Flowmeter for fluids.

p0001The invention relates to a flow measuring device for fluids, or the like according to the preamble of claim 1.

p0002The metering of infusion liquids is done conventionally via a controllable infusion pump, which naturally makes only an indirect detection of the pumped volume. Known infusion devices also work on the principle of an infusion Tropfes; they contain drop sensors for example constructed photoelectric and register the presence of a drop and make a presence signal to a control, evaluation or monitoring device. This determined by integrating on the drops to flow. The drops are produced even in the drop sensor and bypassed by means of gravity on the sensor, which is arranged in a collecting vessel of the drop sensor.

p0003In addition to the disadvantage that drop sensors call for a vertical mounting position, they basically have the disadvantage that can not be accurately determined solely by counting the drops of throughput due to different drop sizes. It is therefore an approximate flow determination. The drop sensors have the further disadvantage that high Meßtotzeiten occur under certain circumstances as a result of the drop frequency, especially at a rate of only a few millimeters per hour. Furthermore, the often-sensitive sensor and the drop distance form an inseparable unity, but at least one unit, wherein the sensor comes in Berühung with the measured liquid flowing through. It is therefore before each new use costly sterilization required.

p0004From DE-PS 29 44 186 a further possibility is known, for example, infusion devices to determine the infusion liquid flow rate accurately. In this aforementioned type, the fact is exploited that, if not any other errors occur, the displacement and the speed of a volumetric pump directly proportional to the votes delivery is such that error-free operation can be ensured by means of a corresponding control in this way. Here a pump with a grid plate is coupled, which is scanned by a scanning device. The scanning device then generates a signal whose magnitude depends on the speed of the grid disc. This signal is woks to a control input of a microprocessor. With the aid of the raster plate and the scanning device is a signal may then be formed that is compared in the microprocessor with a desired signal for the flow rate. A control deviation leads to a corresponding change in the engine speed, for example a stepper motor. This usually means the actual flow volume is thus determined indirectly via the motor speed. For other possible sources of error, a drop sensor is provided in this rule means yet which also emits its signal to the microprocessor, which causes an error message when differences between this actual signal and the actual signal of the grid plate.

p0005Flow meter for liquid or gaseous fluids typically require a line arranged in the rotor, the rotational speed or speed of rotation depends on the rate of flow. The shaft of the rotor is guided over the wall of the conduit to the outside for the generation of a dependent of the shaft rotation measurement signal. If the fluid to be measured chemically aggressive, poisonous or radioactive, extremely good seals must be used for the shaft passage. In addition, the rotor constantly comes into contact with the fluid and needs to be cleaned or sterilized after use, which is associated with a corresponding expense. Finally, it is almost impossible to determine relatively accurately with conventional flowmeters very low flow rates.

p0006The invention has for its object to provide a flow measuring device for fluids, which does not require contact with the fluid and to measure even very small amounts of fluid relatively accurately regardless of their mounting position capable.

p0007This object is solved by the features of the characterizing part of claim 1.

p0008The flow measuring device according to the invention provides in the wake of the flow path in front of at least two pressure chambers which are connected to each other via a calibrated passage. Each pressure chamber is associated with a transducer which measures the pressure in the pressure chamber. The flow measuring device according to the invention is based on the known relationship that the flow rate can be determined when the pressure in the two pressure chambers is measured and the passage between the pressure chambers has a known geometry. The formula is: Flow rate = (π Δ PR⁴) / (8 γl) wherein Δ P is the pressure difference between the pressures in the pressure chambers, R is the radius of the passageway, the kinematic viscosity of the fluid l and γ, the length of the passageway.

p0009The passageway may be formed by a pinhole. Alternatively, a channel-shaped passage are provided in the form of a tube or the like.

p0010There are various structural possibilities are conceivable to measure the pressure in the pressure chambers by means of a pressure sensor. An embodiment of the invention provides that the compression chambers include a resilient wall section and the transducer associated with the resilient wall section for measuring the deflection of the wall portion. The compliant wall portion can be mounted rigidly, but movable in itself. Alternatively can be formed by a preferably thin membrane according to one embodiment of the invention, the wall portion which is substantially flat in the unloaded state. When building up the pressure in the pressure chamber, the diaphragm is bulged outwardly. The deflection of the wall section or the membrane can be detected by means of suitable pressure sensors.

p0011The formation of the deflection of the resilient wall portion identified transducer allows for various possibilities. One is according to the invention is that the transducer also has a flexible wall section, preferably a sensing diaphragm communicating with the membrane or the flexible wall portion of a pressure chamber in contact and which in turn is in operative contact with the sensing face of the transducer or a pressure measuring device.

p0012A particularly advantageous construction of the transducer is the invention is that the compliant WALL COMP cut or a sensing diaphragm formed of rigid walls of the transducer cavity closes, which is associated with the sensing face of the transducer and the pressure gauge. A change in position of the sensing diaphragm and the flexible wall portion leads to a change in pressure of the fluid in the closed cavity, which is manifested in the response or action face of the transducer and the pressure gauge. Preferably, the cavity is filled with a measuring liquid. Because of the liquid Imkompressibilität a deflection of the wall section and the sensing diaphragm is transmitted directly to the sensing face of the transducer. The sensing diaphragm is arched when not in contact with the resilient wall portion of the pressure chamber preferably under tension outwards. When putting on the flexible wall portion of the sensing diaphragm is deformed back, but in the case of measuring liquid in the cavity an alternative must be sought. This consists, for example, in a surge tank, preferably in the form of an elastic balloon that is connected via a stop valve having a connecting line with the cavity.

p0013In an alternative embodiment of the invention belonging to the pressure chambers membranes made of thin elastic piezoelectrically verhaltendem material are formed to produce a deflection of the membrane corresponding signal.

p0014With the help of the flow measuring device according to the invention can be a lot of measuring very low values, for example 0.1 ml / h to a few l / s with the same arrangement are measured. For larger flow rates, a measurement can indeed on the same principle to perform, but it requires a slightly modified apparatus.

p0015Particularly advantageous in the inventive apparatus is the fact that there is no direct connection between the coming into contact with the fluid parts of the apparatus and the transducer or the pressure measuring device; the pressure chambers to the connecting passage to be trained in the form of a cell, which is formed for example of plastics material. They can be replaced after use readily thrown away and by another, while the relatively expensive measuring device can remain in use and also does not have to be cleaned or sterilized.

p0016A main area of ​​application of the flowmeter according to the invention extends to the tax arrangements for medical infusion pumps. However, it can also be used for other metering pumps, especially those containing dangerous fluids, such as toxic, chemically corrosive, radioactive or like support fluids. In any case, a safe, accurate and reliable Durchflußmengenmessung is made possible, which is, above all, in the medical application of great importance. The inventive device can be designed independently of the infusion pump and are therefore used in conjunction with conventional infusion pumps. The inventive device can, however, also be provided with a customized infusion pump. This will be discussed in more detail below.

p0017As already stated, the inventive device can also be provided with more than two pressure chambers. By the pressure difference between more than two pressure chambers is measured irregularities can be easily found, which consist, for example, that not all pressure sensors operate reliably or the evaluation device contains an error.

p0018It is understood that the pressure chambers are formed so, in particular at its outlet end, that irrespective of the position of the measuring device the accumulation of air bubbles is avoided, which would otherwise cause a measuring error.

p0019In a further embodiment of the invention it is provided that, viewed in the flow direction of the first pressure chamber, a prechamber is arranged upstream of the volume of which is greater than the volume of the pressure chamber and the downstream output line downstream of the last pressure chamber, the inlet of the pre-chamber a closure device and the pre-chamber a the working volume of the antechamber is assigned minifying Pumpvorichtung. When used in an infusion system usually the pipe system is filled with infusion fluid before a connection to the infusion pump is performed. Since the diameter of the calibrated passage is relatively small and the fluid normally flows by gravity, it would require a relatively large time until the entire pipe system is filled. For this purpose the prechamber is provided. These can be filled in the usual way by gravity relatively quickly with liquid. Subsequently, the pre-chamber is closed, and for example, by a pressure to the elastic wall is preferably provided with pre-chamber in the liquid transported out of it in the following pressure chambers and the subsequent piping system. Subsequently, the system can be connected in known manner to the infusion pump. It is understood that, for example, a piston for varying the working volume of the pre-chamber and for actuating a clamp for clamping the tubing can be automatically operated before the pre-chamber by means of appropriate actuators, in order to ensure a fast and faultless operation of the infusion system.

p0020The pre-chamber can be closed by a further embodiment of the invention also by an elastomeric stopper or septum. The liquid can be filled in this way with the aid of an injection syringe in the pre-chamber by the injection needle is pricked through the septum. A, for example, for reducing the volume of the pre-chamber piston provided then presses, as described above, the liquid in the system. In this way, the system can also be used as an injection pump, in particular as so-called preferably portable micropump. The piston is driven, for example, mecha nically, electromagnetically, hydraulically or pneumatically and can be used to empty the pre-chamber, and thus for injecting the liquid for instance in the human body. The advantage of a thus constructed micropump is compared to previously known pumps is that the fluid can be conveyed with great accuracy and very uniform, especially for small amounts of liquid from 0.1 ml / h.

p0021The invention will now be described with reference to embodiments shown in drawings.<ul><li>Fig. 1 shows a plan view of a schematically illustrated measuring section of the flowmeter according to the invention.</li><li>Fig. 2 shows a side view of the test section of Fig. 1 with associated pressure transducers.</li><li>Fig. 3 shows a view similar to Fig. 2, but after emplacement of the pressure transducer.</li><li>Fig. 4 shows a side view of a modified test section of the device according to the invention. </li><li>Fig. Figure 5 shows another side view of part of the test section of Fig. 4 with additional support and actuator.</li><li>Fig. Figure 6 shows a view similar to Fig. 4, but with slight modification.</li><li>Fig. 7 shows a view similar to Fig. 5, but as a side view of Fig. 6.</li></ul>

p0022Before discussing the details shown in the drawings, was preceded by that of each of the features described may be alone or in combination with features of the claims of the invention is essential. Furthermore, it is emphasized that the drawings are very schematic way and not to scale.

p0023In Fig. 1 a plastic housing 10 can be seen, are formed in the two pressure chambers 11, 12 with concave walls, which are to prevent the accumulation of air bubbles in particular in the output area. The pressure chamber 11 is connected to an inlet port 13 and the pressure chamber 12 with an outlet fourteenth The chambers 11, 12 are connected via an aperture 15 with each other, the length L and the radius R are defined. The housing 10 with the chambers 11, 12, the aperture plate 15 and the connecting piece 13, 14 thus forms a measurement path in the form that the through-flowing quantity of liquid can be determined, when the pressure in the chambers 11, 12 is measured. The flow rate is calculated according to the above already mentioned formula: Flow rate = (π Δ PR⁴) / (8 γ l) wherein γ the viscosity of the fluid passing indicates.

p0024As is apparent from Fig. 2, the pressure chambers 11, 12 closed on one side by a flat thin diaphragm 20, 21. In FIG. 2, a transducer 30 is shown schematically. It has a rigid housing 31 having a cavity 32 formed in the lower region, which is closed at the bottom by a sensing diaphragm 33rd Via a channel 34 communicates the cavity 32 in connection with a pressure sensor 35 whose effective area of ​​the channel 34 is turned (not shown). The channel 34 communicates with a connecting line 36, in which a shut-off valve is arranged 37th The connection line 36 leading to a balloon 38. The entire system from cavity 32, the channels 34, 36 and the balloon 36 is filled with a measuring liquid. If the transducer 30 is set to, for example, the diaphragm 21 of the pressure chamber 12, the first prestressed bulging outward, sensing diaphragm 33 is deformed back, so that they with the diaphragm 21 of the pressure chamber 12 reaches approximately flat in engagement (see Fig. 3) Here, 37 is opened the stopcock. He will then shut off after the material displaced by returning deformation of the sensing diaphragm 33 volume was conveyed into the compensation tank 38th

p0025The deflection of the membranes 20, 21 of the pressure chambers 11, 12 is proportional to the pressure in the chambers 11, 12. This deflection is transmitted to the sensing diaphragm 33, which is coupled via the measuring liquid in the cavity 32 to the active surface of the sensor 35th In this way, it is possible without contact with the fluid in the chambers 11, 12 to make a very fine Durchflußmengenmessung. The pressure sensor may be of conventional design, and its measuring lines 39 lead to an appropriate evaluation or control device, for example, to regulate an infusion pump and to control and, if necessary, to allow a display of the flow rate. As can be seen, the pressure chamber 11 associated transducer is only indicated. It can be constructed in the same manner as the transducer 30th

p0026It should be noted that even very small deformations of the membranes 20, 21 and 33 lead to Meßausschlägen. Suddenly emerging higher pressures are not harmful because they are damped by the transducer 30th

p0027Fig. 4 shows a housing 40 similar to the housing 10 of Figures 1 to 3, are arranged in the three pressure chambers 41, 42, 43, which are connected to each other through pinhole 44 and 45, respectively. in turn make a measured distance corresponding to the above-described arrangement. Because of the three pressure chambers 41, 42, 43, here shown in a vertical arrangement, can be a pressure difference between the chambers 41, 42; 42, 43 and 41, 43 determine, so that a malfunction of a transducer or transmitter or the like can be readily determined by comparing the measured values. If the pressure differences: P42 - P41 = Δ P41, 42; P43 - P42 = Δ P 43, 42 and P43 - P41 = Δ P43, 41, are the following condition must be met if a vorgebener flow value is to be met: Δ P43, 41 = Δ P41, 42 + Δ P43, 42nd

p0028As seen from Fig. 4, is also a pre-chamber 46 disposed in the housing 40, which is located upstream of the first pressure chamber 43. Their volume is so great that it the volume of the three pressure chambers 41, 42, 43 and the downstream pipe system, for example, the infusion set is at least equal to,. Meaning the pre-chamber 46 is to facilitate the introduction of fluid or liquid into the pressure chambers and the downstream pipe. The relatively large-volume pre-chamber 46 can be filled, for example by gravity. As can be seen from FIG. 5, the pre-chamber 46 is provided with a resilient wall portion 47, which is 48 associated with a piston. The piston can be actuated by a mechanical, electromagnetic, hydraulic or pneumatic device (not shown). The inlet of the pre-chamber 46 is connected with a hose 49, a hose clamp which is associated with 50, which is also operable by an appropriate operation. The parts shown are located, as shown in Fig. 5, within a suitable housing or a holder 51. If the antechamber 46 is filled, for example, with an infusion liquid, the hose clamp is actuated 50 and thus shuts off the pre-chamber 46 from the input side. Subsequently, the piston 48 is operated, the liquid thereby the pushing out of the pre-chamber 46 and, in the pressure chambers 43, 42 and 41 into and in the subsequent tube system In this way, a faster filling of infusion liquid in the pressure chambers and the hose system to take place than would otherwise at normal gravity filling would be the case due to the relatively narrow aperture 44, 45th

p0029In FIG. 6, a housing 60 is illustrated, the housing 40 is similar to Fig. 4 substantially. It includes pressure chambers 61, 62, 63, which are connected to one another by diaphragms 64 and 65th Also, a pre-chamber 66 is provided, according to the pre-chamber 46 of FIG. 4. As so far consists accordance with the embodiment of FIG. 4, is then no longer be made ​​in detail. It is understood that the pressure chambers in accordance with the embodiment of FIG. 4 or FIG. 6 may be associated with pressure transducers, as shown for example in Fig. 2. Deviating from FIG. 4, the pre-chamber 66 is closed by a septum 67, for example, an elastomeric disk that can be pierced by the needle of a syringe easily. The housing 60 is in turn arranged in a suitable mount 68, which also comprises a piston 69, which is accordingly the piston 48 is formed and can be actuated in FIG. 5. With the help of a syringe can thus be 66 filled with infusion fluid the antechamber. By actuation of the piston 69, the fluid can be supplied in a desired amount by the pressure chambers 61 to 63 and the subsequent line, for example for metering the infusion liquid into the human body. With the help of the piston 69 can be to make a very precise dosage. By measuring pressure ung in the manner described above can be made ​​precise control of the liquid being pumped.