JPH04218723A - Level measuring system of liquid by cooling type level sensor - Google Patents

Abstract

PURPOSE:To enable a liquid surface to be measured readily and highly accurately using a cooling sensor. CONSTITUTION:A cooling sensor is dipped into a liquid, a constant current is made to flow to it by a pulse circuit, an initial voltage at the start of conduction of current is stored by a memory means, an output voltage while current is conducting is sampled, an operation means for dividing the sampling voltage by the initial voltage is provided, a prediction means for predicting a voltage at a constant state according to ascent inclination of the divided output for time is provided, and compensation for an ambient temperature is performed by division with the initial voltage.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a level sensor for detecting the level of fuel in a vehicle fuel tank, for example, and particularly to a method for temperature-compensating and accurately measuring the liquid level in a short time. .

0002

[Prior Art] A heat dissipation type level sensor utilizes the fact that the resistance of the sensor, which is a resistor, changes depending on the depth of immersion in the liquid level, and heats the sensor by passing a constant current through the sensor to increase the liquid level of the sensor. This sensor detects the liquid level by converting the corresponding resistance change into voltage.

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

[0004] Therefore, as shown in, for example, Japanese Patent Laid-Open No. 63-311927, which was previously developed by the present applicant, a temperature compensating resistor having a structure similar to that of the sensor is arranged in parallel, and the liquid level of the sensor is adjusted. The level of the liquid was measured by utilizing the fact that a corresponding change in resistance value appears as a voltage change at the connection point with the temperature compensation resistor. In other words, the temperature compensation resistor is immersed in the liquid together with the sensor, but since it is not self-heated, its resistance value does not follow changes in the liquid level, and its resistance changes only with changes in ambient temperature. The value will change and this will automatically cause a liquid level measurement.

[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 compensation resistor constant.

[0006] In addition, these sensors and temperature compensation resistors actually have a structure in which Ni wire is spirally wound around the outer periphery of a rod-shaped support, so they have a considerably large heat capacity and can provide stable output. It took several minutes for the output to stabilize, especially when the tank capacity was close to empty and the immersion depth was small.

[0007] For this reason, if the user reads the meter during an unstable period, the liquid level may be incorrect.
This poses a practical problem.

Furthermore, since the resistor actually requires a higher resistance value than the sensor, the resistance wire is longer and the heat capacity is different. Therefore, if the ambient temperature changes,
During the change, a temperature difference occurs between the two, which has the drawback of temporarily causing an error in liquid level measurement.

The present invention has been made in view of the above drawbacks, and the first invention solves the above-mentioned problems by eliminating the temperature compensating resistor and arranging the resistors in parallel. It is an object of the present invention to provide a liquid level measurement method using a heat dissipation type level sensor that improves level measurement accuracy and enables measurement in a short time.

[0010] The second and third inventions also have an object to provide a liquid level measurement method using a heat dissipation type level sensor, which has further improved measurement accuracy than the first invention.

[0011]

[Means for Solving the Problems] In order to achieve the above object, the invention according to claim 1 provides a pulse circuit that intermittently flows a constant current to a sensor which is a resistor, and an initial voltage output from the sensor. A storage means for storing information, a calculation means for dividing an output voltage from an initial state until a predetermined time has elapsed by the initial voltage, and a steady state voltage to be in a steady state is predicted from an increasing slope of the output obtained from the calculation means over time. and a prediction means, and outputs the calculation result to the display means as a liquid level output.

Further, the invention according to claim 2 provides a pulse circuit for intermittently passing a constant current through a sensor which is a resistor, a storage means for storing an initial voltage outputted from the sensor, and a pulse circuit for storing an initial voltage outputted from the sensor, a calculating means for dividing the output voltage up to the elapsed time by the initial voltage; a predicting means for predicting a steady voltage that will be in a steady state from a rising slope of the output obtained from the calculating means with respect to time; and a steady voltage from the predicting means. The present invention is characterized by comprising a correction means for obtaining a corrected steady voltage by subtracting a correction value obtained by multiplying the initial voltage by a preset coefficient from the initial voltage, and outputting the correction result to the display means as a liquid level output.

Furthermore, the invention according to claim 3 provides a pulse circuit that intermittently supplies a constant current to a sensor that is a resistor;
storage means for storing the initial voltage output from the sensor; calculation means for dividing the output voltage from the initial state to the elapse of a predetermined time by the initial voltage; and compensation from the rising slope of the output obtained from the calculation means over time. a slope determining means for calculating and determining the slope, and subtracting a correction value obtained by multiplying the initial voltage by a preset coefficient from the output of the compensation slope at a predetermined time position by this means, and based on the subtracted correction output. a slope correction means for calculating and determining a corrected compensation slope by correcting the compensation slope; a prediction means for calculating and predicting a steady voltage that will be in a steady state based on the corrected compensation slope from this means; The present invention is characterized by comprising a display means for displaying as a level output.

[0014]

[Operation] In the first aspect of the invention, the sensor is hardly heated at the initial stage of flowing a constant current, so 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 is obtained.

Furthermore, in order to shorten the measurement time, by sampling the liquid level measurement output after energization and approximating the output to the energization time, it is possible to obtain the level output after a sufficient period of time has elapsed. .

[0016] Further, the second invention as set forth in claim 2 and the third invention as set forth in claim 3 provide liquid level measurement using a heat dissipation type level sensor, which has further improved temperature compensation accuracy than the first invention. Before explaining the second and third aspects of the invention, temperature compensation for level measurement using 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 as a result of current application, and the amount of increase is proportional to the liquid level. However, the voltage difference between when the tank is FULL and when the tank is EMPTY at the end of current supply is small, and practical resolution cannot be obtained. Therefore, we decided to obtain an output proportional to the liquid level from the average slope of the voltage rise instead of the amount of rise mentioned above. This is the first invention, and specifically, the sensor voltage is digitally inputted every few milliseconds, and a microcomputer performs first-order approximation processing to obtain the slope (compensation slope) to increase the output resolution.

FIGS. 5(a) and 5(b) are diagrams in which the horizontal axis represents time and the vertical axis represents current and resistance values, where curve a represents constant current and curve b represents ambient temperature. Curve c shows the change in resistance value due to energization in air when the ambient temperature is low, and curve c shows the change in resistance value due to energization in air when the ambient temperature is high. The current is time t
0 and reaches a stable state at time t0'.

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

[0020] The resistance at time t is given by equation 1, taking into account the change in resistance due to ambient temperature.

[0021]

[Math 1]

Since the resistance value changes depending on the ambient temperature, it is necessary to compensate for this effect. Immediately after the current is applied, as mentioned above, there is almost no heating, so the resistance value is the same as that corresponding to the ambient temperature before the current is applied. (It has nothing to do with the level of the liquid.) The resistance value at t=t1 in FIG. 5(a) is given by Equation 2.

[0023]

[Math 2]

Therefore, the influence of the ambient temperature is compensated for by storing the resistance value immediately after the current is applied (hereinafter referred to as the initial resistance value; Equation 2) in the memory and dividing the resistance value sampled at each time.

The compensated resistance value at time t is shown in Equation 3.

[0026]

[Math 3]

The resistance curves b' and c' in FIG. 6(a) are obtained by compensating for the influence of ambient temperature on the resistance curves b and c in FIG. 5(a).

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

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

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

As mentioned above, even after ambient temperature compensation, the output increases due to the rise in ambient temperature, and the reason why the steady outputs do not match is considered to be due to the following reasons.

In other words, if the resistance value is large, the amount of change in resistance value due to current flow will also be large, but according to the compensation method described above, it is normalized by dividing by the initial resistance value (initial voltage value), and the slope with respect to time is remains unchanged. In other words, the effects of differences in resistance values due to ambient temperature and differences in resistance values between samples at the same temperature are compensated for. This is the invention described in claim 1.

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

As mentioned above, when performing temperature compensation, the resistance value (voltage value) immediately after the current is applied is used for division. At this time, no convection is occurring, but immediately after that, warm air gradually rises from the bottom through the sensor surface, warming the sensor and increasing its resistance value. Therefore, it is presumed that for a certain short energization time, as the energization time becomes longer, the rate at which the resistance value increases also increases. This ratio is considered to be proportional to the resistance value before energization.

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

Therefore, the second invention corrects the steady voltage obtained by the first invention to remove the influence of convection. That is, the corrected steady voltage V'' is obtained by subtracting the corrected value obtained by multiplying the initial voltage V1 by the setting coefficient G1 from the steady voltage VtC predicted from the rising slope obtained by division.
tC is the level measurement value, and the influence of convection is removed. That is, V″tC = VtC −V1 ×G1 Note that the coefficient G1
can be determined experimentally using the sensor, tank configuration, etc.

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 that compensates for the ambient temperature. The steady state voltage was predicted and determined. The present invention corrects the fact that this compensation gradient still contains an error, but as mentioned above, this error is considered to occur in proportion to the magnitude of the initial voltage, so Output due to compensation slope (Vp)
In this method, a correction value obtained by multiplying the initial voltage V1 by a preset setting coefficient G2 is subtracted from the initial voltage V1, and a correction compensation slope is set based on the correction output V'p obtained by this subtraction. That is, V'p=Vp-V1×G2.

[0038] The coefficient G2 is determined by the sensor, tank,
It may be set experimentally depending on the configuration of the system, the time position to be set, etc.

[0039]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a first embodiment, a second embodiment, and a third embodiment of the invention will be described in detail with reference to the drawings.

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

A constant current I is passed through the pulse circuit 2 across the level sensor FL. An output voltage V generated across the level sensor FL by flowing this current I
p is taken into the CPU 4 through the AD converter 3.

The current I generated from the pulse circuit 2 is
As shown in Figure (b), a large cycle having a cycle from t0 to tF is repeated after a cooling time, and the entire cycle is set to about 3 seconds. However, even though the current becomes constant I from the start of the circuit, t0'
is necessary.

Therefore, as shown in FIG. 2(a), the voltage Vp changes from the initial state to the liquid level (
When the level is low, the slope is large, and when the level is high, the slope is small).
4 and sequentially stored in the storage unit in the CPU 4 together with the time data (enlarged portion of the figure). A storage means 4a is composed of the CPU 4 and the storage section.

Here, depending on the current I, the initial voltage, that is, the output voltage V1 at t1, can be regarded as the output voltage when the sensor FL is not heated.

In other words, it can be regarded as an output voltage based on a resistance value similar to that of a conventional temperature compensation resistor, and the CPU 4 stores this initial output voltage, and the calculation means 4b constituted by the CPU 4 continuously receives the input voltage. By dividing the values of voltages Vt2 to VtF by this initial voltage V1, the rising slope of these outputs with respect to time is obtained, and this is calculated by the prediction means 4c.
to obtain a compensation slope of the output compensated for ambient temperature, from which liquid level measurement data (steady state voltage VtC) is obtained. Based on this data, the level output of the measured liquid level is displayed on the display section 5.

Note that 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, for example, the period from t1 to tn,
For example, if the sampling interval is 10 msec in 5 seconds, 500 sampling voltages can be obtained.

Therefore, as shown in FIG. 3, the CPU 4 constituting the prediction means has a program that determines the compensation slope from the rising slope and calculates the approximate voltage Vtc at the time tc when the steady state is reached based on this. is built-in, and by displaying the value on the display unit 5, display can be performed with a large output voltage.

Next, a second embodiment will be explained with reference to FIGS. 1 to 3. This is an embodiment of the second invention, and has substantially the same configuration as the first embodiment, except that it includes a correction means 4f.

That is, the steady voltage VtC obtained in the first embodiment is corrected to remove the influence of convection. That is, the correction means 4 constituted by the CPU 4
In f, the corrected value obtained by multiplying the initial voltage V1 by the setting coefficient G1 is subtracted from the steady-state voltage VtC predicted based on the rising slope obtained by the division, and the corrected steady-state voltage V″t is obtained.
C is taken as a level measurement value and output to the display unit 5. The effect of convection has been removed. That is, V″tC = VtC −V1 ×G1 Note that the coefficient G1
may be determined experimentally based on the sensor FL, tank configuration, etc.

Next, FIGS. 1, 3, and 4 for the third embodiment
This will be explained with reference to (a) and (b) of the same figure.

This embodiment is an embodiment of the third invention, and has almost the same configuration as the first embodiment, including a sensor FL, a pulse circuit 2 that supplies a constant current to it, and an initial voltage V of the sensor FL.
1, a calculation means 4b for dividing the output voltage Vp by the initial voltage V1, and a prediction means 4c, and further includes a slope determination means (CPU) 4d and a slope correction means (CPU) 4e. is different from the first embodiment.

The gradient determining means 4d divides the output voltages V1, Vt2 F, Vt3 F, . Calculate the compensation slope m
Calculate and determine.

Next, the gradient correction means 4e corrects the compensation gradient m by removing the influence of convection caused by the heating of the sensor. That is, the predetermined time position of the compensation gradient m, for example tF
From the output VtFF at
Subtract the corrected value V1 × G2 multiplied by the corrected output V'
tFF is determined, and based on this, the modified compensation gradient n is calculated and determined.

Then, based on this modified compensation slope n,
The process up to calculating the steady state output voltage V'tC and displaying it on the display unit 5 is the same as in the first embodiment, so a detailed explanation will be omitted.

Note that the predetermined time position tF is not limited to the above-mentioned position, but may be any position. Further, the coefficient G2 may be determined experimentally, and is determined in relation to a predetermined time position.

[0057]

[Effects of the Invention] As explained above with reference to the embodiments, in the liquid level measuring method using the heat dissipation type level sensor of the present invention, the resistor for measuring the liquid level is eliminated and the resistors are arranged in parallel. There is no output error due to the difference in the temperature coefficient of resistance value, which is a problem with , there is no temporary output error due to the difference in heat capacity, and there is no waiting time for the output to stabilize, so you can quickly check the measured value. It has the advantage of being able to display

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

[Brief explanation of the drawing]

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

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

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

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

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

FIG. 6 is a graph showing the relationship between the current generated from the pulse circuit and the 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 the relationship between ambient temperature and sensor initial voltage.

FIG. 9 is a diagram explaining the effects 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 temperature-compensated sensor output.

[Explanation of symbols]

FL level sensor G1 coefficient G2 coefficient m Compensation slope n Modified compensation gradient V1 Initial voltage VtC Steady voltage V'tC Modified steady voltage tF Predetermined time position V'tFF corrected output 2 Pulse circuit 4 CPU 4a Storage means (CPU) 4b Arithmetic means (CPU) 4c Prediction means (CPU) 4d Gradient determining means (CPU) 4e Gradient correction means (CPU) 4f Correction means (CPU) 5 Display means

Claims (3)

[Claims] 1. A pulse circuit that intermittently supplies a constant current to a sensor that is a resistor; a storage means that stores an initial voltage output from the sensor; calculation means for dividing by voltage;
and a prediction means for predicting a steady voltage that will be in a steady state from the rising slope of the output obtained from the calculation means over time, and outputting the calculation result to the display means as a liquid level output. Liquid level measurement method using a level sensor. 2. A pulse circuit that intermittently supplies a constant current to a sensor that is a resistor; a storage means that stores an initial voltage output from the sensor; calculation means for dividing by voltage;
a prediction means for predicting a steady voltage that will be in a steady state from the rising slope of the output obtained from the calculation means with respect to time; and a correction value obtained by multiplying the initial voltage by a preset coefficient from the steady voltage from the prediction means. A liquid level measuring method using a heat dissipation type level sensor, comprising: a correction means for obtaining a corrected steady voltage by subtracting . 3. A pulse circuit that intermittently supplies a constant current to a sensor that is a resistor; a storage means that stores an initial voltage output from the sensor; and a pulse circuit that stores an initial voltage output from the sensor; calculation means for dividing by voltage;
slope determining means for calculating and determining a compensation slope from the rising slope of the output obtained from the calculation means over time, and an initial voltage obtained by multiplying the initial voltage by a preset coefficient from the output of the compensation slope at a predetermined time position by this means. a slope correction means for calculating and determining a corrected compensation slope by subtracting a correction value and correcting the compensation slope based on the subtracted correction output; and a steady voltage that is in a steady state based on the corrected compensation slope from this means. A liquid level measuring method using a heat dissipation type level sensor, characterized in that it is comprised of a prediction means for calculating and predicting, and a display means for displaying the calculation result as a liquid level output.