WO1993023740A1

WO1993023740A1 - Device for bubble detection in a liquid flowing through a tube

Info

Publication number: WO1993023740A1
Application number: PCT/FR1993/000463
Authority: WO
Inventors: Frédéric Neftel
Original assignee: Debiotech
Priority date: 1992-05-13
Filing date: 1993-05-13
Publication date: 1993-11-25
Also published as: FR2691258A1; AU4075493A

Abstract

Device for bubble detection in a liquid flowing through a tube. The device preferably comprises two detection assemblies (30, 32) each consisting of a light transmitter (40, 40) and a detector (48, 50) disposed on either side of the tube. The emitted light is pulsed at distinct frequencies F1 and F2. The collected signals are filtered and treated (56 to 64). The difference (68) between the two treated signals is calculated. If the difference exceeds a predefined threshold, then an air bubble exists in the tube.

Description

DEVICE FOR DETECTING BUBBLES IN A FLOW IN A PIPELINE

The present invention relates to a device for detecting bubbles in a liquid flowing in a pipe.

More specifically, the invention relates to a device for detecting the accidental presence of bubbles in a translucent liquid flowing in a pipe which is itself translucent.

There are a number of cases where it is important to ensure that a translucent liquid flowing in a pipe which is itself translucent does not accidentally cause bubbles, in particular air bubbles. This is particularly the case in the medical field of the pipes which are used to supply the perfusion or other liquid for a patient. In certain circumstances, this liquid is conveyed to the infusion needle in a pipe not by a simple effect of gravity but by means of a pump, for example a roller pump. Such an arrangement makes it possible to control the injection rate of the liquid much more precisely. In the case of a pump and whatever its operating precision and the tightness it presents, there can always be an inadmissible amount of air in the liquid resulting from an accidental introduction of air into the tank , too much air dissolved in the liquid or possibly an accidental cavitation effect causing the entrainment of air bubbles with the circulating liquid. We understand of course that such a situation is completely unacceptable and that it is particularly important to be able to constantly detect any appearance of air bubbles in the pipe, especially at the outlet of the pump when such a device is provided. , in order to be able to interrupt the arrival of liquid.

It is also understood that the nature of the liquid conveyed can vary from one intervention case to another and in particular its transparency and that it is desirable for the device to adapt to the different types of liquid capable of being circulated in the driving. Given the fact that it is particularly important in the medical field to detect the appearance of a bubble in the liquid, it is understood that it is desirable to have in addition a permanent control of the proper functioning of the detection device itself. It is also understood that the supply system and more particularly the pipe for circulating the liquid may be present in different environments. It is of course essential that the detection device can function satisfactorily whatever the environment encountered.

An object of the present invention is to provide a device for detecting the presence of bubbles in a liquid circulating in a pipe, in particular for medical applications, which ensures very precise and reliable detection of the accidental presence of this bubble, which , in particular, avoids untimely triggers which would be unfavorable for the treatment of the patient and which, moreover, allows optimal functioning of the detection whatever the liquid circulating in the pipe and in particular whatever its transparency.

To achieve this goal, the device for detecting bubbles in a liquid flowing in a pipe is characterized in that it comprises: a first light emitter arranged on a first side of the pipe, a first light detector arranged on the other side of the pipe opposite the first emitter to receive the portion of the light beam emitted by the first emitter having passed through said pipe and the liquid, first means for supplying the first emitter so that the latter emits a pulsed light beam with a first frequency; first means for processing the signal delivered by the first detector comprising at least one high-pass filter and / or a band-pass filter centered on said first frequency, and means for converting the signal processed by the filters into a first continuous signal having an amplitude proportional to the amplitude of the first pulsed signal; means for developing a reference signal corresponding to the circulation of the liquid in the pipe in the absence of bubbles; means for periodically comparing the reference signal with the first continuous signal; and means for generating an alarm signal in response to said comparison; and initial self-calibration means comprising means for comparing, when the bubble-free liquid circulates in the pipe, the signal delivered by said first detector to a setpoint signal, means for controlling said first supply means said first transmitter until said delivered signal is equal to said setpoint signal or that the supply of said first transmitter reaches a maximum admissible level and means for controlling said supply means, in normal use, according to the results of said initial self-calibration. It can be seen that, thanks to the use of a pulsed light emitter having a well-determined frequency, it is possible to overcome the ambient lighting conditions, in particular the ambient light level and parasitic light phenomena such as the different sources. in the driving environment. It is also understood that, thanks to the use of this pulsed light beam, it is possible to constantly check the effective operation of the detection device. In addition, it can be seen that the reference signal being able to be adapted to the particular conditions defined by the circulating liquid and the pipeline, the device can adapt to the various liquids to be circulated. Finally, thanks to the initial self-calibration means, the detection device operates automatically under optimal detection conditions whatever the transparency of the liquid.

According to a preferred embodiment, the means for developing the reference signal comprise a second light emitter disposed on a second side of the pipe; a second light detector disposed on a first side of the pipe opposite the second emitter to receive the portion of the light beam emitted by said second emitter having passed through said pipe and said liquid; second means for supplying the second transmitter so that the latter emits a pulsed light beam with a second frequency; second means for processing the signal delivered by the second detector comprising a high-pass filter and / or a band-pass filter centered on said second frequency and means for converting the signal processed by said filters into a second continuous signal having an amplitude proportional to the amplitude of the second pulsed signal, the second signal constituting said reference signal, furthermore said initial self-calibration means being able to carry out self-calibration of the assembly constituted by said second supply means, said second transmitter and said second receiver.

It can be seen that, in this preferred embodiment, there are two detection chains connected in parallel, the results of which are compared. It is the difference between the measurements provided by these two measurement chains which makes it possible to detect the possible presence of a bubble at one of the two detectors. As a result, the reference signal is constantly adapted to the conditions under which the measurement signal is obtained. This arrangement also allows self-calibration of the detection device since it suffices in an initial phase to adjust one or both measurement chains so that they both deliver the same signal level. A reference signal was then obtained.

Preferably, the two frequencies are distinct and between 120 and a few MHz, which facilitates filtering of the signals. Other characteristics and advantages of the present invention will appear more clearly on reading the following description of several embodiments of the invention given by way of nonlimiting examples. The description refers to the appended figures in which: - Figure 1 is a top view of a roller pump to illustrate an example of use of the detection device;

- Figure 2 is a simplified diagram of the electrical and electronic circuit of the detection device;

- Figure 3 shows schematically the layout of a light transmitter / detector assembly;

- Figures 4a and 4b show the effect of the presence of a bubble on the reception of the light beam;

- Figures 5a and 5b are diagrams showing shapes of usable pulsed light beam; - Figures 6a to 6c are diagrams showing the electrical signals appearing at different points in the circuit of Figure 2; and - Figure 7 shows an exemplary embodiment of the initial self-calibration circuit.

Referring first to Figure 1, we will describe an example of use and installation of the bubble detection device. In this figure, a part of a roller pump 10 has been shown. The pump itself known includes a housing 12 in which is formed a cylindrical cavity 14. Inside the cylindrical cavity 14, there are three cylindrical rollers 16, 18 and 20 which can be generally rotated about an axis 22. Inside the cavity 14 is mounted a deformable tube 24 disposed between the wall of the cavity and all of the rollers 16 to 20. The ends of this tube are connected to two pipe elements, respectively inlet 26 and outlet 28. It is understood that the rotation of the rollers causes a localized pinching of the flexible tube, which ensures the entrainment of the liquid from the inlet line 26 to outlet line 28.

The detection device comprises a first optical detection assembly 30 mounted on the inlet pipe 26 and a second optical detection assembly 32 mounted on the outlet pipe 28. Each detection assembly consists of a light emitter L1, L2 disposed on one side of the pipes 26, 28 and of a light detector PI, P2 mounted on the other side of the pipe opposite the corresponding transmitter. The optical axis of each detection assembly XI, X2 is at the same time a diameter of the pipe. To avoid as much as possible the interference between the two detection systems, we see that the axes XI and X2 are offset according to the length of the pipes and that the light emitters Ll and L2 each emit a light beam towards the outside of the body of the pump. In other words, the light beams are emitted in opposite directions. Referring now to Figure 2, we will describe all the circuits of the bubble detection device. This figure shows the light emitters L1 and L2 and the light detectors or receivers PI and P2. The light emitters are for example each constituted by a light-emitting diode 40, 40 ′ emitting in the infrared mounted between a power supply source of which only the terminals 42 and 44 have been shown and the mass M, in the case of the diode 40 via a bias resistor 44 and in the case of the diode 40 'via a variable resistor 46. With regard to the emitters L1, L2 we have depicted the detectors PI and P2 which are for example constituted by photodetector diodes or photodetector transistors. In the figure, photodiodes 48 and 50 are shown. The resistors RI and R2 make it possible to convert the current created by the photoelectric effect in the photodiodes into a voltage appearing respectively on the conductors 52 and 54. The conductors 52 and 54 are respectively connected to the inputs of the high-pass filters 56 and 58 whose cut-off frequency is for example equal to 500 Hz. The outputs of the filters 56, 58 are respectively connected to the inputs of the band-pass filters 60 and 62. The outputs of the filters bandpass 60 and 62 are connected to the inputs of detectors, respectively referenced 64 and 66. The outputs of detectors 64 and 66 are connected to the inputs of a comparator circuit 68, the output 68a of the latter being connected to the input 70a of microprocessor 70.

According to an essential characteristic of the invention, the emitting diodes 40 and 40 ′ have a pulsed electrical supply 42, 44. The diagrams in FIGS. 5a and 5b illustrate control and supply signals possible for these diodes. The diode 40 is supplied with a frequency voltage FI and the diode 40 'with a frequency voltage F2. For example, the frequency FI is equal to 1 kHz and the frequency F2 is equal to 2 kHz. In the example considered, it can also be seen that the width of the pulses of the frequency signal FI is twice that of the pulses of frequency F2. There is thus generally the same energy in the two signals. The frequencies FI and F2 are chosen in such a way that they are clearly above the parasitic frequencies which can be found in the environment of the detector, that is to say typically that which can come from light sources such as bulbs , etc. For this, the frequencies FI and F2 are chosen to be greater than 120 Hz. It is also desirable that these two frequencies are clearly different in order to be able to dissociate the useful signal received by each detector from the "parasitic" signal which must be received by the other detector . We would not, however, depart from the invention if the two frequencies were equal. It is also understood that, in addition to the advantages which will be emphasized later, the pulsed supply makes it possible to reduce the consumption of electrical energy and of which to increase the autonomy of the system in the hypothesis of a battery supply. More generally, it is preferable to choose frequencies substantially greater than 120 Hz, for example greater than 500 Hz in order to facilitate filtering. There is no upper limit for these frequencies. For reasons of economy, we can limit ourselves to a few MHz, for example 5 MHz. Returning now to the diagram in FIG. 2, it will be understood that the light signals of frequency FI and F2 emitted by the diodes 40 and 40 'are detected by the photodiodes 48 and 50 and converted into electrical quantities. It will of course be understood that these photodiodes collect not only the part of the useful light signal emitted respectively by the diodes 40 and 40 ′ but also the parasitic light signals from the environment of the detector. More specifically, the photo-detectors 48 and 50 collect as useful signal the part of the light signal emitted by the diodes which has passed through the conduits 26 and 28 as well as the liquid which circulates therein. In other words, the frequency and the duty cycle of the useful signals collected by the photo-detectors are not modified but the amplitude of the signals collected is modulated by the light transfer function of the assembly constituted by the driving and the liquid.

FIG. 6a shows a form of signal SI which is collected at the output of the photo-detectors PI or P2. This signal is for example constituted by the superposition of a DC component A corresponding to the ambient light level, an AC component B corresponding to parasitic light sources whose frequency can typically be of the order of 100 or 120 Hz and the collected pulsed signal of frequency FI or F2, the amplitude of which has been modulated by the light transfer function of the system constituted by the pipe and the liquid. At the output of the high pass filters 58, 56 and bandpass 62, 60 respectively, the filtered signal S2 shown in FIG. 6b is obtained. It is an alternating signal whose frequency is equal to FI and whose amplitude represents the measurement sought. It is easily understood that the high-pass filters 56 and 58 eliminate the DC component A of the signal and the parasitic components B of low frequency, typically less than 120 Hz, preferably less than 500 Hz, while the band-pass filters 60 or 62, centered respectively on the frequencies FI and F2, make it possible to eliminate harmonics of the parasitic signals which could exist in the collected signal and whose frequencies would be higher than the cut-off frequency of the bandpass filter. We could simplify the circuit by using only one of the two filters. Similarly, the bandpass filter could be replaced by a synchronous detector calibrated respectively on the frequency IF or the frequency F2. The signal thus filtered is processed by the detector 64 or 66 which has the function of delivering a DC voltage whose amplitude is representative of the amplitudes of the pulses of the pulsed signal. In other words, the amplitude of the signal S3 (FIG. 6c) is representative of the light actually received by the detector P2 or by the detector PI and emitted by the corresponding transmitter. The comparator 68 therefore delivers on its output 68a a signal which is equal to the difference between the signals collected by the detectors 48 and 50. The signals S2 and S3 show the presence of a bubble.

As already explained, each measurement chain, if there are actually two, or the measurement chain, if there is only one, is equipped with a initial self-calibration circuit allowing the power supply level of the light emitter to be defined in order to obtain optimal detection conditions whatever the transparency of the liquid.

Figure 7 illustrates such a circuit. It includes a comparator 80 which receives on the two inputs respectively the measurement signal S delivered by the detector 66 and a reference signal C corresponding to the optimal level of detection in the absence of bubble.

The difference E between these two signals is applied to a zero detection circuit 82 whose output is connected to the input 70e of the microprocessor 70.

Depending on the signal received on the input 70e converted into a digital value, the output 70f of the microprocessor generates a digital or analog signal for controlling the supply circuit 84 of the transmitter L2 in a direction which tends to cancel the deviation E. When the deviation becomes zero, the zero detector 82 delivers a signal to the microprocessor which maintains the supply control signal 84 at a constant value. This control signal value is stored in the memory 86 of the microprocessor and the initial self-calibration circuit is deactivated.

If the liquid is not very transparent, the gap E cannot be canceled. In this case, the increase in the supply current of the transmitter L2 is stopped when this current reaches its maximum admissible value for the transmitter. If the measurement signal S corresponding to this value is greater, for example, than c / 4, the measurement will be accepted and this maximum value of the supply current will be used during the measurement. Otherwise, the device will not work.

In FIG. 7, the comparator 80 and the zero detector 82 are shown in the form of discrete components. It goes without saying, however, that the microprocessor 70 could implement a subroutine performing the two comparison and detection functions. from zero.

In the supply line 26, it can be assumed that there is no a priori bubble and the signal delivered by the detector 64 constitutes a reference signal. When there is no bubble in the pipe 28, the signal delivered by the detector 66 is equal to the reference signal due to the initial calibration which will be described later. A zero or very weak signal is received at input 70a of the microprocessor. On the contrary, if a bubble passes through the pipe 28, the signal delivered by the detector 66 is very significantly lower. To amplify this phenomenon, it is advantageous to maximize the difference in optical transmission through the pipe depending on whether a bubble is present or not. For this, preferably, as shown in FIGS. 4a and 4b, the transmitter Ll, L2 and the detector PI, P2 are provided with optical systems 72, 74, constituted by lenses, which are defined in such a way that, when the liquid is present in the pipe 28, most of the light beam crosses the pipe and is focused on the sensitive surface 76 of the photodiode PI, whereas in the case (Fig. 4b) where a bubble circulates in the pipe 28 , the light beam diverges and a smaller part of the beam is received by the sensitive surface of the PI detector. In alternatively, optical systems producing the opposite effect could be used, that is to say an increase in the optical energy transmitted when a bubble is present in the pipe.

The operation of the device which has been described above is as follows.

In a first phase, an initial calibration of the detection device is carried out to balance the two measurement chains. For this, the microprocessor 70 implements a first program. The difference of the continuous signals received on the input 70a of the microprocessor is converted into a digital value by an analog-digital conversion assembly 72. This difference is converted into a control signal R delivered by the output 70b of the microprocessor which is converted into an analog signal used to modify the value of the bias resistor 46 of the diode 40 '. This produces a servo which modifies the value of the resistor 46 until the signal applied to the input 70a is zero. The detection device is then calibrated and the device is ready to operate, the value of the resistor 46 being kept constant. It goes without saying that the calibration could be obtained by acting on the operating parameters of the diode 40, on the operating parameters of the photo-detectors 48 or 50 or on the parameters of a combination of these components.

Next, the initial self-calibration described in connection with FIG. 7 is carried out. In its normal operating phase, the microprocessor 70 implements a second program. The difference of the continuous signals delivered by the output 68a of the comparator is converted into a digital value which is compared with a lower threshold. If the value of the difference is less than this threshold, this means that no bubble crosses the pipe 28 since the two continuous signals are substantially equal. On the contrary, if the difference is greater than this threshold, this means that a bubble is present in the pipe 28 due to the modification of the optical system constituted by the pipe and its content. The comparison is carried out periodically, for example every 5 milliseconds. If for a predetermined number of successive comparisons, the difference is greater than the lower threshold, it is that a bubble is effectively present in the pipe 28. The microprocessor 70 is preferably programmed to trigger an alarm 80 which causes the immediate stop of the pump 10 only if the quantity of entrained air becomes significant. For example, the microprocessor can be programmed to trigger the alarm only if a predetermined number of successive differences is greater than the threshold. The alarm can also only be triggered if during a predetermined time interval, for example 15 minutes, the number of measurements detecting the presence of air is greater than a predetermined number. This number can be determined so that it corresponds to a volume of air circulating in the pipe during this time interval. Many other types of alarm trigger programming could be considered. The purpose of this procedure is to avoid stopping the pump due to the presence in the pipe of an amount of air, or an air content, which is not significant for the patient.

As shown in FIG. 2, the detection device also comprises means for continuously testing its correct operation or more precisely that of the detection assemblies 30 and 32. In the event of failure of the transmitter L1 (L2) or of the detector PI (P2), the continuous signal delivered by the detector 64 or 66 becomes zero. To detect such a situation, the outputs of the detectors 64 and 66 are directly connected to the inputs 70c and 70d of the microprocessor 70. The latter permanently monitors the level of the signals applied to the inputs 70c and 70d. As soon as one of these signals falls below a predetermined value, it is that one of the detection assemblies 30 or 32 has failed and the alarm circuit 80 is activated.

A substantially equivalent solution consists in comparing the difference signal applied to the input 70a of the microprocessor with an upper threshold. If this threshold is exceeded, it means that one of the detection assemblies has failed.

In the preceding description, it will be understood that one of the two measurement chains, that corresponding to the detection assembly 32, is in fact used to define a reference value using the self-calibration step. The other measurement chain (detection assembly 30) continuously provides the useful measurement. We would not depart from the invention if the measuring device included only one measuring chain constituted for example by the circuits L2, P2, 58, 62 and 66. In a first step, the value of the continuous signal delivered by the detector 66 is determined when there are effectively no bubbles in the line 28. This value is stored by the microprocessor 70. In a second step corresponding to the normal detection phase, the value of the continuous signal delivered by the detector 66 is compared with the reference value previously stored.

In the previously described embodiment, the processing of the signals delivered by the detectors 48 and 50 is analog. Only the comparison of the signal delivered by the circuit 68 with thresholds is done digitally by the microprocessor 70. However, it goes without saying that the signals delivered by the detectors 48 and 50 could be directly converted into digital information. The microprocessor 70 then performs, in digital form, the operations made by the analog circuits 56 to 68 of FIG. 2, that is to say the filtering, the conversion into a continuous signal and the calculation of the difference of the two signals treated.

Claims

1. Device for detecting bubbles in a liquid flowing in a pipe is characterized in that it comprises: a first light emitter (L2) disposed on a first side of the pipe (28), a first light detector (P2 ) arranged on the other side of the pipe opposite the first transmitter to receive the portion of the light beam emitted by the first transmitter having passed through said pipe and the liquid, of the first supply means (42) of the first transmitter so that the -this emits a pulsed light beam with a first frequency (F2); first means for processing the signal delivered by the first detector comprising filtering means including at least one high-pass filter (58) and / or a band-pass filter (62) centered on said first frequency and detection means ( 66) to convert the signal processed by the filtering means into a first continuous signal having an amplitude proportional to the amplitude of the first pulsed signal; means for developing a reference signal corresponding to the circulation of the liquid in the pipe in the absence of bubbles; means (68, 70) for periodically comparing the reference signal with the first continuous signal and means (80) for generating an alarm signal in response to said comparison; and initial self-calibration means comprising means for comparing, when the bubble-free liquid circulates in the pipe, the signal delivered by said first detector to a setpoint signal, means for controlling said first means of supply of said first transmitter until said delivered signal is equal to said setpoint signal or until supply of said first transmitter reaches a maximum admissible level and means for controlling said supply means, in normal use, according to the results of said initial self-calibration.

2. Detection device according to claim 1, characterized in that the means for developing the reference signal comprise: a second light emitter (L1) disposed on a second side of the pipe (26); a second light detector (PI) disposed on a first side of the pipe opposite the second emitter to receive the portion of the light beam emitted by said second emitter having passed through said pipe and said liquid, from the second supply means (44) the second transmitter so that it emits a pulsed light beam with a second frequency (FI); second means for processing the signal delivered by the second detector comprising filtering means including at least one high-pass filter (56) and / or a band-pass filter (60) centered on said second frequency and detection means ( 64) to convert the signal processed by said filters into a second continuous signal having an amplitude proportional to the amplitude of the second pulsed signal, the second signal constituting said reference signal; and in that said initial self-calibration means are capable of carrying out self-calibration of the assembly constituted by said second supply means, said second transmitter and said second receiver.

3. Detection device according to claim 2, characterized in that said first (FI) and second (F2) frequencies are different.

4. Detection device according to any one of claims 2 and 3, characterized in that said frequencies are between 120 and a few MHz.

5. Detection device according to any one of claims 2 to 4, characterized in that said emitters (L1, L2) and light detectors (PI, P2) are respectively provided with an optical system (72, 74) for focusing the beam emitted by each emitter on the sensitive surface (76) of the associated detector when the portion of said pipe disposed between them is completely filled with liquid.

6. Detection device according to any one of claims 2 to 4, characterized in that said light emitters (L1, L2) and detectors (PI, P2) are respectively provided with an optical system (72, 74) for focusing the beam emitted by each emitter on the sensitive surface (76) of the associated detector when the portion of said pipe disposed between them is completely filled with air.

7. Detection device according to any one of claims 2 to 6, characterized in that said emitters (L1, L2) are light-emitting diodes in the infrared and in that said detectors (PI, P2) are photodiodes or phototransistors.

8. Detection device according to any one of claims 2 to 7, characterized in that said means for developing a reference value further comprises means (68, 70) for comparing, in an initial phase, the continuous signals delivered by said two processing means and means (70, 46) for modifying the operating parameters of at least one transmitter and / or at least one detector to cancel the difference between said continuous signals.

9. Detection device according to any one of claims 2 to 8, characterized in that it further comprises means (70) for comparing each continuous signal to a lower threshold and means for triggering an alarm in response to said comparison.

10. Detection device according to any one of claims 2 to 9, characterized in that said light beams have different duty cycles.

11. Detection device according to any one of claims 1 to 10, characterized in that said alarm is triggered if the difference between the value of said continuous signal and said reference signal is greater than a predetermined value for a predetermined duration.

12. Detection device according to any one of claims 2 to 10, characterized in that said first light transmitter and detector (L1, PI) are mounted on a first portion of pipe (28) and said second light transmitter and receiver ( L2, P2) are mounted on a second pipe portion (26), said pipe portions being substantially parallel, said two emitters (L1, L2) being offset in the common direction of said pipe portions and each emitting a light beam of such so that said beams are emitted in opposite directions.

13. Detection device according to any one of claims 2 to 12, characterized in that said filtering means (58, 62), said detection means (64, 66) and the comparison means (68) are of the digital type.