JPH0320692B2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a tank unit (hereinafter abbreviated as "T/U") that outputs the liquid level of fuel as a capacitance.
The fuel weight of the aircraft is calculated based on the values obtained from the compensator unit (hereinafter referred to as "C/U") that outputs the dielectric constant of the fuel as capacitance, and the density meter that measures the density. The present invention relates to a fuel measuring device for an aircraft having a configuration that is determined by the following methods.

<Prior art> Conventionally known fuel measuring devices for this type of aircraft include: "Aviation Instruments" published by Jijin Shokan (published on October 5, 1978); and: Yokogawa Giho (1982). Published by Yokogawa Hokushin Electric Co., Ltd.) Vol.28 No.2, page 179, and
There is one described in JP-A-56-63216.

The technology described in these documents measures the fuel in the fuel tank by utilizing the fact that the output of a capacitive liquid level meter is proportional to the fuel level and the fuel electrostatic coefficient. be.

FIG. 2A is a diagram showing the basic principle of a capacitor.

In FIG. 2A, 1 is a fuel tank for storing the fuel 2 of the aircraft, and 2a is a liquid level electrode that takes out the capacitance C _T from the liquid level X of the fuel 2. At this time, the capacitance C _T becomes C _T =C _D {1+X(K-1)} (1). However, C _D is the capacitance when the fuel tank 1 is completely filled with air (hereinafter referred to as "dry cap"),
K is the dielectric coefficient of fuel 2 (the dielectric coefficient (approximately 2) of fuel 2 is approximately twice that of air (1)).

FIG. 2B is a bridge circuit diagram of a simple construction in which the basic principle of the capacitor of FIG. 2A is applied to one side of a bridge similar to a Whiston bridge.

In FIG. 2B, 3 is a T/U which is a capacitance type liquid level sensor that is a more specific version of the liquid level electrode 2a. This T/U3 is composed of two types of coaxial cylindrical electrodes in which a capacitor is formed between an inner cylinder with radius b and an outer cylinder with radius a. At this time, the dry cap C _D becomes C _D =24.1Kl/log10(a/b) [pF/m]...(2). However, l is the length of the cylinder. Normally, the dry cap C _D is several tens of pF. E is AC power supply,
T is a transformer, 4 is an ammeter, and 50 is a balancing capacitor having a capacitance C _F. Here, T/U3
The voltage at one end of the transformer T connected to the capacitor 50 is V ₁ , the voltage at one end of the transformer T connected to the balancing capacitor 50 is V ₂ , the current flowing from T/U3 to the connection point O is I _T , and from the connection point 0 Let _IF be the current flowing through the balancing capacitor 50, and _IM be the current flowing from the connection 0 to the ammeter 4. At this time, the current I _M becomes I _M = I _T − I _F = ωV ₁ C _T −ωV _{2 CF} (3). Substituting equation (1) into this, the current I _M becomes I _M =ωV ₁ C _D +ωV ₁ X(K−1) _CD −ωV ₂ C _F (4). However, ω is the angular velocity. In equation (4), if it is adjusted so that V ₁ C _D =V _{2 CF} , the current I _M becomes I _M =ωV ₁ X(K-1) C _D (5). Therefore, when fuel 2 is empty, X=0, when fuel is full, X=1, and at this time, ammeter 4
A current of I _M =0 to ωV ₁ (K-1) C _D flows through.
Read this current amount from the current type 4 instruction and
You can know the amount of

FIG. 2C is a block diagram showing an indicating system further embodied in FIG. 2B and comprising a high-precision servo system.

In Fig. 2C, 5 is a servo amplifier, 6 is a servo motor, 7 is an indicator (the indicated value is M) 8
is a potentiometer, and 60 is a balancing capacitor having a capacitance C _B. Here, if the currents flowing on each side of the bridge are I ₁ , I ₂ , I ₃ , and I ₀ , then the currents I ₁ ,
_{I 2 ,} I ₃ , _and I ₀ are respectively I _{1 ( =} ωV _{1 { CD +} , I becomes ₀ . Here, the equilibrium condition of the bridge is I ₀ = I ₁ + I ₂ + I ₃ = 0 (6), so by substituting the values of each current mentioned above, equation (6) becomes V ₁ C _D + 1) V ₁ C _D + V ₂ C _F + MV ₃ C _B = 0...(7). Therefore, _the indicated value M of _the indicator ₇ is as follows: M={ _V1CD + _X (K-1) _V1CD + _V2CF }/- _V3CB ...(8). Now, when the fuel is empty, X=0 and M=0, so equation (7) becomes V ₁ C _D =-V ₂ C _F (9). On the other hand, when the fuel is full, X=1, M
= 1, so equation (7) is: V ₁ C _D + (K-1) V ₁ C _D + V ₂ C _F + V ₃ C _B ∴KV ₁ C _D + V ₂ C _F = -V ₃ C _B …( 10) becomes. Substituting these equations (9) and (10) into equation (8), we get M=X...(10A). V ₁ , V ₂ , C _D ,
By determining the values of C _F and C _B , the bridge circuit shown in Figure 2 C can be used to measure the fuel and issue instructions.

By the way, if fuel instructions are required in units of weight (for example, for gas turbine aircraft), it is necessary to replace volume with weight. That is, since T/U3 is a liquid level sensor, its output is a function of the fuel volume, and in order to find the weight, it is necessary to multiply it by the fuel density ρ. Therefore, by utilizing the fact that the fuel density P is a function of the dielectric constant K, an inductive sensor C/
U9 is provided, and the circuit characteristics are determined by the density-inductivity correlation equation (for example, ρ = T _A (K-1)/{T _B + (K-1)}...(11) (However, T _A , T _B are This is a unique value determined by the airplane manufacturer or a value determined by MILL, etc.)
It is possible to obtain the indicated value M proportional to the fuel weight by making it coincide with the fuel weight.

That is, C/U9 is provided to correct the dielectric constant K of the density ρ.

<Problems to be solved by the invention> By the way, the above-mentioned correlation equation (11) between fuel density ρ and dielectric constant K is a statistical correlation equation, and on the other hand, as is well known, the dielectric coefficient K of fuel is Since it differs depending on the fuel and also changes depending on the temperature, it actually differs depending on the fuel (the variation becomes large). As a result, there is a problem in that a maximum error of about 4% occurs, making it impossible to perform highly accurate measurements.

<Object of the Invention> The present invention has been made in view of the above-mentioned problems, and calculates the true fuel weight value by calculating based on the values obtained from T/U, C/U, and a density meter. An object of the present invention is to provide a highly accurate fuel measuring device for an aircraft, which is equipped with an arithmetic circuit that obtains the following.

<Configuration for Solving Problems> The fuel measuring device for an aircraft according to the present invention for achieving the above-mentioned object has the following configuration.

The density meter outputs a constant current (DC) density signal based on the measured fuel density. This density signal is
It is connected to the connection point between T/U and C/U, and is guided to a fuel density calculation section which is a "circuit that outputs a value proportional to density" and is made up of a density detection circuit and a calculation circuit.
Further, the fuel density calculation section inputs such a density signal and outputs a value (voltage) proportional to the density to T/U and an input terminal of the fuel remaining amount calculation section described below.
As a result of the above, the density signal is converted into a DC voltage by the density detection circuit, and becomes the input value of the other side of the multiplication unit, where the AC voltage from the constant voltage unit is input to one side of the arithmetic circuit.
These voltages are multiplied by the multiplier and output as an AC voltage signal whose amplitude is proportional to the density.
In addition, the capacitance type T/U used as a liquid level sensor for measuring the fuel liquid level is excited by an AC voltage signal from the fuel density calculation section, and measures a capacitance value corresponding to the liquid level. Output. The C/U is an inductivity sensor that is connected in series at one end and connected to the output terminal of the remaining fuel amount calculating section to measure the inductivity. The capacitance is output (the connection point between T/U and C/U is connected to the feedback terminal). On the other hand, in the internal circuit of the fuel remaining amount calculating section, a dry cap canceling circuit for canceling the dry cap of the T/U is arranged between the input terminal and the feedback terminal, and an operational amplifier and a fuel dielectric circuit are arranged between the feedback terminal and the output terminal. The structure includes a dielectric coefficient cancellation circuit that cancels the influence of the coefficient. Therefore, the remaining fuel amount calculating section can eliminate the dielectric coefficient and the dry cap and obtain an output value proportional to the remaining fuel amount. This output value is the part where T/U is immersed in fuel, and T/U is immersed in fuel.
It is also proportional to the excitation voltage of U. As a result, the output value is proportional to fuel volume x density, that is, fuel weight. This output value can be displayed on the display section.

<Embodiment> The present invention will be described in detail below with reference to FIG. 1, a block diagram showing a specific embodiment of the fuel measuring device for an aircraft according to the present invention. Note that in FIG. 1, parts that overlap with those in FIG. 2 are given the same numbers and their explanations will be omitted.

In Figure 1, T/U3 is excited by the output from the fuel density calculation section, which is a "circuit that outputs a value proportional to the density" described below, and has a capacitance corresponding to the liquid level X of fuel 2. Outputs the output current as Ia. The capacitance of T/U3 is shown in equation (1), but in this equation, the dielectric constant of the fuel differs depending on the fuel as mentioned above, and changes with temperature, so T/U3 can be expressed as follows: It was used as a liquid level sensor, and the C/U was configured by having the density meter element in C/U9 (in other words, it refers to C in Figure 2), but by adding a new density meter, which will be described later, to the C/U.
is used to eliminate the factor of dielectric constant K. In other words, C/U9 inputs the output value from the remaining fuel amount calculation section described below and calculates the capacitance corresponding to the dielectric constant K of fuel 2 as an output current.
Output as IC. (This eliminates the factor of inductivity K). This T/U3 and C/U9 are connected at a connection point α. 10 directly measures the density ρ of the fuel 2 in the fuel tank 1 installed in the aircraft, instead of using the density obtained indirectly in C/U9 in Figure 2C. This density meter 10, which is a density meter that outputs a direct current density signal Ie proportional to the density, is connected to a connection point α. Reference numeral 11 denotes a fuel density calculation unit connected to the connection point α. This fuel density calculation section 11 is connected to the connection point α
Input the density signal Ie from the density meter 10 via
For example, an AC voltage signal V _D ·V _ref (where V _D =n ₁ ρ and n ₁ is a constant), whose amplitude is proportional to the density ρ, is output. The structure of this fuel density calculation section 11 includes a density detection circuit 12 which inputs a density signal Ie and outputs a DC voltage signal V _D proportional to the density ρ, and an amplitude based on the DC voltage signal V _D of this density detection circuit 12. and an arithmetic circuit 13 that calculates and outputs an AC voltage signal V _D ·V _ref proportional to the density ρ. Here, the density detection circuit 12 includes a series circuit of a resistor 12b having a resistance value R ₂ and an operational amplifier Q ₄ having, for example, low-pass filter characteristics, and a feedback resistor having a resistance value R ₁ connected in parallel to this series circuit. 1
2a. Now, when a current i flows through the feedback resistor 12a of the density detection circuit 12, the operational amplifier _Q2 in the remaining fuel amount calculation section, which will be described below, outputs a DC voltage of -iR, and the density detection circuit 12
The operational amplifier Q ₄ detects the DC component of the output voltage of the operational amplifier Q ₂ and generates a DC voltage (V _D ) that cancels this (this DC voltage (V _D ) is
2b to operational amplifier _Q2 ). As a result, the DC component appearing at the output of the operational amplifier Q ₂ becomes zero, and the entire current Ie from the density meter 10 flows into the density detection circuit 12. That is, V _D =−R ₂ · Ie〓 (fuel density) ...(12) Therefore, the DC voltage of the density detection circuit 12 (V _D )
is proportional to the fuel density (note that the fuel leak resistance is parallel to the feedback resistance R ₁ when transmitting the density signal, but changes in the resistance R ₁ do not affect the operation of the operational amplifier Q ₄ and do not result in an error) . The arithmetic circuit 13 also includes a constant voltage section 14 and a multiplication section 15 that multiplies the AC voltage [V _ref ) from the constant voltage section 14 by the DC voltage signal V _D from the density detection circuit 12. 16 inputs the AC voltage signal V _D ·V _ref from the input terminal 16a, inputs the combined current of T/U3 and C/U9 from the feedback terminal 16b connected to the connection point α, and calculates the dielectric coefficient K and the dry cap. This is a remaining fuel amount calculation unit that erases the remaining fuel amount and outputs an output value V _O proportional to the remaining fuel amount from the output terminal 16c.
This remaining fuel amount calculating section 16 is configured as follows. Between the input terminal 16a and the operational amplifier _Q2 ,
A dry cap canceling circuit 17 is arranged which cancels the dry cap of T/U3 and is composed of an amplifier Q1 having a gain of ( _-1 ) and a capacitor 17a having a capacitance _CTD . The output current of the dry cap cancellation circuit 17 is Ib
shall be. The connection point between the dry cap cancellation circuit 17 and the input terminal of the operational amplifier _Q2 is connected to the feedback terminal 16b. The output terminal of operational amplifier _Q2 is connected to output terminal 16c. Furthermore, the input terminal of operational amplifier Q ₂ is connected to the output V _O of operational amplifier Q ₂ .
The feedback current Id is fed back through the dielectric coefficient cancellation number 18, which cancels the influence of the dielectric coefficient K of the fuel, which is composed of an amplifier Q3 having a gain (-1 ₎ and a capacitor 18a having a capacitance _CCD .

The remaining fuel amount calculating section 16 will be explained in more detail.

The capacitance C _TU of T/U3 is
If C _TO is used, then from equation (1), C _TU = C _TO {1+X(K-1)} ...(13), and on the other hand, if the capacitance C _CU of C/U9 is the dry cap C _CO , C _CU = K・C _CO …(14). On the other hand, for each current Ia to Id, if the operator is S, Ia=SC _TU・n ₁ ρV _ref =SC _TO {1+X(K-1)} ・n ₁ ρV _ref …(15) Ib=−SC _TD・n ₁ ρV _ref …(16) Ic=SC _CU・V _O =SKC _CO・V _O …(17) Id=−SC _CD・V _O …(18) Therefore, the bridge equilibrium condition is Ia+Ib+Ic+Id=0 (19), so equation (18) is: SC _TO {1+X(K-1)}・n ₁ ρV _ref −SC _TD・n ₁ ρV _ref +SK C _CO・V _O −SC _CD・V _O …(20) Therefore, the output value V _O of the remaining fuel amount calculation section 16
is V _{O = - [ {} ( _{C TO +} Here, if C _{TD and C CD are chosen so that C TO = C TD and C CO = C CD , equation ( 19} ) becomes V _O = - (C _TD / C _CO )・Xρ・n ₁ V _ref … (22), and the output voltage V _O is (fuel volume) x (density) =
(fuel weight).

Note that the dry cap cancellation circuit and dielectric coefficient cancellation circuit of FIG. 1 of the present invention are not limited to the circuits described herein. For example, if amplifiers Q ₁ and Q ₃ with a gain of (-1) are made to have a gain of (-N), the capacitances of capacitors 17a and 18a are (C _TD /N) and (C _CD /N). If so, no difference in characteristics will occur.

Here, the output value V _O can be displayed, for example, on a display section 19 that includes a digital-to-analog conversion circuit and a display device, as shown by a broken line.

<Effects of the Invention> As described above in detail with reference to specific examples, the present invention includes a density meter that measures the density of fuel, and a fuel density that outputs a value proportional to the density based on the output of this density meter. A calculation unit, a T/U that is excited by the output of the fuel density calculation unit and measures the liquid level of the fuel, a C/U that measures the dielectric constant of the fuel, a fuel density calculation unit, the T/U, and the C/U. The fuel measuring device for an aircraft according to the present invention, which is configured with a fuel remaining amount calculation section that is connected to a U and a density meter and outputs a value proportional to the remaining fuel amount (fuel weight), multiplies the volume and density. Therefore, there is no error of up to 4% that occurs when using the statistical "fuel density-permittivity correlation equation" as in the prior art, and the true fuel weight can be obtained. It is possible to provide an extremely effective technique for measuring body fuel. In addition, by using a density detection circuit that uses a direct current balance method as a circuit that converts the density signal, which is a current value, into voltage, the density signal (DC) and fuel remaining amount signal (AC) can be output on the same line. It makes it possible to transmit. There is an effect.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing a specific embodiment of the fuel measuring device for an aircraft according to the present invention, Fig. 2 is a diagram showing the prior art, and Fig. 2A shows the basic principle of a capacitor. Figure 2B shows the type of
Figure 2C is a bridge circuit diagram of a simple configuration in which the basic principle of the capacitor shown in Figure 2A is used on one side of a bridge similar to the Wheatstone bridge.
FIG. 3 is a block diagram showing an instruction system comprising a high-precision servo system, which is a further embodiment of FIG. B; DESCRIPTION OF SYMBOLS 1... Fuel tank, 2... Fuel, 3... Tank unit (T/U), 9... Compensator unit (C/U), 10... Density meter, 11... Fuel density calculating section, 16... Fuel remaining amount calculating section.

Claims (1)

[Scope of Claims] 1. In a fuel measuring device for an aircraft that measures the liquid level of fuel in a fuel tank provided in an aircraft using a tank unit that outputs the liquid level of the fuel as a capacitance, A: The dielectric constant of the fuel is determined by static capacitance. B: A compensator unit (for example, 9) that outputs the capacitance, and B: a density meter (for example, 1) that measures the density of the fuel.
0); C: a tank unit (e.g. 3) having one end connected to a circuit that outputs a value proportional to density and the other end connected to one end of the compensator unit and the density meter; D: the compensator a fuel density calculation section (for example, 11), which is a circuit that is connected to a connection point between the unit and the tank unit and outputs a value proportional to the density, which includes a density detection section (for example, 12) and a calculation circuit (for example, 13); , E: The fuel calculation section is connected to the input terminal, the other end of the compensator unit is connected to the output terminal, the connection point of the tank unit, the compensator unit, and the density meter is connected to the feedback terminal, and the A dry cap cancellation circuit (e.g. 17) for canceling the dry cap of the tank unit between the input terminal and the feedback terminal is connected to an amplifier (e.g. Q ₂ ) between the feedback terminal and the output terminal to cancel the effect of the dielectric coefficient of the fuel. dielectric coefficient cancellation circuit (e.g. 1
8), and a remaining fuel amount calculating section (for example, 16) that calculates and outputs a value proportional to the remaining amount of fuel in the fuel tank (for example, 1). fuel measuring device.