Measuring and testing – Fluid pressure gauge – Diaphragm
Patent
1994-06-09
1999-08-17
Dombroske, George
Measuring and testing
Fluid pressure gauge
Diaphragm
G01L 906
Patent
active
059396407
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention concerns pressure sensors and in particular their application to a pressure monitoring device in an infusion apparatus.
2. Description of Prior Art
Infusion pumps are used to inject medicamentous substances into a patient's body, usually intravascularly, but equally by other appropriate access channels.
It is useful to be able to monitor the flow pressure of the fluid as it comes down from the infusion pump, so as to detect any possible anomaly in the apparatus in operation. Indeed, various incidents may occur: the pump may race or adversely stop working, the catheter through which the medicamentous substance is injected may progressively close up with blood deposits, the infusion tube may be plicated, a leak may occur at any point in the infusion tube, etc . . .
Switches are currently used to monitor flow pressure in an infusion tube, but they work as a two-way system (on or off) and are activated by a substantial variation in pressure in relation to the nominal operating pressure. Such devices are not very precise, with measurement precision being of the order of 50% of the value of measured pressure. They are often used simply to control the shutting down of the motor driving the pump when the pressure exceeds a certain level.
Other more sophisticated devices are also known, such as those described in patents U.S. Pat. No. 4,446,344 and U.S. Pat. No. 4,431,425. The devices described in said patents comprise switches capable of not only stopping the motor when the pressure is too high but also restarting the motor once the pressure has descended to an acceptable value. However, there still remains the disadvantage of insufficient precision.
A device specially designed for the medical field is described in patent DE-A-2,461,424. Said device consists of a chamber filled with glycerine which transmits pressure to a sensor, said pressure being exerted on the wall of the sensor's chamber. Such a device with liquid (glycerine) as a pressure transmission fluid is difficult to use for measuring pressure in an infusion tube. Indeed, so that there may be an instantaneous reaction to variations of pressure in an infusion tube, it is necessary for the transmission fluid response to be linear, and such is not the case of liquid.
SUMMARY OF THE INVENTION
The purpose of this invention therefore is to propose a pressure measurement device which enables continuous and sufficiently precise measurement of fluid contained in an infusion tube.
Another purpose of the invention is to create a pressure measurement device in an infusion tube using a sensor with a linear response curve which reacts to variations in pressure.
The object of the invention therefore is a pressure measurement device consisting of a pressure sensor, a housing comprising at least one chamber with one side defined by a deformable membrane contacting the wall of the infusion tube and containing said sensor, with a fluid between the membrane and the sensor. Said fluid is non-liquid and has a Poisson ratio of at least 0.49 as well as an instantaneous modulus of elasticity of under 10 MPa so that the sensor response curve is linear.
In conformity with another characteristic, the fluid is a silicone gel.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Other characteristics and advantages of the invention shall become apparent in the following description given with references to the appended diagram which is presented purely as an example and provides a cross-section, schematic view of a sensor according to the invention, associated with an infusion tube.
In the diagram, part of an infusion apparatus is schematically represented comprising a pump with part 10 of its housing from which an infusion tube 12 is supplied which may be made of silicone, for example. A device according to this invention is used to continuously measure flow pressure in an infusion tube.
Said device comprises a housing 14 defining at least one chamber 16 with one of its walls formed by a deformable membrane 18. Said m
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patent: 5209125 (1993-05-01), Kalinoski et al.
IEEE Transactions on Electron Devices, vol. ED26, No. 12, Dec. 1979; J.M. Borky et al; "Integrated Signal Conditioning for Silicon Pressure Sensors".
Patent Abstracts of Japan; vol. 7, No. 10 (P-168); Pressure Wave Sensor; Rikoo Tokei K.K.
Siemens Forschungs-Und Entwicklungsberichte; V. 10, No. 2, 1981; pp. 72-77; F. Breimesser et al; "Piezoresistive Pressure Sensor With Silicon Diaphragm".
Soviet Inventions Illustrated; Week 8726, Jul. 6, 1993; SU 1270-593-A.
Dombroske George
Hancock Earl C.
Sirr Francis A.
Thompson Jewel V.
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