output, a filter 16 is provided after the comparator 13, and the power supply of the comparator 16 is connected between the constant voltage source Vs and the common as shown in parentheses in Fig. 2. Connect to. In this case, if the gain of the filter 16 is α, then the DC voltage averaged by the filter 16 is
V ₆ ′ is becomes. Therefore, for the same reason as in the case of digital output, _V'6 is proportional to the fuel weight.

As described above, compared to the conventional servo mechanism, the present invention eliminates failures due to wear because there is no mechanical drive part, and because it is configured purely electronically, it is economically efficient and static. A capacitive fuel gauge is obtained.

In addition, in the embodiment of the present invention, the amplitude of the sawtooth wave output is changed in relation to the value of the dielectric constant detection capacitor, but it is also possible to keep the amplitude of the sawtooth wave output constant and change the period. A similar effect can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a conventional capacitance type fuel meter, FIG. 2 is a block diagram showing an embodiment of the present invention, and FIG. 3 is an explanatory diagram illustrating the operation of the present invention. 1: Transformer, 3: Capacitor for volume measurement,
4: Comparison capacitor, 5: Fixed capacitor for calculation, 6: Capacitor for dielectric constant detection, 9, 10, 1
5: half-wave rectifier element, 11: converter, 12: integrator for generating sawtooth wave output, 13: comparator.

Claims (1)

[Claims] 1. A volume measuring capacitor connected to one end of the secondary winding of the power transformer to measure the volume of fuel, a comparison capacitor connected to the other end of the secondary winding, and a volume measuring capacitor connected to the other end of the secondary winding. a parallel circuit of a dielectric constant detection capacitor that detects the dielectric constant of the fuel and a fixed calculation capacitor; a first rectifying element that half-wave rectifies the current flowing to the volume measuring capacitor; and a first rectifying element that half-wave rectifies the current flowing to the volume measuring capacitor; a second rectifying element that performs half-wave rectification of the current; a converter that adds the currents flowing through the first and second rectifying elements and converts it into a voltage; and a third rectifying element that performs half-wave rectification of the current flowing through the parallel circuit. , an integrator that receives the output of the third rectifying element and generates a sawtooth wave output, and compares the output of the converter and the integrator until the output of the integrator becomes equal to the output of the converter. A capacitance type fuel meter comprising: a comparator that generates an output corresponding to a time of .