Measuring and testing – Gas content of a liquid or a solid – By vibration
Patent
1997-07-03
2000-07-11
Chapman, John E.
Measuring and testing
Gas content of a liquid or a solid
By vibration
128DIG13, 600 67, G01N 2902
Patent
active
060855746
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a device for monitoring the flow of a liquid in a tubular duct.
More precisely, the monitoring device serves at least to detect the presence of bubbles of gas in the liquid flow, in particular when said tubular duct is the tube of a peristaltic pump.
There exist certain situations in which it is important to make sure that a liquid flowing in a duct does not accidentally entrain bubbles, and in particular air bubbles. This is particularly true of the medical field for ducts which serve to convey perfusion or other liquid for a patient.
In certain circumstances, the liquid is conveyed towards the perfusion needle in a duct, not merely under gravity, but with the help of a pump, e.g. a wheel or peristaltic pump. Such a pump is described, in particular, in French patent application No. 2 691 258 filed in the name of the Applicant. Such a disposition makes it possible to control more accurately the rate at which the liquid is injected. When using a pump, and regardless of the operating accuracy and leak-proofing it presents, it can always happen that there is an unacceptable quantity of air in the liquid, coming from an accidental insertion of air into the tank, from too great a quantity of air dissolved in the liquid, or possibly from an accidental cavitation effect causing bubbles of air to be entrained with the flowing liquid. It will naturally be understood that such a situation is completely unacceptable and that it is particularly important to be able to detect continuously any appearance of air bubbles in the duct, particularly at the outlet from the pump when such a device is designed to be able to interrupt the admission of the liquid.
In order to detect the possible presence of gas or air bubbles, proposals have already been made for optical detection systems. That is described, in particular, in the above-mentioned French patent application. Nevertheless, that optical detection can naturally only be used only when the liquid and the wall of the duct are translucent or substantially translucent.
To perform such detection, proposals have also been made to use ultrasound, given that it is known that the transmission coefficient or transmission impedance varies depending on the nature of the fluid, and thus varies depending on whether the liquid has no air bubbles or on the contrary includes air bubbles. In known ultrasound detection systems, a transmitter and a receiver are used which are constituted by piezoelectric cylinder disposed on either side of the tube, and the cylinders are excited in radial mode. That solution suffers from a first drawback which consists in the fact that, if the tube is placed in an environment that is itself liquid, the propagation of ultrasound due to the poorly-directional transmission from the piezoelectric cylinder is disturbed, thereby running the risk of allowing air bubbles to pass without being detected. Another drawback of such ultrasound transmitter/receiver devices is that, in order to obtain an ultrasound beam that is relatively directional, it is necessary to use relatively high excitation frequencies and consequently to perform detection on electric signals that are likewise at high frequency. Typically, these frequencies are greater than one megahertz and generally lying in the range 2 MHz and 5 MHz. As a result, the electrical and electronic environment of such detectors is relatively complex and thus expensive.
Advantageously, the present invention provides a device for monitoring the flow of a liquid in a duct, in particular for detecting bubbles of gas in the liquid. This device is very reliable while being of low cost and compact.
To achieve this aim, the device for monitoring the flow of a liquid in a tubular duct is characterized in that it comprises: orthogonal to said duct in the detection zone and which is mounted on said support structure to be disposed on a first side of said duct; predetermined frequency F in order to transmit ultrasound waves; that of the first cylinder and mounted on said support structure so as
REFERENCES:
patent: 4487601 (1984-12-01), Lindemann
patent: 5123275 (1992-06-01), Daoud et al.
Bouvier Bernard
Neftel Frederic
Chapman John E.
Debiotech S.A.
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