JPH04364425A - Method for measuring level of liquid by cooling-type level sensor - Google Patents

Abstract

PURPOSE:To achieve an accurate compensation according to a change in previous and later conditions by setting an arithmetic means among a stationary sensor output at this time and a plurality of stationary sensor outputs within a set range which are obtained at the time which is close to this time to a compensation level measurement data and eliminating outputs outside the set range. CONSTITUTION:A voltage Vp according to a current I which is generated from a pulse circuit 2 is stored in a memory portion of a CPU 4 successively together with a time data. The CPU 4 stores an initial output voltage V1, divides values after a voltage V2 which are continuously input by a voltage V1 by using an operation means, and then obtains a stationary output voltage (stationary sensor output) Vtc which becomes stationary from a rising inclination for these times according to operation and prediction. Although this is a level measurement data of a liquid of an ambient temperature compensation, an error is generated when a body oscillation is large, thus obtaining a compensation level measurement data by calculating an arithmetic mean among the stationary sensor output and a specified number of stationary sensor outputs which were obtained at times which are before and are close to this time.

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 dissipation type level sensor suitable for detecting the level of fuel in a vehicle fuel tank, for example.

0002

2. Description of the Related 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 surface. To briefly describe the method using pulsed constant current (details will be described later), in the pulsed method, a constant current is passed through the sensor for several seconds. The sensor voltage increases due to constant current application, and the amount of increase is proportional to the liquid level. However, FULL at the end of current supply
The voltage difference between and EMPTY is so small that practical resolution cannot be obtained. Therefore, it was decided to obtain an output proportional to the liquid level from the average slope of the voltage rise instead of the above-mentioned rise amount. Specifically, the sensor voltage is digitally input every few milliseconds, and a microcomputer performs first-order approximation processing to obtain the slope, thereby increasing the output resolution. . To explain this with reference to FIGS. 7(a) and 7(b), FIG. 7(b) is a diagram in which the horizontal axis represents time and the vertical axis represents current. It shows a pulse current that intermittently repeats a constant current that becomes stable at tf and turns off at time tf. FIG. 7(a) shows a state in which the sensor output during this energization is sampled, and starting from the initial voltage V1 at time t1, V2, V3, . . . Vf are obtained. Therefore, each output voltage is divided by the initial voltage V1 to perform temperature compensation for the ambient temperature. Then, the rising slope of this output with respect to time is subjected to first-order approximation processing to obtain the slope, which is then subjected to arithmetic processing to finally obtain a stable steady sensor output, which is used as liquid level measurement data.

However, while the vehicle is running, the fuel may oscillate and the fuel level may fluctuate when the level is measured, making it impossible to obtain an output corresponding to the remaining amount of fuel.

[0004] Furthermore, in the heat radiation type, since the sensor is heated, the sensor temperature at the end of measurement is higher than the ambient temperature, and it is necessary to cool the sensor until the sensor temperature and the ambient temperature match. . Therefore, since the measurement interval is quite long, simple processing such as increasing the number of measurements and averaging them in a short period of time is not possible.

[0005]

As described above, in the liquid level measurement method using a heat dissipation type level sensor, since the liquid level fluctuates during driving, it may not be possible to obtain an accurate remaining amount of fuel.

Furthermore, since the sensor is heated, the temperature is higher than the surroundings when the measurement is completed. Since the initial value needs to match the ambient temperature, the measurement interval becomes long, and there are disadvantages such as a simple process of increasing the number of measurements and averaging them in a short period of time.

The present invention has been made in order to eliminate the above-mentioned disadvantages, and uses a heat dissipation type level sensor that can obtain level measurement data that corrects errors caused by the behavior of the liquid level even if the liquid level changes due to rocking or the like. The purpose is to provide a method for measuring the level of liquid.

[0008]

[Means for Solving the Problems] In order to achieve the above object, the invention according to claim 1 intermittently supplies a constant current to a sensor, which is a resistor immersed in liquid, and detects the liquid level based on changes in sensor output. A level detection method that obtains liquid level measurement data by predicting the steady sensor output according to In the level measurement method, the level correction method detects the current steady sensor output and the previous steady sensor output when the current steady sensor output newly obtained by the level detection method is within a preset range. The arithmetic mean value of a predetermined number of steady sensor outputs obtained at a point close to this and whose output is within the set range is determined, and this is used as the current correction level measurement data, and the current steady sensor output is within the set range. This is a liquid level measuring method using a heat dissipation type level sensor, which is characterized in that the previous corrected level measurement data is held when the temperature is outside.

Further, in the level detection method according to the second aspect of the invention, a constant current is intermittently passed through a sensor which is a resistor immersed in a liquid, an initial output voltage of a sensor output from the sensor is memorized, and an initial output voltage is stored. The output voltage from the state until a predetermined time elapses is divided by the initial voltage, and the steady state sensor output in the steady state is calculated and predicted from the rising slope of the output obtained by this division with respect to time to obtain the level measurement data. 2. A liquid level measuring method using a heat dissipation type level sensor according to claim 1.

Furthermore, the invention according to claim 3 is characterized in that the level correction method corrects the setting range based on previous correction level measurement data for the current steady sensor output. This is a liquid level measuring method using the heat dissipation type level sensor according to item 2.

[0011]

[Operation] In the invention as claimed in claim 1, when the newly obtained steady state sensor output is within the set range, this output and a plurality of steady states within the set range obtained at a point close to this output are combined. Since the arithmetic mean with the sensor output is used as the correction level measurement data, and outputs outside the set range are excluded, highly accurate correction that incorporates changes in the situation before and after is possible, unlike simple average processing.

[0012] Furthermore, according to the second aspect of the invention, correction for ambient temperature can be easily performed.

Furthermore, in the invention as set forth in claim 3, since the setting range is corrected based on the average value including the steady sensor outputs obtained sequentially, it is possible to provide an appropriate range that follows changing conditions.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be explained below with reference to the drawings and an apparatus in which it was carried out.

Regarding the device in which the method of the present invention was first implemented,
An outline thereof will be explained with reference to FIGS. 1 to 3, and an embodiment thereof will be explained as an example of the present invention along with its operation.

1 is a fuel tank, and FL is a sensor serving as a resistor immersed in the tank 1. A constant current I is applied to both ends of the sensor FL through a constant current pulse circuit 2. The output voltage Vp generated across the level sensor FL by flowing this current is taken into the CPU 4 through the A/D converter 3. Then, the CPU 4 executes the level detection method and level correction method described below, and the corrected level measurement data is displayed on the display section 5.

First, the function of the present device and the level detection method will be explained.

The current I generated from the pulse circuit 2 is shown in FIG.
As shown in b), a large period having a period from t0 to tf is repeated after a cooling time,
The entire period is set to about 3 seconds. Therefore, as shown in FIG. 2(a), the voltage Vp rises from the initial state at a gradient corresponding to the level of the liquid level (the lower the level, the higher the slope is, and the higher the level, the lower the slope). This is repeated, sequentially taken into the CPU 4, and sequentially stored in the storage section of the CPU 4 together with the time data (enlarged portion in FIG. 1).

Here, the initial voltage, ie, the output voltage V1 at t1, can be regarded as the output voltage in a state where the sensor FL is not yet heated by the current I.

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 V1, and calculates the voltages V2 to Vn that are subsequently inputted by the calculation means consisting of the CPU 4.
The value of is divided by this initial voltage V1, and the steady output voltage (steady sensor output) Vtc which will be in a steady state is calculated and calculated from the rising slope with respect to these times. This is liquid level measurement data compensated for ambient temperature.

Therefore, as shown in FIG. 3, the CPU 4 has a built-in program that calculates the approximate steady output voltage (steady sensor output) Vtc at the time tc when the steady state is reached from the rising slope of the first-order approximate straight line. ing.

Further, for example, if the period from t1 to tf is 3 seconds, and the sampling interval is 10 msec, 300 sampling voltages Vp can be obtained.

The liquid level measurement data obtained in this way has no problem during normal driving, but when the vehicle body is shaken significantly, errors occur due to the behavior of the liquid level. This is corrected by the level correction method described below to obtain corrected level measurement data.

In other words, the arithmetic mean of the current steady sensor output newly calculated by the level detection method and a predetermined number of steady sensor outputs obtained at previous and close points in time is calculated. This is a method of using correction level measurement data.

(1) Regarding the average of data. (Hereinafter, the steady sensor output will be referred to as data.) It is preferable to select the optimal value as a result of experiments for the number of data, but in this example, it is set as 5 times, and from the first to the fourth time, the number of data obtained is After the fifth time, the data from the previous four times are added and averaged.

[0026] These averaged values are referred to as average output.

(2) Regarding data selection, if the Nth data exceeds a preset range (set range), it is not added to the data for averaging. The average output at this time retains the previous average output. Also, from now on, the Nth data will not be used, and at the N+1st time, N-
The 4th to N-1 and N+1-th data are added and averaged to obtain the average output. (However, at this time, it is assumed that other data does not exceed the set range.) Then, at the Nth time, the set range is newly revised based on the average output value at the N-1st time. Set. See Figure 4 for the setting range.
Shown below. The white and black circles are the current values, and the double circles are the previous values.

(3) As the initial value for selecting data up to the set data count, use, for example, the value input into the memory of the final data from the last time the car was moved. In the case of 5 times average, 2
If data exceeding the set range is generated between the 5th and 5th times, that value is not used and the previous average output is maintained. When the number of data within the set range reaches 5, the process shifts to the method shown in section (2).

As described above, in this embodiment, the average value is calculated by adding the current data within the set range and a predetermined number of data obtained at a previous approaching point and within the set range. Correction level measurement data is obtained from this average output.

Furthermore, an example of the five-time average model is shown in FIG.
Shown below.

This is an example of how to handle the case where the fifth data (indicated by a black circle) is outside the set range.

Next, regarding the overall flow of the level correction method,
This will be explained with reference to the flowchart shown in FIG.

First, the case where the number of set data is three or less will be explained.

When started, a range is set in step P1 based on data from the previous operation (for example, when using a car).

Data is input in step P2. Initially, the previous data of step P3 (stored in memory) is input.

[0036] In step P4, it is determined whether or not this data is an initial value.Since it is an initial value, the answer is YES, and step P4 is performed.
5, the initial value is retrieved from the memory, and step P3
is output as the average output. Then, in step P1, the range is set again based on this output.

In step P2, the next data (the uncorrected level measurement data described above for the second time) is input, and in step P4, it is determined whether or not it is the initial value.Since the answer is NO this time, the process goes to step P6. Then, it is determined whether the number of data within the setting range is four or more, and since the answer is NO, the process goes to step P7.

In step P7, it is determined whether the current (second) data is within the set range, and if YES, the process goes to step P8.

In step P8, the arithmetic mean value with the previously input data (initial value) is calculated, and step P3
is output as the average output.

If the answer is NO in step P8, the previous average output is held in step P9, and the process proceeds to step P3.
and is output.

Next, if there are four or more pieces of data within the set range (for example, during normal driving), after going through steps P1, P2, and P4, it is determined in step P6 whether there are four or more pieces of data within the set range. is determined and is YES, so step P10
In step P11, it is determined whether or not the current data is within the set range, and if YES, four pieces of data V1, V2...V4 and V5 at the previous close point within the set range are determined.
(current data) are called in and their arithmetic average is calculated in step P12, and this average output is outputted as correction level measurement data in step P3.

If NO in step P10, the previous average output is held in step P9, and output as correction level measurement data in step P3.

This concludes the description of the embodiment.

In this embodiment, the average value of five pieces of data (steady sensor output) is used, but the number is not limited to this and may be determined according to the actual situation.

Furthermore, when the setting range is sequentially corrected based on the average output as in this embodiment, accuracy is further improved because the setting range is finely adapted to the current situation.

[0046]

Effects of the Invention As described in detail above, the liquid level measurement method using the heat dissipation type level sensor of the present invention is based on the newly obtained steady sensor output and multiple sensor outputs obtained at a point close to the current sensor output. Since the arithmetic average of the steady sensor output within the setting range is used as the correction level measurement data, and the output outside the setting range is excluded, unlike simple averaging processing, it is possible to detect changes in the situation before and after the measurement even if the measurement interval is not short. You can obtain stable measurement data that takes into consideration the situation, and you can make accurate corrections that suit the situation.

[Brief explanation of drawings]

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

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

FIG. 3 is a diagram explaining the relationship between steady output voltage (steady sensor output) and slope in the same embodiment.

FIG. 4 is a diagram explaining the relationship between data (steady sensor output) and setting range.

FIG. 5 is an explanatory diagram of an embodiment showing an example of data selection.

FIG. 6 is a flowchart illustrating an embodiment.

FIG. 7 is a diagram illustrating a conventional example.

[Explanation of symbols]

FL Sensor V1, initial output voltage V1, V2,...Vn Output voltage Vtc Steady output voltage, steady sensor output V1, V2,...V4 Previous steady sensor output, previous data

Claims (3)

[Claims] 1. A level detection method in which a constant current is intermittently applied to a sensor that is a resistor immersed in a liquid, and a steady sensor output corresponding to the liquid level is predicted from changes in the sensor output to obtain liquid level measurement data. and a level correction method for correcting errors caused by the behavior of the liquid level with respect to the steady sensor output. If the steady sensor output obtained this time is within a preset range, the current steady sensor output and a predetermined number of sensors obtained before and at a time close to this and whose output is within the preset range The heat dissipation method is characterized in that the arithmetic mean value with the steady state sensor output is determined and this is used as the current correction level measurement data, and if the current steady state sensor output is outside the set range, the previous correction level measurement data is held. Method for measuring liquid level using a type level sensor. 2. The level detection method involves intermittently passing a constant current through a sensor that is a resistor immersed in a liquid, storing the initial output voltage of the sensor output from the sensor, and detecting the voltage from the initial state until a predetermined time elapses. 2. The level measurement data is obtained by dividing the output voltage by the initial voltage, and calculating and predicting a steady state sensor output based on the rising slope of the output obtained by this division with respect to time. A liquid level measurement method using a heat dissipation type level sensor. 3. The heat dissipation type level sensor according to claim 1 or 2, wherein the level correction method corrects the setting range based on the previous correction level measurement data for the current steady sensor output. How to measure the level of liquid by.