Gel-coupled pressure sensor device with interference-independent contact side for connection to an infusion tube

Description

Technical area

[0001] The present disclosure relates to a gel-coupled pressure sensor device according to the preamble of claim 1 and in particular to a gel-coupled pressure sensor device which can be mounted on (flexible) tubes, in particular medical infusion tubes, for detecting the internal pressure of the tube in a manner which is essentially free of measurement fluctuations. Background of the invention

[0002] In medical technology, flexible tubes are used, for example, to supply fluid to a patient through an infusion, to withdraw fluid, or to transport fluid between devices or equipment. Such tubes are also used, for example, in blood treatment machines, heart-lung machines, and similar intensive care devices. In this case, it is necessary to detect a partial or complete blockage of the flexible tube, such as could occur due to a kink in the tube. Furthermore, depending on the set infusion parameters, it is necessary to monitor the internal pressure of the infusion tube and regulate it accordingly. State of the art

[0003] EP 1 269 145 B1, EP 0 897 528 B1, EP 0 594 836 B1, EP 1 357 372 B1, as well as DE 196 10 828 C1 and DE 296 02 065 U1 each disclose pressure sensor devices, generally comprising, among other things, a pressure sensor housing in which a pressure receiving and pressure transmission medium or pressure transmission element is arranged, and a pressure force sensor that is in contact with the pressure transmission element. In particular, the pressure transmission element is designed to engage the infusion tube to detect radial tube expansion as a result of the current internal tube pressure and to allow the most precise and sensitive pressure transmission possible from the infusion tube to the pressure force sensors located in the pressure sensor housing in order to measure the internal pressure of the infusion tube.

[0004] Gel has been recommended as a potentially suitable medium for pressure transmission. This gel is inserted / filled into a chamber of a sensor housing and can have a contact section protruding from the sensor housing, where the gel rests against a tube. The gel / gel element / gel pad / gel cushion or gel body thus forms a pressure transmission element. However, in an application area involving active medical devices such as infusion pumps and / or dialysis machines, particularly high demands are placed on the accuracy of the monitored parameters, particularly internal pressures in infusion tubes.

[0005] However, temperature fluctuations and the associated changes in the dimensions and material properties of individual functional elements, especially gel-based pressure transmission elements, can lead to significant measurement fluctuations in pressure sensors. In other words, temperature fluctuations demonstrably lead to measurement fluctuations, although it has not been clear until now which material or geometric parameters are influenced by these temperature fluctuations and are primarily responsible for the measurement fluctuations.

[0006] The current state of the art does not currently offer gel-coupled pressure sensor devices that reliably meet the high requirements of infusion pumps and dialysis machines (or other medical applications for blood or fluid pressure measurement in a tube) and are robust against temperature-dependent interference. The current state of the art therefore has the disadvantage that measurement fluctuations caused by temperature influences cannot be adequately compensated for in order to perform reliable and highly precise measurements using gel-coupled pressure sensor devices. Summary of the invention

[0007] Accordingly, it is the object of the present disclosure to provide a system as defined in claim 1, consisting of a fluid pressure hose and a pressure sensor device, which is or can be connected to the fluid pressure hose / infusion hose by means of gel-based coupling from the pressure transmission element, preferably a gel body, and can continuously perform precise measurements over the widest possible temperature range.

[0008] In the search for a solution to the technical problem, empirical tests have shown that the contact side geometry of the pressure transmission element, on which the hose is placed and on which a contact surface between the pressure transmission element and the hose is formed, has a great influence on the measuring accuracy in the pressure sensor device and that the contact surface formed on the contact side of the pressure transmission element can change significantly when the temperature changes.

[0009] Further tests have also shown that certain contact side geometries of pressure transmission elements form contact surfaces with the hose that change less under the influence of temperature than contact surfaces with other contact side geometries. In other words, the contact side geometry has a significant influence on how much the contact surface formed between the contact side and the hose changes under temperature fluctuations, thus triggering the corresponding measurement fluctuation.

[0010] It was concluded that the less the contact area changes with temperature changes, the more precisely the pressure force sensor can output voltages corresponding to the actual pressures prevailing in the hose. The observations made in the tests can be plausibly explained using the formula for pressure calculation P = F x A. If the contact area formed between the contact surface and the hose remains nearly constant, the pressure changes can be determined consistently and precisely using the measured force.

[0011] The tests carried out for the invention demonstrated that the measuring accuracy of the pressure sensor device was particularly higher when the contact surface of the contact side geometry of the pressure transmission element lying against the hose changed little when the temperature changed.

[0012] However, the known contact side geometries from the prior art, such as circular or teardrop-shaped along the tube direction as published in EP 1 269 145 B1, did not lead to the achievement of satisfactory measurement results of a gel-based pressure sensor device under temperature fluctuations.

[0013] Accordingly, the specific technical problem to solve the task at hand was to create a contact side geometry that, in conjunction with the remaining spatial pressure transmission element design, could form a contact surface to the hose that remained as constant as possible under temperature fluctuations.

[0014] This technical problem for solving the problem posed at the outset is specifically solved by a system consisting of a fluid pressure hose and a gel-coupled pressure sensor device according to claim 1. Advantageous further developments are the subject of the subclaims.

[0015] According to a first aspect of the invention, the system comprising the fluid pressure hose and the pressure sensor device comprises a gel stored in a pressure sensor housing as a pressure absorption and pressure transmission element, which gel has a bearing or contact side defining an insertion direction for the fluid pressure hose inserted into the pressure sensor device on a pressure introduction section freely projecting from the pressure sensor housing and extends from the contact side through the pressure sensor housing, preferably forming a funnel or stepped constriction, to a pressure force sensor. The contact side of the pressure introduction section has a shape symmetrical to both its longitudinal and transverse axes, and the longitudinal extent of the contact side parallel to the insertion direction is greater than in the transverse direction thereto.

[0016] A geometric shape with the proportions of the aforementioned contact side, which is larger in the longitudinal direction of the hose than in the circumferential direction and is symmetrical in both its longitudinal and transverse axes, offers the advantage of being able to compensate for associated material conditions even in the event of significant temperature fluctuations in the pressure sensor device's environment, while barely changing its overall surface area. At the same time, pressure changes occurring in the hose continue to be transmitted unaltered to the pressure transmission element and the connected pressure force sensor.

[0017] The axially symmetrical shape of the contact side, which runs along the longitudinal axis of the hose, ensures evenly distributed pressure transfer from the hose to both halves of the contact side. The axial symmetry with the transverse axis of the contact side also contributes to even pressure distribution along the longitudinal direction of the contact surface and prevents unevenly distributed stress states that can be caused by an asymmetric surface distribution.

[0018] Furthermore, according to a further aspect of the invention, it is preferably provided that the contact side of the pressure introduction section tapers in its longitudinal extension toward its respective ends. This further improves the above-described effect of greater resistance to temperature fluctuations.

[0019] According to a further aspect of the invention, the contact surface of the pressure introduction section can taper to a point in its longitudinal extent or have the shape of a rhombus.

[0020] Furthermore, the contact side can form an outer line without corners.

[0021] A contact side without corners offers the advantage that stress conditions between the hose and the pressure transmission element are distributed more evenly due to the rounded shape of the contact side than is the case in corner areas with pointed or angular transitions, so that the more even stress distribution also leads to less locally concentrated torsion of the contact side and the associated measurement distortions.

[0022] Furthermore, the contact side can have almost the shape of a rectangle, with transitions between the narrow side and the long side being curved.

[0023] An almost rectangular contact surface offers the advantage of creating as much contact surface as possible along a strip. At the same time, transition areas between the narrow and long sides designed as curves or radii offer the possibility of avoiding sharp or pointed corners, which can lead to locally concentrated stress states and thus to distortions and changes or falsifications in the measurement results.

[0024] Furthermore, the geometry of the contact side can taper continuously from its transverse axis to its ends.

[0025] In a further aspect, the geometry of the contact side may have the shape of an ellipse whose major or longitudinal axis is parallel to the longitudinal axis of the hose.

[0026] Experiments have shown that the geometry of an ellipse, in particular, proves to be extremely robust against temperature-induced surface changes and is therefore particularly preferred. In summary, and in other words, the invention of a first, particularly preferred embodiment is based on an elliptical geometry of the gel surface or gel contact side of a gel-coupled pressure sensor, which leads to an optimized tube-gel-sensor coupling in order to reduce the environmental dependence of the performance parameters, particularly due to temperature fluctuations.

[0027] The tube-sensor coupling is crucial for the sensor's performance, as existing sensors exhibit temperature dependencies, for example, due to unstable contact sides and contact surfaces as well as interfaces. In contrast, the state of the art does not consider the shape of the contact side and the resulting contact surface with regard to flexibility / consistent performance across the temperature range. Therefore, to date, there is no gel-coupled sensor that meets the requirements for high performance stability in active medical devices, such as infusion pumps and / or dialysis machines.

[0028] In order to reduce the temperature dependence of the pressure sensor device, according to the present disclosure, it is now essential to identify the optimal shape or geometry of the contact surface between the tube and the gel or gel pad in order to ensure a constant sensor output voltage due to an optimal and stable contact surface under different environmental conditions.

[0029] Due to temperature influences, the height of the gel in a gel-coupled pressure sensor device changes. Due to the change in height, the contact side and contact area between the gel and the tube are not constant. However, as already explained above, the contact area of ​​the tube has a direct influence on the output level of a gel-coupled pressure force sensor. An elongated side / surface shape in the longitudinal direction of the tube (with respect to the X and Y axes) that is axisymmetric and, in particular, an elliptical shape or geometry of the gel surface of a gel-coupled pressure sensor device unexpectedly leads to an optimized tube-gel-sensor coupling in order to reduce environmental dependencies (e.g., temperature drift) of the sensor output voltage. The resulting lower tolerances and lower output fluctuations open up new fields of application for this type of sensor, e.g., for infusion pumps and dialysis machines.

[0030] In a preferred arrangement, the tube lies exactly on the main axis of the elliptical contact side. The coupling surface or contact area between the pressure transmission element and the tube is and remains constant – even if the gel material in the pressure transmission element contracts or expands due to temperature changes.

[0031] For sealing and as a protective measure, a silicone cap and other separating materials, preferably in the form of membranes, can additionally be used in the pressure sensor device between the gel of the pressure transmission element and the hose, which, due to their comparatively thin wall thickness or material thickness, has no influence on the effects according to the disclosure.

[0032] In a particularly preferred aspect of the invention, the pressure sensor device can have an elliptical contact side, wherein the cross section of the pressure transmission element below the pressure introduction section tapers in a funnel shape, preferably monotonically decreasing in the direction of the pressure force sensor.

[0033] The elliptical contact side and the pressure transmission element with a funnel-shaped cross-section complement each other particularly well when combined. The elliptical contact side maintains its stable contact surface with the hose even under temperature changes, while the funnel-shaped cross-section is less affected by temperature fluctuations due to the reduced gel volume in the pressure transmission element. At the same time, the forces introduced from the contact side are transmitted to the pressure force sensor in a concentrated, smaller cross-section.

[0034] The combination of these two design features—namely, the elliptical contact surface and the funnel-shaped cross-section—increases both the measurement reliability and the measurement accuracy and sensitivity of the pressure sensor. The effects of these two design features thus interact synergistically, reducing the overall temperature dependence of the pressure sensor device.

[0035] The present disclosure is explained in more detail below using preferred embodiments with reference to the accompanying figures. Short description of the characters

[0036] Fig. 1 is a plan view of a pressure sensor unit 1 with a contact side geometry known from the prior art, Fig. 2 is a perspective view of the pressure sensor device according to a first embodiment of the present disclosure, Fig. 3 is a perspective view of the pressure sensor device according to the first embodiment with a detailed view of the pressure transmission element, Fig. 4 is a partial sectional view of the pressure sensor device according to the first embodiment with a cushion-like pressure introduction section of the pressure transmission element, which tapers monotonously in a funnel shape towards the pressure force sensor, Fig. 5 is a partial sectional view of a second embodiment with a cushion-like pressure introduction section of the pressure transmission element, wherein the pressure transmission element runs cylindrically below the pressure introduction section to the pressure force sensor, Fig. 6 is a plan view of the support body and of the contact side and contact surface of the pressure transmission element of the pressure sensor device, Fig. 7 is a partial sectional view of the pressure sensor device according to a third embodiment with a pressure transmission element with a stepwise constriction shape, Fig. 8 is a perspective view of the pressure sensor device according to a fourth embodiment, Fig. 9 is a perspective view of the hose of the pressure sensor device with the contact side highlighted, Fig. 10 is a sectional view perpendicular to the longitudinal axis of the hose of the pressure sensor device according to the fourth embodiment. Description of the embodiments

[0037] Embodiments of the present disclosure are described below based on the accompanying figures. The same elements are provided with the same reference numerals. Features of the individual embodiments may be interchanged.

[0038] In Fig. 1 A pressure sensor device 1 is shown with a pressure sensor housing 2 and a contact side 3 of a pressure transmission element 4. A fluid pressure hose 5, hereinafter referred to as the hose, is placed on the contact side 3 of the pressure transmission element 4. The geometry of the contact side 3 corresponds to known application geometries from the prior art.

[0039] Under favorable temperature conditions, a contact surface 3a is formed between the contact side 3 of the pressure transmission element 4 and the hose 5 over the entire surface of the contact side 3. However, during temperature fluctuations, the contact surface 3a formed between the pressure transmission element 4 and the hose 5 varies greatly, so that the contact surface 3a can be significantly smaller than the contact side 3, as shown in Fig. 1 shown. Due to these unwanted fluctuations in the surface characteristics of the contact surface 3a on the contact side 3 of the pressure transmission element, significant fluctuations in the measurement accuracy of the pressure sensor 1 occur in the prior art.

[0040] In Fig. 2 is a perspective view of a pressure sensor 1 according to the invention, which Fig. 1 The pressure sensor 1 has a pressure sensor housing 2 with a contact side 3 of a Fig. 3 shown in more detail pressure transmission element 4, on which a tube 5, preferably infusion tube 5, rests. Of particular note here is the elliptical geometry of contact side 3, which is extremely stable in relation to temperature fluctuations, so that the contact surface 3a formed between pressure transmission element 4 and tube 5 remains constant, almost corresponding to the surface of contact side 3.

[0041] In Fig. 3 The pressure sensor 1 according to the invention is shown without hose 5 and with a detailed view of the funnel-shaped pressure transmission element 4 removed from the pressure sensor housing 2. Depending on the embodiment, the funnel shape can be of different shapes and, for example, also have a stepwise constriction shape, as in Fig. 7 The pressure introduction section 6 of the pressure transmission element 4 located towards the hose can also be convex or concave in the direction of the hose 5, as shown in Fig. 5 and Fig. 7 shown.

[0042] In Fig. 4 The pressure sensor 1 of the first embodiment is shown in a partial sectional view along the longitudinal axis L of the tube 5, which itself is not cut. The tube 5 is made of a flexible material that is elastic and thus has a resilience. The cross-section of the tube 5 is round. A liquid, for example an infusion solution, is located in the tube 5 and is supplied to a patient. As can be seen from Fig. 4 As can be seen, the hose 5 rests only indirectly on the pressure sensor housing 2 and rests directly on a cushion-like, freely projecting pressure introduction section 6 of the pressure transmission element 4. The pressure transmission element 4 extends from a contact side 3 on the pressure introduction section 6, via which the hose 5 rests on the pressure transmission element 4, in a funnel shape and with an elliptical base area through the pressure sensor housing 2 and is supported on a circuit board 8 and a pressure force sensor 9 arranged thereon.

[0043] The pressure force sensor 9 can, for example, comprise strain gauges connected in a bridge circuit or a piezo pressure force sensor. Both the strain gauges and the piezo pressure force sensor generate an electrical signal that is proportional to the force F acting on the pressure force sensor 9.

[0044] If pressure changes occur in the hose 5, for example due to changes in the composition of the fluid or due to a kink in the hose 5, these changes are absorbed via the contact side 3 of the pressure transmission element 4 and transmitted via the gel-like force transmission medium 4 to the pressure force sensor 9, which emits an electrical, measurable signal proportional to the acting force.

[0045] The pressure transmission element 4 is preferably made of incompressible gel, which is particularly well suited for force transmission between the tube 5 and the pressure force sensor 9. However, temperature fluctuations can have a significant impact on the volume of the pressure transmission element 4, so that the height of the gel in the pressure transmission element 4 can change. Due to the change in height, the contact side 3 and contact surface 3a between the gel and the tube are not constant in the geometries used to date in the prior art.

[0046] Due to the elliptical coupling surface 3 or contact side 3 according to the invention, the contact surface 3a formed between contact side 3 and tube 5 remains constant, even when the gel material contracts or expands due to temperature changes. This makes it possible to achieve precise measurement results even under varying temperature influences, meeting the high standards for infusion and dialysis applications in terms of measurement accuracy.

[0047] In particular, the funnel-shaped, monotonically decreasing cross-section of the pressure transmission element 4 of the first embodiment of the pressure sensor 1 allows, on the one hand, the design of a relatively large contact side 3 on the pressure introduction section 6 towards the hose 5 and, on the other hand, a significant cross-sectional taper in the direction of the pressure force sensor 9, so that the support area of ​​the pressure transmission element 4 around the pressure force sensor 9 is kept as small as possible. With the funnel shape of the cross-section of the pressure transmission element 4, pressure changes in the hose 5 can thus be detected over a relatively large area and, thanks to the tapered cross-section of the funnel shape, these changes can be transmitted to the pressure force sensor 9 in the most concentrated way possible, without a significant portion of the transmitted forces being introduced into the peripheral area around the pressure force sensor 9.The funnel-shaped cross-section of the pressure transmission element 4 thus contributes to the pressure force sensor 9 being able to measure with high sensitivity.

[0048] A further advantageous effect of the funnel-shaped cross-section is that gel volume can be saved in the pressure transmission element 4, compared to a pressure transmission element 4 with a constant cross-section from contact side 3 to pressure force sensor 9. The volume reduction of the temperature-dependent gel in the pressure transmission element 4 thus reduces the sensitivity of the pressure sensor 1 to temperature changes and increases the measurement reliability.

[0049] Overall, it can be said that the positive effects of the elliptical contact side 3 and the funnel-shaped cross-section of the pressure transmission element 4 complement each other. The elliptical contact side 3 stably maintains its contact surface 3a with the hose 5 under temperature changes, while the funnel-shaped cross-section is less affected by temperature fluctuations due to the reduced gel volume in the pressure transmission element 4 and simultaneously transmits the forces introduced from the contact side 3 to the pressure force sensor in a concentrated manner.

[0050] In Fig. 5 the pressure sensor unit 1 of a second embodiment is shown in a partial sectional view along the longitudinal axis L of the hose 5, which itself is not cut. As can be seen from Fig. 5 As can be seen, the hose 5 rests only indirectly on the pressure sensor housing 2 and rests directly on a cushion-like, freely projecting pressure introduction section 6 of the pressure transmission element 4. The pressure transmission element 4 extends below the cushion-like pressure introduction section 6 with a constant cylindrical cross-section and an elliptical basic shape (seen from above) through to the pressure sensor housing 2 and is supported on a circuit board 8 and a pressure force sensor 9 arranged thereon.

[0051] In Fig. 6 The cross-section of the contact side 3 is shown in a top view against the background of the pressure sensor housing 2. The main axis H of the ellipse formed by the contact side 3 is parallel to the longitudinal axis L (in Fig. 6 not shown) of the hose 5, whereby pressure changes in the hose 5 are distributed evenly on both sides of the main axis H of the ellipse of the contact side 3. The contact side 3 has almost the same area as the contact surface 3a formed between the pressure transmission element 4 and the hose 5, as in Fig. 6 shown.

[0052] In Fig. 7 The pressure sensor unit 1 of a second embodiment is shown in a partial sectional view along the longitudinal axis L of the tube 5, which itself is not cut. The pressure transmission element 4 is designed in a funnel-like, stepwise constriction shape with a significantly reduced gel volume compared to the first embodiment.

[0053] The pressure introduction section 6 of the pressure transmission means 4 is concavely curved into the pressure sensor housing 2, and the cross-section of the pressure transmission element 4 below the contact side 3 is shaped in a narrow cylindrical manner to the pressure force sensor 9. The volume reduction of the gel in the pressure transmission element 4 represents a further possibility for reducing the temperature influence on the temperature-dependent gel volume of the pressure transmission element 4 and for better controlling or compensating for associated changes in the material states. Furthermore, the comparatively narrow cylindrical cross-section reduces the support surface of the gel around the pressure force sensor 9, whereby the force transmission takes place in a more concentrated manner on the pressure force sensor 9, thus making it possible to increase the pressure sensor sensitivity.

[0054] In Fig. 8 a fourth embodiment of the pressure sensor device 1 is shown, in which the pressure sensor housing 2 as well as the pressure transmission element 4 and the pressure force sensor 9 are fluid-tight and protected from contamination by a silicone cap 7.

[0055] As in Fig. 9 As can be seen, the hose 5 is also placed on the silicone cap 7 with an elliptical contact side 3.

[0056] In Fig. 10The pressure sensor device 1 of the fourth embodiment is shown in section perpendicular to the longitudinal axis L of the hose 5. In contrast to the first, second, and third embodiments of the pressure sensor device 1, the hose 5 in the fourth embodiment is only indirectly placed on the pressure transmission element 4 and directly placed on the silicone cap 7. The pressure changes occurring in the hose 5 are transmitted via the elastic silicone cap to the pressure transmission element 4 connected underneath and extending through the pressure sensor housing 2, and to the pressure force sensor 9 located on the circuit board 8. The functioning of the pressure sensor device 1 of the third embodiment is identical to the functioning of the pressure sensor device 1 of the first and second embodiments, apart from the additional cover and force transmission through the silicone cap 7.

Claims

1. A system consisting of a fluid pressure hose (5) and a pressure sensor device (1) with a gel (4) mounted in a pressure sensor housing (2) as pressure absorption and pressure transmission element (4), which has, on its pressure inlet portion (6) projecting freely from the pressure sensor housing (2), an abutment or contact side (3) defining an insertion direction for the fluid pressure hose (5) inserted into the pressure sensor device (1) and, starting from the contact side (3), extends through the pressure sensor housing (2), preferably configuring a funnel or stepwise constriction shape, up to a compressive force sensor (9), wherein the contact side (3) of the pressure inlet portion (6) has a symmetrical shape both to its longitudinal axis and to its transverse axis, characterized in that the longitudinal extent of the contact side (3) parallel to the insertion direction is greater than in the transverse direction thereto.

2. The system according to claim 1, characterized in that the contact side (3) of the pressure inlet portion (6) tapers in its longitudinal extension towards its respective ends.

3. The system according to claim 1 or 2, characterized in that the contact side (3) of the pressure inlet portion (6), tapers to a point in its longitudinal extent or has the shape of a rhombus.

4. The system according to claim 1 or 2, characterized in that the contact side (3) forms an outer line without corners.

5. The system according to claim 1 or 2, characterized in that the contact side (3) has almost the shape of a rectangle, wherein transitions between narrow side and long side are arc-shaped.

6. The system according to claim 1 or 2, characterized in that the geometry of the contact side (3) tapers continuously from its transverse axis towards its ends.

7. The system according to claim 1 or 2, characterized in that the geometry of the contact side (3) has the shape of an ellipse.

8. The system according to claim 7, characterized in that the main or longitudinal axis (H) of the contact side (3) runs parallel to the longitudinal axis (L) of the insertable hose (5).

9. The system according to one of claims 1 to 8, characterized by a silicone cap (7) and preferably further separating materials, preferably in the form of membranes, which are arranged between the pressure transmission element (4) and the hose (5) for sealing and as a protective measure.

10. The system according to claim 7 or 8, characterized in that the cross-section of the pressure transmission element (4) below the pressure inlet portion (6) tapers in a funnel-shaped, preferably monotonously decreasing manner in the direction of the compressive force sensor (9).