JP2504632B2 - Liquid level measurement method using heat radiation type level sensor - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid level measuring method using a heat radiation type level sensor suitable for detecting a fuel level in a fuel tank for a vehicle, for example.

[0002]

2. Description of the Related Art A heat radiation type level sensor utilizes the fact that the resistance of a sensor, which is a resistor, changes depending on the depth of immersion in the liquid surface. To briefly describe the method using a pulsed constant current, a constant current is applied for several seconds in the pulse method. The sensor voltage increases due to the passing of current, and the amount of increase is proportional to the liquid level. However, the voltage difference between FULL and EMPTY at the end of current application is small, and practical resolution cannot be obtained. Therefore, an output proportional to the liquid level is obtained from the average slope of the voltage rise instead of the above-mentioned rise amount. Specifically, the sensor voltage was digitally input every few msec, the first-order approximation processing was performed by the microcomputer, the slope was obtained, and the output resolution was increased. This FIG. 12 (a), the will be described with FIG. (B), FIG. 12 (b) the horizontal axis represents time, diagrammatically took current on the vertical axis, and the sensor ON at time t _0, the time A pulse current that is stable at t ₀ ′ and turns off at time t _f is intermittently repeated. FIG. 12A shows a state in which the sensor output during the energization is sampled, and the initial voltage V _{1 at} time t ₁ begins with V ₂ , V ₃ , ... V _f . Therefore, each output voltage is divided by the initial voltage V ₁ ,
Perform temperature compensation for ambient temperature. Then, the rising gradient of this output with respect to time is subjected to first-order approximation processing to obtain the inclination as shown in FIG. 13, and the steady output voltage Vtc is obtained from this,
It is liquid level measurement data.

The above output will be described with reference to FIG.
(A) and (b) of FIG. 3 show a gradient a of sensor resistance change (which has the same meaning as the output voltage) due to energization when the ambient temperature is high, and a sensor resistance change gradient b when the ambient temperature is low. However, at the initial stage of energization, the temperature of the sensor is considered to be the same as the ambient temperature, so the higher the ambient temperature, the larger the output.

5 (a) and 5 (b), as described above, each output is divided by the initial voltage to compensate for the difference in ambient temperature shown in FIG. In both cases, the slopes are almost the same at low values.

FIG. 6 is a diagram comparing the gradient d of resistance change when the ambient temperature is the same as the sensor temperature and the gradient e of resistance change when the ambient temperature is lower than the sensor temperature. It can be seen that the output (resistance) decreases with the slope e, although the above-mentioned compensation is performed with respect to the resistance change and the initial resistance is the same.

That is, the above-mentioned temperature compensation is compensation when the temperature at the beginning of energization of the sensor and the ambient temperature are always the same. For example, when the ambient temperature changes suddenly, Due to its heat capacity, the temperature does not follow the change, and the output may change as shown in FIG. 6, for example, which may cause a measurement error.

[0007]

As described above, in the liquid level measuring method using the pulse type heat radiation type level sensor, there is a possibility that a measurement error may occur in response to a sudden change in ambient temperature.

The present invention has been made to solve the above problems, and provides a liquid level measuring method using a heat radiation type level sensor which does not cause a measurement error even when the ambient temperature changes suddenly. With the goal.

[0009]

In order to achieve the above object, the present invention intermittently supplies a constant current to a sensor, which is a resistor immersed in a liquid, and stores an initial output voltage output from the sensor. Then, the output voltage from the initial state to the lapse of a predetermined time is divided by the initial output voltage, and the steady output voltage in the steady state is calculated and predicted from the rising slope of the output obtained by this division and A liquid level measuring method using a heat radiation type level sensor, characterized in that a corrected steady output voltage V ″ tc that compensates for the difference between the sensor temperature and the ambient temperature is calculated and obtained as the liquid level measurement data.

V ″ tc = Vtc + (V ₁ −V ′ ₁ ) × G ... ## EQU1 ## where the initial voltage is V ₁ , the initial voltage in the previous measurement is V ′ ₁ , and the steady output voltage is Vtc. , G is a preset constant.

[0011]

With respect to the above-mentioned correction formula, more specifically, regarding the error caused by the difference between the sensor temperature and the ambient temperature, it is necessary to determine the compensation amount of the output by judging the change and the speed of the ambient temperature. Consider inserting an object with a different temperature into air with a constant temperature. At this time, the movement of heat, that is, the heat flow velocity (the amount of movement of heat per unit volume or unit length) is proportional to the temperature difference between the object and the surrounding medium (air). By measuring the temperature of the object at regular time intervals, the temperature difference between the surrounding medium and the object at that time (accurately between the measurements) can be estimated.
For example, the larger the difference in temperature of the object at the two measured times is, the more the temperature of the surrounding is different from that of the object. When considering, the temperature of the object (sensor) is obtained from the initial resistance, and the temperature difference between the object (sensor) and the surrounding, that is, the change in ambient temperature and its speed are the initial resistance value measured last time and the initial resistance measured this time. It was judged from the difference in value. Then, the difference in the initial resistance was multiplied by a constant G obtained from the experiment, and the sensor output (steady output voltage) was added and compensated. This constant depends on the shape of the sensor, the heat capacity, the material of the coating, etc., so it must be determined by experiment.

(1) The detection of the difference between the sensor temperature and the ambient temperature will be described.

FIG. 7 shows that the sensor temperature is equal to the ambient temperature,
Moreover, when the temperature is constant, the sensor temperature, that is, the initial resistance value does not change. FIG. 8 shows the followability of the sensor temperature when the ambient temperature changes.
₁ , T ₂ , ... indicate the ambient temperature, and Ts ₁ , Ts ₂ , ...
Indicates the temperature of the sensor (initial resistance value R). When the ambient temperature is changing, a temperature difference occurs in the sensor.

In FIG. 9A, the vertical axis represents the difference between the sensor temperature and the ambient temperature (sensor temperature-ambient temperature), and in the FIG. 9B, the vertical axis represents the difference in the initial resistance value, that is, in the current measurement. The initial resistance value is R 2, the initial resistance value of the previous measurement is R ₁ , and the difference R ₂ -R ₁ is shown in correspondence with the position of the temperature difference in FIG. 9A.

According to these measures, the difference between the sensor temperature and the ambient temperature is almost proportional to the difference in the initial resistance value.

(2) The difference between the sensor temperature and the ambient temperature and the output change will be described.

When there is a temperature difference, the output changes compared to when there is no temperature difference. That is, as can be seen from FIGS. 5 and 6, the output changes in proportion to the temperature difference.

From the above, as shown in FIG. 10, the difference between the sensor temperature and the ambient temperature is proportional to the difference in the initial resistance value.
As shown in FIG. 11, the difference between the sensor temperature and the ambient temperature is
Proportional to output change. Therefore, the difference between the initial voltage of the previous measurement and the initial voltage of this time is calculated by the constant G
By multiplying by and adding this to the steady output voltage calculated in this measurement, it is possible to compensate for the effect of the difference between the sensor temperature and the ambient temperature on the output. (In this case, G becomes negative.)

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the apparatus implemented with reference to the drawings.

First, an apparatus for carrying out the method of the present invention will be described with reference to FIGS. 1 to 3, and its operation will be described as an embodiment of the present invention.

Reference numeral 1 is a fuel tank, and FL is a sensor which is a resistor immersed in the tank 1. A constant current I flows through both ends of the sensor FL through a constant current pulse circuit 2.
The output voltage Vp generated at both ends of the level sensor FL by flowing this current is taken into the CPU 4 through the A / D converter 3.

The current I generated from the pulse circuit 2 is shown in FIG.
As shown in (b), t ₀ large cycle having a period of up to ~t _f has become a manner to repeat at a cooling time, the cycle of the whole of which is set to about 3 seconds. Therefore, as shown in FIG. 2 (a), the voltage Vp rises in a cycle corresponding to the level of the liquid surface from the initial state (a low level has a large gradient, and a high level has a low gradient) from cycle to cycle. Are sequentially taken into the CPU 4 and sequentially stored in the storage unit in the CPU 4 together with the time data (enlarged portion in FIG. 1).

[0023] Here, the output voltages V ₁ at the initial voltage, i.e. t ₁ can be regarded as the output voltage in the state which is not heated yet sensors FL by the current I.

That is, it can be regarded as an output voltage based on a resistance value similar to that of the conventional temperature compensating resistor, and the CPU 4
This initial output voltage V ₁ is stored, and the values of the voltages V _{2 to} V _n that are continuously input are divided by this initial voltage V ₁ by the calculating means composed of the CPU, and the rising gradient with respect to these times is calculated. The steady output voltage Vtc in the steady state is calculated and predicted. This is the liquid level measurement data that compensates the ambient temperature. In addition, the value obtained by subtracting the initial voltage value (initial resistance value) of the previous measurement from the initial voltage value (initial resistance value) of this measurement in advance A value obtained by multiplying the set constant G is added to the above-mentioned steady output voltage Vtc to calculate a corrected steady output voltage V ″ tc. With this, the output of the liquid that compensates for the output difference due to the temperature difference between the sensor FL and the surroundings is calculated. Level measurement data, which is displayed on the display unit 5
Display with. Since the heat capacity of the sensor FL is large, V
The sampling voltage from _{0 to Vf} does not reach a steady voltage level.

On the other hand, when the sampling interval is, for example, 10 msec in a period from t _{1 to} t _f , for example, 3 seconds,
300 sampling voltages Vp can be obtained.

Therefore, as shown in FIG. 3, the CPU 4 has a program for calculating an approximate steady output voltage Vtc at the time tc in which the steady state is obtained from the rising gradient of the first-order approximation straight line, and a corrected steady output by a correction formula. A calculation program for calculating the voltage is built in.

[0027]

As described above in detail, since the present invention compensates the output change due to the difference between the sensor temperature and the ambient temperature,
Even in the case of a sudden change in ambient temperature, highly reliable and accurate liquid level measurement data can be obtained.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an apparatus that implements a measurement method of the present invention.

FIG. 2 is a diagram showing a relationship between a constant current and a sensor output according to the embodiment.

FIG. 3 is a diagram for explaining the relationship between the steady output voltage and the gradient in the same embodiment.

FIG. 4 is an explanatory diagram of a relationship between a resistance change of a sensor and an ambient temperature.

FIG. 5 is a diagram showing a resistance change of a temperature-compensated sensor.

FIG. 6 is a diagram showing a resistance change when the sensor temperature and the ambient temperature are different.

FIG. 7 is an explanatory diagram of the relationship between the ambient temperature and the sensor temperature when the ambient temperature is constant.

FIG. 8 is a diagram illustrating the followability of sensor temperature with respect to changes in ambient temperature.

FIG. 9 is a diagram showing the relationship between the temperature difference between the sensor and the surroundings and the difference between the front and rear initial resistance values.

FIG. 10 is a diagram showing that the temperature difference between the sensor and the surroundings is proportional to the difference in initial resistance value.

FIG. 11 is a diagram showing that the temperature difference between the sensor and the surroundings is proportional to the output change.

FIG. 12 is an explanatory diagram of a relationship between a sensor current and a sensor output voltage.

FIG. 13 is an explanatory diagram of a steady output voltage.

[Explanation of symbols]

FL sensor V ₁ , V ′ ₁ initial output voltage V ₁ , V ₂ , ... V _n output voltage Vtc steady output voltage V ″ tc modified steady output voltage

Claims (1)

(57) [Claims] 1. A constant current is intermittently applied to a sensor, which is a resistor immersed in a liquid, and an initial output voltage output from the sensor is stored. Corrected steady output obtained by dividing by the output voltage, calculating and predicting the steady output voltage in a steady state from the rising slope of the output obtained by this division, and compensating for the difference between the sensor temperature and the ambient temperature by the following correction formula. A liquid level measuring method using a heat radiation type level sensor characterized in that a voltage V ″ tc is calculated and used as liquid level measurement data. V ″ tc = Vtc + (V ₁ −V ′ ₁ ) × G However, the initial voltage is V ₁ , the initial voltage in the previous measurement is V ′ ₁ , the steady output voltage is Vtc, and a preset constant is G.