METHOD FOR QUANTITATIVELY AND QUALITATIVELY DETECTING PARTICLES IN LIQUID

Abstract

A method for the quantitative and/or qualitative detection of particles in fluid, with which the fluid to be examined is introduced into a beam path of an optical device, between at least one light source and the image acquisition sensor with a matrix of light-sensitive cells. Pixel values of the cells are detected and the distribution of the pixel values is at least partly determined. The pixel value or values which have been determined most often are used as a value or average value for a background signal. A signal is outputted or the method is interrupted, on reaching a maximal permissible value for the background signal.

Claims

1. A method for the quantitative and/or qualitative detection of particles in fluid, the method comprising the steps of: introducing the fluid to be examined into a beam path of an optical device, between at least one light source and the image acquisition sensor with a matrix of light-sensitive cells; detecting pixel values of the light-sensitive cells and at least partially determining a distribution of the pixel values; forming with the pixel value or values which have been determined most often a value or average value for a background signal; and outputting a signal or interrupting the method on reaching a certain limit value for the background signal.

2. A method according to claim 1, wherein a signal is outputted on reaching a first predefined limit value for the background signal and the method is interrupted on reaching a second predefined limit value.

3. A method according to claim 1, wherein the background signal is formed by the mean of values or average values of several images which are recorded one after the other, comprising 500 to 1500 images of different picture planes.

4. A method according to claim 1 wherein the values for the background signal of detections of particles in fluid which are effected temporally one after the other are registered, and speed change is determined by way of the temporal change of the registered values.

5. A method according to claim 1, wherein the values for the background signal of detections of particles in fluid which are effected temporally one after the other are registered, and a determination is made as to when a predefined limit value for the background signal is expected to be reached, by way of the temporal change of the registered values.

6. A method according to claim 1, wherein the background signal is used as a measure for contamination in the beam path and that a fluid carrier receiving the fluid to be examined is cleaned or exchanged on reaching a predefined limit value.

7. A method according to claim 1, wherein the evaluation of the background signal is effected before each detection of particles or at defined temporal intervals.

8. A method according to claim 1, wherein on evaluation of the pixel values, the cell matrix of the sensor is divided into a multitude of part-matrices and a background signal is formed for each part-matrix, and part-matrices with a background signal that exceeds a predefined further limit value, are excluded from the further evaluation for the detection of the particles.

9. A method according to claim 1, wherein the distribution of the pixel values is used to categorize the particles with regard to size.

10. A method according to claim 1, wherein the limit value for the background signal of the cell matrix and/or for the background signal of a part-matrix is defined at 10% to 20% of a maximal pixel value.

11. A method according to claim 1, wherein the limit value for the background signal of the cell matrix given an 8-bit resolution of a pixel value is defined between 30 and 50.

12. A method according to claim 1, wherein the further limit value for the background signal of a part-matrix given an 8-bit resolution is defined between 35 and 45.

13. A device for optical detection of particles in a fluid, the device comprising: a light source; an image acquisition sensor having a matrix of light-sensitive cells; a fluid carrier arranged between the light source and the matrix of light-sensitive cells in a beam path of the light source, and with control and evaluation electronics which is connected to the image acquisition sensor and is configured to detect pixel values of the cells, at least partly determine a distribution of the pixel values and use the pixel value or values which have been determined most frequently, as a value or average value for a background signal, wherein the control and evaluation electronics are configured to output a signal or for interrupting the detection procedure, on reaching a predefined limit value for the background signal.

14. A device according to claim 13, wherein the control and evaluation electronics are further configured to output a signal on reaching a first predefined limit value for the background signal and interrupt the detecting and determination on reaching a second predefined limit value.

15. A device according to claim 13, wherein the control and evaluation electronics forms the background signal by the mean of values or average values of several images which are recorded one after the other, comprising 500 to 1500 images of different picture planes.

16. A device according to claim 13, wherein the control and evaluation electronics registers the values for the background signal of detections of particles in fluid which are effected temporally one after the other and determines speed change by way of the temporal change of the registered values.

17. A device according to claim 13, wherein the control and evaluation electronics registers values for the background signal of detections of particles in fluid which are effected temporally one after the other, and the control and evaluation electronics makes a determination as to when a predefined limit value for the background signal is expected to be reached, by way of the temporal change of the registered values.

18. A device according to claim 13, wherein the control and evaluation electronics uses the background signal as a measure for contamination in the beam path and provides an indication that a fluid carrier receiving the fluid to be examined is to be cleaned or exchanged on reaching a predefined limit value.

19. A device according to claim 13, wherein the control and evaluation electronics effects an evaluation of the background signal before each detection of particles or at defined temporal intervals.

20. A device according to claim 13, wherein the control and evaluation electronics, on evaluation of the pixel values, divides the cell matrix of the sensor into a multitude of part-matrices and a background signal is formed for each part-matrix, and part-matrices with a background signal that exceeds a predefined further limit value, are excluded from the further evaluation for the detection of the particles.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In the drawings:

[0025] FIG. 1 is a diagram, which on the one hand shows the course of the background signal over a time period of more than a year and on the other hand the frequency distributions of the pixel values for this time period;

[0026] FIG. 2a is an image of a sample which is detected by way of a CCD sensor;

[0027] FIG. 2b is an image of the frequency distribution of the pixel values of the image according to FIG. 2a;

[0028] FIG. 3a is a further image according to FIG. 2a, with an increased deposit formation;

[0029] FIG. 3b is an image of the frequency distribution of the pixel values of the image according to FIG. 3a;

[0030] FIG. 4a is, in a greatly simplified representation, an image with large and small particles;

[0031] FIG. 4b is an image showing how the large particles of the image 4a are faded out with the evaluation;

[0032] FIG. 5a is a further image corresponding to FIG. 4a; and

[0033] FIG. 5b is an image of the respective fading-outs with the evaluation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] Referring to the drawings, a device which is known per se is used with the quantitative and qualitative detection of particles in a fluid, with which a sample carrier with a window is arranged between a light source and a CCD sensor. Thereby, the illumination of the window can either be effected in a direct manner (brightfield technique) or in an indirect manner (darkfield technique), which however is of no significance for the methods which are being discussed here. The representations according to FIG. 2a to 5a, as is useful for examining drinking water, are taken in the darkfield technique, but are represented in an inverted manner, in particular in order to ensure the replication and the optical recognizability. Indeed, the detected particles in the darkfield technique appear white against a black or grey background. A value for a background signal is firstly determined before the actual signal evaluation of the sensor, with the application of the brightfield technique as well as with the application of the darkfield technique. This is effected by way of a multitude of individual images, but hereinafter this is represented in each case only by way of one image for reasons of a better overview.

[0035] Thus for example, a frequency distribution of the pixel values is determined for the image according to FIG. 2a. The CCD sensor, with which the image according to FIG. 2a has been created comprises a matrix of light-sensitive cells, wherein each cell produces electrical charges corresponding to the fed light quantity, and these charges are outputted as an electrical signal, wherein a pixel value corresponding to the charge value of the cell is determined for each cell. Thus each cell can determine 256 brightness values, from the brightest white to the darkest black, with the resolution of 8 bits which is selected here.

[0036] Thereby, for the image according to FIG. 2a it is firstly determined which brightness values, i.e. which pixel values occur in the matrix and in which number. The result is reproduced in the diagram according to FIG. 2b. The pixel value 1 which in the image according to FIG. 2a occurs most often has a brightness of 25 with a frequency of 3.5×105, as is to be recognized in FIG. 2b. Directly adjacent are further brightness values which have a similarly high frequency, and specifically between 20 and 30. The peak 2 of FIG. 2b is arranged in this region and represents the light-grey region of the image according to FIG. 2a. A mean which forms the background signal and represents the bright grey area in FIG. 2a is formed from this peak 2.

[0037] This background signal is of a hindrance with the image evaluation, since it glares the entire image. For this reason, it is deducted from each individual pixel value with the later image evaluation, so that an image which in the ideal case has no grey, but a white (actually black) background is provided for the evaluation. This is effected in the reverse manner with the darkfield technique, so that a dark black background is formed in the ideal case, wherein the particles do not distinguish themselves against this black background in a dark color as in FIG. 2a, but in a bright color.

[0038] A large dark spot 3 can be recognized in FIG. 2a at the upper left corner of the picture, and this does not affect the background signal since it is comparatively distinctly demarcated. Hereby, it is the case of a spot 3 as is typically produced by an air bubble in the fluid. This dark spot 3 in FIG. 2b is represented by the flat peak 4 next to the peak 2. As can be recognized by way of FIG. 2a as well as by way of the diagram of FIG. 2b, this comparatively distinctly demarcated dark spot 3 has practically no influence on the background signal. Irrespective of this, this region is excluded with the signal evaluation, as will yet be explained further below by way of FIGS. 4 and 5.

[0039] The background signal which can be determined for each image of a fluid sample analyzed by a multitude of images, is formed from a multitude of such images of the same sample, for example as an average value of 500 images, and stored. Thereby, this background signal is not only used for image evaluation, but is also registered over time, as is represented by way of FIG. 1. The temporal course of the background signal is indicated at 5, wherein the horizontal axis indicates the temporal course (in FIG. 1 over roughly one year) and the vertical (right) axis indicates the pixel value, on the basis of which the background signal was formed.

[0040] The diagram according to FIG. 1 shows the background signal of a device for monitoring drinking water, with which an exchangeable sample carrier is provided, which, in defined time intervals of e.g. an hour is rinsed with the drinking water to be examined, and then examined in the quasi stationary condition, when the feed and discharge of the sample carrier are closed. Thereby, a biofilm typically is formed at least in the region of the window of the sample carrier in the course of time and this film renders the optical analysis difficult or, from a certain extent, no longer permits the particle detection with the required reliability and accuracy. The sample carrier must then be exchanged or at least cleaned.

[0041] The maximal permissible pixel value for the background signal lies at 40 in the diagram according to FIG. 4. The sample carrier must be exchanged or cleaned if this value is reached as a background signal. It is clearly evident from FIG. 1, that this predefined maximal value of 40 has been reached at four locations, whereupon the sample carrier has been exchanged and the background signal has fallen back again below the value 20. These four points in time are roughly at 01-01 (stands for 1st of January), at 01-04 (stands for 1st of April), at 01-06 (stands for 1st June) and at 01-08 (stands for 1st August). The pixel value 40 here represents the predefined limit value for the background signal, with which the method is interrupted, as least the evaluation is interrupted.

[0042] Moreover, the speed of the contamination can also be determined by way of the steepness of the curve 5 in the rising regions, and with this, one can reliably predict to a certain extent, as to when the next necessary change of the sample carrier is to be expected. Finally, a predefined limit value can be selected below this upper limit value and this signalizes to the user that the contamination of the window has reached a value which renders an exchange of the sample carrier necessary in the foreseeable future, and thus gives good notice of this.

[0043] However, not only the temporal course of the background signal 5 is plotted in FIG. 1, but also the frequency distribution of the detected particles, and specifically in the curve 6, which comprises the particles classified as bacteria, and in the curve 7 which comprises the particles which are classified as non bacteria. As to how such a classification is effected is not the subject matter of the present invention and is therefore not mentioned in more detail. Thereby, although the same horizontal axis as the curve 5 is assigned to these curves 6 and 7, however the vertical axis specifies the frequency distribution on the left scale of the diagram. In particular, as the maximally occurring frequency of 20×104 in the middle of the curve 6 illustrates, this steep increase in the bacteria quantity within the fluid sample accompanies a likewise sharp increase of the background signal, which means of the fouling film in the window which then forms. Otherwise, the diagram however shows that these fluctuations generally have no influence on the coating formation within the window.

[0044] FIG. 3a shows a picture, with which the contamination degree of the sample carrier window has significantly increased, and thus the black regions 8 and the streak-like regions 9 are formed by deposits which renders the measurement procedure, which is to say the quantitative and qualitative detection of the particles located in the window, considerably more difficult. As the frequency distribution according to FIG. 3b illustrates, the peak 10 which forms with this image is significantly flatter and wider than the peak 2 which forms with the image according to FIG. 2a. The average value for the background signal and which results from this is accordingly significantly higher, by which means the higher contamination degree is represented.

[0045] Not only is the background signal subtracted, but moreover individual groups of cells of the cell matrix are excluded in individual images, on evaluation of the signal, in order to improve the evaluation of the sensor signal. For this, the cell matrix of the sensor which for example can comprise 2560 times 1920 cells is divided into 400 equally large sub-matrices, wherein in the same manner a background signal is formed for each sub-matrix, as was effected in the previously described manner for the complete matrix of cells, for forming the background signal. Again a predefined limit value, specifically a further limit value, which with an 8-bit resolution lies between 0 and 255 and here for example is likewise selected at 40, is set for these sub-matrices. If then sub-matrices result, whose background signal exceeds 40 due to large particles, for example air bubbles 11, accumulations of particles 12 or reflection appearances 13 at the edge, then these are excluded from the further image evaluation, as is represented by way of FIGS. 4b and 5b. Thus there, black, distinctly demarcated fields 14 are to be seen in FIG. 4b, where the air bubbles 11 are to be seen in FIG. 4a, and these fields are formed by a number of such disconnected sub-matrices of cells. Accordingly in FIG. 5b, centrally a field 15 is left out where in FIG. 5a the accumulation of particles 12 is arranged, as well as fields 16 where in FIG. 5a the reflection appearances 13 at the edge are to be seen. A coarse characterization of larger particles with regard to the size can be effected by way of this evaluation. One can moreover ascertain that a further image evaluation is not effected given a maximal number of faded-out fields 14, 15, 16, in order to ensure that the evaluations are always sufficiently statistically reliable.

[0046] While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.