Measuring and testing – Liquid level or depth gauge
Reexamination Certificate
1998-04-02
2001-02-27
Williams, Hezron (Department: 2856)
Measuring and testing
Liquid level or depth gauge
C073S061440
Reexamination Certificate
active
06192752
ABSTRACT:
BACKGROUND
1. The Field of the Invention
The present invention relates generally to non-invasive techniques for detecting and characterizing the contents of containers. More specifically, the invention relates to non-invasive measurement of materials within a container using microwave technology.
2. The State of the Art
Medical science often requires that liquids be administered to a patient in a variety of situations. These liquids include simple intravenous feeding solutions, saline solutions for providing pressure to the eye during ocular surgery, contrast media infused to enhance imaging abilities, blood administered during transfusions, and nutrient solutions delivered via an enteral feeding pump. In virtually all such situations, it could be dangerous for the liquid supply to inadvertently “run dry.” In some applications, allowing the container to run dry may decrease the pressure of the liquid below that desired. In other situations, it can result in air entering the blood stream, causing complications or even death.
Several approaches have been suggested for monitoring containers of liquids so that inadvertent “running dry” can be avoided. For example, one system involves use of an electrical needle skewered into the bottom of a bottle containing liquid to be monitored. A constant electrical current is applied to the needle, and when the liquid level drops below the end of the needle, the break in the electrical current causes a lamp to light on a master control panel. A major disadvantage of this approach is that the fixed location of the needle results in a fixed triggering position. Thus, the user cannot select the liquid level at which the system will signal that the container needs to be refilled or replaced. And yet, the desired triggering position of the indicator may vary for different medical procedures. Additionally, some procedures may benefit from being able to vary the location at which the indicator signal reacts during different periods of the procedure.
An additional disadvantage of this system is that it is invasive. By placing the needle in the solution, the risk of contamination is increased.
Yet another disadvantage of such a system is that it is limited in the types of fluids which may be monitored therewith. For example, this system is designed to work with an ionic solution, but will not work with many solutions which are not ionic.
Other available systems have ultrasonic liquid level detectors for blood containers in which the transducer is placed against an exterior wall of the container. Ultrasonic signals are emitted into the container and reflected signals are used to determine when the liquid level has dropped below a designated point. The coupling between the transducer and container sidewall, however, requires that gel be placed on the sidewall to conduct the ultrasonic signals from the transducer into the container and from the container back into the transducer. This approach can be time consuming and messy as gel must be applied to the transducer or sidewall each time the two are coupled.
Other systems, such as that disclosed in U.S. Pat. No. 5,303,585, teach fluid volume sensors to determine the volume of gas or liquid within a container. However, the sensors transmit the signals to remote processing units which indicate to the user whether the volume of liquid is below the desired level.
All of these systems lack provision of a simple, non-invasive, inexpensive and disposable sensor which may be easily installed on the monitored container without cumbersome cables or coupling gel. Thus, there is a need for a simple, inexpensive and disposable sensor which may be quickly and conveniently applied to a container to be monitored.
A feature common to all of the sensor systems mentioned above is that the sensors are designed for placement on jars, bottles and containers which have rigid sidewalls. This limitation is due to the type of sensor being used. Specifically, the sensors are designed to detect signal reflections from the container sidewalls. The sensors also require reliable contact when mounted flush to the container to assure transfer of the majority of signal energy between the sensor and the container at all times.
Accordingly, there is a need for a sensor system which is versatile enough to accomplish liquid level detection, but which can also provide the capability of content characterization through analysis of signals. It would therefore be an advantage to be able to look at more than just reflected energy or energy loss from a sensor. While both of these energy signatures can provide useful information, it would be an advantage over the state of the art to generate electromagnetic fields which are perturbed or compressed, depending upon the nature of the container contents.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the present invention to provide a sensor which is capable of non-invasively detecting contents of containers.
It is another object to provide a sensor which is capable of non-invasively detecting a level of a fluid within a container.
It is another object to provide a sensor which is capable of non-invasively detecting condensation on a container wall.
It is another object to provide a sensor which is capable of non-invasively measuring flow rates of a fluid within a fluid line.
It is another object to provide a sensor which is capable of non-invasively characterizing properties within a container, including material purity, material density, material temperature, container pressure, material conductivity, etc.
It is another object to provide a sensor which is capable of non-invasively detecting leakage from a container.
It is another advantage to provide a sensor system which uses direct analog driving of human perceptible alarms, or conversion of analog data to digital data, and then using indirect driving of the human perceptible alarms.
It is another object to provide a sensor system which takes advantage of various configurations of multi-port couplers to characterize a container's contents.
It is another advantage to provide a sensor system of multi-port couplers which enable sensing of differences of the same container contents at different locations within a same container.
It is another advantage to provide a sensor system which uses common mode rejection ratio data to modify sensitivity of the sensor to external factors which can affect sensor readings.
It is another object to provide a sensor system which forms a balanced bridge which uses constructive and destructive interference at a sensor output port.
It is another object to provide a sensor system which contains a memory of previous sensors readings of container contents so that a comparison can be made between past and present sensor readings to thereby detect changes in the contents.
It is another object to provide a sensor system which can measure various attributes simultaneously.
It is another object to provide a sensor system which is capable of pattern recognition.
These and other objects of the invention are realized in a sensor system which can be used as a liquid level indicator for determining the level of liquid in a container, which includes a sensor mechanism powered by an electric current, a means for mounting the sensor to a container, a processing module, and a means for transmitting signals between the processing module and the sensor. The sensor is mountable by adhesive which is integral to the sensor at selectable locations on the exterior of the container.
In a first aspect of the invention, the sensor system generates a level detection signal which is applied to the container at the level at which the sensor mechanism is positioned and which indicates whether or not fluid in the container is above or below the level of the sensor. In particular, the processing module generates a human perceptible signal indicating whether the fluid is present at the same level as the sensor mechanism. The exact positioning of the sensor mechanism on the container depends on the application for which the fluid in the cont
Cygan Michael
Morriss Bateman O'Bryant & Compagni
Williams Hezron
Zevex, Inc.
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