FR2488399A1 - Liq. level detector for capillary tube - uses internal wall as cylindrical mirror illuminated by laser beam whose reflection is detected for determination of level of liquid - Google Patents

Abstract

The process is used to detect the presence of a liquid (18) at a certain level (20) in a transparent tube (10), such as a capillary tube. The inner surface of the tube (10) is used as a cylindrical mirror. The tube (10) is lit, at the level (20) at which the liquid (18) is to be detected, by a narrow light beam (12) such as a laser beam. The reflected light (14) is detected by a light detector (16). When the liquid (18) reaches the level (20) lit by the light beam (12) the tube (10) stops reflecting light to the detector (16). The process can be adapted to detect liquids at several levels in several tubes. The tube is capillary of the capillary type.

Description

 The present invention relates to a method for the detection, with precision, of the passage of a liquid in front of at least one mark in at least one transparent tube, for example capillary, and more generally, the absence or the presence of liquid in the tube whatever the surrounding environment provided that it is transparent.

 It is often necessary to control the flow of a liquid in a transparent capillary tube or to locate the passage of this liquid at different levels, either to trigger various sequences of automation, or more simply to measure the speed of flow of this liquid . Such checks are necessary for example in the field of automatic medical analyzes, in that of viscosity measurements or even in that of temperature measurements by bulb and column of liquid.

For these measurements, it is common to place the tubes in gas or liquid baths at high temperature or in corrosive or dangerous environments.

 The devices used until now to detect the passage of liquid in a transparent capillary tube have been found to be of limited use, either because the temperature of the baths is too high, or because the capillaries are too large or too thin. In addition, their use is difficult due to the lack of reliability, or the imprecision of the detections.

 The invention makes it possible to eliminate all these drawbacks and offers a systematic solution to the problem of detecting liquid in transparent capillary tubes, whatever the surrounding environment in which they are immersed, provided that it is transparent.

 In principle, the method according to the invention consists in using the internal surface of the tube (s) as a cylindrical mirror, in illuminating each tube at the level of the level (s) where the liquid must be detected, by means of a narrow light beam. incident and detecting the light that said surface reflects all the time that the liquid has not reached the point of incidence of the incident beam on the tube.

 Each capillary> when empty, reflects the incident beam in all directions of the plane which is perpendicular to it and which contains said incident beam, so that the reflected light can be detected at any point on this plane except, of course, in the axis of the incident beam.

 According to the simplest embodiment, the detection device for the implementation of this method comprises at least one tube, a light source providing at least one narrow light beam perpendicular to the tube at a point corresponding to the level at which the presence of liquid must be detected and at least one light detector, such as photodiode, photoresistor or photomultiplier tube, placed at any point on the plane normal to the capillary and containing the incident beam, in order to detect the light reflected by the tube.

 The principle of the invention, based on the reflection of an incident beam by a cylindrical mirror constituted by a capillary tube, remains valid in the case where the tube is immersed in a bath of gas or liquid transparent to the incident and reflected beams . In this case, the container containing the bath must have one or more walls that are at least partially transparent (glass for example).

 It is understood that the detection of the passage of the liquid at a given level of the capillary is all the more precise the finer the incident beam. In fact, if the incident beam has a not insignificant thickness, the reflected light will be extinguished only when the liquid flowing in the capillary has passed through the entire illuminated segment, which can take some time for liquids viscous.

 The usual means of optics make it possible to obtain very fine beams by the use of appropriate diaphragms and lenses but, in this case, the light energy reaching the capillary and, a fortiori, reaching the photodetector is all the weaker. that the beam is finer.

 We are then limited by the sensitivity of the light detector. We could certainly use very high incident energies, but then, we risk disturbing the temperature of the medium surrounding the capillary, which is often a crippling obstacle in certain techniques, for example that of viscosimetry where this temperature must be stable at a few 1/1000 close.

 According to the invention, this drawback is remedied by using a laser beam generated by a heliumneon source. Such a beam offers the double advantage of being extremely thin and of conveying significant light energy which can excite the photodetector without practically transmitting heat energy to the medium.

 It is also frequent that one must simultaneously monitor several identical or different capillary tubes, immersed in the same medium. This is particularly the case for multi-station medical analysis or viscosimetric measurement devices.

 It is therefore advantageous to use only a single light source, especially when using a laser source whose coat is not negligible.

To solve this problem for n tubes
observe simultaneously, according to the invention, a system is used which consists of n cylindrical mirrors of different diameters, stacked on top of each other in decreasing order of diameters, each of the n-1 upper mirrors being provided on its upper circular edge with a chamfer of angular amplitude equal to n1 .3600, and offset
n relative to the chamfer of the next mirror of the stacking of an angle of 3600 always in the same direction, and so
n that the chamfers of all the mirrors are contained in the same conical surface, said mirror system being driven in rotation in block around the axis of said conical surface in front of a light beam, such as a laser beam, which propagates substantially along an edge of the conical surface, so as to reflect in turn on the upper surfaces of the non-chamfered parts of the upper edges of the mirrors, giving rise to as many reflected beams usable to illuminate the tubes to be observed.

 For the detection of m marks on the same tube, it is possible according to the invention to use m-1 blades with parallel faces, arranged parallel to one another with adjustable spacing and the upper faces of which are semi-reflecting, and a mirror. plane arranged parallel to said blades and following them.

Such a system gives, from a single incident beam, m reflected beams on the paths of which can be arranged perpendicularly the tube to be observed.

Several embodiments of the invention will now be described with reference to the appended drawings in which:
FIGS. 1a, 1b and 2a, 2b are respectively longitudinal and transverse section views of an empty capillary tube, then filled with liquid, illustrating the principle of the detection of a liquid at a given level;
Figure 3 shows the application of this principle in case the capillary tube is immersed in a liquid or gaseous medium;
FIG. 4a shows a plan view of a stack of cylindrical mirrors used to obtain several beams reflected from a single incident beam;
Figure kb shows a device using the mirrors of Figure 4a to detect the level of liquid on several capillary tubes simultaneously; ;
FIG. 5 is an elevation view of a blade with parallel faces also making it possible to obtain two reflected beams from a single incident beam, and
Figure 6 is an elevational view of a device for detecting the liquid level at two points of several capillary tubes.

 With reference to FIGS. 1 a and 1 b, the transparent capillary tube 10 is empty and the incident beam 12 coming from the source S and arriving perpendicular to the tube 10, is reflected on the internal wall of the latter in all directions in bundles 14 located in a plane perpendicular to the tube and containing the incident beam 12.

At any point on this plane except on the path of the incident beam, there is disposed a light detector 16 directed towards the tube, for example a photodiode, a photoresistor, a photomultiplier tube or the like.

 As long as the liquid 18 has not reached the point of incidence 20 of the beam 12 on the tube, the detector will be excited by the light reflected by the tube. As soon as the liquid has reached level 20 (Figures 2a, 2b) the capillary tube stops reflecting the incident beam.

 The signals supplied by the photodetector are then processed by appropriate electrical circuits which are not within the scope of the invention.

In the case of FIG. 3, the capillary tube 10 is immersed in a liquid or gaseous medium 22, transparent vis-à-vis the incident and reflected beams 14. This medium is contained in a container 24 whose walls
AD, AB are transparent. The wall CD can also be transparent in order to allow an observer 26 to monitor the proper functioning of the operations.

 As explained above, the accuracy in detecting the passage of the liquid at the level considered is all the better when the incident beam is fine.

For this, a laser source is used which has the additional advantage of providing an extremely fine beam conveying significant light energy and practically no heat energy. By means of a single laser source, it is also possible to monitor several capillary tubes simultaneously, as will now be explained in connection with FIGS. 4a and 4b.

The device used for this purpose comprises several cylindrical mirrors, four in the case under consideration, M1,
M2, M3 and M4. These mirrors have different diameters and are stacked concentrically in order of decreasing diameters. Each of the three upper mirrors M2, M3 and
M4 is chamfered on its upper circular edge.

The respective chamfers 30, 32 and 34 have an angular amplitude of 2700 and are offset from each other by 900.

As shown in FIG. 4b, the diameters of the mirrors are chosen so that the chamfers are contained in a conical surface of the same axis as the different mirrors. The mirrors are secured by any means, such as an axis 36 and are rotated about their common axis xx by an electric motor 38, in front of an incident laser beam 40 emitted by the source
S and propagating parallel and in the vicinity of an edge of the conical surface defined above.

Figure 4b shows the system in the position for which the beam 40 is reflected on the base mirror M1 and gives a reflected beam 40riz on the path of which is disposed perpendicularly a capillary tube
T1. When the system rotates 900, the mirror M1 is obscured by the non-chamfered part 30 'of the mirror M2. It is then this mirror which reflects the laser beam into a reflected beam 402 which illuminates a capillary tube
T2 arranged perpendicularly on its path. After an additional rotation of 900, the non-chamfered part 32 ′ of the mirror M3 obscures the incident beam 40, and
3 reflects this by giving a reflected beam 40 which
3 lights up a T3 tube. Finally, at the next quarter turn, the non-chamfered part 34 of the mirror M4 obscures the mirror M3. The beam 40 is therefore reflected on the mirror M4 by giving a reflected beam 404 which illuminates a capillary tube T4.

 If the engine is running at a speed of N revolutions per second, each of the tubes T1 to T4 will be lit N times per second. N is chosen so that the detection is satisfactory.

 The electronic circuits intended to process the signals received by the photodetectors, not shown, are adapted to these sequential operations. The signals can be filtered by an integrating circuit, but any other similar device can also be used, for example by synchronous detection.

The device illustrated in FIGS. 4a, 4b is designed for detecting the level of liquid in four capillary tubes, but it is obvious that its principle can be applied to the case of n tubes. In this case, we will use n cylindrical mirrors, the first n-1 of which are chen nl braked at an angle of .3600, the offset of the chamfer
n of a mirror compared to that of the following mirror being v 3600 equal to
It will be noted that at distance d separating two neighboring tubes and the thickness e of the mirror included between these tubes are linked by the relation d = e \ m2. It therefore suffices to play on the thickness of the mirrors (or on the distance separating the upper surfaces of two neighboring mirrors) to vary the distance d.

 In these devices, the passage of a liquid at a single level of the capillary tube or tubes is detected. When it is desired to detect the passage of a liquid in two levels of a capillary tube, use is made, as shown in FIG. 5, of a blade with parallel faces 50 whose upper face 52 is semi-reflecting. A light beam 54, such as a laser beam, falling on the face 52, at an incidence of 450 for example, gives a first reflected beam 541 and a refracted beam 542 which crosses the blade and leaves parallel to the incident beam 54. Said refracted beam is reflected on a plane mirror 56 giving a second reflected beam 543 parallel to the beam 541. The two reflected beams 541 and 543 are used to detect the passage of a liquid at two different levels distant from 1, on the same capillary tube 58. It will be appreciated that when the distance h between the plane mirror 56 and the plate 50 is varied, we manage to adjust the distance 1 separating the two reflected beams 541 and 543 so as to make it equal to the difference between the two levels to identify.

 For the identification of m levels on a capillary tube, a system of m-l blades with parallel faces disZ is used, placed in parallel with one another with a slight spacing and a plane mirror placed parallel to said blades and following them. From a single incident beam, we then obtain m parallel reflected beams.

In practice, however, we are limited to 2 or 3 blades.

 It goes without saying that it is also possible to use the system of FIG. 4b for locating n levels on the same tube. It suffices to place the tube in question parallel to the incident beam and perpendicular to the reflected beams from the cylindrical mirrors.

 In the case where it is necessary to simultaneously detect the passage of a liquid in several tubes at m different levels on each tube, the system with chamfered rotating mirrors of FIG. 4b is combined with that comprising ml blades with parallel faces and a mirror. plan.

 Figure 6 shows the device used when we want to detect two marks on four tubes T1 to T4. This device comprises four mirrors M1 to M4 which reflect the incident beam 60 into four reflected beams 601 to 604, which fall on a blade with parallel faces 62 which gives each beam 601 to 604 a reflected ray 601l, 6021, 603lu 6041 and a refracted beam. This is reflected on a plane mirror 64 in the beams 6012, 6022, 6032 and 6042. The pairs of beams 601l-60l2, 21 6022, 6031-6032, 6041-6042 are respectively associated with the tubes T1 to T4.

 Of course the principle of the invention is also applicable to the detection of the presence of liquid in a non-capillary tube.

Claims (10)

 1.- A method of detecting the presence of a liquid at at least one level of at least transparent tube, characterized in that it consists in using the internal surface of the tube or tubes 10 as a cylindrical mirror, in illuminating each tube with the height of the level (s) 20 where the liquid 18 is to be detected, by means of a narrow incident light beam 12 and to detect the light 14 that said surface reflects all the time that the liquid has not reached the point of incidence 20 of the incident beam on the tube.  2. Detection device for implementing the method according to claim 1, characterized in that it comprises at least one tube 10, a light source S providing at least one narrow light beam 12 perpendicular to the tube at a point 20 corresponding to the level at which the presence of liquid must be detected and at least one light detector 16, such as a photodiode, photoresistor or photomultiplier tube, placed at any point on the plane normal to the tube and containing the incident beam in order to detect the light 14 reflected by the tube.  3.- Device according to claim 2, characterized in that the tube 10 is capillary.  4.- Device according to claim 2, characterized in that the source S is a laser source.  5.- Device according to one of claims 2 to 4, characterized in that the tube or tubes 10 are immersed in a container 24 containing a bath of gas or liquid 22 transparent vis-à-vis the incident beam 12 and the reflected beams 14.  6.- Device according to claim 5, characterized in that said container 24 comprises at least two transparent walls, one AD for the passage of the incident beam 12 and the other AB for the reflected beam (s) 14.  7.- Device according to one of claims 5 and 6, characterized in that said container comprises a third transparent wall CD allowing an observer 26 to monitor the proper functioning of operations.  8.- Device according to one of claims 2 to 7, for the simultaneous detection of the presence of a liquid in a level on n tubes, characterized in that it comprises a system consisting of n cylindrical mirrors M1 ... M4 of different diameters, stacked on top of each other in decreasing order of diameters, each of the nl upper mirrors being provided on its upper circular edge with a chamfer 30, 32, 34 of angular amplitude equal to n-- 3600, and offset from the chamfer of the mirror  n following the stacking of an angle of 3600 still in the  n same direction, and so that the chamfers of all the mirrors are contained in the same conical surface, the said system of mirrors being rotated in block around the axis xx of the said conical surface in front of a light beam 40, such that a laser beam, which propagates substantially along an edge of the conical surface, so as to reflect in turn on the upper surfaces of the non-chamfered parts 30 ′, 32, 34 of the upper edges of the mirrors by giving birth to so many reflected beams 401 .... 4 4 usable for  404 illuminate the tubes T1 .... T4 to be observed.  9.- Device according to one of claims 2 to 8, for the simultaneous detection of the presence of a liquid in m levels on a single tube, characterized in that it comprises ml blades with parallel faces 50, arranged in parallel by one compared to the others with an adjustable spacing and of which the upper faces 52 are semi-reflective, and a plane mirror 56 disposed parallel to said blades and following them.  10.- Device according to one of claims 2 to 9, for the simultaneous detection of the presence of a liquid in m levels on n tubes, characterized by the combination of n cylindrical chamfered rotating mirrors, capable of giving n parallel reflected beams from a single incident beam, ml blades with parallel faces and a plane mirror arranged perpendicular to the paths of said reflected beams, so that each of said reflected beams is divided into m beams used for locating m levels on the tube corresponding.