WO2005085823A1

WO2005085823A1 - A method of precise volume size measurement of air bubbles in a liquid flowing through a hose and an electrode of capacity sensor and a capacity sensor for realization of the measurement

Info

Publication number: WO2005085823A1
Application number: PCT/CZ2005/000022
Authority: WO
Inventors: Jirí VANEK
Original assignee: Vanek Jiri
Priority date: 2004-03-08
Filing date: 2005-02-22
Publication date: 2005-09-15
Also published as: DE112005000387T5

Abstract

Before the medium is going to be pumped into the hose, this hose is placed between the sensing heads of the sensing electrodes of the capacity sensor of special design, which allows to measure only changes of permittivity of the environment inside the inserted hose. Physical qualities of each pumped medium are different, therefore it is necessary to calibrate the limit values of permittivity inside the pumping hose for specific conditions of pumping. This is achieved by repeated input and output of the pumped medium into the zone between the sensing heads of the capacity sensor, which results in obtaining statistically accurate values of permittivity of completely filled hose and permittivity of completely empty hose, however with wetted inner walls. Measured permittivity of pumped medium with however large air bubbles must lie between the limit values of calibrated permittivity. The pump's linear characteristics, in given case the unique relation of the angular displacement of the impeller to the volume of pumped-out medium, allow easy calculation of the size of possible air bubbles passing through the capacity sensor by means of linking-up the start and end of measured change of permittivity with the volume of pumped-out medium, i.e. with the angular displacement of the pump impeller.

Description

A method of precise volume size measurement of air bubbles in a liquid flowing through a hose and an electrode of capacity sensor and a capacity sensor for realization of the measurement

Technical Field of the Invention

The submitted invention deals with a method of volume size measurement of air bubbles in a liquid flowing through a hose, e.g. a pump segment. It involves electrical measurements of non-electric values induced by the operation of the device. Simultaneously, it deals with the solution of an electrode of capacity sensor and this sensor for the described measurement by means of capacity variations of permittivity of the environment between the electrodes of the sensing condenser.

Background of the Invention

At present, the only known measurement method of changing size of an air bubble in a liquid flowing through a hose, e.g. a pump segment, based on ascertainment of permittivity changes of the environment in the segment, is only an orientational one.

Orientational, therefore considerably inaccurate, measurement of the air bubbles size in pumped medium is a consequence of significant non- linearity of manufactured peristaltic pumps and inappropriately selected, especially not sufficiently sensitive, electrodes of the capacity sensor of the measured environment permittivity. As the used peristaltic pumps are non^¬ linear, the decisive level of detected air bubble must be firmly related to the geometry of - even inappropriately selected - electrodes of the capacity sensor, when the area of the measuring electrodes considerably exceeds the area, on which the purposefully measured variations of permittivity may occur, and thus the electric sensitivity of the whole measurement significantly decreases. The length of deformed hose leading through the bubbles detector determines the presumable volume of an air bubble, further biased by the non-linearity of the pump, which the electronic equipment is capable to distinguish orientationally into a group "larger than ..." and a group "smaller than ...".

This state does not allow for sufficient guarantees of fulfillment of the standard CSN EN ISO 60601-2-24, article 51 Protection against hazardous output, item 51.10 for infusion pumps, which stipulates the following:

Infusion of 1 ml of air over 15 minutes is not considered as a DANGER TO SAFETY. Individual air bubbles smaller than 50 μl are neglected up to the total volume of 1 ml. Sensing e lectrodes of t he c apacity s ensor for c omparable m eans o f use so far are made in two-dimensional, i.e. plate-shaped, design. The whole conductive area of the sensing electrode simultaneously forms a sensing head of the sensing condenser. This construction and its operational use allow inducing the desired change of permittivity of the environment between two plates of the capacity sensor only on part of their area. The disadvantage of this solution is that the area of measuring electrodes considerably exceeds the area, on which the measured changes of permittivity may occur, which significantly decreases electrical sensitivity of the measurement as a whole. It is a common knowledge that linear superposition of the change of the total capacity during the change of permittivity ε occurs only between small parts of the same area S. In most cases the electrodes of the capacity sensor are not shielded or the shielding is designed separately on the body supporting the sensing electrodes.

Summary of the Invention

Disadvantages described hereinabove are removed by the method of precise measurement of volume size of air bubbles in a liquid flowing through a hose and an electrode of capacity sensor and a capacity sensor for realization of the measurement according to the submitted invention. The substance of this method is following: before the medium is going to be pumped into the hose, this hose is placed between the sensing heads of the sensing electrodes of the capacity sensor of bubbles and subsequently the limit values of permittivity are calibrated for current conditions of the pumping. The calibration is performed as follows: using a linear pump with calibrated dosing volume per unit of angular displacement equipped with the sensor of position of the pump impeller's angular displacement, the column of the pumped media is repeatedly forced in and out the hose so that it repeatedly and entirely fills in and fills out the areas between the sensing heads of the sensing electrodes of the capacity sensor. During each complete fill-in and each complete fill-out of this area of the hose, the amounts of local permittivity are measured in selected time intervals. Ascertained values are archived and continuously used for determining the mean value of permittivity. The calibration is finished at the moment when the measured values of local permittivity compared to its mean value ascertained during multiple preceding measurements vary less than by the selected measurement accuracy. In this way, both the value of the permittivity of bubble-free pumping of the chosen medium and the value of the permittivity of the environment of completely empty, however with inner walls wetted, hose are determined. These two mean values are stored and subsequently the pumping of the given medium begins. Current values of the permittivity between the sensing heads of the sensing electrodes of the capacity sensor are c ontinuously m easured i n t he i dentical time i ntervals a s w ere t he t ime intervals selected for calibration. These values are compared with the two limit values determined by the calibration measurement stored in the memory of the device for given dosing medium. A permittivity step variation of individually measured p ermittivity values of local environment compared to the calibration values indicates an occurrence of an air bubble. From the moment such permittivity step variation occurs, the positions of angular displacement of the pump impeller begin to be recorded and counted until the moment the next permittivity step variation occurs. The volume size of given air bubble is determined by transformation of its specific volume and shape to a corresponding volume of a cylinder with its height directly proportional to the angle of the linear pump impeller displacement given by the number of unit angular displacements between the two consecutive permittivity step changes and with its base area directly proportional to the measured permittivity of the mixture of the air bubble and the pumped medium passing between the electrodes of the capacity sensor within the range of the limit values of permittivity ascertained during calibration. Very expedient is to press the hose before the pumping of the medium to the hose begins in such a way that the whole area of the head of the sensing electrode is in direct contact with the surface of the hose and both the calibration and the detection are carried out on such initially pressed hose as described.

In order to maintain simple usage and low cost, it is expedient to use as the sensor of the position of the pump impeller's angular displacement its driving step motor complemented with a circuitry of objective checking of performed number of step impulses at least 3 times per 1 revolution of the driving shaft.

The entrance of an air bubble of geometrical length shorter than the geometrical length of the sensing head of the sensing electrodes will induce a local change of permittivity ranging between the calibrated limit values of local permittivity and the base area of transformation cylinder is reduced by a reduction factor given by the ratio of a change of permittivities measured at the moment the air bubble is detected to a change of permittivities ascertained during calibration. The invention, therefore, is based on measuring of the volume size of air bubbles in the pumped medium flowing through a hose located between the sensing heads of the sensing electrodes of the capacity sensor by means of capacity measurement of the environment permittivity changes at this place and relating these permittivity changes to the volume of pumped-out medium. Thus, a unique linear relation between the accuracy of the bubble- free dosing of calibration medium and dosing the mixture of this medium with air is created. Each measurable, unique and linear physical relation consequently allows its easy and exact mathematic expression and electronic processing.

Subject matter of the invention closely follows solutions described in patents No. 292309 and No. 292594. This fact does not exclude fulfilling the required entry conditions necessary for successful function of this invention in other ways than those described in already granted patents or in pending patents.

In the broad sense, this method allows to ascertain, or measure respectively, any abnormalities in pumped medium, which induce measurable changes of its permittivity.

The substance of the new electrode for the given measurement is the fact that it consists of the non-conductive plate-shaped support, on the front of the plate there is created a sensing head of the measuring plate of the condenser with a conductor leading from the support at its side. This sensing head and the conductor are enclosed by an electrically conductive front shielding area separated from the sensing head and the conductor by a non- conductive separating area. The rear side of the support is on its whole area equipped with an electrically conductive rear shielding area. The front shielding area and the rear shielding area are electrically interconnected. The size and shape of the sensing head is equal or approximately equal to presumed size and shape of the area to be measured. As an expedient arrangement, the front shielding area and the rear shielding area are interconnected by a layer of electrically conductive paint applied along the side rim of the support outside the rim area of this support. As an expedient arrangement, the length of the sensing head in relation to its width is within the ratio from 0.5 : 1 to 1 : 5.

In the support can be made at least one aperture leading through the front shielding area and the rear shielding area and provided with at least one soldering point from each side of the support. To the soldering point of the aperture on one side of the support can be connected one end of the connecting wire, the other end of this wire shall be connected with the soldering point of the aperture on the opposite side of the support.

The newly created electrodes allow to realize a capacity sensor formed by two electrodes where the front and the rear side of individual electrodes are interconnected by means of the soldering points of the apertures. The advantage of the described solution is that the new construction of the electrodes of the capacity sensor, while maintaining easy operation of the device, allows to obtain the maximum available measurable permittivity changes of the environment in the measured zone between the sensing heads of the capacity sensor. Easy and accurate placement of the electrode of the capacity sensor to the body intended for installation of the sensor allows repeated and accurate creating of the spatial alignment of the measurement areas given by the sensing head of the area where the changes are m easured. Another advantage is that the directional effect of electrostatic shielding formed by the conductive shielding and the conductive paint allows simultaneously an easy operational handling with the device. The described electrode can be used in a pair of identical electrodes of the capacity sensor or separately in configuration with suitable conductive environment forming the other measuring plate of the condenser. Advantages of accurate and low-cost serial production of printed circuits can be expediently used for producing one piece of multiple electrodes of the capacity sensor using the principle of a single sensing head and its one external connection by a wire to the side of the support of the electrodes. Overview of Figures in the Drawings

The submitted invention will be further described in closer detail by means of enclosed drawings. Fig. 1 shows the behaviour of the environment permittivity changes at the bubbles detector when an air bubble longer than the length of sensing heads of the capacity sensor passes through the detector. Fig. 2 shows the behaviour of the environment permittivity changes at the bubbles detector when an air bubble of equal length as the length of sensing heads of the capacity sensor passes through the detector. Fig. 3 shows the behaviour of the environment permittivity changes at the bubbles detector when an air bubble shorter than the length of sensing heads of the capacity sensor passes through the detector. Other drawings show the capacity sensor, or its electrode respectively, intended for the described measurement of the volume size of air bubbles. Fig. 4 shows axonometric projection of a single electrode of the capacity sensor with directional electrostatic shielding in the front view. Fig. 5 shows axonometric projection of this electrode of the capacity sensor with directional electrostatic shielding in the rear view. Fig. 6 shows the geometry of maintaining the spatial alignment of the measuring area and the area of changes in the detection zone, or measuring zone respectively, the electrostatic shielding is omitted in the drawing.

Detailed Description of the Invention

The submitted invention will be applied on a pump driven by a step motor and constructed according to the granted patents No. 292309 and No. 292594. The electrodes of the capacity sensor of possible air bubbles occurrence shall be assembled according to the figures enclosed in the patent application No. PV 2004-338, and shall be located in the suction branch of the pump close to the entry of the pump segment to the pump's working path. The forming of the electrodes will be described after the description of the new method of the measurement.

Inserting the pump segment into the pumping head of the pump will ensure that this pump segment is accurately placed between the electrodes of the capacity sensor in such a way that the sensing heads of the sensing electrodes of the capacity sensor are in close area contact with the surface of the pump segment - in the given example of the area 3 mm wide and 6 mm long. Critical size of an air bubble with length equal to the length of the electrodes, see fig. 2, in the pre-pressed pump segment is thus determined by the length of 6 mm. Close contact of the sensing head of the sensing electrode with the surface of the pump segment suppresses negative effects of possible changes of the ambient humidity on undesirable changes of permittivity at the measured point.

The measurement of permittivity itself is performed by measurement of the amount of capacity of thus created fixed condenser connected to one input of the measuring m odule made by S martec, which i s offered for this purpose. Reading the function of the sensing and velocity contact of the pump (see patent No. 292594) by other inputs of the Smartec measuring module and comparing this function to the number of step impulses allows for repeated confirmation of correct evaluation of the angular displacement of the pump impeller at the control computer level. Prior the infusion will be applied to a patient, the device operator starts the stage of pushing the air out from the infusion set up to the syringe needle by switching the device to this program. The pump impeller starts to revolve thus creating underpressure at the suction side of the pump and the column of the pumped medium more and more fills the suction branch of the infusion set.

After this, the calibration of limit values of permittivity for current conditions of pumping will be carried out, where one limit value of calibrated permittivity corresponds to the permittivity of the pump segment completely filled with the dosing medium, this permittivity limit is marked in the fig. 1 to 3 as ε_med- The other calibrated permittivity limit value corresponds to the permittivity of the pump segment completely empty but having done the previous step, with wetted inner walls. This second permittivity limit value is marked in the fig. 1 and 2 as vz_d. Same marking is used also in fig. 3, here however it is used only for comparison in relation to the permittivity ει_< as will be described hereinafter. Calibration of the permittivity limit values for current conditions of pumping is done in the suction branch of the pump by forcing the column of the pumped media repeatedly in and out the part of the hose inserted between the sensing heads of the sensing electrode of the capacity sensor. After each complete fill-in and each complete fill-out of this area of the hose, the amounts of local permittivity are measured in selected time intervals. The values ascertained during multiple individual measurements are used for determining and specifying the mean values of both permittivity limits, which are archived. Archiving the results of the calibration measurement for the current conditions of pumping, i.e. also the calibration itself, is finished at the moment when the measured values no longer change significantly, e.g. with respect to the selected measurement accuracy for the both limits of 1% compared to their mean values ascertained during multiple preceding measurements. The course and completing the permittivity calibration process for current conditions of pumping is visually represented by the infusion device, which automatically stops and waits for the manual action of the operator for completing the stage of forcing the air out of the pump segment up to the syringe needle. After this is done, the needle may be applied to the patient and automatic infusion may begin. Operational measurement during pumping the dosing medium is performed in the identical time intervals as were the time intervals selected for calibration. The detection of air bubbles itself is performed by continuous and repeated comparing the actual value of local permittivity measured by the bubbles detector with the two values of permittivity limits ascertained during calibration measurement stored in the memory of the device for given dosing medium. Statistically significant tendency of the step variation of individually measured permittivity values compared to the calibration values indicates the start and end of an air bubble passing between the electrodes of the capacity sensor.

In case a step variation of several consecutive individually measured values of the local environment permittivity compared to the calibration values is detected, the computer calculates the volume of the air bubble, which p assed through the bubbles detector by calculating the volume of a cylinder determined by calibration of dosing accuracy by the pump, angular displacement of the pump impeller and possibly also by current reduction factor x, which expresses the percentage composition of the mixture of the pumped medium and air. Obtained accuracy of the volume measurement of possibly occurred air bubbles is closely related to linking-up the changes of permittivity and related volume of pumped-out medium.

During the measurement itself, only three different versions of the air bubble size may occur relating to the length of the sensing heads of the sensing electrodes of the capacity sensor, and these versions are described in fig. 1 to 3. The scales are expressed by a relative relation of mutual length of an air bubble to the length of the sensing heads of the sensing electrodes of the capacity sensor scaled to the angular displacement of the pump impeller given e.g. by the number of steps of the step motor. Application of the step motor is very simple and financially undemanding, it is however possible to use also other sensor of the position of angular displacement of the pump impeller. Fig. 1 shows an example of ideal behaviour of changes of permittivity of the environment at the bubbles detector when an air bubble longer than the operational length of the sensing heads of the sensing electrodes of the capacity sensor passes through. The y-axis represents relevant permittivity ε and the x-axis represents the length L. This length L actually represents the distance of the borders of the air bubble from the edges of the sensing heads of the sensing electrodes of the capacity sensor in direction this air bubble moves and it is given in scale to the angular displacement of the pump impeller, which means that a single length unit corresponds to one step impulse. Operational length of the sensing head of the sensing electrodes of the capacity sensor, again in scale to the angular displacement of the pump impeller, is marked by the relation number 500. Horizontally along the axis L, two straight lines are lead, where the lower line 100 marks the permittivity of air calibrated inside the wetted pump segment and the upper line 101 marks the permittivity of pumped medium εm_έd of the calibrated pump segment. The difference of the values of these lines, or their distance respectively, is assigned the value of 100%. At the moment the air bubble enters the bubbles d etector, the first condition 200 sets in, when the front side of the bubble gets to the front edge of the sensing head of the sensing electrode and at this moment the permittivity starts to decrease from the level gm_ed and keeps decreasing until the front side of this air bubble gets through the bubbles detector to the end of the sensing head of the sensing electrode, i.e. the second condition 300, when it reaches the level of the permittivity of air z_d. In the third condition 30_1, the end of the air bubble is positioned at the front edge of the sensing head of the sensing electrode as the bubble comes out from the bubbles detector and the permittivity starts to increase again from the value ε^ and keeps increasing up to the value gmed, when the end of the air bubble gets to the end of the sensing head of the sensing electrode, as the bubble comes out from the bubbles detector, i.e. to the condition 201. Operational length 400 of the air bubble in scale of the angular displacement of the pump impeller is given by the distance of centers of connecting lines between the points marking the first condition 200 and the second condition 300, or the third condition 301 and the fourth condition 201 respectively. It is obvious that this length may also be determined as a distance between the points marking the first condition 200 and the third condition 30_1, or between the points marking the second condition 300 and the fourth condition 201 respectively. Now, after the air bubble has passed through the capacity sensor, it is necessary to find out its size. For this purpose, the bubble is electronically transformed to a cylinder with height given by the number of step impulses, as described above, i.e. from the center o f t he d istance b etween 200 a nd 3001 o t he c enter o f t he d istance between 301 a nd 01, or from 200 up to 301, o r from 300 to 20 ., of the pump, and with the base area given by the calibration constant of accuracy of bubble-free pumping, which is expressed by 100% difference of amounts of calibrated permittivities ε^ and gm_όd for given dosing medium. Similarly, fig. 2 shows behaviour of permittivity of the critical size of an air bubble while passing through the bubbles detector when the geometrical length of the air bubble is just equal to the geometrical length of the sensing head of the sensing electrodes of the capacity sensor, regardless of the current rate of pre-pressing of the pump segment at this point. Thus, the limit border, from which the reduction factor for calculation of the cylinder base area starts to apply, is determined. This case, when the limit border is exceeded, is shown in fig. 3, when an air bubble shorter than the length of the sensing head of the sensing electrodes passes between the electrodes. Measured permittivity in this case does not reach the limit value corresponding to ε^_d but the higher value εj_< and the line 102 related to this case lies between the limit borders given by the lines Έ^Δ and gmed- The difference of ascertained permittivities ε_mέd and _k is here marked as x%. For electronic determination of the bubble size, the bubble is electronically transformed to a volume of cylinder with height given by the number of step impulses of the pump's step motor and with the base area given by the reduced calibration constant of accuracy of bubble-free pumping, which is expressed by the reduction factor given by the ratio x%/100%. The condition 600 in fig. 3 therefore corresponds to a situation when the whole air bubble, which is shorter than the length of the sensing head of the sensing electrode, travels along the length of the sensing head of the sensing electrode together with the pumped medium. When another, e.g. isecond and third, unit of stored blood is to be connected to continuous iinfusion, the device operator enters this information to the computer program, which will allow for automatic and continuous re- calibration of the device ^; to the new value of one of the limits of long-term permittivity of the pumped medium, i.e. the limit value ε_med, without interrupting the infusion! and without occurrence of false indications of bubbles of minimum si?e while maintaining extremely high level of the measurement accuracy and slightly different values of gme_d for individual units of stored blood.

The control computer software allows during the course of time to collect, evaluate, display and dellete individually measured values of air bubbles size in compliance with the article 51 of the standard CSN EN ISO 60601-2-24. The following will be a description of the electrode of the capacity sensor and the capacity sensqr itself intended for application of the described method of precise volume size measurement of air bubbles in a liquid flowing through a hose. In the arrangement according to the fig. 4 and 5, the electrode of the capacity sensor is formed by the non-conductive support 6, on the front side of which is located th sensing head 1 of the measuring plate of the condenser in one level, Which is lead by the conductor 4 to the rim of the support 6 in the area marked by the relation number 9. The sensing head 1 and the conductor 4 are enclosed from all sides at this level by an electrically conductive front shielding area 5 separated from the sensing head 1 and the conductor ^ by a n on-cόnductive s eparating a rea 1_3. The rear s ide of the support 6 of the electrode of the capacity sensor is on its whole area electrically conductive rear shielding area 5'.

In the given example the front shielding area 5 and the rear shielding area EL are electrically conductively connected by application of layer 7 of electrically conductive paint on the base material of the non-conductive support 6 of the electrode of the capacity sensor. The layer 7 of electrically conductive paint is applied along the whole cut-off rim of the support 6 except for the part of the rim forming the area 9. The electrode of the capacity sensor is produced using common, sufficiently accurate technology of manufacture of printed circuits by surface etching followed by application of the layer 7 of the conductive paint applied to t he r im of t he c ut-off s upport 6 of t he electrode. The p art o f the C u-foil removed by etching and forming the separation area 13 will non-conductively separate the electrostatic shielding formed by the front shielding area 5 from the sensing head 1 of the measuring plate of the condenser and from its lead-out by the conductor 4 in the area 9 of the support 6. It is possible to use any arbitrary arrangement from offered prefabricated plates. The most often used one is the printed circuit plate 1.5 mm thick, plated on both sides by Cu- foil 35 μm thick. In order to prolong the mechanical lifetime cycle of the electrode of the capacity sensor exposed to stronger wear, it is possible to use the printed circuit plate with Cu-foil thicker than 35 μm, or with Cu-foil coated with hard metal, or simply tin-plated. In the support 6 it is possible to create expediently at least one aperture 8, which subsequently allows electrically conductive connection of the front shielding area 5 with the rear shielding area 5J. by common connecting wire lead through this aperture 8 and subsequently soldered with tin from both sides. The purpose of this arrangement is to ensure electrically conductive connection between the front shielding area 5 with the rear shielding area & in case the layer 7 of the electrically conductive paint would become corrupt.

When installing two opposite electrodes of the capacity sensor, this construction allows for easy connection of correct soldering points of the apertures 8 with the opposite electrode and also the three-wire connection of the whole sensing assembly to the measuring module. The soldering points of the apertures 8 may be expediently used for mechanical fixing of the electrodes of the capacity sensor in the body intended for i nstallation of the sensor. This can be achieved by s light p re- tightening of the ends of electrodes with positions 8 and 9 by bending them around the lug between the electrodes of the body intended for installation of the sensor, by leading the connecting wires through the apertures 8 and subsequent soldering by tin in the pre-tightened condition.

The principle of the measurement consists in repeated electronic calculation of the equation C = ε . ε₀S/d, which characterizes the dependence of the condenser capacity on its geometrical arrangement and on the environment between its electrodes. In this equation, S is the area of electrodes, d is their distance from each other, εo is permittivity of vacuum and ε is the measured permittivity. This method exploits easily available and technically sophisticated method of measuring the capacity C. Construction arrangement and functioning of the whole capacity sensor then transforms the information on measured permittivity ε into the value of measured capacity C. Considering a fixed and open condenser, i.e. accessible from the outside, only the ε, i.e. the permittivity, may be changed and this can be done only by action of the operator or the operation of the device. Changes of the ambient air permittivity, which act simultaneously, may be considered as relatively insignificant in the given conditions where the device is going to be used.

The construction and usage of the new construction of the electrode of the capacity sensor are based on maintaining the ratio of operational area of the sensing head 1 to the operational area 2 of induced physical changes of permittivity in the closest possible surrounding of value 1 for all required types of measurements, on maintaining the spatial alignment of the area of the sensing head 1 and area of changes 2 in the first direction 3 of detection, or measuring respectively, as shown in fig. 3, and on maximum possible electrical shielding of interfering influences accidentally occurring in the closest surrounding of the sensor while maintaining easy operational handling with the device. The electrode of the capacity sensor is a spatial, three-dimensional element consisting of both conductive and non-conductive parts. It may be used in pairs of identical electrodes of the capacity sensor or individually, in configuration with suitable conductive environment forming the other measuring plate of the condenser.

Now, the following will be a specific example of arrangement and using the described solution for ascertaining the presence of air bubbles in the dosing medium in the entry part of the pump segment into the infusion pump. This infusion pump is designed incorporating patents No. 292309 and No. 292594 dealing with linear rotational peristaltic pump with precise dosing.

The pump segment 10 of the infusion set IS 121 has the outer diameter of flexible hose 3.9 mm and the inner diameter 2.7 mm. Applying a slight pressure to the pump segment 10 between the measuring electrodes up to the distance of 3 mm presumes forming an elliptic deformation of also the inner, initially circular, section of the hose to the length of the main axis of the inner ellipse of approximately 3 mm. For the selected pump segment 10 of the infusion set IS 121 , the size of the sensing head 1 was preliminarily selected with dimensions 3x6 mm.

Forced flowing of the pumped medium with air bubbles through the pump segment 10 in the second direction H on the area 2 of the measured space induces changes of permittivity of the measured environment evoked by the operation of the device.

Changing the pump segment 10 of the infusion set IS 121, which got worn-out by operation, by removing it from the space between the sensing areas 1 in the third direction 12 induces changes of permittivity of the measured environment evoked by the action of the device operator.

A specific arrangement may be as follows: two electrodes of the capacity sensor are inserted and fixed in the body of the pump cabinet on positions determined by design. Thus, a fixed condenser, accessible from the outside, i s c reated, w hich d oes n ot a How c hanging m utual p ositions of the electrodes of the capacity sensor, neither the size of the sensing head 1. Simultaneously, the design fulfills the precondition of spatial alignment of measurement a reas g iven b y t he s ensing h ead 1 and a reas of c hanges 2 according to the fig. 6.

Using a three-wire connection, i.e. 2x the sensing head 1 and 1x the front shielding 5, or rear shielding 5^ respectively, with the capacity measuring module, the assembly is ready for measuring. Individual stages of measurement may occur consequently one after another or absolutely separately as follows.

The first measurement of capacity gives information on the value of the permittivity of the environment between the measuring electrodes, i.e. on permittivity of the environment in the laboratory where the device is placed and on the fact that no pump segment has been inserted to the device yet.

The second measurement of capacity gives information on the value of the permittivity of the environment between the measuring electrodes after the pump segment has been inserted into the measurement zone of the measuring sensor.

The third measurement of capacity gives information on the value of the permittivity of the environment between the measuring electrodes during the first pass of the column of the pumped medium through the pump segment in the measurement zone of the measuring sensor. The fourth and subsequent measurements of capacity give information on the value of the permittivity of the environment between the measuring electrodes after the first and subsequent passes of the air bubbles through the pump segment in the measurement zone of the measuring sensor, possibly on the fact that the charge of the pumped medium has been fully pumped out and it is necessary to stop the process of pumping.

Descriptions given above clearly show the method of unique and non- interchangeable connection of information on the change of permittivity of the environment between the measuring electrodes with the information on actual acting of the device operator or real functioning operation of the device.

Industrial Applicability

The method of precise volume size measurement of air bubbles in a liquid flowing through a h ose according to the submitted i nvention may b e exploited outside the medical care also for precise dosing feeders in chemical and pharmaceutical laboratories or pilot-plants.

The operational calibration of permittivity of the measured zone for the current conditions of pumping as such may also be exploited for detection of abnormalities in the pumped medium, which induce changes of permittivity, e.g. insufficient mixing of two or more solutions with different permittivities or suction of sludge and other remnants by the pump.

The electrodes of. the capacity sensor according to the submitted solution may be, in addition to the described method of measurement, used anywhere where a high resolution capacity of changes of the measured environment permittivity is required, where high rate of interfering electrostatic influences suppression is required to be performed by the sensor itself, and where it is simultaneously possible to ensure repeated and sufficiently precise fixing of the components used for measuring. They may also be used for detection of long-term invariability of the dosing medium permittivity under constant temperature and therefore also correct and thorough previous mixing of liquids with different values of permittivity dosed from large vessels, or possibly for detection of the dosing medium degradation, if this appears in a form of measurable change of permittivity.

Further, in chemical pilot-plants it is possible to detect any accidental other chemical processes, during which a measurable permittivity change occurs while such local abnormality passes through the measuring sensor.

Claims

P A T E N T C L A I M S

1. The method of precise volume size measurement of air bubbles in a liquid flowing through a hose characterized by the fact that before the medium is going to be pumped into the hose, this hose is placed between the sensing heads of the sensing electrodes of the capacity sensor of bubbles and subsequently the limit values of permittivity are calibrated for current conditions of the pumping while the calibration is performed by using a linear pump with calibrated dosing volume per unit of angular displacement equipped with the sensor of position of the pump impeller's angular displacement, which forces the column of the pumped media repeatedly in and out the hose so that it repeatedly and entirely fills in and fills out the areas between the sensing heads of the sensing electrodes of the capacity sensor and during each complete fill-in and each complete fill-out of this area of the hose, the amounts of local permittivity are measured in selected time intervals, thus ascertained values are archived and continuously used for determining the mean value of permittivity and the calibration is finished at the moment when the measured values of local permittivity compared to its mean value ascertained during multiple preceding measurements vary less than by the selected measurement accuracy and in this way, both the value of the permittivity of bubble-free pumping of the chosen medium and the value of the permittivity of the environment of completely empty, however with inner walls wetted, hose are determined, these two mean values are stored and subsequently the pumping of the given medium begins and current values of the permittivity between the sensing heads of the sensing electrodes of the capacity sensor are continuously measured in the identical time intervals as were the time intervals selected for calibration and these values a re compared with the two I imit values determined by the calibration measurement stored in the memory of the device for given dosing medium, while a permittivity step variation of individually measured permittivity values of local environment compared to the calibration values indicates an occurrence of the air bubble and from the moment such permittivity step variation occurs, the positions of angular displacement of the pump impeller begin to be recorded and counted until the moment the next permittivity step variation occurs and consequently the volume size of a given air bubble is determined by transformation of its specific volume and shape to a corresponding volume of a cylinder with its height directly proportional to the angle of the linear pump impeller displacement given by the number of unit angular displacements between the two consecutive permittivity step changes and with its base area directly proportional to the measured permittivity of the mixture of the air bubble a nd the p umped medium passing between the electrodes of the capacity sensor within the range of the limit values of permittivity ascertained during calibration.

2. A method according to the claim 1 characterized by the fact that before the pumping of the medium to the hose begins, the hose is pressed in such a way that the whole area of the sensing head of the sensing electrode is in direct contact with the surface of the hose and both the calibration and the detection are carried out on such initially pressed hose as described.

3. A method according to the claim 1 or 2 characterized by the fact that the sensor of the position of the angular displacement of the pump impeller is its driving step motor complemented with a circuitry of objective c hecking of performed number of step i mpulses at I east 3 times per 1 revolution of the driving shaft.

4. A method according to any of the claims 1 to 3 characterized by the fact that on the entrance of an air bubble of geometrical length shorter than the geometrical length of the sensing head of the sensing electrodes, which will induce a local change of permittivity ranging between the calibrated limit values of local permittivity, the base area of transformation cylinder is reduced by a reduction factor given by the ratio of a change of permittivities measured at the moment the air bubble is detected to a change of permittivities ascertained during calibration.

5. An electrode of the capacity sensor for realization of the method according to the claims 1 to 4 characterized by the fact that it consists of the non-conductive plate-shaped support (6), on the front of the plate there is created a sensing head (1) of the measuring plate of the condenser with a conductor (4) leading from the support (6) at area (9) of rim of the support (6) where this sensing head (1) and conductor (4) are enclosed by an electrically conductive front shielding area (5) separated from the sensing head (1) and the conductor (4) by a non-conductive separating area (13) and where the rear side of the support (6) is on its whole area equipped with an electrically conductive rear shielding area (5'), while the front shielding area (5) and the rear shielding area (5') are electrically interconnected and the size and shape of the sensing head (1 ) is equal or approximately equal to presumed size and shape of the area (2) to be measured.

6. An electrode according to the claim 5 characterized by the fact that the front shielding area (5) and the rear shielding area (5') are interconnected by a layer (7) of electrically conductive paint applied along the side rim of the support (6) outside the area (9) of the rim of this support (6).

7. An electrode according to the claim 5 or 6 characterized by the fact that the length of the sensing head (1) in relation to its width is within the ratio from 0.5 : 1 to 1 : 5.

8. An electrode according to the claim 5 or 6 or 3 characterized by the fact that in the support (6) is made at least one aperture (8) leading through the front shielding area (5) and the rear shielding area (5') and provided with at least one soldering point from each side of the support (6).

9. A capacity sensor formed by two electrodes located opposite each other according to the claim 8 characterized by the fact that these electrodes are interconnected with connecting wire by means of the soldering points of the apertures (8) in supports (6) from the rear shielding area (5^') of one electrode via its front shielding area (5) and further via the front shielding area (5) of the second electrode to its rear shielding area (5^').