JP2557570B2 - Liquid level measurement method with 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 level sensor, for example, for detecting the level of fuel in a vehicle fuel tank, and more particularly to a system for performing temperature compensation and accurately measuring a liquid level in a short time. .

[0002]

2. Description of the Related Art A heat radiation type level sensor utilizes the fact that the resistance changes depending on the immersion depth of the sensor, which is the surface of the sensor. It is a sensor of a system that converts a corresponding resistance change into a voltage and detects a liquid level.

The output voltage of this sensor is affected not only by the immersion depth but also by the ambient temperature.

Therefore, as disclosed in, for example, Japanese Patent Application Laid-Open No. 63-311927 previously developed by the present applicant, temperature compensating resistors having the same structure as that of the above-mentioned sensor are arranged in parallel so that the liquid level of the sensor is increased. The liquid level is measured by utilizing the fact that the corresponding change in resistance value appears as a change in voltage at the connection point with the temperature compensating resistor. That is, the temperature compensating resistor is immersed in the liquid together with the sensor, but since it is not self-heated, the resistance value does not follow the level change of the liquid level, and the resistance is changed only by the ambient temperature change. The value changes, which results in automatic level measurement of the liquid.

[0005]

In order to accurately measure the level of this type of liquid, it is necessary to make the temperature coefficients of resistance of the sensor and the temperature compensating resistor uniform.

Further, since the sensor and the temperature compensating resistor have an actual structure in which a Ni wire is spirally wound around the outer periphery of a rod-shaped support, the heat capacity is considerably large and a stable output can be obtained. It took a few minutes, and especially when the tank capacity became almost empty and the immersion depth decreased, it took a long time for the output to stabilize.

Therefore, when the user side reads the meter during an unstable period, the liquid level will be incorrect,
It becomes a problem in practical use.

Furthermore, since the resistor actually requires a higher resistance value than the sensor, the resistance wire becomes long and the heat capacity is different. Therefore, if the ambient temperature changes,
During the change, a temperature difference occurs between the two, which causes a temporary error in the liquid level measurement.

The present invention has been made in view of the above drawbacks, and the first invention eliminates the temperature compensating resistor, and solves the above-mentioned problems caused by arranging the resistors in parallel to each other. It is an object of the present invention to provide a liquid level measuring method using a heat radiation type level sensor capable of improving the level measuring accuracy and measuring in a short time.

It is another object of the second and third inventions to provide a liquid level measuring system using a heat radiation type level sensor, which has improved measurement accuracy as compared with the first invention.

[0011]

To achieve the above object, the invention according to claim 1 provides a pulse circuit for intermittently flowing a constant current to a sensor which is a resistor, and an initial voltage output from the sensor. Storage means for storing, operation means for dividing the output voltage from the initial state to the lapse of a predetermined time by the initial voltage, and predicting a steady voltage in a steady state from the rising gradient of the output obtained from the operation means with respect to time It is characterized in that it comprises a predicting means, and outputs the calculation result as a liquid level output to the display means.

According to a second aspect of the present invention, a pulse circuit for intermittently supplying a constant current to the sensor which is a resistor, a storage means for storing an initial voltage output from the sensor, and a predetermined time from the initial state. Computation means for dividing the output voltage up to the lapse of time by the initial voltage, prediction means for predicting a steady voltage that is in a steady state from the rising slope of the output obtained from the computation means with time, and steady voltage from the prediction means And a correction means for subtracting a correction value obtained by multiplying the initial voltage by a preset coefficient to obtain a corrected steady voltage, and outputting the correction result as the liquid level output to the display means.

Further, the invention according to claim 3 is a pulse circuit, in which a constant current is intermittently supplied to a sensor which is a resistor.
A storage unit that stores an initial voltage output from the sensor, a calculation unit that divides an output voltage from an initial state until a lapse of a predetermined time by the initial voltage, and a compensation of an output obtained from the calculation unit from a rising slope with respect to time A slope determining means for calculating and determining the slope, and a correction value obtained by multiplying the initial voltage by a preset coefficient are subtracted from the output at a predetermined time position of the compensation slope by this means, and based on the subtracted correction output Slope correction means for correcting the compensation slope to calculate and determine the correction compensation slope, prediction means for calculating and predicting a steady voltage which becomes a steady state based on the correction compensation slope from this means, and a calculation result of this for liquid And a display means for displaying as a level output.

[0014]

In the first aspect of the present invention, since the sensor is hardly heated at the initial stage of passing the constant current, the initial voltage can be regarded as the output voltage based on the resistance value due to the ambient temperature. By dividing the voltage output from the heated sensor by this value, the liquid level measurement output can be obtained.

Further, in order to shorten the measurement time, by sampling the level measurement output of the liquid after energization and approximating the output with respect to the energization time, the level output after a sufficient time has elapsed can be obtained. .

The second invention according to claim 2 and the third invention according to claim 3 measure the level of a liquid by a heat radiation type level sensor which is more accurate in temperature compensation than the first invention. Before explaining the second and third inventions, the temperature compensation of the level measurement by the pulse method of the first invention will be described in more detail.

In the pulse method, a constant current is applied for several seconds. 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 the case where the tank is FULL and the case where it is EMPTY at the end of current application is small, and practical resolution cannot be obtained. Therefore, instead of the above-described amount of increase, it was decided to obtain an output proportional to the liquid level from the average slope of the voltage rise. This is the first aspect of the invention. Specifically, for example, a sensor voltage is digitally input every few msec, and a first-order approximation process is performed by a microcomputer to obtain a slope (compensation slope) and the output resolution is increased.

5 (a) and 5 (b) are diagrams in which the horizontal axis represents time and the vertical axis represents current value and resistance value, respectively. Curve a is constant current and curve b is ambient temperature. Curve c shows the change in resistance value due to energization in the air when the temperature is low, and curve c shows the change in resistance value due to energization in the air when the ambient temperature is high. Current is time t
_It starts from ₀ and becomes stable at time t _{0 ′} .

As shown in this figure, the resistance value changes differently depending on the ambient temperature.

The resistance at time t is given by Equation 1 in consideration of the change in resistance due to the ambient temperature.

[0021]

[Equation 1]

Since the resistance value changes depending on the ambient temperature, it is necessary to compensate for the influence. Immediately after the current is supplied, as described above, the resistance value is substantially the same as the resistance value corresponding to the ambient temperature before the current is supplied, because it is hardly heated. (It has nothing to do with the liquid level.) The resistance value at t = t ₁ in FIG.

[0023]

[Equation 2]

Therefore, the effect of ambient temperature is compensated by storing the resistance value (hereinafter referred to as the initial resistance value, which is referred to below as the mathematical expression 2) immediately after passing the current in the memory and dividing the resistance value sampled at each time.

Equation 3 shows the compensated resistance value at time t.

[0026]

(Equation 3)

Resistance curves b ', c'in FIG. 6 (a)
Shows the resistance curves b and c in FIG. 5A compensated for the influence of the ambient temperature.

However, this figure shows that even when the ambient temperature is compensated in this way, the gradient (compensation gradient) differs depending on the ambient temperature and a difference occurs in the output.

FIG. 7 shows the ambient temperature and output (final steady voltage).
In contrast to the output line d before compensation, the output line d ′ after compensation shows a substantially constant output, but the output increases as the ambient temperature rises.

FIG. 8 also shows that the initial voltage (initial resistance) also rises as the ambient temperature rises.

As described above, it is considered that the reason why the output increases due to the increase in ambient temperature even after the ambient temperature compensation and the steady outputs do not match is as follows.

That is, when the resistance value is large, the amount of change in the resistance value due to current application also becomes large, but according to the compensation method described above, it is standardized by dividing by the initial resistance value (initial voltage value), and the slope with respect to time. Does not change. That is, the difference in resistance value due to the ambient temperature and the influence of the difference in resistance value between samples at the same temperature are compensated. This is the invention according to claim 1.

On the other hand, the larger the amount of heat generated by the entire sensor, the larger the resistance value. If the amount of heat generated from one part of the sensor does not affect the other, the temperature compensation described above is sufficient. However, since convection is generated on the sensor surface, heat generated by energization from the lower part moves upward.

As described above, when temperature compensation is performed, the resistance value (voltage value) immediately after passing the current is used for division.
At this time, convection does not occur, but immediately after that, the warmed air gradually propagates from the lower part to the sensor surface, the sensor is warmed, and the resistance value also rises. Therefore,
It is presumed that at a certain short energization time, the rate of increase in the resistance value increases as the energization time increases. It is considered that this ratio is proportional to the resistance value before energization.

Next, data supporting this will be shown. That is, sensors with different resistance values were created, a constant current was passed, and the relationship between the initial voltage and the output voltage (steady voltage) was investigated. As a result of this, as shown in FIG. 9, the higher the initial voltage is, the higher the output voltage is, and the more heat is generated.

Therefore, the second aspect of the present invention corrects the steady-state voltage obtained by the first aspect of the invention to eliminate the influence of convection. That is, the correction value obtained by multiplying the initial voltage V ₁ by the set coefficient G ₁ is subtracted from the steady voltage Vt _C predicted from the rising slope obtained by the division, and the corrected steady voltage V ″ t _C is taken as the level measurement value, and the convection The effect is removed.
That is, V ″ t _C = Vt _C −V ₁ × G ₁ , the coefficient G ₁ is
It can be obtained experimentally.

Next, in the third invention, each output in the first invention is divided by the initial voltage, the slope of this output with respect to time is calculated, and this is used as a compensation slope in which the ambient temperature is compensated. It was calculated by predicting the steady-state voltage. The present invention corrects that the compensation slope still contains an error. However, as described above, since it is considered that this error occurs in proportion to the magnitude of the initial voltage, the error at the preset time position Output by compensating gradient (Vp)
From this, a correction value obtained by multiplying the initial voltage V ₁ by a preset setting coefficient G ₂ is subtracted, and the correction output V ′ obtained by this subtraction is subtracted.
This is a method of setting a corrected compensation gradient based on p. That is, V'p = Vp-V ₁ × G ₂ .

The coefficient G ₂ may be experimentally set according to the configuration of the sensor and the tank, the time position to be set, and the like.

[0039]

The first, second and third embodiments of the present invention will be described in detail below with reference to the drawings.

First, the first embodiment will be described. This is an embodiment of the first invention, and in FIG. 1, 1 is a fuel tank,
FL is a level sensor which is a resistor immersed in the tank 1.

A constant current I is applied to both ends of the level sensor FL through the pulse circuit 2. The output voltage V generated across the level sensor FL by flowing the current I
p is taken into the CPU 4 through the AD conversion unit 3.

The current I generated from the pulse circuit 2 is the second
As shown in FIG. 6B, a large cycle having a cycle from t ₀ to t _F has a mode in which it repeats with a cooling time,
The entire cycle is set to about 3 seconds. However,
It takes t0 'to reach the constant current I from the rise of the circuit.

Therefore, the voltage Vp is, as shown in FIG. 2A, the level of the liquid surface from the initial state in each cycle (a low level has a large gradient, and a high level has a small gradient).
The cycle of rising with a gradient according to
It is taken into U4 and the CPU4 sequentially along with the time data.
It is stored in the internal storage unit (enlarged portion of the figure). The CPU 4 and the storage unit constitute the storage means 4a.

[0044] Here, the output voltages V ₁ at the initial voltage, i.e. t ₁ can be regarded as the output voltage in the state where the sensor FL is the current I is not heated.

That is, it can be regarded as an output voltage based on the same resistance value as the conventional temperature compensating resistor, the CPU 4 stores this initial output voltage, and the calculating means 4b constituted by the CPU 4 is continuously input. by performing dividing the value of the voltage Vt ₂ ~Vt _F at the initial voltage V _1, to obtain a rising slope with respect to time of the output, which was treated by the prediction unit 4c, the output which is compensated to ambient temperature A compensation gradient is obtained from which liquid level measurement data (steady-state voltage Vt _C ) can be obtained. Based on this data, the display unit 5 displays the measured level output of the liquid.

Since the heat capacity of the sensor FL is large, V
The sampling voltage from t0 to VtF does not reach a steady voltage level.

On the other hand, if the sampling interval is 10 msec for a period of, for example, t _{1 to} t _n , for example 5 seconds, then 5
A sampling voltage of 00 can be obtained.

[0048] Therefore, as the CPU4 constituting the prediction means are shown in Figure 3, to determine the compensation gradient from the increase gradient, computes the approximate voltage Vt _c at time tc to be a steady state based on this Has a built-in program,
By displaying the value on the display unit 5, display can be performed with a large output voltage.

Next, a second embodiment will be described with reference to FIGS. This is an embodiment of the second aspect of the invention and has a configuration similar to that of the first embodiment, except that the correction means 4f is provided.

That is, the steady voltage Vt _C obtained in the first embodiment is modified to remove the influence of convection. That is, the correction means 4f configured by the CPU 4
In the above, the correction value obtained by multiplying the initial voltage V ₁ by the setting coefficient G ₁ is subtracted from the steady voltage Vt _C predicted based on the rising slope obtained by the division, and the corrected steady voltage V ″ t _C is taken as the level measurement value. , Is output to the display unit 5. That is, the effect of convection is removed, that is, V ″ t _C = Vt _C −V ₁ × G _{1 The} coefficient G ₁ is experimentally determined by the sensor FL and the tank configuration. You can ask.

Next, the third embodiment will be described with reference to FIGS.
A description will be given with reference to (a) and FIG.

This embodiment is an embodiment of the third aspect of the invention and has a configuration similar to that of the first embodiment, and the sensor FL,
It has a pulse circuit 2 for supplying a constant current thereto, a storage means 4a for storing the initial voltage V ₁ of the pulse circuit 2, a calculation means 4b for dividing the output voltage Vp by the initial voltage V ₁ , and a prediction means 4c. The difference from the first embodiment is that a (CPU) 4d and a gradient correcting means (CPU) 4e are provided.

The gradient determining means 4d has an initial voltage V for the output voltages V ₁ , Vt _{2 F} , Vt _{3 F,} ...
_Although division was performed by ₁ , the rising slope from this division result is processed to calculate the average slope, and the compensation slope m is calculated and determined.

Next, the gradient correction means 4e removes and corrects the effect of convection due to heating of the sensor from the compensation gradient m. That is, a predetermined time position of the compensation gradient m, for example, t _F
From the output Vt _FF in, subtracting the correction value V ₁ × G ₂ to the initial voltages V ₁ multiplied by the factor G _2, we obtain a corrected output V't _FF, calculates determine a correction compensation gradient n based on this.

Then, based on this modified compensation slope n,
The steps up to calculating the output voltage V't _C in the steady state and displaying it on the display unit 5 are the same as those in the first embodiment, so detailed description will be omitted.

The predetermined time position t _F is not limited to the above-mentioned position and may be any position. The coefficient G ₂ may be experimentally determined, and is determined in relation to the predetermined time position.

[0057]

As described above with reference to the embodiments, in the liquid level measuring system using the heat radiation type level sensor of the present invention, the liquid level measuring resistor is eliminated and the resistors are arranged in parallel. There is no output error due to the temperature coefficient difference of the resistance value, which is a problem due to, and there is no temporary output error due to the difference in heat capacity, and there is no waiting time until the output stabilizes. Can be displayed.

Furthermore, in the second and third inventions, not only the compensation for the ambient temperature but also the influence of the convection of the sensor is compensated, so that the measurement can be performed with extremely high accuracy.

[Brief description of drawings]

FIG. 1 is a block diagram showing a system configuration of each embodiment of the first, second and third inventions.

FIG. 2 is a graph showing the relationship between the cycle of current generated from the pulse circuit and the output voltage from the sensor in each of the first and second inventions.

FIG. 3 is a graph showing a voltage change until a steady state is achieved in each of the embodiments of the first, second and third inventions.

FIG. 4 is a graph showing the relationship between the cycle of the current generated from the pulse circuit and the output voltage from the sensor in the embodiment of the third invention, and explaining the compensation gradient setting.

FIG. 5 is a diagram for explaining the operation of the first, second and third inventions, and is a graph showing changes in the sensor resistance value due to current and current generated from the pulse circuit.

FIG. 6 is a graph showing a relationship between a current generated from a pulse circuit and a temperature-compensated resistance value.

FIG. 7 is a graph showing the relationship between ambient temperature and sensor output (steady state).

FIG. 8 is a graph showing a relationship between ambient temperature and sensor initial voltage.

FIG. 9 is a diagram illustrating the operation of the second and third inventions, and is a graph showing the relationship between the initial voltage and the sensor output voltage.

FIG. 10 is a graph showing the relationship between the ambient temperature and the output of the temperature-compensated sensor.

[Explanation of symbols]

FL level sensor G ₁ coefficient G ₂ coefficient m Compensation gradient n Corrected compensation gradient V ₁ Initial voltage Vt _C Steady voltage V′t _C Corrected steady voltage t _F Predetermined time position V′t _FF Corrected output 2 Pulse circuit 4 CPU 4a Storage means (CPU) 4b Calculation means (CPU) 4c Prediction means (CPU) 4d Gradient determination means (CPU) 4e Gradient correction means (CPU) 4f Correction means (CPU) 5 Display means

Claims (3)

(57) [Claims] 1. A pulse circuit for intermittently supplying a constant current to a sensor which is a resistor, a storage means for storing an initial voltage output from the sensor, and an output voltage from an initial state until a predetermined time elapses. The calculation means for dividing by the voltage, and the prediction means for predicting the steady voltage in the steady state from the rising gradient of the output obtained from the calculation means with respect to time are output to the display means as the liquid level output. A liquid level measuring method using a heat radiation type level sensor. 2. A pulse circuit for intermittently supplying a constant current to a sensor which is a resistor, a storage means for storing an initial voltage output from the sensor, and an output voltage from an initial state until a predetermined time elapses. The initial voltage is preset from the calculating means for dividing by the voltage, the predicting means for predicting the steady voltage which becomes the steady state from the rising slope of the output obtained from the calculating means, and the steady voltage from the predicting means. A liquid level measuring method using a heat radiation type level sensor, characterized in that it comprises correction means for subtracting a correction value obtained by multiplying a coefficient to obtain a corrected steady voltage, and outputs the correction result to a display means as a liquid level output. . 3. A pulse circuit for intermittently flowing a constant current to a sensor which is a resistor, a storage means for storing an initial voltage output from the sensor, and an output voltage from an initial state until a predetermined time elapses. The initial voltage is calculated in advance from the calculating means for dividing by the voltage, the slope determining means for calculating and determining the compensation slope from the rising slope of the output obtained from the calculating means, and the output by the means at the predetermined time position of the compensation slope. A correction value obtained by multiplying the set coefficient is subtracted, a slope correction means for correcting the compensation slope on the basis of the subtracted correction output to calculate and determine a correction compensation slope, and a correction compensation slope from this means are used. The heat radiation type relay is composed of a predicting means for calculating and predicting a steady voltage that becomes a steady state and a display means for displaying the calculation result as a liquid level output. Liquid level measurement method with bell sensor.