CN110361073B - Liquid level detection method based on liquid waveguide - Google Patents
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- G01F23/00—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm
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Abstract
The invention discloses a liquid level detection method based on liquid waveguide, which relates to the technical field of liquid level detection and is used for measuring the liquid level height of transparent liquid, and a photoelectric liquid level detection device is adopted for detection, and the method comprises the following steps: s1, under the condition of no light, measuring and storing the light intensity curve of the array photoelectric detection device, taking the light intensity curve as the dark current noise of the system, S2 turning on the light source, reading the light intensity curve of the array photoelectric detection device under the same liquid level condition for multiple times, carrying out signal average processing on the light intensity curve read for multiple times to smooth the light intensity curve so as to reduce the shot noise brought by the array photoelectric detection device, S3 processing to obtain the light intensity curve of the liquid to be detected, adopting the signal acquisition processing unit to carry out analysis and calculation on the light intensity curve of the liquid to be detected, reducing the dark current noise and the shot noise in the analysis and calculation process, and obtaining the calculated value of the liquid level height. The detection method is convenient to operate, simple, practical and low in cost.
Description
Technical Field
The invention relates to the technical field of liquid level detection, in particular to a photoelectric liquid level detection method based on liquid waveguides.
Background
The liquid level detection is widely applied to a plurality of devices such as intelligent control and industrial production, and the existing liquid level detection methods with wide application range mainly comprise capacitance type, ultrasonic type, optical fiber type and the like.
Capacitive liquid level detection is with electric capacity immersion liquid in, when the liquid level changed, the dielectric material and the number between the electric capacity two poles of the earth changed and lead to the capacitance value to change, and it can indirectly detect the level change to detect the capacitance change, but because the precision that detects electric capacity is not high and the noise is great in the circuit, is difficult to realize high accuracy level measurement to capacitive liquid level detection is the contact measurement who takes the electrical property, can not measure inflammable and explosive liquid.
Ultrasonic wave formula liquid level detection belongs to the non-contact measurement, and device transmission pulse ultrasonic wave hits the liquid surface reflection echo when detecting the liquid level, detects the time of echo reflection and just can indirect measurement liquid level, but because the sound velocity is too fast and the reflection echo is more mixed and disorderly, ultrasonic wave formula liquid level detection is difficult to realize high accuracy liquid level detection and has the detection blind area, and general ultrasonic wave liquid level detection device all is greater than 1 mm's error.
The optical fiber type liquid level detection principle is that the liquid level is detected by the change of the effective refractive index when a specific optical fiber is immersed in liquid, for example, when the long-period fiber grating is immersed in liquid, the effective refractive index of the fiber grating changes to cause the resonance wavelength to change, a wide-spectrum light source is incident on the fiber grating, the light wave corresponding to the resonance wavelength is filtered out, the resonance wavelength of the fiber grating changes along with the change of the length of the fiber grating immersed in the liquid, then, the liquid level is detected by detecting and analyzing the resonance wavelength (Khaliq S, James S W, Tatam R P. fiber-optical liquid-level sensor using the aspect-periodic grating [ J ]. Optics setters, 2001,26(16): 1224-.
Therefore, it is necessary to develop a novel liquid level detection method which is convenient to operate, simple, practical and low in cost.
Disclosure of Invention
Aiming at the defects or improvement requirements of the prior art, the invention provides a photoelectric liquid level detection method of a liquid waveguide, which is used for carrying out liquid level detection based on a photoelectric liquid level detection device, wherein the liquid level detection device skillfully connects common optical structures to form photoelectric liquid level detection equipment with high precision, simple structure and low cost.
In order to achieve the above object, the present invention provides a liquid level detection method based on a liquid waveguide, which is used for measuring the liquid level height of transparent liquid, and adopts a photoelectric liquid level detection device for detection, wherein the photoelectric liquid level detection device comprises a light source, an array photoelectric detection device and a signal acquisition and processing unit, and comprises the following steps:
s1: under the condition of no light, measuring and storing the light intensity curve received by the array photoelectric detection device, taking the light intensity curve as the dark current noise of the system,
s2: the light source is started, the light intensity curve of the array photoelectric detection device under the same liquid level condition is read for a plurality of times, the signal average processing is carried out on the light intensity curve read for a plurality of times so as to smooth the light intensity curve and further reduce the shot noise brought by the array photoelectric detection device,
s3: and measuring to obtain a light intensity curve of the liquid to be measured, analyzing and calculating the light intensity curve of the liquid to be measured by adopting a signal acquisition and processing unit, and reducing the dark current noise and the shot noise in the analyzing and calculating process to obtain a liquid level height calculated value.
Further, in step S3, the specific process of analyzing and calculating is as follows:
s31: firstly, a first-order difference curve of a light intensity curve of the liquid to be measured after filtering is solved to obtain a difference curve with the length being the pixel number of the array photoelectric device in the vertical direction minus one,
s32: binarizing the difference curve obtained in the step S31, selecting 0 as a threshold, correcting data which is larger than or equal to the threshold in the difference curve to be 1, correcting data which is smaller than the threshold to be-1, and then carrying out a second-time first-order difference operation on the obtained binary data, wherein the difference direction is the same as the first-time difference operation, so as to obtain a group of reprocessed difference curves which are only 0,2 and-2, wherein 2 is a peak, 2 is a trough,
s33: analyzing the reprocessed differential curve obtained in step S32 to obtain the correct peak and valley,
s34: and after the correct wave crests and wave troughs are obtained, calculating the positions of the vertical pixels of the wave troughs on the array photoelectric detection device, and calculating to obtain the liquid level of the liquid to be detected.
Further, in step S33, the specific process of analyzing the reprocessed differential curve obtained in step S32 is:
correct detection is indicated if there are only two peaks on the reprocessed differential curve obtained at S32 and there is a valley between the two peaks,
if the number of peaks and troughs on the reprocessed differential curve obtained in S32 is large, it means that the target peak and trough detection is affected by the tiny peaks and troughs caused by noise in the intensity curve, and the influence of the tiny peaks and troughs needs to be removed until the reprocessed differential curve that can be used is obtained,
if the number of the detected wave crests and wave troughs is less than the theoretical number, the liquid level is not detected, and the detection is required again.
Further, the method for removing the influence of the tiny peaks and valleys caused by the noise is to increase the difference order of the first difference operation, and then perform the same subsequent operations again until a reusable reprocessed difference curve is obtained.
In general, compared with the prior art, the above technical solution contemplated by the present invention can achieve the following beneficial effects:
firstly, the precision of liquid level detection is only limited by the precision of an array photoelectric detection device, and because the current array photoelectric detection devices such as CCD, CMOS and the like have extremely high precision and the pixel size can reach the micron level, high-precision liquid level detection can be realized by selecting the array photoelectric detection devices; the core part of the liquid level detection device only comprises a light source, a container, a condensing column lens, an optical filter and an array photoelectric detection device, and belongs to devices which are simple, easy to use and low in price, so that the device is simple in structure, easy to maintain and low in cost.
The method carries out liquid level detection based on the photoelectric liquid level detection device, firstly considers dark current noise of a system and shot noise brought by an array photoelectric detection device, can greatly improve detection accuracy, carries out twice differential operation on a light intensity curve of liquid to be detected, can accurately obtain wave crests and wave troughs, and then calculates the position of a vertical pixel of the wave trough on the array photoelectric detection device, namely can calculate and obtain the liquid level of the liquid to be detected. The method also comprehensively considers three conditions of reprocessing the difference curve, ensures to obtain correct wave crests and wave troughs, and further ensures the correctness of the detection method.
Drawings
FIG. 1 is a schematic diagram of the optical path of the apparatus of the present invention;
FIG. 2 is a schematic diagram of the structure of the apparatus of the present invention;
FIG. 3 is a schematic diagram of the device of the present invention after range expansion;
FIG. 4 is a schematic flow diagram of a method for detecting liquid level based on the apparatus of the present invention.
The same reference numbers will be used throughout the drawings to refer to the same or like elements or structures, wherein:
1-transparent liquid container 2-light source
3-condensing cylindrical lens 4-optical filter
5-array photoelectric detection device 6-signal acquisition processing unit
7-liquid to be measured 8-liquid conduction pipe
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
FIG. 1 is a schematic diagram of the optical path principle of the device of the present invention, FIG. 2 is a schematic diagram of the structure of the device of the present invention, as can be seen from the figure, the present invention provides a photoelectric liquid level detection device, which is used for measuring the liquid level height of transparent liquid, and comprises a transparent liquid container 1, a light source 2, a light-gathering column lens 3, a light filter 4, an array photoelectric detection device 5 and a signal acquisition processing unit 6, wherein the transparent liquid container 1 is communicated with a main container for accommodating the liquid to be measured, and the height of the transparent liquid container is high enough to observe the actual liquid level through the transparent liquid container 1, i.e. visually, the liquid level can be observed by naked eyes, the liquid to be measured forms an inclined liquid surface at the container wall in the transparent liquid container 1, the light source 2 is a divergent light source, and is located at the bottom of the transparent liquid container 1, the divergent light beam emitted by the light source, the liquid level detection device is characterized in that the liquid level detection device is emitted from the side wall of the transparent liquid container 1, the emergent light carries liquid level height information of liquid to be detected, the light-gathering column lens 3 is close to the outer wall of the transparent liquid container 1, the light-gathering column lens 3 is long enough to receive light emitted from the upper position and the lower position of the actual liquid level of the transparent liquid container 1, the light filter 4 is arranged in the direction of the emergent light of the light-gathering column lens 3 and used for filtering stray light in the emergent light of the light-gathering column lens 3, the array photoelectric detection device 5 is arranged in the direction of the emergent light of the light filter 4 and used for receiving optical signals carrying the liquid level height information of the liquid to be detected and converting the optical signals into electric signals, and the signal acquisition processing unit 6 is connected with the array photoelectric.
In detail, the transparent liquid container is a transparent light guide medium. The light source is a light source with a certain divergence angle, namely a divergent light source, and the condensing lens can use a plano-convex cylindrical lens with a proper focal length to converge the light on the same horizontal line. The optical filter can filter stray light which influences liquid level detection in the environment. The array photoelectric detection device can be any linear array or area array photoelectric detection device capable of detecting light intensity in a certain space. The signal acquisition and processing unit is used for acquiring and processing light intensity data of the array photoelectric detection device and calculating the liquid level.
In operation, light beams emitted by the light source 2 are incident from the bottom of the container, and the light beams are transmitted in the transparent liquid 7 to be measured in the container (the device can only measure the liquid level of the transparent liquid). When the liquid 7 to be measured capable of infiltrating the container wall exists in the container 1, the liquid level of the surface of the liquid 7 to be measured close to the container wall is higher than that of the middle part due to the existence of the surface tension of the liquid, so that the inclined liquid surface close to the container wall is formed, and the optical effect of the inclined liquid surface is similar to a triangular prism. When light emitted by the light source 2 is incident from the bottom of the container, one part of light with a larger angle is emitted from the container, liquid is emitted from the container and is irradiated onto the array photoelectric detection device 5 through the condensing lens 3 and the optical filter 4, the other part of light is irradiated onto the array photoelectric detection device 5 through the same path after being totally reflected on the inclined liquid surface, and then an area with smaller light intensity is formed between the two parts of light, so that a minimum value of the light intensity exists between the two maximum values of the light intensity on a light intensity curve in the vertical direction, and the liquid level height can be measured by detecting the position of the minimum value through the data acquisition and processing unit 6. One end of the liquid communicating pipe 8 is connected with the liquid container 1 of the liquid level detection device, the other end of the liquid communicating pipe 8 can be connected with a main container of liquid 7 to be detected, the liquid level heights of the main container and the liquid container 1 in the device are the same due to the existence of the liquid communicating pipe 8, and the liquid level height in the main container can be detected by detecting the container in the liquid container 1.
FIG. 3 is a schematic diagram of the device of the present invention after range expansion, and it can be seen that, in order to increase the measurement range of the liquid level detection device of the present invention, the number of optical filters, column lenses and array photoelectric sensing devices can be increased. In practical engineering practice, the condensing column lens 3, the optical filter 4 and the array photoelectric detection device 5 can form a set of optical detection units, and the optical detection units are provided with a plurality of sets according to practical engineering requirements, and the plurality of sets of optical detection units are closely and adjacently arranged along the height direction of the transparent liquid container 1 so as to detect liquid levels with different heights. A single signal acquisition and processing unit is used for simultaneously acquiring and processing signals of a plurality of array photoelectric sensing devices to realize wide-range measurement, only the structural schematic diagram of the device of two array photoelectric sensing devices is shown in figure 3, and theoretically, infinite array photoelectric sensors can be used for realizing infinite range liquid level measurement.
In one embodiment of the present invention, the light-collecting cylindrical lens 3 is parallel to the outer wall surface of the transparent liquid container 1. Actually, the condensing column lens 3 may be nonparallel, and may have a minute narrow peak in close contact with or close proximity to the outer wall surface of the transparent liquid container 1.
In another embodiment of the present invention, the apparatus further comprises a liquid conducting pipe 8, wherein the liquid conducting pipe 8 is arranged at the bottom of the transparent liquid container 1, and is communicated with the bottom of the body container containing the liquid to be measured, and is used for introducing the liquid with the liquid level to be measured into the transparent liquid container 1. The transparent liquid container 1 has a circular, rectangular or elliptical cross section. That is, the transparent liquid container may be cylindrical, rectangular cylinder-shaped, or oval-shaped. The center of the cross section of the transparent liquid container 1 can be positioned on the central axis of the emergent light beam of the light source 2, and can also be slightly deviated, in short, the spot size of the emergent light beam of the light source 2 incident on the bottom of the transparent liquid container needs to be ensured to be capable of completely covering the bottom as much as possible.
In another embodiment of the present invention, the light-gathering cylindrical lens 3, the optical filter 4 and the array photodetector 5 are parallel to each other.
The working principle of the invention is as follows: the light beam emitted by the light source is incident from the bottom of the container, and the light beam is transmitted in the transparent liquid in the container. When liquid capable of infiltrating the container wall exists in the container, the liquid level of the liquid surface close to the container wall is higher than that of the liquid surface in the middle due to the existence of the surface tension of the liquid, so that the inclined liquid surface close to the container wall is formed, and the optical effect of the inclined liquid surface is similar to a triangular prism. When the light reaches the liquid surface, part of the light beam will be transmitted at the liquid surface. On the other hand, due to the presence of the approximate triangular prism at the liquid level, a portion of the light beam is totally reflected there. The two light beams are transmitted from the side wall of the container, then the light rays are collected through the condenser lens, stray light is filtered by the optical filter, the light beams are received by the array photoelectric detection device and converted into electric signals, and finally the electric signals are processed by the signal acquisition processing unit. There is a light intensity small area between the two light beams, so that a light intensity minimum value exists between two light intensity maximum values on the light intensity curve in the vertical direction, and the position of the light intensity minimum value is the liquid level position.
Based on the device, the invention provides a liquid level detection method, which comprises the following steps:
s1: under the condition of no light, measuring and storing the light intensity curve of the array photoelectric detection device, using the light intensity curve as the dark current noise of the system,
s2: the light source is started, the light intensity curve of the array photoelectric detection device under the same liquid level condition is read for a plurality of times, the signal average processing is carried out on the light intensity curve read for a plurality of times so as to smooth the light intensity curve and further reduce the shot noise brought by the array photoelectric detection device,
s3: and measuring to obtain a light intensity curve of the liquid to be measured, analyzing and calculating the light intensity curve of the liquid to be measured by adopting a signal acquisition and processing unit, and reducing the dark current noise and the shot noise in the analyzing and calculating process to obtain a liquid level height calculated value. The specific process of the analysis and calculation is as follows:
s31: firstly, a first-order difference curve of a light intensity curve of the liquid to be measured after filtering is solved to obtain a difference curve with the length being the pixel number of the array photoelectric device in the vertical direction minus one,
s32: binarizing the difference curve obtained in the step S31, selecting 0 as a threshold, correcting data which is larger than or equal to the threshold in the difference curve to be 1, correcting data which is smaller than the threshold to be-1, and then carrying out a second-time first-order difference operation on the obtained binary data, wherein the difference direction is the same as the first-time difference operation, so as to obtain a group of reprocessed difference curves which are only 0,2 and-2, wherein 2 is a peak, 2 is a trough,
s33: analyzing the reprocessed differential curve obtained in step S32 to obtain the correct peak and valley,
the specific process of analyzing the reprocessed differential curve obtained in step S32 is as follows:
correct detection is indicated if there are only two peaks on the reprocessed differential curve obtained at S32 and there is a valley between the two peaks,
if the number of peaks and troughs on the reprocessed differential curve obtained in S32 is large, it indicates that the target peak and trough detection is affected by the tiny peaks and troughs caused by noise in the intensity curve, and the influence of the tiny peaks and troughs needs to be removed until the reprocessed differential curve that can be used is obtained. The method for removing the influence of tiny peaks and troughs caused by noise is to increase the difference order of the first difference operation and then perform the same subsequent operation again until a reprocessed difference curve which can be used is obtained.
If the number of the detected wave crests and wave troughs is less than the theoretical number, the liquid level is not detected, and the detection is required again.
S34: and after the correct wave crests and wave troughs are obtained, calculating the positions of the vertical pixels of the wave troughs on the array photoelectric detection device, and calculating to obtain the liquid level of the liquid to be detected.
The liquid level calculation method described in the above S31 to S34 is only a preferred liquid level calculation method of the present invention, and is not limited to the present invention, and other algorithms for detecting and calculating the liquid level by the light intensity curve of the present invention, such as an extreme value detection peak method, a wavelet detection peak method, etc., are all included in the protection scope of the present invention.
FIG. 4 is a schematic flow chart of a liquid level detection method based on the apparatus of the present invention, and it can be seen that the specific working flow of the apparatus of the present invention is as follows:
in order to eliminate dark current noise existing in the array photoelectric detection device, a light intensity curve of the array photoelectric device needs to be detected and stored under the condition of no light, the light intensity curve is regarded as the dark current noise, and the dark current noise is subtracted after the light intensity curve is read in the subsequent liquid level measurement process to prevent the influence of the dark current noise on liquid level detection.
And starting a light source to start liquid level detection, and in order to reduce shot noise in the array photoelectric detection device and a driving circuit thereof and smooth a light intensity curve, the light intensity curve of the same liquid level array photoelectric device needs to be read for multiple times at a high speed to carry out signal average processing so as to reduce the noise.
After the light intensity curve is obtained and processed, the liquid level is identified and calculated, and the flow schematic diagram of the identification and calculation algorithm of the liquid level is shown as the attached figure 3, which is specific:
(1) firstly, a first-order difference curve of the filtered light intensity curve is obtained, namely the light intensity of the pixel of the whole light intensity curve is subtracted by the light intensity of the previous pixel (or the opposite direction difference operation is also adopted), so that a difference curve with the length being one less than the number of pixels in the vertical direction of the array photoelectric device is obtained.
(2) In order to facilitate the subsequent judgment of the positions of the peaks and the troughs, the obtained difference curve needs to be binarized, 0 is selected as a threshold, data which are larger than or equal to the threshold in the difference curve are corrected to be 1, data which are smaller than the threshold are corrected to be-1, then the obtained binarized data are subjected to second first-order difference operation, the difference direction is the same as that of the first difference, and a group of data which are only 0,2 and-2 is obtained, wherein 2 is the peak and-2 is the trough.
(3) If the detected effect is that only two peaks exist and a valley exists between the two peaks, the detection is correct, if more peaks and valleys are detected, the target peak and valley detection is influenced by tiny peaks and valleys caused by noise in the light intensity curve, in order to remove the influence of the tiny peaks and valleys, the difference order of the first difference operation can be increased, and then the same subsequent operation is carried out again until a correct result is detected; if the number of the detected wave crests and wave troughs is less than the theoretical number, the liquid level is not detected, and the adjusting device is required to detect again.
(4) And after the correct wave crests and wave troughs are obtained, calculating the positions of the wave troughs on the pixels in the vertical direction on the array photoelectric detection device, namely calculating the measured liquid level.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (1)
1. A liquid level detection method based on liquid waveguide is characterized in that the method is used for measuring the liquid level height of transparent liquid, a photoelectric liquid level detection device is adopted for detection, the photoelectric liquid level detection device comprises a light source, an array photoelectric detection device and a signal acquisition and processing unit, and the method comprises the following steps:
s1: under the condition of no light, measuring and storing the light intensity curve of the array photoelectric detection device, using the light intensity curve as the dark current noise of the system,
s2: the light source is started, the light intensity curve of the array photoelectric detection device under the same liquid level condition is read for a plurality of times, the signal average processing is carried out on the light intensity curve read for a plurality of times so as to smooth the light intensity curve and further reduce the shot noise brought by the array photoelectric detection device,
s3: measuring to obtain a light intensity curve of the liquid to be measured, analyzing and calculating the light intensity curve of the liquid to be measured by adopting a signal acquisition and processing unit, and reducing the dark current noise and the shot noise in the analyzing and calculating process to obtain a liquid level height calculated value;
in step S3, the specific process of the analysis and calculation is as follows:
s31: firstly, a first-order difference curve of a light intensity curve of the liquid to be measured after filtering is solved to obtain a difference curve with the length being the pixel number of the array photoelectric device in the vertical direction minus one,
s32: binarizing the difference curve obtained in the step S31, selecting 0 as a threshold, correcting data which is larger than or equal to the threshold in the difference curve to be 1, correcting data which is smaller than the threshold to be-1, and then carrying out a second-time first-order difference operation on the obtained binary data, wherein the difference direction is the same as the first-time difference operation, so as to obtain a group of reprocessed difference curves which are only 0,2 and-2, wherein 2 is a peak, 2 is a trough,
s33: analyzing the reprocessed differential curve obtained in step S32 to obtain the correct peak and valley positions,
s34: after the correct wave crests and wave troughs are obtained, calculating the positions of the vertical pixels of the wave troughs on the array photoelectric detection device, and calculating to obtain the liquid level of the liquid to be detected;
in step S33, the specific process of analyzing the reprocessed differential curve obtained in step S32 is:
correct detection is indicated if there are only two peaks on the reprocessed differential curve obtained at S32 and there is a valley between the two peaks,
if the number of peaks and troughs on the reprocessed differential curve obtained in S32 is large, it means that the target peak and trough detection is affected by the tiny peaks and troughs caused by noise in the intensity curve, and the influence of the tiny peaks and troughs needs to be removed until the reprocessed differential curve that can be used is obtained,
if the number of the detected wave crests and wave troughs is less than the theoretical number, indicating that the liquid level is not detected, and needing to detect again;
the method for removing the influence of tiny peaks and troughs caused by noise is to increase the difference order of the first difference operation and then perform the same subsequent operation again until a reprocessed difference curve which can be used is obtained.
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