JP2021043042A - Range-finding device, range-finding method and liquid-level meter - Google Patents

Abstract

To provide a range-finding device, range-finding method and a liquid-level meter that eliminate a ripple component included in a detection signal form a range-finding device such as a liquid-level meter and the like, using a digital filter, and can perform a measurement in real-time.SOLUTION: A range-finding device, which outputs a range-finding signal in a form of a digital signal, has: a tilt calculation unit that calculates a tilt of a detection signal; a digital filter that is aimed at eliminating a ripple generated in the detection signal; a delay-amount calculation unit that calculates a delay amount of an output of the digital filter derived from processing of eliminating the ripple on the basis of the tilt of the detection signal and a filter length of the digital filter; a correction-amount calculation unit that multiplies the delay amount by the tilt of the detection signal to calculate a correction amount of the output of the digital filter; and a correction unit that adds the correction amount to the output of the digital filter to correct the output of the digital filter. Thereby, the range-finding device outputs the range-finding signal in real-time.SELECTED DRAWING: Figure 8

Description

The present invention relates to a distance measuring device, a distance measuring method, and a liquid level gauge.

The distance measuring device is required to monitor and record the distance measurement result in real time. However, the distance measurement value may fluctuate depending on the distance measurement system. In such a case, if the distance measurement result is displayed as it is, it is difficult to see the value or tendency that you really want to know. Therefore, for example, there is an example of performing statistical processing such as averaging. However, a simple averaging process may not be able to sufficiently suppress fluctuations in the distance measurement value.

An example of a distance measuring device is a liquid level gauge installed in a tanker that transports crude oil, liquefied gas, and the like. This type of liquid level gauge is mainly used during loading and unloading operations of crude oil as cargo, and can continuously measure the distance from a reference point to a liquid level that changes with time.

There is a radio wave type distance measuring device as one of the distance measuring methods in the distance measuring device such as the liquid level gauge. In the radio wave type distance measuring device, it is desirable that there is no obstacle to the radio wave between the distance measuring device and the distance measurement target, but for the convenience of the system, there is no choice but to implement a radio wave obstacle. There is. Since this radio wave obstacle reflects the radio wave emitted from the distance measuring device, if the liquid level as the distance measuring target and the radio wave obstacle are close to each other, a large ripple of a low frequency occurs in the distance measuring result. ..

Since it is necessary for the user of such a radio wave type liquid level gauge to be unaware of the existence of the radio wave obstacle, it is necessary to prevent the ripple from affecting the distance measurement signal. When the ripple is suppressed, only the original distance measurement result up to the distance measurement target can be known. However, it is not possible to know the real-time distance measurement result by simply averaging the detection signals of the distance measuring device to suppress the ripple. By using the distance measuring method according to the present invention, it becomes possible to measure in real time.

Patent Document 1 describes a technique for removing ripples contained in a digital signal by using a digital filter such as an FIR filter or an IIR filter.

Japanese Unexamined Patent Publication No. 8-280199

The present invention uses a distance measuring device, a distance measuring method, and a liquid level meter capable of removing a ripple component contained in a detection signal from a distance measuring device such as a liquid level gauge by using a digital filter and measuring in real time. The purpose is to obtain.

The distance measuring device according to the present invention is
It is a distance measuring device that outputs a distance measuring signal as a digital signal.
A slope calculation unit that calculates the slope of the detection signal,
A digital filter for the purpose of removing ripples generated in the detection signal, and
A delay amount calculation unit that calculates the delay amount of the output of the digital filter caused by the ripple removal processing based on the slope of the detection signal and the filter length of the digital filter.
A correction unit that gives a correction corresponding to the delay amount to the digital filter,
Have,
The most important feature is to output the ranging signal in real time.

According to the present invention, the ripple component contained in the detection signal can be removed by using a digital filter, and the distance measurement signal can be output in real time without being affected by the time delay caused by the digital filter processing. ..

An example of the detection signal of the liquid level gauge by simulation is shown, and it is a graph in which the horizontal axis is time and the vertical axis is distance. It is a graph which shows together the said detection signal and the signal obtained by passing this detection signal through a digital filter. It is a graph explaining that the signal obtained through the digital filter is time-shifted and superposed on the detection signal. It is a figure for demonstrating the essence of this invention, and is the graph for demonstrating that the signal obtained through the digital filter is distance-corrected by the delay amount and superimposed on the detection signal. It is a graph which shows the part of FIG. 4 enlarged in order to explain the correction. It is a graph which shows the main part enlarged to explain another example of correction. It is a graph which shows the result of the correction. It is a flowchart which shows the Example of the distance measuring method which concerns on this invention. It is a schematic diagram which shows the outline of the Example of the liquid level gauge which concerns on this invention.

Hereinafter, examples of the distance measuring device, the distance measuring method, and the liquid level gauge according to the present invention will be described with reference to the drawings. The distance measuring device and the distance measuring method according to the present invention are widely applicable not only to the liquid level gauge, but the outline of the liquid level gauge will be described.

[Overview of liquid level gauge]
FIG. 9 shows a tank 10 constructed in a tanker or the like. A waveguide 15 is lowered vertically from the ceiling plate 12 of the tank 10 toward the bottom plate 11. The liquid 13 is loaded in the tank 10 as cargo, and the gas 14 is accumulated between the liquid level of the liquid 13 and the ceiling plate 12.

Since the waveguide 15 has a cylindrical shape and the lower end is open, and a plurality of holes for passing gas are formed on the outer periphery of the uppermost portion of the waveguide 15, the waveguide 15 is formed. The liquid 13 also penetrates into the inside. The liquid level in the waveguide 15 also fluctuates as the liquid level in the tank 10 fluctuates, and the heights of these liquid levels are equal. A liquid level gauge (not shown) is installed above the upper end of the waveguide 15. The liquid level gauge is, for example, a radio wave type liquid level gauge. The measurement method is not limited, but is, for example, a frequency-modulated continuous wave radar (FMWC radar) method. The liquid level gauge measures the distance from the reference point to the liquid level that changes over time.

In the waveguide 15, the measurement reference member 16 is installed at a known distance position predetermined from the reference position of the liquid level gauge for various purposes. The liquid level gauge reaches the liquid level by the relationship between the actual measurement data to the liquid level, the known physical distance to the measurement reference member 16, and the actual measurement distance to the measurement reference member 16 measured by the liquid level gauge. Correct the measured data and calculate the actual distance to the liquid level.

In the example shown in FIG. 9, the measurement reference member 16 is installed at a position 18.5 m from the reference position of the liquid level gauge. In the following description, the case where the measurement distance by the liquid level gauge fluctuates from 18 m to 19 m, that is, the fluctuation of the liquid level at the time of unloading will be described as an example. Here, the distance is treated as a zero value at the reference point of the liquid level gauge, that is, the upper end of the waveguide, and the distance value increases toward the lower side of the waveguide, that is, the bottom of the tank.

[Ripple appearing in measured values]
FIG. 1 shows a detection signal 20 by the liquid level gauge when the liquid level fluctuates from 18 m to 19 m in the example of the liquid level gauge shown in FIG. The horizontal axis is the time axis, the vertical axis is the liquid level distance (m), and the detection signal 20 is a digital signal, for example, it is sampled every second, and the time axis is represented by the number of sample points. In the example of this graph, when a liquid cargo is unloaded, the liquid level fluctuates by 1 mm per second, that is, the measurement distance gradually increases.

As shown in FIG. 1, a ripple 21 is generated in the detection signal 20 while the distance to the liquid surface fluctuates from 18 m to 19 m. The cause of the ripple 21 is the interference of the reflected wave of the radio wave. In the example of the liquid level gauge shown in FIG. 9, the ripple 21 is generated by the interference of the reflected wave from the liquid surface of the radio wave and the reflected wave from the measurement reference member 16 with each other. This means that the measurement result of the original liquid level is disturbed by the influence of the measurement reference member 16, and this is the reason why the measurement reference member 16 was previously expressed as an electromagnetic interference.

In the radio wave level gauge, the multipath of radio waves generated by the structure of the tank is also a factor of ripple. If a ripple occurs in the detection signal in a radio wave type liquid level gauge installed in a tanker or the like, the distance to the liquid level cannot be measured accurately, so it is necessary to eliminate the influence of the ripple.

The upward-sloping detection signal 20 shown in FIG. 1 is a distance measurement value based on the movement of the liquid surface, and is an unprocessed signal that has not been processed in any way. Further, the detection signal 20 shown in FIG. 1 is rippled in a range of about 300 points before and after the number of sample points n = 500 corresponding to the position of the measurement reference member 16, that is, the number of sample points n = approximately 200 to 800. Is occurring. The removal of this ripple by real-time processing will be described below.

[Removing the effects of ripple and problems]
A digital filter such as an FIR filter or an IIR filter is used to remove the influence of ripple contained in the digital signal. FIG. 2 shows an example of the FIR filter output 22 obtained by passing the detection signal 20 of the radio wave type liquid level gauge shown in FIG. 1 through the FIR filter together with the detection signal 20.

The specifications of the FIR filter in this example are as follows.
Filter length: n = 241
Filter type: LPF
Window type: Blackman window Normalized cutoff frequency: 0.035

In the example shown in FIG. 2, the FIR filter acquires one sample every second and sets the filter length: n = 241. Therefore, the FIR filter output 22 has a delay of 120 samples, which is 1/2 of the filter length n, with respect to the detection signal 20. Since the actual fluctuation speed of the liquid level is 1 mm / sec as described above, when the FIR filter output 22 is output to the monitor, it is displayed 120 mm shorter than the distance to the liquid level in real time.

Therefore, as shown in FIG. 3, it is conceivable that the FIR filter output 22 is time-shifted to the front side of 120 samples of the delay amount. The graph 24 shown in FIG. 3 shows a state in which the FIR filter output 22 and the detection signal 20 overlap each other due to the time shift of the FIR filter output 22 as described above.

By time-shifting the FIR filter output 22, the FIR filter output 22 moves to the position of the detection signal 20 and overlaps with the detection signal 20. That is, by shifting the FIR filter output 22 in time, the delay due to the FIR filter can be corrected correctly.
However, in this method, since the time shift is performed after the filtering process, the correction in real time cannot be performed. If the FIR filter output 22 is only time-shifted, the distance 120 samples before, that is, 2 minutes before, is displayed with respect to the distance to the liquid level in real time, and the effect of the time delay is not corrected. Is.

[Distance correction]
In order to make up for the above drawbacks, a real-time processing method is used in this embodiment. That is, instead of the time shift of the FIR filter output 22, as shown in FIG. 4, the FIR filter output 22 is shifted on the vertical axis, that is, the axis indicating the liquid level distance, thereby correcting the delay amount. Here, the fluctuation amount of the liquid level distance predicted to occur when the time is delayed due to the ripple removal processing by the FIR filter is calculated, and the calculated fluctuation amount is added to the FIR filter output 22 to obtain the distance measurement value. It is corrected in real time.

FIG. 5 shows a specific example of correcting the FIR filter output 22 by shifting it on an axis indicating the liquid level distance, and is an enlargement of the n = 0 to 400 portion in FIG. As described above, the filter length n of the FIR filter is 241. The FIR filter performs filter calculation when 241 samples of input data are prepared.

Then, the slope of the detection signal 20 is obtained by the least squares method using the input data from n = 0 to n = 240 used in the first filter calculation. The graph 26 of FIG. 5 shows the inclined portion of the detection signal 20 obtained in this way.

Next, the obtained slope is multiplied by 120, which is a 1/2 sample of the filter length n, to calculate the delay amount of the FIR filter output 22 generated corresponding to the delay time caused by the ripple removal processing by the FIR filter. The FIR filter output 22 is corrected by the amount corresponding to the delay amount. That is, the FIR filter output 22 is shifted on the liquid level distance axis by the amount corresponding to the delay amount in FIG. 5, and the measured value of the distance to the liquid surface is corrected. After that, filter operations are performed in order such as n = 1 to 241, n = 2 to 242, n = 3 to 243, and so on, and each time, the same processing as described above is performed.

[Another example of distance correction]
In the example of distance correction shown in FIG. 5, the inclination of the detection signal 20 is obtained using the data of 241 points. However, when the data itself used to obtain the slope includes the ripple 21, it is easily affected by the ripple 21 when obtaining the slope of the detection signal 20. Therefore, in practice, as in the example of distance correction shown in FIG. 6, the slope of the detection signal 20 is calculated based on the detection signal of the number of sample points less than half of the filter length 241. Here, the slope of the detection signal 20 is obtained using 120 samples corresponding to the latter half of the detection signal to which the digital filter is applied. Since the ripple is partially generated on the detection signal 20 corresponding to the position of the measurement reference member 16, the inclination of the detection signal cannot be accurately obtained by using only the sample near the portion where the ripple is large. .. Further, if the number of sample points used for distance correction is increased, the processing time becomes long. Therefore, by detecting the slope of the detection signal using the latter 120 samples, which are samples having less ripple and approaching a straight line, the slope of the detection signal can be obtained more accurately in a short processing time.

More specifically, at each time point of n = 241, 242, 243 ..., the number of sample points n = 121-240, 122-241, 123-242, ... The slope of the detection signal 20 is obtained using 120 samples immediately before the target data. In FIG. 6, the graph 30 shows the slope of the detection signal 20 thus obtained.

After that, as in the above example, the error of the liquid level distance due to the delay of the digital filter is calculated as the correction amount, and the filter output 22 is corrected. The delay amount of the output 22 of the FIR filter is calculated corresponding to the delay time caused by the ripple removal processing by the FIR filter, and the output 22 of the FIR filter is corrected by the amount corresponding to the delay amount. In this way, the output of the FIR filter 22 is corrected, and the corrected output of the FIR filter 22 overlaps the detection signal 20 without a time delay. This will reduce the impact of ripple.

FIG. 7 shows the result of correcting the distance by shifting the FIR filter output 22 described above. In FIG. 7, the graph 28 shown by the thin line partially overlapping the thick line detection signal 20 is a graph corrected by shifting the FIR filter output 22 on the distance axis. In the graph 28, the FIR filter output 22 is shifted as described above, so that the detection signal 20 of the liquid level gauge is overlapped without a time delay, and the ripple is also removed.

Although the description so far has assumed a liquid level gauge, the present invention is not limited to the liquid level gauge, and is generally applicable to distance measuring devices. This is particularly effective when the measurement target fluctuates on the time axis.

[flowchart]
FIG. 8 shows an operation flow of the liquid level distance measurement value data processing in the liquid level gauge described above. Reference numerals S1, S2, ... Indicates an operation step.

In FIG. 8, when a detection signal is input from the liquid level gauge, this detection signal is input to the digital filter (S1). The digital filter is an FIR filter in the above example.

Next, the slope of the detection signal is obtained by an appropriate method such as the least squares method (S2). Next, the delay amount of the filter output 22 is calculated based on the slope of the detection signal and the filter length (S3). The correction amount is calculated by multiplying this delay amount by the slope of the detection signal (S4). Then, the correction amount is added to the filter output 22 to correct the filter output 22 (S5). The corrected filter output 22 is output as a ranging signal.

Step S2 is executed by the inclination calculation unit that calculates the inclination of the detection signal of the distance measuring device.

Step S3 is executed by the delay amount calculation unit that calculates the delay amount due to the digital filter.
Step S4 is executed by the correction amount calculation unit that calculates the correction amount of the output of the digital filter by multiplying the delay amount and the slope of the detection signal.

Step S5 is executed by the correction unit that corrects the output of the digital filter by the correction amount.

The function as the inclination calculation unit, the function as the correction amount calculation unit, and the function as the correction unit can be executed by a digital signal processing device (DSP), a microcomputer, or the like.

The output of the FIR filter 22 that overlaps the detection signal 20 becomes a high-precision ranging signal from which the influence of ripple is removed. Further, as described above, since the output of the FIR filter 22 can be corrected to measure the distance in real time, even if the position of the distance measurement target is constantly changing, there is no time delay and the distance is measured in real time. You can measure the distance with.

The distance measuring device and the distance measuring method according to the present invention can be applied to a liquid level gauge installed in a tank such as a tanker.

In the embodiment, the method of using the least squares method has been described for obtaining the slope of the detection signal 20, but the method is not limited to the method of least squares, and other methods may be used.

10 Tank 15 Waveguide 20 Detection signal 21 Ripple 22 FIR filter output 28 Shifted FIR filter output

Claims (11)

It is a distance measuring device that outputs a distance measuring signal as a digital signal.
A slope calculation unit that calculates the slope of the detection signal,
A digital filter for the purpose of removing ripples generated in the detection signal, and
A delay amount calculation unit that calculates the delay amount of the output of the digital filter caused by the ripple removal processing based on the slope of the detection signal and the filter length of the digital filter.
A correction amount calculation unit that calculates the correction amount of the output of the digital filter by multiplying the delay amount and the slope of the detection signal.
It has a correction unit that corrects the output of the digital filter by adding the correction amount to the output of the digital filter.
Output the ranging signal in real time,
Distance measuring device. The distance measuring device according to claim 1, wherein the inclination calculation unit calculates the inclination of the detection signal by the method of least squares. The distance measuring device according to claim 1 or 2, wherein the digital filter is an FIR filter. The distance measuring device according to claim 1, 2 or 3, wherein the inclination calculation unit calculates the inclination of the detection signal based on the number of sample points corresponding to the filter length of the digital filter. The distance measuring device according to claim 1, 2 or 3, wherein the inclination calculation unit calculates the inclination of the detection signal based on the number of sample points in the latter half of the filter length. It is a distance measurement method that outputs a distance measurement signal as a digital signal.
Calculate the slope of the detection signal and
The ripple of the detection signal is removed by a digital filter, and the ripple is removed.
Based on the slope of the detection signal and the filter length of the digital filter, the amount of delay in the output of the digital filter caused by the ripple removal processing is calculated.
By multiplying the delay amount by the slope of the detection signal, the correction amount of the output of the digital filter is calculated.
By adding the correction amount to the output of the digital filter, the output of the digital filter is corrected and the distance measurement signal is output in real time.
Distance measurement method. The distance measuring method according to claim 6, wherein the inclination of the detection signal is calculated by the number of sample points corresponding to the filter length of the digital filter. The distance measuring method according to claim 6, wherein the inclination of the detection signal is calculated based on the number of sample points in the latter half of the filter length of the digital filter. It is a liquid level gauge that outputs a distance measurement signal to the liquid level as a digital signal.
A slope calculation unit that calculates the slope of the detection signal,
A digital filter for removing ripples generated in the detection signal, and a digital filter for removing the ripples.
A delay amount calculation unit that calculates the delay amount of the output of the digital filter caused by the ripple removal processing based on the slope of the detection signal and the filter length of the digital filter.
A correction amount calculation unit that calculates the correction amount of the output of the digital filter by multiplying the delay amount and the slope of the detection signal.
It has a correction unit that corrects the output of the digital filter by adding the correction amount to the output of the digital filter.
Output the ranging signal in real time,
Liquid level indicator. The liquid level gauge according to claim 9, wherein the slope calculation unit calculates the slope of the detection signal based on the number of sample points corresponding to the filter length of the digital filter. The liquid level gauge according to claim 9, wherein the slope calculation unit calculates the slope of the detection signal based on the number of sample points in the latter half of the filter length.

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