FR2510749A1 - Batch liq. metering and dispensing system - employs microprocessor to compute flow from liq. velocity in calibrated tube - Google Patents

Abstract

Method for precision dosing of batches of liq., applicable also to very small quantities, features an automatic flushing of the dosing tube at the end of each batch delivery. The principle of flow measurement is the determn. of the velocity at which the meniscus of the liq. travels along a calibrated tube, enabling flow rate to be determined. Subsequently flow is allowed to continue for such a time as is required to batch the required quantity. Used in medical and chemical applications for the batch measurement of small samples.

Description

METHOD AND DEVICE FOR COLLECTING A STOC LIQUID
KE IN A TANK CONTAINER AND DELIVER A QUANTITY
DETERMINED TE FOR ITS USE AND INSTALLATION OF
DOSING EQUIPPED WITH SUCH A DEVICE.

 It is known that the assay operations generally comprise the taking of a known and predetermined quantity of a sample followed by the addition of one or more reagents also liquid in predetermined quantity.

 The precision of the dosage depends on the precision of these volume measurements.

 The assay operations are frequent in the field of chemistry (for example in biochemistry, medical analyzes, hygiene as well as for certain manipulations which require a constant addition of reagents, for example to adjust a pH, cause the neutralization of a product...).

 In all cases, the volume measurements must be made with very high precision, precision which is difficult to achieve when the quantities involved are micro-quantities, which is frequent.

 To carry out these sampling operations, numerous methods of pumping the liquid have been envisaged, involving in particular piston pumps which, however, have numerous drawbacks, in particular by the fact that they involve the presence of moving mechanical members. , therefore likely to take play. In addition, such pumps are necessarily associated with a tube (or equivalent) intended to immerse in the liquid to be sampled, which necessarily involves a cleaning operation when the device is intended to be used with different liquids.

Now we have found, and this is what is the subject of the present invention, a simple and effective method as well as a device for its implementation which not only makes it possible to obtain samples of liquids with a very great precision and this, when it comes to micro-quantities but which, moreover, ensures automatic cleaning of the tube by means of which the sampling is carried out
some cash.

In general, the invention therefore relates to a method allowing the withdrawal of a liquid stored in a reservoir container (such as for example a closed container or an open sample tube) and of delivering a determined quantity thereof with a view to its use, this process being characterized by the fact that it comprises the succession of the following stages
- expulsion of the liquid at practically constant speed through a calibrated horizontal conduit,
- measurement of the speed of the front of the product between two points spaced from the tube at the start of the expulsion phase,
- flow for a determined period depending on the sample to be taken to deliver the desired quantity of liquid,
- injection of air into a middle part of the tube in order to cut the stream of liquid and to discharge it in two opposite directions, the part of the excess liquid being discharged into the reservoir container.

 Preferably, for the implementation of the method, the expulsion of the liquid is carried out either by pressurizing the product to be withdrawn stored inside a sealed storage tank, said tank being reduced to a pressure normal to the end of the sample, either by causing a vacuum at the outlet end of the sample tube.

The invention also relates to a device for implementing such a method, device which comprises in combination:
- at least one tube having a horizontal portion and the two free ends of which plunge one into the liquid to be sampled, the other into a recovery container,
- two spaced detectors arranged on the horizontal portion of the tube and making it possible to determine the speed of flow of the liquid at the start of the sampling,
a conduit downstream of the detectors opening into the horizontal portion of the tube is connected to a source of pressurized gas, means (valve) being provided on this conduit for opening or closing the supply of gas under pressure, this conduit being intended injecting air into a middle part of the tube in order to cut the vein of liquid at the end of the sampling,
- Means for causing the flow of liquid through the calibrated tube during the actual sampling phase.

 The means for causing the flow (propulsion) of the liquid may be constituted either by a source of pressurized gas opening into a closed, sealed reservoir container containing the liquid to be withdrawn in order to exert a pressure on the surface of said liquid, either by a source creating a depression at the outlet end of the sampling tube.

The invention and the advantages which it brings will however be better understood thanks to the exemplary embodiments given below by way of indication but not limitation and which are illustrated by the appended diagrams in which
FIGS. 1 and 4 schematically illustrate a device according to the invention making it possible to take a sample of a liquid stored in a tank, in order to deliver a determined quantity of it in a receiving container,
- Figure 2 is a schematic view showing an embodiment of a device according to the invention for taking a sample from an open tank, this device being associated with means for performing automatic cleaning of the end of the tube which plunges into the liquid to be sampled,
- Figure 3 is a schematic view of a metering and analysis installation comprising a plurality of sampling devices produced in accordance with the invention.

 FIG. 1 illustrates a device according to the invention making it possible to dispense a liquid (1) contained in a reservoir container (2) with a view to delivering a determined quantity thereof, for example in a test tube (3) for perform an assay or analysis. This device comprises a tube designated by the general reference (4), calibrated, in non-wettable material (for example in Teflon), the section of which, depending on the measurements to be carried out, will for example be one millimeter.

 This tube has a horizontal portion (5) rectilinear in this case. Optionally, this horizontal portion (5) may not be straight. The tube (4) plunges through one end (6) to the bottom of the liquid reservoir container (1). The other, curved end (7) is held above the receiving member, for example a test tube (3).

 Two detectors (8a-8b) constituted for example by infrared emitter-receiver pairs, connected to a microprocessor of known type (9) are arranged, spaced from each other, on the horizontal portion (5) of the tube ( 4). These detectors (8a-8b) have the function of allowing the calculation of the fluid flow speed at the start of the sampling operation, speed which, as is well known, will vary depending on the viscosity and the density of the liquid.

 In addition, a second conduit (10) opens into the horizontal portion (5) of the tube downstream of the second detector (7j. This conduit (10) is connected to a source of pressurized gas (11) (compressed air tank for example) via a valve (12) in this case a conventional three-way valve.

 Furthermore, the means which make it possible to cause the liquid to flow through the calibrated tube (4) are constituted, in the present case, also by the source of pressurized air (11). For this, the second tank (2) is hermetically closed and an auxiliary tube (13) opens at the top, this tube (13) being connected to the inlet of the three-way valve (12).

 The operation of such a device is as follows.

 When it is desired to take a sample, the microproeessor is started up and controls the opening of the valve (12) so that it comes to position ab, position shown in solid lines in FIG. 1, which has the consequence of placing the reservoir bottle (2) under pressure. As a result, the liquid (1) is expelled inside the tube (4). After draining for a determined period, depending on the volume of liquid which it is thus desired to recover, the valve switches to position ac, which results in the overpressure present in the reservoir container (2) , inject air into a middle part of the horizontal tube (5), slightly downstream of the detectors (8). The air coming from the tube (10) therefore cuts the vein of liquid and discharges it in two opposite directions , the excess liquid being returned to the storage tank (2). As a result, the tube (4) is, after sampling, completely emptied, the air also having the function of drying it and a new sampling can then be carried out.

 FIG. 2 illustrates a device according to the invention which can be used more particularly for sampling. In this FIG. 2, the organs similar to those of the device which is the subject of FIG. 1, will be designated by the same references.

 As before, the essential organ is a calibrated tube (4) made of non-wettable material (Teflon for example) having a determined section of one millimeter in diameter for example. This tube (4) has a rectilinear horizontal portion (5). Its end (6) plunges into the bottom of the sealing tube (2). The other curved end (7) is held above the receiving tube (3).

 As in the previous example, the detectors (8a-8b) connected to the microprocessor (9) make it possible to calculate the speed of the liquid front between two points spaced from the tube (4) and this, at the start of the measurement.

Furthermore, a few centimeters before the curved end (7), for example at a distance of three centimeters the tube has, without modification of section or discontinuity of material, a T-shaped deviation (10) connected to the inlet a a three-way valve (12) remote controlled. In addition, the end (6) located on the side of the sample tube (2) is lined, for example over a length of two centimeters and recessed from the sample tube (2), with a concentric tube (14). This concentric tube (14) is connected to the outlet d of a valve (15) as well as to the outlet c of the three-way valve (12). The two other outputs e and f of the valve (15) are respectively connected to a water tank
(16) and to the source of pressurized air (11).

 In this embodiment, the sample is obtained by creating a depression at the end of the tube (4). For this, a third, e valve (17) is provided at the outlet of the pressurized air tank (11) the outputs g, h, i of this valve (17) ~ being connected respectively, for the outlet ffi to the tank (11), for the outlet h to a tube (18) forming a venturi and the end (19) of which is located near the end (7) of the tube (4), and for the outlet i, through the through a tube (20) at the inlet b of the valve (12).

 The operation of such a sampling device is as follows. After fitting the sample tube (2) and the receiver tube (3), valves (12-15 and 17) are placed in the following positions respectively.

 For the valve (12) and the valve (15) put in the closed position, i.e. position a-b and position f-d. The valve (17) is put in the position g-h.

 Furthermore, the valve (21) provided at the outlet of the air tank (11) is placed in the open position while the valve (22) is placed in the closed position.

 As a result, the venturi (19) is primed and the liquid (1) is drawn into the tube (4). Its speed is measured by the detectors (8a-8b) and the calculation of the passage time is carried out to determine the speed of the liquid.

 After a flow corresponding to the desired quantity of sample, the venturi (19) is stopped, air is injected inside the horizontal portion of the tube (5), so that the vein of liquid contained in said tube is pushed back towards the two ends. For this, the valve (12) is placed in the position b-a, the valve (15) in the position f-d and the valve (17) in the position -i. During this delivery phase, the valve (21) is open, the valve (22) remaining closed.

 The liquid being completely discharged, the sample tube (2) and the receiver tube (3) are removed. Then performs a cleaning of the tube (4) by injecting water from the reservoir (16). For this, the two taps (21-22) are closed and the valves (12, 15, 17) are put in the positions c-a, e-d, g-i.

 After cleaning, it is possible to dry by sending air inside the tube (4). For this, the valves (12, 15, 17) are placed in the positions c-a, f-d, g-h. The tap (21) is kept closed while the tap (22) is open.

 A perfectly clean and dry sample set is therefore obtained and it is possible to carry out a new measurement.

 Various variants can be envisaged in the use of such a device.

 Thus, it is possible, after removal and cleaning, to also send air into the venturi (19) so that it is possible to carry out drying of the end of the tube (7) and eliminate '' any drops.

 For this, the valves (12, 15 and 17) will be in the same position as above, that is to say position c-a, f-d and g-h, the valve (21) being open as well as the valve (22).

 Another variant consists in putting the valves (12-1517) in the positions ba, fd and -i, the two taps (21-22) being open, which makes it possible to send air not only inside of the tube (4) but also on its periphery at its end (6) which must be immersed in the sample tube.

 Such devices allow samples to be taken very precisely.

In effect, the flow speed (flow) of a liquid in a horizontal tube is a function
- of the section of the tube (1 <r2),
- the length of the tube (Q)
- the viscosity of the liquid (v),
- the pressure difference created-between
the ends of the tube: (p2 - pal),
- the density of the liquid (d).

As a result ss cm3 / min K.r4. (p2 - pî) .d
Consequently, for a given tube (r,), a liquid
given (v), a given and constant pressure difference
(p2 - pal), the quantity passing through the tube is proportion
at the flow time.

As the parameters of the tube (r, e) are easy to fix
and to keep constant, but on the other hand the parameters
pressure, viscosity and density of the liquid are more subject to fluctuation, a correction of the ratio (p2-pî) is carried out, in accordance with the invention.
v by practicing a flow measurement, at the start of operation of the device by means of the two detectors (8a-8b) connected to a microprocessor of known type (9).

 The flow measurement being fixed, it suffices therefore to calculate the passage time of the liquid and to interrupt it at the appropriate time to obtain the desired volume.

 The exemplary embodiments illustrated by FIGS. 1 and 2 clearly show the advantages provided by the method according to the invention, since at each measurement the sampling tube is completely empty, dry, or even washed in the case of the example illustrated by figure 2. There is therefore no risk of interference between two measurements.

 Finally, this invention makes it possible, as shown diagrammatically in FIG. 3, to complete medical assay and analysis installations where different reagents can be added to a determined liquid to perform different measurements.

 Indeed, it is possible to mount in parallel a series of devices in accordance with the invention, one serving to carry out the sampling in the sample tube (2), the others making it possible to bring reagents contained in containers (30 ) arranged for example in a refrigerated cabinet.

 Both the liquid to be analyzed and the reagents are sampled as above.

 Of course, the invention is not limited to the embodiments described above but it covers all the variants produced in the same spirit.

 Thus, in the example illustrated in FIG. 2, a regulator (25) can be provided on the tube (20) if the pressure used to cut the stream of liquid is too high.

 Likewise, the embodiment of FIG. 1 could be adapted in the manner illustrated by FIG. 4, this adaptation consisting essentially of replacing the three-way valve (12) of FIG. 1, on the one hand by a three-way valve (26) mounted on the duct (13) and having an exhaust to the open air and, on the other hand, by a two-way valve (27) disposed on the duct (10), a pressure reducer ( 25) also being provided on this conduit (10). In this variant, during the measurement, the three-way valve (26) is placed in the position shown in solid lines, so that the pressure of the reservoir (11) allows the liquid to flow through the conduit (5) . When the measurement is complete, the valve (26) is tilted to an open air exhaust position (position marked with dotted lines) and, simultaneously, the two-way valve (27) is open, which makes it possible to cut the vein of liquid. Such a variant is of interest, in particular in the case where it is desired to have a relatively low pressure for cutting the stream of liquid, this being made possible by the regulator (25).

Claims (8)

 1 / Method for withdrawing a liquid stored in a reservoir container and delivering a determined quantity for its use characterized in that it comprises the succession of the following steps  - expulsion of the liquid at practically constant speed through a calibrated horizontal conduit,  - measurement of the speed of the front of the product between two points spaced from the tube at the start of the expulsion phase,  - sale for a determined period depending on the sample to be taken to deliver the desired quantity,  - injection of air into a middle part of the tube in order to cut the flow of liquid and to discharge it in two opposite directions, the excess liquid in the tube being returned to the storage tank.  2 / A method according to claim 1, characterized in that the expulsion of the liquid through the calibrated conduit is obtained by pressurizing the product to be collected inside its storage container.  3 / A method according to claim 1, characterized in that the expulsion of the liquid is obtained by creating a vacuum at the outlet of the sampling tube.  4 / Method according to one of claims 1 to 3 characterized in that after sampling, it performs a drying and / or cleaning of the tube.  5 / Device for withdrawing a liquid (1) stored in a tank (2) characterized in that it comprises in combination  - at least one tube (4) representing a horizontal portion (5) and whose two free ends (6-7) plunge, one in the liquid (1) to be sampled, the other in a recovery container (3),  - two spaced detectors (8a-8b) arranged on the horizontal portion (5) of the tube (4) allowing the speed of the liquid to be calculated at the start of sampling;  - a conduit (10) downstream of the detectors opening into the horizontal portion (5) of the tube (4) and connected to a source of pressurized gas (11), means (12) being provided on this conduit (10) for open or close the supply of pressurized gas, this duct (10) being intended to inject air into a central part of the tube (5) in order to cut the vein of liquid at the end of sampling,  - Means for causing the flow of liquid (1) through the calibrated tube (4) during the actual sampling phase.  6 / Apparatus according to claim 5 characterized in that the means for causing the flow of liquid (1) through the calibrated tube (4) consist of a source of pressurized gas opening into a closed, sealed reservoir container (2) containing the liquid to be sampled in order to exert pressure on the surface of the liquid.  7 / Device according to claim 5 characterized in that the means for causing the flow of liquid (1) are constituted by a source creating a vacuum at the outlet end of the sampling tube.  8 / Metering installation equipped with a series of sampling devices according to one of claims 5 to 7 characterized in that one of the devices is used to perform the sampling in the sample tube (2), the others allowing d '' bring reagents contained in the container (30) arranged for example in a refrigerated cabinet.