METHOD FOR DETECTING THE ARRIVAL OF A LIQUID FRONT IN A VALVE

Abstract

The invention relates to a method for detecting the arrival of a liquid front in a valve (10) comprising: - a step of applying a control signal (Uper) to the valve so as to continuously switch the valve (10) between two switching positions, namely an open position and a closed position, the duration between the transition from one switching position to the other corresponding to one operating cycle, - a step of measuring at least one parameter of an electrical signal (Irep) of the valve (10) during each operating cycle, and - a step of detecting the arrival of a liquid front in the valve (10) based on a temporal change in the parameter of the electrical signal (Irep) of the valve (10). Figure 1

Description

Title of the invention: METHOD FOR DETECTING THE ARRIVAL OF A LIQUID FRONT IN A VALVE

[0001] The present invention relates to a method for detecting the arrival of a liquid front in a valve. The invention finds a particularly advantageous, but not exclusive, application for detecting the arrival of a liquid front in a valve of a microfluidic circuit.

[0002] In a manner known per se, microfluidic systems, particularly those based on the movement by pressurization of an input liquid reservoir, use electronically controlled valves to control the fluid. These valves are generally so-called "solenoid" valves mainly composed of a magnet, a coil and optionally a return spring.

[0003] It is often necessary to know precisely the position of a liquid front passing through a circuit initially filled with air, generally at atmospheric pressure. Indeed, knowing the position of the fluid front makes it possible to control the transient phase of flow initiation in the microfluidic circuit, rather than leaving it to chance. In the context of a mixing process, this makes it possible to know, in particular, when a mixing of two fluids will begin within a microfluidic circuit.

[0004] Air bubble detectors exist that can detect air within a dead volume located beneath the sensor. They can be used to detect an initial liquid front. However, using an air bubble detector to determine the position of a liquid front is complex and introduces an additional dead volume, which can pose problems when handling very small quantities of liquid, on the order of tens of microliters.

[0005] The invention aims to effectively overcome the aforementioned drawbacks by proposing a method for detecting the arrival of a liquid front in a valve comprising: - a step of applying a control signal to the valve so as to continuously switch the valve between two switching positions, namely an open position and a closed position, the duration between the transition from one switching position to the other corresponding to one operating cycle, - a step of measuring at least one parameter of an electrical signal from the valve during each operating cycle, and - a step of detecting the arrival of a liquid front in the valve from a temporal change in the electrical signal parameter of the valve.

[0006] The invention thus allows, by using the valve as a liquid front detector, cost savings by eliminating the need for an air bubble sensor. The invention is also simple to implement, requiring only a software update of the valve control module and the integration of means for measuring the system's electrical response. The invention also makes it possible to precisely determine when liquid mixing will begin and, if a flow measurement is available, to control the volume of fluid passing through the system.

[0007] According to one embodiment of the invention, the parameter(s) of the electrical signal are chosen from: a maximum amplitude, a minimum amplitude, a level of an electrical signal dip, a duration of a signal dip, a time to reach a maximum or a minimum amplitude.

[0008] According to one embodiment of the invention, the arrival of a liquid front in the valve is considered when the temporal change of the electrical signal parameter is observed over several operating cycles in order to avoid the detection of false positives.

[0009] According to one embodiment of the invention, the temporal change of the electrical signal parameter(s) is detected by comparing a value of the electrical signal parameter(s) with respect to one or more corresponding predetermined value ranges.

[0010] According to one embodiment of the invention, the temporal change of the electrical signal parameter(s) is detected in a relative manner by comparing a value of the electrical signal parameter(s) measured during one or more given operating cycles with a value of the electrical signal parameter(s) measured during one or more previous operating cycles.

[0011] According to one embodiment of the invention, the valve is an on / off type solenoid valve.

[0012] According to one embodiment of the invention, the valve is a microfluidic valve with a low internal volume, on the order of tens of microliters.

[0013] According to one embodiment of the invention, the valve is a microfluidic valve with a very low response time of between 0.2ms and 15ms.

[0014] According to one embodiment of the invention, the viscosity of the liquid is between 0.1 and 200 cPo.

[0015] The invention also relates to a control unit comprising a memory storing software instructions for the implementation of the process as previously defined.

[0016] The present invention will be better understood and other features and advantages will become apparent upon reading the following detailed description, which includes embodiments given by way of illustration with reference to the attached figures, presented by way of non-limiting examples, which may serve to complete the understanding of the present invention and the explanation of its implementation and, where appropriate, contribute to its definition, on which:

[0017] [Fig.1] Fig.1 is a schematic representation of a solenoid valve installed on a liquid line and controlled by a control unit capable of implementing the method of detecting the arrival of a liquid front according to the present invention;

[0018] [Fig.2] The [Fig.2] is a time-dependent graphical representation of a control voltage of the solenoid valve of the [Fig.1] and the corresponding current response under normal valve operation;

[0019] [Fig.3] The [Fig.3] is a time-dependent graphical representation of the control voltage signal of the solenoid valve of the [Fig.1] for the implementation of the method for detecting the arrival of a liquid front according to the invention;

[0020] [Fig.4] The [Fig.4] is a time-dependent graphical representation of the current response observed during the implementation of the liquid front arrival detection method according to the invention during a valve operating cycle.

[0021] It should be noted that, in the figures, structural and / or functional elements common to the different embodiments may have the same reference numerals. Thus, unless otherwise stated, such elements have identical structural, dimensional and material properties.

[0022] Figure 1 shows a valve 10 installed on a liquid line 11. Preferably, the valve 10 is a solenoid valve consisting mainly of a magnet, a coil, and optionally a return spring. Alternatively, a solenoid valve without a magnet, comprising a magnetically sensitive metal, is used.

[0023] The on / off valve 10 is capable of assuming an open position allowing liquid to pass through the valve 10 and a closed position preventing liquid from passing through the valve 10. The open and closed positions correspond to the two switching positions of the valve 10. In order to minimize the volume of fluid passing through the valve 10, the valve 10 is a microfluidic valve with a small internal volume, on the order of tens of microliters. The valve 10 is also a microfluidic valve with a very short response time, between 0.2 ms and 15 ms.

[0024] As illustrated in [Fig. 2], the valve 10 moves from one switching position to another, in other words, switches, when it is subjected to a switching voltage known as the "spike voltage" in Anglo-Saxon terminology. A switching voltage at opening, Ucom_ouv, is distinguished, allowing the valve 10 to move from the closed position to the open position, and a voltage at Switching at closing Ucom_ferm allows the valve 10 to move from the open position to the closed position. In an example implementation, the switching voltage at opening Ucom_ouv is, for example, on the order of +20 Volts and the switching voltage at closing Ucom_ferm is, for example, on the order of -20 Volts, or vice versa.

[0025] The valve 10 is subjected to a holding voltage, also known as a "hold voltage" in Anglo-Saxon terminology, to maintain it in a given switching position. A holding voltage for opening, Uh_ouv, is used to keep the valve 10 in the open position, and a holding voltage for closing, Uh_ferm, is used to keep the valve 10 in the closed position. In one example implementation, the switching voltage for opening, Ucom_ouv, is, for example, on the order of +5 Volts, and the switching voltage for closing, Ucom_ferm, is, for example, on the order of -5 Volts, or vice versa.

[0026] Of course, the values ​​of the switching voltages at opening and closing as well as the values ​​of the holding voltages at opening Uh_ouv and at closing Uh_ferm can vary from one application to another.

[0027] The Irep curve represents the current response of valve 10.

[0028] A control unit 12 includes a memory 13 storing software instructions for implementing a method of detecting the arrival of a liquid front in the valve 10 described below with reference to Figures 1, 3 and 4. The control unit 12 may be considered the same as the electronic circuit that controls the valve 10. Alternatively, the control unit 12 is separate from the electronic circuit that controls the valve 10.

[0029] To this end, the control unit 12 controls the application, in a step 100, of a control signal to the valve 10, in this case a periodic voltage signal Uper, so as to continuously switch the valve 10 between an open position and a closed position, a duration Te between the transition from one position to the other corresponding to one operating cycle. For voltage control, periodic pulses are generated with a period between 100 ops and 10 ms. For current control described below, similar periodic pulses are generated, but the control unit 12 will need to react 10 to 100 times faster to ensure compliance with the current setpoint.

[0030] Preferably, as illustrated in [Fig. 3], the switching of the valve 10 is carried out by switching from one switching voltage Ucom_ouv, Ucom_ferm to another over very short periods on the order of milliseconds, without necessarily passing through the holding voltages at opening or closing. The voltages and currents involved in actuating a solenoid valve 10 for this method are on the order of 1 to 50 V and from a few milliamperes to 5 A.

[0031] The control unit 12 manages a step 102 of measuring at least one parameter of a current response signal Irep of the valve 10 during each operating cycle.

[0032] The control unit 12 detects, in a step 103, the arrival of a liquid front in the valve 10 based on a time evolution of the current response signal parameter Irep of the valve 10. Initially, the circuit is filled with air, so the valve 10 switches quickly due to the absence of liquid in the valve body. When liquid enters the valve 10 and replaces the air, the valve 10 switches more slowly because it needs to move some liquid that opposes the movement of the valve 10 with each operating cycle, which modifies the current response signal Irep. It is therefore possible to detect the arrival of the liquid front by comparing the time evolution of the current response signal Irep during different operating cycles.

[0033] The current response signal parameter(s) are chosen from: a maximum amplitude, a minimum amplitude, a current dip level, a current dip duration, a time to reach a maximum or minimum amplitude. In the example shown in [Fig. 4], it is possible to consider the level N, N' of a current dip and / or a duration T, T' of the current dip. Indeed, when the liquid enters valve 10, the movement of valve 10 is slower, therefore the current dip (represented by dashed lines) lasts longer and / or is more pronounced than the current dip shown by solid lines observed in the absence of liquid flowing through valve 10. In [Fig.4], the current trough exhibits a level N (relatively low) and a duration T (relatively low) when valve 10 is not traversed by a liquid and a level N' (relatively high) and a duration T' (relatively high) when valve 10 is traversed by a liquid. .

[0034] The temporal change of the current response signal parameter(s) Irep can be detected by comparing a value of the current response signal parameter(s) Irep to one or more corresponding predetermined value ranges. For example, a range of values ​​for the current response signal parameter Irep is predetermined during a calibration phase for a valve 10 not carrying a liquid. If the value of the current response signal parameter Irep lies outside this range, then it is inferred that the valve 10 is carrying a liquid.

[0035] Alternatively or in addition, the temporal change of the current response signal parameter(s) Irep can be detected relatively by comparing a value of the response signal parameter(s) measured during one or more given operating cycles with a value of the parameter(s) of the current response signal measured during one or more previous operating cycles.

[0036] It is possible to consider the detection of the liquid front inside the valve 10 when the temporal change of the current response signal parameter Irep is observed on a single operating cycle.

[0037] Alternatively, it is possible to consider the detection of the liquid front inside the valve 10 when the temporal change of the current response signal parameter Irep is observed over several operating cycles. This ensures that the detection is reliable and thus avoids false detection of the liquid front due to untimely variations in the current response signal Irep.

[0038] Alternatively or in addition, a median filter or its variations on the current response signal Irep can be used to detect a temporal change in a parameter of the response signal Irep. Any other signal processing method suitable for the application can be implemented.

[0039] Advantageously, the process is implemented with pressures on the order of 0-10 bar (105 - 106 Pascals) but the loss of fluid will be minimized with pressures on the order of a hundred millibars (104 Pascals).

[0040] The detection of the liquid front is all the easier when the fluid is viscous, insofar as it slows down the movement of the valve 10 accordingly. The viscosity of the liquid must nevertheless remain compatible with the capabilities of the valve 10. The viscosity of the fluid can be between 0.1 and 200 cPo.

[0041] In the example of implementation of the process described above, the valve 10 is voltage controlled while the current response Irep is observed.

[0042] Alternatively, the valve 10 can be controlled by an electrical current signal, which requires a feedback control system consisting of adjusting the voltage at a very high frequency to obtain a desired current intensity. It is then the observation of the voltage level required to obtain the setpoint current that allows the presence of liquid inside the valve 10 to be detected. More generally, at least one parameter of the electrical voltage signal of the valve 10 is measured during each operating cycle, and the arrival of a liquid front in the valve 10 is detected from a temporal change in the electrical voltage signal parameter in a manner analogous to what was described previously for a current response signal Irep.

[0043] The invention can be implemented with a microfluidic mixer which would require knowing the arrival time of a liquid front inside the valve 10 in order to avoid wasted liquid due to late detection of the liquid front in the valve 10 or a degraded mixture that would have started before the presence of a liquid in valve 10 of the mixer. The invention also makes it possible to precisely determine the volume of liquid used in the preparation of a liquid mixture when a flow measurement is available.

[0044] Of course, the different features, variants and / or embodiments of the present invention can be combined with each other in various ways insofar as they are not incompatible or mutually exclusive.

[0045] Furthermore, the invention is not limited to the embodiments described above and provided solely by way of example. It encompasses various modifications, alternative forms, and other variants that a person skilled in the art may consider within the scope of the present invention, and in particular all combinations of the different modes of operation described above, which may be taken separately or in combination.

Claims

Demands

1. A method for detecting the arrival of a liquid front in a valve (10), characterized in that, given that liquid is initially absent in a body of the valve (10), said method comprises: - a step (101) of applying a control signal to the valve (Uper) so as to continuously switch the valve (10) between two switching positions, namely an open position and a closed position, the switching of the valve (10) being carried out by passing from one switching voltage (Ucom_ouv, Ucom_ferm) to another over very short periods on the order of milliseconds without necessarily passing through holding voltages at opening or closing, a duration (Te) between the passage from one switching position to another corresponding to one operating cycle, - a step (102) of measuring at least one parameter of an electrical signal (Irep) of the valve (10) during each operating cycle,and - a step (103) for detecting the arrival of a liquid front in the valve (10) based on a temporal change in the electrical signal parameter (Irep) of the valve (10).

2. Method according to claim 1, characterized in that the parameter(s) of the electrical signal (Irep) are chosen from: a maximum amplitude, a minimum amplitude, a level of an electrical signal dip, a duration of a signal dip, a time to reach a maximum or a minimum amplitude.

3. Method according to claim 1 or 2, characterized in that an arrival detection of a liquid front in the valve (10) is considered when the temporal change of the electrical signal parameter (Irep) is observed over several operating cycles in order to avoid the detection of false positives.

4. A method according to any one of claims 1 to 3, characterized in that the time change of the electrical signal parameter(s) (Irep) is detected by comparing a value of the electrical signal parameter(s) (Irep) with respect to one or more corresponding predetermined value ranges.

5. A method according to any one of claims 1 to 4, characterized in that the temporal change of the signal parameter(s)

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10. electrical (Irep) is detected relatively by comparing a value of the electrical signal parameter(s) (Irep) measured during one or more given operating cycles with a value of the electrical signal parameter(s) measured during one or more previous operating cycles. A method according to any one of claims 1 to 5, characterized in that the valve (10) is an on / off solenoid valve. A method according to any one of claims 1 to 6, characterized in that the valve (10) is a microfluidic valve with a small internal volume, on the order of tens of microliters. Method according to any one of claims 1 to 7, characterized in that the valve (10) is a microfluidic valve with a very low response time of between 0.2ms and 15ms. A method according to any one of claims 1 to 8, characterized in that the viscosity of the liquid is between 0.1 and 200 cPo. Control unit (12) comprising a memory (13) storing software instructions for implementing the method defined according to any one of the preceding claims.

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