U.S. patent application number 09/734318 was filed with the patent office on 2001-08-23 for non-invasive electromagnetic fluid level sensor.
Invention is credited to Blaine, David.
Application Number | 20010015099 09/734318 |
Document ID | / |
Family ID | 27368622 |
Filed Date | 2001-08-23 |
United States Patent
Application |
20010015099 |
Kind Code |
A1 |
Blaine, David |
August 23, 2001 |
Non-invasive electromagnetic fluid level sensor
Abstract
A disposable sensor is disclosed for non-invasively detecting
and characterizing a container's contents. By generating microwave
frequency signals, electromagnetic fields are produced by a sensor
and penetrate a container. The EM fields are analyzed in regards to
how they are perturbed by the container contents. Analysis of the
perturbed EM fields enables determination of content level, content
purity, content density, content temperature, container pressure,
content conductivity, etc.
Inventors: |
Blaine, David; (Salt Lake
City, UT) |
Correspondence
Address: |
David W. O'Bryant
MORRISS, BATEMAN, O'BRYANT & COMPAGNI
Suite 300
5882 South 900 East
Salt Lake City
UT
84121
US
|
Family ID: |
27368622 |
Appl. No.: |
09/734318 |
Filed: |
December 1, 2000 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09734318 |
Dec 1, 2000 |
|
|
|
09054354 |
Apr 2, 1998 |
|
|
|
6192752 |
|
|
|
|
09054354 |
Apr 2, 1998 |
|
|
|
08831205 |
Apr 2, 1997 |
|
|
|
6023970 |
|
|
|
|
08831205 |
Apr 2, 1997 |
|
|
|
08511380 |
Aug 4, 1995 |
|
|
|
5789675 |
|
|
|
|
Current U.S.
Class: |
73/290R |
Current CPC
Class: |
G01F 23/284 20130101;
G01N 9/24 20130101; G01F 23/2845 20130101 |
Class at
Publication: |
73/290.00R |
International
Class: |
G01F 023/00 |
Claims
What is claimed is:
1. A sensor system for use in characterizing contents of a
container, wherein said sensor system analyzes microwave frequency
electromagnetic signals generated therefrom to thereby determine
characteristics of the container contents, said system comprising:
an electromagnetic sensor which is disposable on a container, and
which is capable of transmitting the microwave frequency
electromagnetic signals; a processing device which is electrically
coupled to the electromagnetic sensor, wherein the processing
device develops the microwave frequency electromagnetic signals to
be transmitted, analyzes the transmitted microwave frequency
electromagnetic signals to thereby detect perturbations therein,
and provide a human perceptible alarm when the detected
perturbations indicate that an alarm condition is met; and a power
supply for supplying electrical current to the sensor system.
2. The sensor system as defined in claim 1 wherein the processing
device is further comprised of: an oscillator which is electrically
coupled to the electromagnetic sensor, and which develops the
microwave frequency electromagnetic signals for transmission
therefrom; a detector circuit which is electrically coupled to the
electromagnetic sensor to thereby detect the perturbations in the
microwave frequency electromagnetic signals; and a controller for
activating the oscillator and the detector circuit when the
electromagnetic sensor is in a sensing mode, and for deactivating
the oscillator and the detector circuit when the sensor system is
in a sleep mode, and wherein a duration of the sensing and the
sleep modes is programmable.
3. The sensor system as defined in claim 2 wherein the processing
device is further comprised of: a digital signal processor (DSP)
which is electrically coupled to the detector circuit, wherein the
DSP filters data received therefrom so as to determine whether at
least one alarm condition is met, and which transmits a signal if
it is determined that the at least one alarm condition is met; and
a human perceptible alarm which is electrically coupled to the DSP
for receiving the signal indicating that the at least one alarm
condition is met, and which activates the human perceptible
alarm.
4. The sensor system as defined in claim 2 wherein the processing
device further comprises an analog driven human perceptible alarm
which is electrically coupled to the detector circuit, and which
receives a signal indicating that the at least one alarm condition
is met, and which activates the analog driven human perceptible
alarm in response to receiving the signal.
5. The sensor system as defined in claim 3 wherein the processing
device is further comprised of a data output port so that the
signal indicating that the at least one alarm condition is met can
be transmitted to a remote location.
6. The sensor system as defined in claim 1 wherein the
perturbations are manifested as a compression of electromagnetic
fields generated by the microwave frequency electromagnetic
sensor.
7. The sensor system as defined in claim 1 wherein the
electromagnetic sensor is coupled to the container by an adhesive
which binds a sensing surface of the electromagnetic sensor
generally flush against the container.
8. The sensor system as defined in claim 2 wherein the
electromagnetic sensor is further comprised of a microwave
frequency multi-port coupler which includes: an input port for
receiving from the processing device the microwave frequency
electromagnetic signals to be transmitted; and at least one output
port for detecting the perturbations in an electromagnetic field
generated by the transmitted microwave frequency signals and for
transmitting an output signal to the processing device.
9. The sensor system as defined in claim 8 wherein the input port
is interchangeable with at least one of the at least one output
ports.
10. The sensor system as defined in claim 8 wherein the microwave
frequency multi-port coupler is selected from the group of
microwave frequency multi-port couplers including 2-port, 3-port
and 4-port microwave frequency couplers.
11. The sensor system as defined in claim 10 wherein the microwave
frequency multi-port couplers which are suitable as the microwave
frequency electromagnetic sensor are formed on generally planar
surfaces as stripline traces.
12. The sensor system as defined in claim 11 wherein the microwave
frequency multi-port couplers are configured in a direct coupling
or parallel coupling arrangement.
13. The sensor system as defined in claim 2 wherein the oscillator
further comprises an oscillating transistor having a common-base
bipolar configuration, and which utilizes feedback to tune the
oscillator to a desired microwave frequency.
14. The sensor system as defined in claim 13 wherein the system
further comprises the oscillator having an output impedance which
generally matches an input impedance of the microwave frequency
electromagnetic sensor to thereby obtain maximum power transfer
therebetween.
15. The sensor system as defined in claim 13 wherein the
oscillating transistor is biased via a direct current (DC) voltage
through a current limiting resistor and a microwave frequency
blocking inductor.
16. The sensor system as defined in claim 13 wherein the controller
controls the sensing mode and the sleeping mode through a power
supply transistor which is caused to provide bias current to the
oscillating transistor when in sensing mode, and which is caused to
terminate the bias current to the oscillating transistor when in
sleeping mode.
17. The sensor system as defined in claim 8 wherein the detector
circuit is comprised of: a rectifying circuit which is electrically
coupled to the at least one output port to thereby receive and
rectify the output signal; and an integrating circuit which is
electrically coupled to an output of the rectifying circuit and
which integrates the rectified output signal to thereby develop an
output voltage which is proportional to an integral of the output
signal, and which is a measure of a degree of coupling in the
microwave frequency electromagnetic sensor.
18. The sensor system as defined in claim 17 wherein the rectifying
circuit is comprised of: a diode which when forward biased enables
the output signal to be rectified to thereby create a time-varying
DC current, and which is capable of operating at microwave
frequencies; and a biasing network which is electrically coupled to
an input of the diode and which causes the diode to be forward
biased when the sensor system is in the sensing mode.
19. The sensor system as defined in claim 18 wherein the detector
circuit further comprises: the integrator which is comprised of a
capacitor for generating a steady-state DC output voltage; and a
length of conductor between an output of the diode and the
capacitor, wherein the length of the conductor is a quarter
wavelength of the microwave frequency electromagnetic signals, so
that a zero impedance of the capacitor to microwave frequencies is
transformed to an infinite impedance as seen by the diode.
20. The sensor system as defined in claim 19 wherein the detector
circuit further comprises a resistor coupled to the diode output
and ground which bleeds off a charge on the capacitor so that a
voltage across the capacitor can be reduced as strength of the
output signal from the microwave frequency electromagnetic sensor
decreases.
21. The sensor system as defined in claim 20 wherein the detector
circuit further comprises the resistor having a value that when
combined with an impedance of the diode, a combined diode and
resistor impedance is generally equal to an output impedance of the
microwave frequency electromagnetic sensor.
22. The sensor system as defined in claim 21 wherein the detector
circuit further comprises a differential amplifier which is
electrically coupled to the integrator and a reference voltage, and
which receives as inputs the voltage across the capacitor of the
integrator, and a reference voltage.
23. The sensor system as defined in claim 22 wherein the detector
system further comprises an analog-to-digital (A/D) converter which
is electrically coupled to the differential amplifier and which
receives as input an output signal therefrom.
24. The sensor system as defined in claim 23 wherein the detector
system further comprises the DSP which is electrically coupled to
the A/D convertor and which receives as an input signal an output
signal therefrom.
25. The sensor system as defined in claim 24 wherein the DSP is a
programmable device for executing at least one algorithm to
accomplish error correction, noise filtering, signal enhancement,
pattern recognition and internal calibration.
26. The sensor system as defined in claim 24 wherein the DSP
further comprises filters for executing low-pass filtering,
high-pass filtering, non-linear filtering and combinations thereof
to enable reduction of environmental effects, microwave frequency
electromagnetic sensor sensitivity, liquid level detection, noise
reduction, edge enhancement, and increased sensitivity to
anticipated electromagnetic sensor output.
27. The sensor system as defined in claim 24 wherein the DSP is
electrically coupled to a human perceptible alarm system capable of
generating different alarms for different alarm conditions, wherein
the human perceptible alarm system receives input signals from the
DSP which indicate when an alarm condition exists, and what type of
alarm condition exists.
28. The sensor system as defined in claim 8 wherein the system
further comprises: a plurality of output ports on the microwave
frequency electromagnetic sensor; and a plurality of detector
circuits, wherein each of the plurality of detector circuits is
coupled to a corresponding one of the plurality of output ports to
thereby enable the sensor system to simultaneously detect different
alarm conditions.
29. The sensor system as defined in claim 10 wherein the sensor
system further comprises a sensor circuit having a high common mode
rejection ratio to thereby reduce sensor system sensitivity, said
sensor system comprising: the 3-port coupler used as the microwave
frequency electromagnetic sensor which has a first output port and
a second output port; and the detector circuit which processes each
signal from the first and the second output ports of the 3-port
coupler by rectifying, integrating, and then comparing the
rectified and integrated signals from the first and the second
output ports using a differential amplifier circuit which amplifies
any difference between each signal, wherein the detector circuit
will minimize an influence of external factors so that it can then
be determined whether an alarm condition exists.
30. The sensor system as defined in claim 29 wherein the
differential amplifier circuit includes: a first operational
amplifier which has coupled at a first positive terminal a first
voltage divider which divides a first signal from the first output
port, and which is also coupled to a first resistor which modifies
hysteresis, said operational amplifier also being coupled at an
output port to an opposite side of the first resistor, and to a
second resistor which modifies a gain of the first operational
amplifier, said operational amplifier also being coupled at a
negative terminal to an opposite side of the second resistor, and
to a third resistor which attenuates a second signal from the
second output port; a second operational amplifier which has
coupled at a second positive terminal a second voltage divider
which divides the second signal from the second output port, and
which is also coupled to a fourth resistor which modifies
hysteresis, said operational amplifier also being coupled at an
output port to an opposite side of the fourth resistor, and to a
fifth resistor which modifies a gain of the second operational
amplifier, said operational amplifier also being coupled at a
negative terminal to an opposite side of the fifth resistor, and to
a sixth resistor which attenuates the first signal from the first
output port; and wherein the output ports of the first and the
second operational amplifiers are compared to determine if they are
approximately equal.
31. A method for characterizing contents of a container using a
sensor system, wherein said method includes analyzing microwave
frequency electromagnetic signals which are generated by an
electromagnetic sensor to thereby determine characteristics of the
container contents, said method comprising the steps of: (1)
disposing the electromagnetic sensor, which is capable of
transmitting the microwave frequency electromagnetic signals, on a
container; (2) developing the microwave frequency electromagnetic
signals in a processing device which is electrically coupled to the
electromagnetic sensor, and transmitting said signals from the
electromagnetic sensor; (3) analyzing the transmitted microwave
frequency electromagnetic signals to thereby detect perturbations
therein; and (4) providing a human perceptible alarm when the
detected perturbations indicate that an alarm condition is met.
32. The method as defined in claim 31 wherein the method further
comprises the steps of: (1) generating a microwave frequency
utilizing an oscillator which is electrically coupled to the
electromagnetic sensor, and which develops the microwave frequency
electromagnetic signals for transmission therefrom; (2) utilizing a
detector circuit which is electrically coupled to the
electromagnetic sensor to thereby detect the perturbations in the
microwave frequency electromagnetic signals; (3) activating the
oscillator and the detector circuit when the electromagnetic sensor
is in a sensing mode; and (4) deactivating the oscillator and the
detector circuit when the sensor system is in a sleep mode.
33. The method as defined in claim 32 wherein the method further
comprises the step of programming a duration of the sensing modes
and the sleep modes to thereby limit energy consumption when the
sensor is used as a stand-alone device.
34. The method as defined in claim 32 wherein the method further
comprises the steps of: (1) filtering data from the detector
circuit through a digital signal processor (DSP) so as to determine
whether at least one alarm condition is met; (2) transmitting a
signal from the DSP if it is determined that the at least one alarm
condition is met; and (3) generating a human perceptible alarm in
response to the signal from the DSP, thereby indicating that the at
least one alarm condition is met.
35. The method as defined in claim 32 wherein the method further
comprises the step of activating an analog driven human perceptible
alarm directly from the detector circuit when the detector circuit
determines that at least one alarm condition is met.
36. The method as defined in claim 34 wherein the method further
comprises the step of transmitting the signal indicating that the
at least one alarm condition is met to a remote location.
37. The method as defined in claim 31 wherein the step of detecting
perturbations more specifically comprises the step of detecting a
compression of electromagnetic fields generated by the microwave
frequency electromagnetic sensor, wherein a degree of compression
indicates properties of the contents.
38. The method as defined in claim 31 wherein the method further
comprises the step of coupling the electromagnetic sensor to the
container by an adhesive which binds a sensing surface of the
electromagnetic sensor generally flush against the container.
39. The method as defined in claim 32 wherein the method further
comprises the step of utilizing a multi-port coupler as the
microwave frequency electromagnetic sensor, wherein the multi-port
coupler includes an input port for receiving from the processing
device the microwave frequency electromagnetic signals to be
transmitted, and at least one output port for detecting the
perturbations in an electromagnetic field generated by the
transmitted microwave frequency signals and for transmitting an
output signal to the processing device.
40. The method as defined in claim 39 wherein the method further
comprises the step of interchanging the input port with the at
least one output port when desired.
41. The method as defined in claim 39 wherein the method further
comprises the step of selecting the microwave frequency multi-port
coupler from the group of microwave frequency multi-port couplers
including 2-port, 3-port and 4-port microwave frequency
couplers.
42. The method as defined in claim 41 wherein the method further
comprises the step of configuring the microwave frequency
multi-port couplers in a direct coupling or parallel coupling
arrangement.
43. The method as defined in claim 32 wherein the method further
comprises the step of generating microwave frequencies utilizing a
transistor having adjustable feedback to modify the microwave
frequency being generated.
44. The method as defined in claim 43 wherein the method further
comprises the step of biasing the transistor via a direct current
(DC) voltage through a current limiting resistor and a microwave
frequency blocking inductor.
45. The method as defined in claim 43 wherein the method further
comprises the step of controlling the sensing mode and the sleeping
mode through a power supply transistor which is caused to provide
bias current to the transistor when in sensing mode, and which is
caused to terminate the bias current to the transistor when in
sleeping mode.
46. The method as defined in claim 39 wherein the method further
comprises the steps of: (1) rectifying a signal from the at least
one output port to thereby create a signal having a time-varying DC
current; and (2) integrating the signal having the time-varying DC
current to thereby develop an output voltage which is proportional
to an integral of the output signal, and which is a measure of a
degree of coupling in the microwave frequency electromagnetic
sensor.
47. The method as defined in claim 46 wherein the method further
comprises the steps of: (1) rectifying the signal from the at least
one output port through a diode which is forward biased and
operates at microwave frequencies; and (2) forward biasing the
diode when the sensor system is in the sensing mode.
48. The method as defined in claim 47 wherein the method further
comprises the steps of: (1) integrating the time-varying DC signal
using a capacitor to thereby generate a steady-state DC output
voltage; and (2) preventing excessive loading on the sensor system
by inserting a length of conductor between an output of the diode
and the capacitor which is a quarter wavelength of the microwave
frequency electromagnetic signals, so that a zero impedance of the
capacitor to microwave frequencies is transformed to an infinite
impedance as seen by the diode
49. The method as defined in claim 48 wherein the method further
comprises the step of bleeding off a charge on the capacitor so
that a voltage across the capacitor can be reduced as strength of
the output signal from the microwave frequency electromagnetic
sensor decreases.
50. The method as defined in claim 49 wherein the method further
comprises the step of matching an output impedance of the
electromagnetic sensor with an input impedance of the detector
circuit by selecting the resistor to have a value which when
combined with an impedance of the diode results in the input
impedance being generally equal to the output impedance of the
microwave frequency electromagnetic sensor.
51. The method as defined in claim 50 wherein the method further
comprises the step of obtaining a signal which is generally
proportional to a coupling coefficient of the electromagnetic
sensor by electrically coupling a differential amplifier to the
integrator and a reference voltage so that the differential
amplifier receives as inputs the voltage across the capacitor of
the integrator, and a reference voltage.
52. The method as defined in claim 51 wherein the method further
comprises the step of generating a digital output signal
representative of the coupling coefficient by electrically coupling
an analog-to-digital (A/D) converter to the differential
amplifier.
53. The method as defined in claim 52 wherein the method further
comprises the step of digitally processing the digital output
signal from the A/D converter using a digital signal processor to
thereby accomplish error correction, noise filtering, signal
enhancement, pattern recognition and internal calibration.
54. The method as defined in claim 53 wherein the method further
comprises the steps of: (1) filtering the digital output signal
from the A/D converter utilizing low-pass filtering to reduce
environmental effects and to modify electromagnetic sensor
sensitivity; (2) filtering the digital output signal from the A/D
converter utilizing high-pass filtering to increase sensitivity to
rapidly occurring events; and (3) filtering the digital output
signal from the A/D converter utilizing non-linear filtering and
combinations of low-pass, high-pass and non-linear filtering to
enable liquid level detection, edge enhancement, and increased
sensitivity to anticipated electromagnetic sensor output.
55. The method as defined in claim 53 wherein the method further
comprises the step of generating a selectable human perceptible
alarm depending upon which alarm condition is indicated as being
received from the digital signal processor.
56. The method as defined in claim 55 wherein the method further
comprises the step of simultaneously checking for a plurality of
different alarm conditions, all of which can trigger an alarm
event, by providing a plurality of output ports on the
electromagnetic sensor.
57. The method as defined in claim 56 wherein the method further
comprises the step of generating a plurality of different human
perceptible alarms, each of which is indicative of a different
alarm condition.
58. The method as defined in claim 39 wherein the method further
comprises the step of providing a sensor system having a high
common mode rejection ratio to thereby reduce sensor system
sensitivity, wherein the sensor system includes the 3-port coupler
used as the microwave frequency electromagnetic sensor which has a
first output port and a second output port, and wherein the
detector circuit processes each signal from the first and the
second output ports of the 3-port coupler by rectifying,
integrating, and then comparing the rectified and integrated
signals from the first and the second output ports using a
differential amplifier circuit which amplifies any difference
between each signal, wherein the detector circuit will minimize an
influence of external factors so that the detector circuit can
determine whether an alarm condition exists.
59. The method as defined in claim 51 wherein the method further
comprises the step of quantifying the coupling coefficient using
the following equation: 2 c = 10 log p ( in ) p ( out ) , ( out ) -
( in ) where p(in) is a magnitude and .O slashed.(in) is a phase of
input power, and p(out) and .O slashed.(out) are a measurable
output power and phase, respectively.
60. A method for characterizing contents within a container,
wherein said method includes analyzing microwave frequency
electromagnetic signals which are generated by an electromagnetic
sensor element to thereby determine characteristics of the
container contents, said method comprising the steps of: (1)
selecting a multi-port coupler as the electromagnetic sensor
element which generates the microwave frequency electromagnetic
signals; (2) disposing the multi-port coupler on the container; (3)
developing the microwave frequency electromagnetic signals in a
processing device which is electrically coupled to the multi-port
coupler, and transmitting said signals therefrom as electromagnetic
fields; and (4) analyzing a degree of compression of the
electromagnetic fields to thereby characterize the container
contents.
61. The method as defined in claim 60 wherein the method further
comprises the step of generating a human perceptible alarm when the
degree of compression of the electromagnetic fields passes a
predetermined threshold of compression which is indicative of a
predetermined alarm condition.
Description
FILE HISTORY
[0001] This patent application is a continuation-in-part of U.S.
patent application Ser. No. 08/831,205 filed Apr. 2, 1997, which is
a continuation-in-part of U.S. patent application Ser. No.
08/511,380, filed Aug. 4, 1995.
BACKGROUND
[0002] 1. The Field of the Invention
[0003] 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.
[0004] 2. The State of the Art
[0005] 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.
[0006] 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.
[0007] An additional disadvantage of this system is that it is
invasive. By placing the needle in the solution, the risk of
contamination is increased.
[0008] 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.
[0009] 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.
[0010] 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.
[0011] 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.
[0012] 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.
[0013] 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
[0014] It is an object of the present invention to provide a sensor
which is capable of non-invasively detecting contents of
containers.
[0015] It is another object to provide a sensor which is capable of
non-invasively detecting a level of a fluid within a container.
[0016] It is another object to provide a sensor which is capable of
non-invasively detecting condensation on a container wall.
[0017] It is another object to provide a sensor which is capable of
non-invasively measuring flow rates of a fluid within a fluid
line.
[0018] 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.
[0019] It is another object to provide a sensor which is capable of
non-invasively detecting leakage from a container.
[0020] 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.
[0021] 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.
[0022] 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.
[0023] 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.
[0024] 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.
[0025] 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.
[0026] It is another object to provide a sensor system which can
measure various attributes simultaneously.
[0027] It is another object to provide a sensor system which is
capable of pattern recognition.
[0028] 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.
[0029] 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 container is
used.
[0030] In a second aspect of the invention, the sensor system is
capable of non-invasively detecting and characterizing a
container's contents. By generating microwave frequency signals,
electromagnetic fields are produced by a sensor and penetrate the
container. The EM fields are analyzed in regards to how they are
perturbed by the container's contents, the results of which enables
characterization thereof.
[0031] In a third aspect of the invention, the advantages of
different sensor coupler configurations are taught so that more
information can be obtained regarding the container's contents.
[0032] These and other objects, features, advantages and
alternative aspects of the present invention will become apparent
to those skilled in the art from a consideration of the following
detailed description taken in combination with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] FIG. 1 shows a plan view of the disposable fluid level
sensor with an accompanying processing module, made in accordance
with the present invention;
[0034] FIG. 2 shows a side view of the disposable fluid level
sensor with the accompanying processing module of FIG. 1;
[0035] FIG. 3 shows a plan view of the flex circuit electromagnetic
sensor of the present invention; and
[0036] FIG. 4 shows a side view of the flex circuit shown in FIG.
3.
[0037] FIG. 5 is a block diagram which shows the components of the
sensor system described in a preferred embodiment which is made in
accordance with the principles of the present invention.
[0038] FIG. 6 is a schematic of a circuit diagram which shows the
preferred embodiment of an oscillator which is used in the present
invention to provide a microwave frequency signal.
[0039] FIG. 7A is a perspective view of a sensor coupled to a
bottle.
[0040] FIG. 7B is a perspective view of a sensor coupled to a
collapsible bag.
[0041] FIG. 7C is a perspective view of a sensor coupled to a
tube.
[0042] FIG. 7D is a perspective view of a sensor coupled to a
tank.
[0043] FIG. 7E is a perspective view of a sensor coupled to a sheet
covering a mound of material.
[0044] FIG. 8A is a top cut-away view of a container and a sensor
attached to the container wall.
[0045] FIG. 8B is an enlarged profile view of the sensor shown in
FIG. 8A.
[0046] FIG. 8C is a profile view of a 2-port coupler which has
input and output paths on opposite sides of a substrate.
[0047] FIG. 8D is a profile view of a 2-port coupler which has
input and output paths on a same side of the substrate.
[0048] FIG. 8E is a profile view of a 2-port coupler which has a
single input and output path, on a same side of a substrate, and
where the input and output paths are electrically coupled.
[0049] FIG. 8F is a profile view of a 3-port coupler.
[0050] FIG. 8G is a profile view of a different 3-port coupler.
[0051] FIG. 8H is a profile view of a different 3-port coupler.
[0052] FIG. 8I is a profile view of a 4-port coupler.
[0053] FIG. 8J is a profile view of a different 4-port coupler.
[0054] FIG. 8K is a profile view of a different 4-port coupler.
[0055] FIG. 8L is a profile view of a different 4-port coupler.
[0056] FIG. 8M is a profile view of a different 4-port coupler.
[0057] FIG. 8N is a profile view of a different 4-port coupler.
[0058] FIG. 8O is a profile view of a 3-port coupler consisting of
a conductive stripline separated from a solid ground plane by a
thin gap. The stripline forms a serpentine patterns to reduce the
overall size of the sensor while maintaining the length of the
stripline.
[0059] FIG. 8P is a profile view of a 3-port coupler consisting of
two parallel serpentine striplines separated by a thin gap.
[0060] FIG. 8Q is a profile view of a 3-port coupler consisting of
a stripline separated from the ground conductor by a thin gap.
[0061] FIG. 9A is a graph showing a plot of coupling coefficient
measurements. These measurements were taken using a concentric ring
coupler such as the type shown in FIG. 8B. The graph shows the
magnitude of coupling in decibels relative to the fraction of the
coupler covered by water.
[0062] FIG. 9B is a graph showing a plot of coupling coefficient
measurements. These measurements were taken using a concentric ring
coupler such as the type shown in FIG. 8B. The graph shows the
phase of coupling in degrees relative to the fraction of the
coupler covered by water.
[0063] FIG. 10 is a circuit diagram showing a rectifier/integrator
(R/I) circuit.
[0064] FIG. 11 is a schematic circuit/block diagram showing how a
differential amplifier is used to quantify the differential output
of FIG. 10.
[0065] FIG. 12 is
[0066] FIG. 13 is a profile view of a 3-port coupler on a container
wall using a difference between signals from outputs to determine a
liquid level.
[0067] FIG. 14 is a profile view of two 2-port couplers on a
container wall using a difference between signals from outputs to
determine a liquid level.
[0068] FIG. 15 is schematic diagram of a differential amplifier
circuit used to achieve a high common mode rejection ratio, where
two output signals are compared to determine if the signals are
approximately equal or not, and where the circuit sensitivity is
adjustable.
[0069] FIG. 16 is a profile view of a sensor being attached to a
tube structure and being used to determine characteristics of a
fluid and the fluid flow.
[0070] FIG. 17 is a cut-away perspective view of a sensor coupled
to a pump housing and which can determine characteristics of the
pump housing contents and of the pump itself.
DETAILED DESCRIPTION OF THE INVENTION
[0071] Reference will now be made to the drawings in which the
various elements of the present invention will be given numerical
designations and in which the invention will be discussed so as to
enable one skilled in the art to make and use the invention. It is
to be understood that the following description is only exemplary
of the principles of the present invention, and should not be
viewed as narrowing the claims which follow.
[0072] Before addressing the specific embodiments of the present
invention, it is useful to present definitions for some words which
will be presented herein. First, a container is any closed or open
set of walls used to separate a sensor from a material being
sensed. It is important that the container walls be composed of
essentially non-conductive materials such as plastics, glass,
fiberglass, ceramic, etc. It is also important that the walls be
sufficiently thin to enable fringing fields of electromagnetic
signals from the sensor to penetrate the walls and usually the
contents as well. The container walls may be rigid or flexible, as
well as flat, curved or of an irregular shape.
[0073] The contents being sensed within the container walls can be
any type. However, most embodiments use as an example for
illustrations purposes of fluid or fluid with air bubbles. The
fluid is defined to be any contents which can flow or which might
settle within a container. This fluid therefore includes solids
(such as sand), liquids (such as blood), gasses (such as air), or
any mixture thereof.
[0074] The present invention is a sensor which is designed to
provide enhanced non-invasive container-content detection and
characterization. It will become apparent that although the
specific embodiments described hereinafter are directed to medical
applications, the invention is also applicable to other contexts as
will be explained.
[0075] Components of the present invention combine to provide an
electromagnetic signal from a coupler adjacent to a container.
Electromagnetic energy is either radiated into a liquid within the
container if the liquid level is at or above the level where the
coupler is attached, or is radiated into the air within the
container if liquid is not present at the coupler location. By
measuring coupled electromagnetic energy, it is then possible to
determine if liquid is above or below the coupler location.
[0076] FIG. 1 shows a non-invasive liquid level indicator 10 made
in accordance with the present invention as it would be mounted to
an exterior sidewall (plane of paper) of a container 12. The
indicator 10 includes a flex circuit sensor 16, an integral
adhesive patch 18, and a processing module 20.
[0077] The flex circuit sensor 16 couples to the integral adhesive
patch 18 at a transmitting and receiving end 26. The adhesive patch
18 has an attachment surface 21 to which is applied an adhesive
material. The adhesive material securely binds the attachment
surface 21 to a front side of the flex circuit transmitting and
receiving end 26 so as to provide a means of adhering/securing the
sensor 16 to the container 12. The attachment surface 21 is
sufficiently large so as to securely couple the flex circuit sensor
16 to a container 12.
[0078] The flex circuit sensor 16 also couples to the processing
module 20 by a flex circuit edge connector 28 (FIG. 3) that slides
into a friction coupling connector 29.
[0079] The processing module 20 includes a visual indicator means
32, such as a small light, and an audible indicator means 34, such
as a speaker, to warn the user when the fluid in a container passes
below the position of the transmitting and receiving end 26 of the
flex circuit sensor 16. The processing module 20 also includes an
on/off switch 36 to conserve power source 50 when the sensor 10 is
not in use.
[0080] FIG. 2 is a profile view of the liquid level indicator 10
shown in FIG. 1. Distinct layers with exaggerated thicknesses of
the flex circuit 16 are shown to clearly distinguish the various
components of the invention. For example, while a gap 25 appears to
indicate a substantial separation between the flex circuit
transmitting and receiving end 26 and the container 12, it is only
the scale of the drawing. The actual gap 25 is approximately 0.005
inches, which accommodates the adhesive patch 18. The nature of the
flex circuit sensor 16 enables it to bend so as to be mounted flush
against the container 12 with the adhesive patch 18.
[0081] A conductive patch 14 is placed on the flex circuit sensor
16 at the transmitting and receiving end 26. The conductive patch
14 is on the side of the flex circuit sensor 16 opposite the
adhesive patch 18 and covers the entire transmitting and receiving
end 26. Alternatively, the conductive patch 14 is fabricated as
part of the flex circuit. The purpose of the conductive patch 14 is
to electrically shield the transmitting and receiving end 26 in
such a manner as to force the entire transmitted electromagnetic
signal into the container 12. This prevents the flex circuit sensor
16 from detecting air on the backside of the transmitting and
receiving end 26, and reduces interference from other
electromagnetic energy sources.
[0082] Combined with the substrate of the flex circuit 16 is a
nonconductive material 47 attached to a portion 51 of the flex
circuit sensor 16 which slides into the processing module 20. The
nonconductive material 47 is a support which stiffens the flex
circuit sensor to give the flex circuit sensor 16 strength so as to
not unduly bend and prevent a reliable contact when inserted in the
processing module connector 29. When the liquid level indicator 10
is not in use, the on/off switch 36 can be moved into an off
position to conserve power in the power source 50. Because the
processing module 20 is not disposable, the power source 50 is
stored within the processing module 20 so that the power source 50
is user replaceable. In a typical embodiment, the power source 50
would contain enough charge to enable the liquid level indicator 10
to function for about 50 hours in an "on" mode. It is envisioned
that further refinement will show that the optimum power source 50
will likely be a lithium battery.
[0083] This figure also shows that the on/off switch 36 and the
visual indicator means 32 extend slightly above an outward surface
of the processing module 20. This feature makes the liquid level
indicator 10 easier to turn on and off, and allows the visual
indicator means 32 to be seen from a wider angle of view.
[0084] Referring now to the structure of FIGS. 3 and 4, there is
shown a more detailed view of the flex circuit sensor 16 so as to
illustrate the specific components of the flex circuit sensor. The
flex circuit sensor 16 is oriented in FIG. 3 such that the surface
22 which faces a container sidewall is shown, without the
processing module 20 attached to the flex circuit edge connector
28. Specifically, this view provides detail of the flex circuit
traces 30, edge connector 28.
[0085] The flex circuit sensor 16 is designed to transmit and
receive a signal from a transmitting and receiving end 26. An edge
connector 28 is formed at the opposite end of the flex circuit 16
for coupling to the processing module 20 as previously described.
The distance between flex circuit ends 26 and 28 is approximately 6
centimeters in a preferred embodiment, but could be longer or
shorter. Copper traces 30 electrically couple the transmitting and
receiving end 26 to the edge connector 28.
[0086] In a preferred embodiment, the circuit traces 30 are formed
of copper with a thin layer of gold deposited thereon to prevent
tarnishing of the copper surface. This gold layer also helps to
ensure that the edge connector 28 makes a reliable electrical
contact with the processing module friction connector 29.
[0087] As shown, the three copper traces 30 actually form only two
distinct paths. The two outer traces 42 beginning at the edge
connector 28 run parallel to the center trace 44, and form a circle
around the center trace 44 at the transmitting and receiving end 26
of the flex circuit sensor 16. The center trace 44 has formed on an
end 46 thereof a small copper disk 46.
[0088] Having described components of the present invention in
detail, it is now possible to see how they provide the necessary
structure and circuits to accomplish the objects is a coupler which
operates on the principle of radiating electromagnetic energy to
different media and then measuring coupled energy. A full container
12 or one in which a fluid is above or at a position where the
transmitting and receiving end 26 is currently attached couples
almost no electromagnetic energy to the flex circuit sensor 16 of
the present invention because electromagnetic energy broadcast by
the flex circuit sensor 16 couples to the fluid within the
container 12 and is perturbed and compressed.
[0089] On the other hand, if the container 12 is empty or there is
no fluid in the container 12 at the position of the transmitting
and receiving end 26, almost all of the electromagnetic energy is
coupled back to the flex circuit sensor 16 because there is no
fluid to couple with the energy and cause perturbation. Unlike an
acoustic sensor where the timing between emission of a broadcast
signal into a container and receipt of a return signal to the
antenna is the critical parameter which indicates the presence of
fluid, it is simply the presence or absence of coupled
electromagnetic energy which is indicative of fluid in a container
12. Thus, if the fluid has passed below the position of the sensor
transmitting and receiving end 26, there is coupling of a
substantial portion of incident electromagnetic energy, and the
liquid level indicator 10 alerts a user that the fluid in the
container 12 has fallen below the level of the transmitting and
receiving end 26 of the flex circuit sensor 16.
[0090] To obtain a reliable result from the liquid level indicator
10, the flex circuit sensor 16 must be securely attached to the
sidewall of the container 12 by the adhesive patch 18 so as to
ensure maximum transfer of electromagnetic energy emitted from the
flex circuit sensor 16 to the coupled media, in this case the
container 12 and possibly the fluid therein. Maximum
electromagnetic energy transfer is crucial because the liquid level
indicator 10 determines the level of liquid as a function of the
magnitude and phase of electromagnetic energy coupled through the
liquid near the sensor 16. A flex circuit sensor 16 held loosely
against the container 12 is likely to result in a false indication
that a liquid has fallen below the level of the transmitting and
receiving end 26 of the flex circuit sensor 16.
[0091] While the type of adhesive material used to secure the
liquid level indicator 10 to the container 12 is not a material
element of the present invention, the use of adhesive results in
the need to create a partially self-destructing flex circuit sensor
16. The adhesive patch 18 is sufficiently strong so as to be able
to secure the flex circuit sensor 16 flush against the container 12
to ensure maximum electromagnetic energy transfer. However, such a
strong adhesive is required to ensure maximum energy transfer that
it is unlikely that the adhesive patch 18 could be reliably
reattached to a container 12 once it is removed. If the flex
circuit sensor 16 position must be changed on the container 12, a
new disposable flex circuit sensor 16 must be applied at a new
position, and the processing module 20 removed from the used flex
circuit sensor 16 and coupled to a new flex circuit sensor.
[0092] To ensure that the flex circuit sensor 16 is not reused, it
is designed to be unusable once the flex circuit 16 is pulled in
sufficient tension to remove the adhesive. It is currently
envisioned that a preferred embodiment is configured so that
removing the flex circuit 16 will cause delamination of flex
circuit copper traces 30, while leaving the adhesive patch 18
attached to the container 12. Such damage will force an operator to
place a new flex circuit sensor 16 at a new location on the same
container 12 because the flex circuit sensor 16 will be damaged and
because the adhesive can no longer provide a reliable attachment to
the container 12. Alternatively, the processing module 20 could
produce an alarm signal indicative of the decoupling of the
transmitting and receiving end 26 of the flex circuit sensor 16
from a container.
[0093] The processing module 20 contains the circuitry necessary to
generate an electromagnetic signal to be transmitted from the flex
circuit transmitting and receiving end 26, as well as to measure
the amount of coupled energy after transmission by methods well
known to those skilled in the art. When coupled energy changes
sharply, the circuit activates the LED 32 and the speaker 34,
alerting someone that the liquid level is below a predetermined
level defined by the position of the transmitting and receiving end
26 of the flex circuit sensor 16 on the container 12.
[0094] The processing module 20 is also constructed of sufficiently
small and lightweight materials so as to be light enough to hang
suspended from the edge connector 28 without danger of decoupling.
Such a material is impact resistant plastic. While the edge
connector 28 is presently in tight sliding engagement with the
friction coupling connector 29 of the processing module 20, any
other connector which will enable the processing module 20 to hang
from the flex circuit sensor 16 without pulling free by its own
weight may be used. The flex circuit sensor 16 can be manufactured
of any appropriate materials which enable the circuit to function
as described above. In the preferred embodiment, the flex circuit
16 is constructed of a substrate composed of Kapton, polyamide or
some other suitable plastic-like polyamide material. The formation
of the traces 30 can be accomplished by numerous methods which will
be apparent to those skilled in the art of forming flex
circuits.
[0095] To further clarify use of the electromagnetic sensor, the
flex circuit transmitting and receiving end 26 is firmly held
against a sidewall 12 of the container by the adhesive patch 18.
The processing module 20, powered by a power source such as a
battery 50, sends an electromagnetic signal to the transmitting and
receiving end 26 through the center trace 44. The flex circuit
sensor 16 typically transmits an electromagnetic pulse in the range
of 1 MHz to 10 GHz. It is believed, however, that refinement of the
range to occur during further testing will result in an actual
broadcast frequency of approximately 900 Mhz. Preferably, the
antenna is a driven by a gated pulse signal of about 5 to 10 volts
peak to peak in amplitude.
[0096] If the flex circuit sensor 16 has been properly applied to
the container 12 and there is fluid within the container 12 above
where the transmitting and receiving end 26 of the flex circuit
sensor 16 is attached, a negligible amount of electromagnetic
energy is coupled back to the flex circuit sensor 16. In response,
any coupled electromagnetic energy is sent through the traces 42
and 44 to the processing module 20, where the signal is processed
to determine the amplitude or phase or both of coupled energy. The
processing module 20 actuates a visual indicator 32 and/or some
other perceptible indicator, such as an audible indicator 34, to
inform the user that the fluid level is adequate. Alternatively,
the processing module 20 could be programmed or wired to not emit
any indication signals until the liquid level passes below the
transmitting and receiving end 26 of the flex circuit sensor
16.
[0097] The processing module 20 monitors the liquid level in a
container 12 at least approximately 10 times per second.
Consecutive responses are averaged to reduce the bit error rate and
eliminate the influence of noise on the system. Upon receiving
several consecutive negative responses, defined as a sharp change
in coupled electromagnetic energy, the processing module 20
activates the alarm mechanisms.
[0098] The processing module 20 provides specific signals
indicating the mode and status of operation. For example, the
processing module 20 issues a single LED 32 pulse every five
seconds to indicate a safe (high) liquid level indication. The
module 20 issues an audible alarm through the speaker 34 consisting
of four pulses in one second, repeated every five seconds, if there
is an unsafe (low) liquid level indication. The LED 32 also blinks
continuously at a rate of four times per second at a low liquid
level condition. The module 20 also issues an audible alarm from
the speaker 34 if the flex circuit sensor 16 is not within the
vicinity of a detection media, or if the flex circuit sensor 16 is
not properly connected to the processing module 20 when power is
switched on.
[0099] When 50 hours of battery life have been expended, the liquid
level indicator 10 provides an early warning audio alert to
indicate a low battery condition. In a preferred embodiment, the
audio warning alert consists of a single pulse repeated every 10
seconds. During this period of low battery alert, the sensor 10
continues to operate, including the single LED pulse repeated every
5 seconds. After approximately 30 minutes of low battery alert, an
audio alarm sounds continuously at a rate of 4 pulses per second
until the battery is completely expended. During this low battery
alarm period, the LED 32 is completely off.
[0100] The motivation for creating this liquid level indicator 10
which uses electromagnetic signals is a desire to simplify
operation of a liquid level sensor, and to create a more versatile
sensor which may be used with both rigid and nonrigid containers
while maintaining the same level of accuracy. It is believed that
an electromagnetic liquid level indicator 10 accomplishes this
simplification and versatility because for electromagnetic waves in
the sub-gigahertz range, container wall thickness is much smaller
than one wavelength. This means reflections off the outer wall
surface of the container are approximately 180.degree. out of phase
with those off the inner wall surface The net effect is that the
container is virtually invisible, and the reflected pulse magnitude
depends only on the combined impedance of the coupler and the
contents of the container. This is not true with ultrasound because
the sonic wavelength is close to container thickness in many cases,
and because acoustic impedances are such as to produce phase
differences generally not close to 180.degree.. This means
reflections off the container dominate the processed signal, (i.e.
the container is acoustically present). Ultrasonic sensing is,
therefore, highly sensitive to container wall thickness, impedance
and acoustic velocity.
[0101] Another advantage of this electromagnetic liquid level
indicator 10 is that placement of the flex circuit sensor 16 is
much simpler. No mounting projections are required to ensure that
the flex circuit sensor 16 is oriented properly with respect to a
container 12 and a reflected signal. It is only important that the
flex circuit sensor traces 30 on the transmitting and receiving end
26 be flush against a container sidewall 12 so that transmitted
electromagnetic energy is coupled to the attached container 12
resulting in variations in electromagnetic energy being
coupled.
[0102] In addition to rigid wall containers such as glass balanced
saline solution containers, this method for determining the level
of liquid is also useful for thin walled plastic containers such as
the containers used for blood, saline, medication and enteral
feeding solutions. Unlike a glass container, the walls of a plastic
container may collapse towards each other in an uncontrolled,
random manner with a decrease in fluid volume within the container.
Thus, the fact that the container can be flexible, or that a
sidewall opposite to the attached container sidewall is not
parallel to the coupled sidewall is no longer relevant to sensor
accuracy or reliability with the present invention.
[0103] By applying the embodiment of the present invention and
obvious modifications thereto, medical personnel can ensure that
balanced saline solution and numerous other containers do not
accidentally "run dry". The embodiment of the present invention can
be used to detect air bubbles passing through medical tubing or
non-metallic industrial hoses or piping, as it detects the presence
and absence of liquid contained within the tubing. The embodiment
can also be applied to numerous liquid level monitoring
applications outside the medical environment, where accurate,
low-cost liquid level monitoring on non-metallic tanks or vessels
is desired.
[0104] The presently preferred embodiment of the present invention
is a relatively small, lightweight and battery powered device
consisting of a processing module and a sensor. There are
mechanical and electrical connections between the processing module
and the sensor.
[0105] There are several reasons why the preferred embodiment is a
small, lightweight and battery operated device. First, it is a
matter of convenience that the entire device be relatively small in
comparison to the containers to which it is likely to be attached
in medical applications. Accordingly, the container is typically a
small bottle or bag being used to deliver medications or fluids to
a patient.
[0106] Second, the sensor is preferably a single-use item. By
providing a strong adhesive which ensures good contact between the
sensor and the container, the chances of failure of the device are
all but eliminated. This use of a strong adhesive also prevents
re-use. However, given the low cost of the device and the desire to
provide a sensor which will not detach accidentally, the single-use
nature of the device is an asset. The adhesive is therefore strong
enough to support the weight of the processing module as the device
hangs from the container to which the sensor is attached.
[0107] Third, the ability to place the sensor at any location on
the container enables the device to be adapted to specific user
requirements.
[0108] It is mentioned before addressing the specific configuration
of the preferred embodiment that the present invention is also
capable of being integrated into larger systems such as a surgical
console, heart-lung machine etc. What is important is that the
device can be a portable and stand-alone device, and in this
context the preferred embodiment will be explained.
[0109] FIG. 5 is a block diagram of the elements which comprise the
presently preferred embodiment. The sensor system 110 includes a
processing module 112 and a sensor 114. The processing module 112
is preferably a digital device. A digital controller 116 operates
to control all functions of the sensor system 110. These systems
include an oscillator 118, detection circuitry 120, a digital
signal processor (DSP) 122, an alarm system 124, a data port 126,
and an integrated power supply and power supply monitor 128. It
should be noted that the digital controller 116 is capable of
sending commands to the oscillator 118, the detection circuitry
120, the DSP 122, the alarm system 124 and the data port 126.
[0110] When the sensor system 110 is operated as a stand-alone
unit, it is advantageous to utilize power conservation techniques
to thereby operate as long as possible without maintenance. In
order to conserve battery life, the digital controller 116
activates microwave circuitry for only brief periods of time during
which detection of the container's contents occurs. The microwave
circuitry is then deactivated, or put in a sleep mode. During this
sleep mode, very little battery power is used.
[0111] The duration of the activation period during the sleep mode
period is advantageously configurable according to the user's
specific needs. For example, when the sensor system 110 is being
used to detect air bubbles in a fluid line, the sleep mode period
will be much shorter in comparison to when the system 110 is being
used to detect a fluid level in a container.
[0112] Of course, there are many factors which can influence the
length of the activation and sleep mode periods. These factors are
all related to the time sensitivity of the data. It is likely that
detection of all air bubbles is critical. Furthermore, air bubble
detection is also likely to occur in a tube where fluid can flow
relatively swiftly, so data changes rapidly. In contrast, fluid
level detection is likely to occur in a container in which change
occurs much slower. However, a rate of fluid flow from a container
can be varied, and thus a programmable sensing vs. sleep mode
period is advantageous to the adaptability of the invention.
[0113] It is also important to recognize that while the preferred
embodiment is sensitive to power requirements, this is not a
critical factor when the sensor system 110 is integrated in larger
systems of alternative embodiments. In these conditions where power
consumption is not a factor, the sleep mode period can be reduced
to zero seconds without concern, and regardless of the nature of
the rate of data change.
[0114] The digital controller 116 can be programmed using any
appropriate method. For example, the digital processor 116 might be
a microprocessor or microcontroller with on-board memory, a
programmable gate array, or programmable memory such as an EPROM
(erasable programmable read only memory). In these devices, the
program is typically described as residing in firmware. As such,
the firmware can be changed by replacement of the programming
instructions, or replacement of the device itself (such as swapping
out the EPROM). Replacement of the instructions is accomplished by
removing the device, erasing the previous instructions, burning in
the new instructions, and placing the same device back into the
sensor system 110.
[0115] The programming instructions can also reside in software.
Accordingly, the memory device which stores the instructions must
be capable of overwriting or remotely erasing and then writing the
new instructions. The device is typically one which utilizes RAM
(random access memory). RAM is updated in the presently preferred
embodiment using a computer which is external to the sensor system
110. However, it should be apparent that flash memory (requiring
erasure before writing to the memory) could also be used and
programmed externally from the computer. A physical connection
between the sensor system 110 and the external computer occurs
through the data port 126.
[0116] The oscillator 118 provides a desired operating frequency of
the sensor 114. In the context of the presently preferred
embodiment, the sensor 114 is capable of generating an
electromagnetic signal at a frequency in the range of 1 to 100
GHz.
[0117] It is advantageous to select a microwave oscillator which
strikes a reasonable balance between cost and performance. This
balance may be affected by the particular application for which the
sensor system 110 will be used. For example, high resolution
sensing of container contents requires an oscillator with good
frequency and phase stability. In contrast, for liquid level
detection, probably any tuned oscillator will provide sufficiently
accurate results.
[0118] FIG. 6 is a schematic view of an oscillator 118 which is
used in the presently preferred embodiment. The microwave
oscillator shown is a common-base bipolar gallium-arsenide
transistor 130 having feedback through microstrip lines 132 and a
capacitor 140. The frequency of the oscillator 118 is controlled by
varying the length of the microstrip lines 132 and the value of the
capacitor 140, as is known to those skilled in the art.
[0119] The output impedance of the oscillator 118 is matched to the
input impedance of the sensor 114 to thereby obtain maximum power
transfer from the oscillator 118 to the sensor 114. In this
example, the output impedance of the oscillator is shown as 50
ohms.
[0120] The transistor 130 has DC biasing provided through a current
limiting resistor R(bias) 134 and a microwave blocking inductor
136. The microwave blocking inductor 136 is also referred to as a
radio frequency choke (RFC).
[0121] The output power and the oscillation frequency of the
oscillator 118 is fine tuned by controlling bias current to the
transistor 130. A field effect transistor 138 (not shown) driven by
the digital controller 16 controls current from the power supply
128 to the transistor 130. In the preferred embodiment, the power
supply 128 is a nine volt battery, but this can be modified. The
nine volt battery was selected for its small size and because in
typical operation, the current drain on the battery will be
relatively small. Accordingly, the nine volt battery should provide
power for adequate durations of time.
[0122] By providing bias current through the transistor 138, the
transistor activates the oscillator 118 when the sensor 14 is to be
in operation, and deactivates the oscillator 118 in order to enter
the sleep mode period. These operations all occur under the
direction of the digital controller 116. It should be apparent to
those skilled in the art that the specific circuitry designed to
provide power to the oscillator in order to drive the sensor 114
can also be implemented in other ways. It is also noted that in
this presently preferred embodiment, a ground plane 90 is provided
for grounding of circuit components.
[0123] The sensor 114 receives input directly from the oscillator
118. The input is in the form of a microwave frequency radio signal
which is transmitted along the sensor's circuit as will be
described later. In the presently preferred embodiment, the sensor
circuit is a microwave device commonly known as a coupler.
Ordinarily, couplers are used in microwave circuits as filters,
signal mixers, signal splitters, tuners, matching networks, and for
other functions known to those skilled in the art. It is believed
that the use of a microwave coupler for determining characteristics
of the contents of a container is a substantially new application
of microwave sensing technology. A coupler provides a controlled
electromagnetic connection from one circuit to another. The degree
of connection versus isolation is controlled by many parameters
including electromagnetic propagation modes within the coupler.
[0124] The type or configuration of microwave coupler which can be
used as the sensor 114 in the present invention includes two-port
couplers, three-port couplers, and four-port couplers. These
microwave multi-coupler configurations can also be used in direct
coupling and parallel coupling arrangements. In effect, the present
invention can function properly using any coupler which is
fabricated in generally planar surfaces. This includes couplers
fashioned as concentric stripline rings as will be described.
[0125] In FIGS. 7A through 7E in the interest of context, the
following figures are provided to show how the sensor appears when
coupled to a container. The figures are intended to show that the
sensor is attached to the container, and the circuitry hangs down
below the sensor in some sort of housing to protect the components.
The figures which are shown are also provided to demonstrate only a
few of the many types of containers to which the sensor can be
attached. FIG. 7A shows a sensor 310 coupled to a bottle 312 which
contains intravenous fluids. FIG. 7B shows the sensor 310 attached
to a collapsible bag 314 which also contains intravenous fluids.
FIG. 7C shows the sensor attached to a section of tube, hose or
pipe 316. FIG. 7D shows the sensor 310 attached to a tank 318 of
fluid. Finally, FIG. 7E shows the sensor 310 attached to a sheet
320 for detection of bulk contents or proximity sensing.
[0126] FIG. 8A is a cross-sectional top view of a sensor 114 which
is constructed as shown in an elevational view in FIG. 8B. However,
the scale of FIG. 8B does not exactly match that of FIG. 8A. FIG.
8A shows the sensor 114, as well as an arcuate portion of a
container wall 142. The portion 144 of the sensor 114 which is in
contact with the container wall 142 generates EM (electromagnetic)
fields 150 which are used in the content determination process.
When seen from above, it is noticed that an input signal 148 to the
portion 144 of the sensor 114 which is in contact with the
container wall 142 is carried by striplines 146.
[0127] A stripline is a circuit trace configuration that is
characterized by strips of conductors on an insulating substrate,
thereby providing an input path 152 and an output path 154 for the
microwave frequency signal 148. The width, length, thickness,
material and orientation of the conductors and substrate are
engineered as integral parts of electronic circuits. In the
embodiments of the present invention, striplines may be of any
quasi-planar shape and are disposed on any insulating surfaces of a
substrate. In comparison, it is noted that micro-striplines are a
stripline configuration in which conductors are placed on one side
of a planar substrate and an essentially solid conductor plane on
the other side of the substrate. The solid plane is the return path
for the signals carried on the conductors. This geometry creates a
nearly transverse electromagnetic (TEM) propagating field mode, as
opposed to striplines in general which usually create a non-TEM
field.
[0128] As shown, the EM fields 150 of the sensor 114 extend through
the container wall 142, and usually penetrate the contents. Of
course, this is a generalization in that it is assumed that the EM
fields 150 are sufficiently strong enough to touch the
contents.
[0129] The contents of the container will perturb or cause
disruption in the EM fields 150. What is important to realize is
that different contents will perturb the EM fields 150 in-various
ways. This is a result of the properties of the contents being
detected. For example, non-magnetic non-conductive contents will
cause electric fields to compress to a greater density than would
otherwise occur in air. In contrast, ferrous contents will greatly
compress the magnetic fields. Of course, conductive contents will
essentially prevent the EM fields 150 from penetrating at all. It
is this consequence of different materials causing different
perturbations in the EM fields 150 which enables the present
invention to accomplish determination of presence or absence of
contents, as well as purity, density, pressure and temperature.
However, this list should not be considered all-inclusive.
[0130] While the input signal 148 is sent to the sensor 114 via the
input path 152, it is analysis of an output signal 156 from the
output path 154 which enables container content determination. More
specifically, the output signal represents the input signal 148
which is scaled to a specific degree, in accordance with the
material properties of the contents. Thus, measurement of the
output signal 156 can be used to accurately identify and even
determine specific properties of the contents.
[0131] The EM fields 150 which surround the sensor 114 (also
referred to as a coupler) support many "hybrid" coupling modes. For
detailed analysis, these hybrid coupling modes are typically
decomposed into many pure coupling modes that add up constructively
and/or destructively at the coupler's output. Because analysis of
many pure coupling modes is an involved process, it is possible to
characterize a coupler by defining a coupling coefficient which is,
in general, a complex number to represent the overall degree of
coupling due to geometry and material properties of the coupler.
For example, the coefficient can be quantified as:
[0132] Equation 1: 1 c = ( 10 log p ( in ) p ( out ) , ( out ) - (
in ) )
[0133] With known input power p(in) and input phase .O
slashed.(in), it is possible to measure output power p(out) and
output phase .O slashed.(out) to thereby determine the coupling
coefficient while the coupler's EM fields are perturbed by the
contents.
[0134] Before proceeding with a description of other components of
the invention, it is useful to present some common coupler
configurations using striplines and which can be used in the
present invention. These couplers should only be considered
examples of possible embodiments, and not as being an exclusive
list of the only possible configurations.
[0135] FIGS. 8C, 8D and 8E are all embodiments of 2-port couplers.
A sensor area is generally described as being formed from
striplines which are shaped as rings. These rings do not have to be
circles. FIG. 8C shows a 2-port coupler which has input striplines
200 on the same side of a substrate (not shown) as the sensor rings
202, and which has output striplines 204 on an opposite side of the
substrate. FIG. 8D varies in that the input and the output
striplines 206 are on a same side of a substrate (not shown) and on
an opposite side of the substrate as the ring sensors 208. Finally,
FIG. 8E shows an input 210 which is electrically coupled to an
output 212 because they share a common sensor ring 214.
[0136] FIGS. 8F, 8G, and 8H are all embodiments of 3-port couplers.
FIG. 8F shows a 3-port coupler which has a single input 216, and
two outputs 218. FIG. 8G shows a single input 220 and two outputs
222. FIG. 8H shows input striplines 224, and output striplines
226.
[0137] FIGS. 81, 8J, 8K, 8L, 8M and 8N are all embodiments of
4-port couplers. FIG. 8I has a single input 228, and three outputs
230. FIG. 8J has a single input 232, and three outputs 234. FIG. 8K
has a single input 236, and three outputs 238. FIG. 8L has a single
input 240, and three outputs 242. FIG. 8M has a single input 244,
and three outputs 246. FIG. 8N has a single input 248, and three
outputs 250. FIG. 8O has a single input 322, and two outputs 324.
FIG. 8P has a single input 326, and two outputs 328. FIG. 8Q has a
single input 330, and two outputs 332.
[0138] An important observation to make is that all of the 2-port,
3-port and 4-port couplers shown in FIGS. 8B, 8C, 8D, 8E, 8F, 8G,
8H, 8I, 8J, 8K, 8L, 8M, 8N, 8O, 8P, and 8Q generally can be
considered to have arbitrarily selected input and output ports. In
other words, the inputs and outputs are generally interchangeable.
However, there are often advantages for a particular selection of
input and output lines because of geometry. For example, it is
probably better to have the output come from an inner ring in FIG.
8B because of the shielding from stray electromagnetic signals
which is naturally provided by the outer input ring.
[0139] FIG. 9A is a graph showing a plot of coefficient coupling
measurements. These measurements were taken using a concentric ring
coupler such as the type shown in FIG. 8B. The magnitude of the
coupling coefficient varies from -1.2 dB to -17.5 dB as one type of
contents in a container was replaced by another type of contents.
More specifically, air replaced water as water was permitted to
drain from the container. The graphs provide the plots of coupling
coefficient with respect to the portion or fraction of the coupler
which is "covered" by water inside the container.
[0140] FIG. 9B is a graph showing a plot of coefficient coupling
measurements. The phase of the coupling coefficient varies from 2
to 83 degrees relative to the source as air is replaced by water in
the container.
[0141] FIG. 10 is a circuit diagram showing a rectifier/integrator
(R/I) circuit 160. The R/I circuit 160 shown is a presently
preferred circuit for the detection circuitry 120 of FIG. 5. This
R/I circuit 160 is used for measuring the degree of coupling in the
sensor. This is accomplished by converting the coupled microwave
signal (the output signal 156 in FIG. 8A) to a DC voltage. While a
detailed description will now be provided for the circuit of FIG.
10, it should be apparent that other circuit designs can accomplish
the same function, and these equivalent circuits should be
considered to be within the scope of the present invention.
[0142] The input to the R/I circuit 160 is shown as V(in) 162. This
input signal 162 is rectified by a diode 164. The effect is to
create a time-varying DC current at point A 166. The diode 164 may
be a schottky barrier diode, or any other diode that is capable of
rectifying microwave frequencies. However, any diode used cannot
significantly attenuate the input signal 162.
[0143] Depending upon the diode 164 which is selected, a biasing
network 168 may be required. In this embodiment, the bias network
168 contains a field effect transistor (FET) 170 which is used to
control bias current 172. The biasing network 168 is also used to
turn off bias current 172 when the sensor system 110 is in a sleep
mode. A DC blocking inductor 174 is also coupled in series with a
current limiting resistor 176 to thereby provide the required bias
current 172 without interfering with performance of the microwave
output signal 156 which is input to the R/I circuit 160 as V(in)
162.
[0144] After the R/I circuit 160 generates a rectified signal 178,
the signal 178 is integrated by a capacitor 180. The result is a
steady-state DC voltage V(out) 182. Capacitor charge is slowly bled
off through a resistor 184 so that the voltage across the capacitor
180 can be reduced as the strength of the sensor's output signal
156 (the input signal to the R/I circuit 160) decreases. The rate
of decay is set so that V(out) 182 generally shows no ripple, but
is also fast enough that V(out) 182 can accurately track the sensor
system output signal 156 at V(in) 162.
[0145] In applications requiring fine temporal resolution, rapidly
changing sensor output signals are important. Accordingly, the
resistor 184 and the capacitor 180 can be selected to achieve the
desired resolution. Advantageously, microwave sensing has time
resolution which is on the order of a millionth of a second.
[0146] The capacitor 180 is essentially a short circuit to ground
for microwave frequency signals. Therefore, a method is required to
prevent excessive loading on the microwave circuit by the capacitor
180. One method which is often used is to use a quarter wavelength
line 186 in the circuit. The result is a transformation of the zero
impedance due to the capacitor 180 to an infinite impedance as seen
by the diode 164. The inclusion of the quarter wavelength lines 186
does not interfere with DC signals of the detection circuit 160, so
the capacitor 180 still discharges through the resistor 184. It is
noted that the value of the resistor 184 is chosen so that the
combined impedance of the forward-biased diode 164 and the resistor
184 will be equal to the output impedance of the sensor 114.
Consequently, maximum power transfer to the capacitor 180 is
achieved.
[0147] The detection circuitry 120 (FIG. 5) provides an integrated
output voltage V(out) 82 (FIG. 10). The voltage V(out) 182 is then
compared with a reference voltage 192. Those skilled in the art
will recognize that this can be accomplished using a differential
amplifier 194 as shown in FIG. 11.
[0148] FIG. 11 shows that in the presently preferred embodiment, an
A/D converter 198 receives as an input the output 196 of the
differential amplifier 194 in order to quantify the differential
amplifier output 196. The output 196 from the differential
amplifier 194 is a continuous voltage that is nearly proportional
to the coupling coefficient of the sensor 114. A resulting digital
signal from the A/D converter 198 is capable of characterizing the
coupling coefficient with arbitrarily high resolution. The digital
signal is transmitted to the digital signal processor 122 (FIG.
5).
[0149] The digital signal processor 122 can perform various
functions. These functions include but are not limited to executing
algorithms for error correction, noise filtering, signal
enhancement, pattern recognition and internal calibration of
digital and microwave functions. These algorithms are typically
implemented using a microprocessor or a programmable gate array
(FPGA).
[0150] The digital signal processor 122 is designed to provide
output for alarms 124. In other words, the DSP 122 is designed to
determine when an alarm condition has occurred, and to then take
the appropriate action to trigger a human perceptible alarm.
[0151] The DSP 122 also receives input from the digital controller
116. In the preferred embodiment, the DSP 122 and the digital
controller 116 are configured concurrently. Virtually any operating
parameter of the DSP 122 can be configured as required.
Configurable parameters include bias currents, linear and
non-linear filtering, timing and sensor sensitivity. Filtering
involves processing the digital data using programs which are
written to emphasize or de-emphasize selected characteristics of
the signal.
[0152] More specifically, linear low-pass filtering may be used to
reduce environmental effects in some applications such as saline
level detection in an IV bottle. When the bottle is bumped or
tipped, bubbles and waves may wash across a sensing region where
the sensor 114 is coupled to the outside of the IV bottle. With
proper filtering, such disturbances will not interfere with
detection of slow events like a falling fluid level.
[0153] Linear high-pass filtering may be used to increase
sensitivity to rapidly occurring events. For instance, small air
bubbles in a fluid line are generally more easily detectable with
high-pass filtering, especially if the composition of the fluid
itself is not uniform.
[0154] In addition to the low and high-pass filters, various
non-linear filters may be used to eliminate the effects of noise
and to enhance the sensor output signal 156. For example, a median
filter is implemented to reduce impulse noise. Edge enhancement is
performed to increase the sensitivity to abrupt changes in
coupling.
[0155] Advantageously, linear filtered signals can also be combined
with non-linear filters to provide increased sensitivity to any
anticipated sensor output.
[0156] The power supply 128 of the preferred embodiment is a
battery. This is owing to the portable nature, compact size, and
typically low power requirements of the invention. However, because
a battery is preferred, it is also desirable to monitor the voltage
of the battery, and provide a means of warning a user of impending
failure of the battery.
[0157] FIG. 12 shows that in the preferred embodiment, a voltage
divider 334 is used in combination with a comparator 336 to thereby
generate digital signals 338. The digital signals 338 are used to
trigger an alarm when the voltage of the battery 340 drops below a
desired voltage level, as is understood by those skilled in the
art.
[0158] The alarms 124 (FIG. 5) of the present invention are
preferably of two different types. These include visual and audible
devices for attracting attention. However, it is possible that the
sensor system 110 might not be located within the visual or audible
range of a user. Therefore, the preferred embodiment also includes
a data port which can signal a status of the sensor system 110 to a
remote monitoring device such as a computer.
[0159] The alarm conditions of the present invention not only
include a warning signal for whatever alarm condition is designed
to trigger the sensor system 110 (such as a low liquid level), but
also for unlikely but not impossible occurrences such as the sensor
114 becoming detached from a container or other device being
monitored. To assist the user with determination of what event has
triggered the alarm or alarms, the visual and audible alarms are
varied. For example, a different tone or pattern of sounds can be
created for the audible alarm. Likewise, a different pattern or
intensity of light is used for the visual alarm.
[0160] There are several alternative embodiments for various
components of the present invention described above. For example,
FIG. 11 shows that an A/D converter 198 is used to generate digital
signals which represent a continuous voltage that is nearly
proportional to the coupling coefficient. However, instead of
digitizing the output of the differential amplifier 194, the output
is used to directly activate an alarm mechanism which is driven by
an analog signal. For example, the analog alarm mechanism can be a
visual alarm such as a light, or an audible alarm such as a buzzer.
Accordingly, this alternative embodiment would also eliminate the
DSP 122 because no digital signals are being generated.
[0161] A second alternative embodiment involves using a single
3-port coupler. The presently preferred embodiment describes using
a 2-port coupler as shown in FIG. 8B where there is one input and
one output. However, a 3-port coupler as shown in FIGS. 8F, 8G and
8H use one input path and two output paths. One of the advantages
of these 3-port configurations is that it enables simultaneous
sensing of container contents at multiple locations. The sensors
are able to distinguish between differences in the contents at the
outputs. Accordingly, each output is characterized by its own
coupling coefficient.
[0162] A 3-port coupler and its associated circuitry provide a high
common mode rejection ratio (CMRR). A high CMRR results in a type
of sensing that ignores everything but the difference between the
coupling coefficient on each side of the coupler. In practical
terms, this means that CMRR is a measure of insensitivity of the
sensor to environmental interference, manufacturing variations, and
anything else that can influence all regions of the sensor
equally.
[0163] A 3-port coupler is ideal for level sensing in a container
when oriented as shown in FIG. 13. What will occur using this
particular design is that when the level of the contents (a fluid)
reaches the axis 252, the difference between the two output signals
254, 256 is maximized. Generally, this will be the alarm condition
which results in the activation of a human perceptible alarm.
[0164] Another alternative embodiment of the present invention
involves replacing the 3-port coupler used in FIG. 13 with two
2-port couplers as shown in FIG. 14. Whereas the 3-port coupler has
a fixed spacing between outputs, the spacing 258 between two
independent 2-port couplers can be arbitrary so as to meet specific
needs of more applications.
[0165] In another alternative embodiment, level sensing of a
container's contents can also be achieved using a single 2-port
coupler having dimensions designed to form a balanced bridge. This
type of coupler produces constructive interference and a strong
output signal at the output port when the sensor is adjacent to
fluid, and destructive interference when the sensor is adjacent to
the fluid-air boundary. It should also be apparent that the
interference can also be reversed depending upon whether the sensor
is adjacent to fluid or the fluid-air boundary.
[0166] What is important to realize is that a coupler's dimensions
allow for the creation of sensors which are sensitive to the
fluid-air boundary, or to any other property which the sensors are
able to detect. The sensors may be resonant or non-resonant at the
sensing frequency. Sub-resonant couplers, those smaller than half a
wavelength, may be used to reduce sensor size. This makes it
possible to offer different sensor configurations for different
applications, without having to modify the supporting circuitry.
However, a sensor with a single 2-port coupler has the advantage of
requiring simpler interconnections between the sensor and the
supporting circuitry than sensors with two couplers or with a
single multi-port coupler.
[0167] When a 3-port coupler is being used, the present invention
requires a differential amplifier circuit in order to achieve high
CMRR. An example of such a detector circuit is shown in FIG. 15.
This circuit includes an equality detector. Specifically, each of
the two outputs from the 3-port coupler are rectified and
integrated using the circuit shown in FIG. 10. The integrated
output signals V(in1) 260 and V(in2) 262 are compared to determine
if the digital signal processing circuitry 122 (FIG. 5) will
trigger an alarm.
[0168] The gain of amplifiers 268 and 270 is controlled by
resistors R264 and R266, respectively. Hysteresis is controlled by
resistors R272 and R274. Advantageously, it is possible to tune
each side of the amplifiers 268 and 270 separately to thereby
compensate for component and environmental variations. For example,
reducing the value of R272 will increase hysteresis when voltage
level V(in1) 260 drops below V(in2) 262. Resistor R274 has the same
affect on hysteresis when V(in1) 260 rises above V(in2) 262.
[0169] The amplifiers 268 and 270 will trigger the digital
circuitry which follows this circuit when V(in1) 268 and V(in2) 270
are not approximately equal. The ratio R2/(R1+R2) is adjusted to
define just how close V(in1) 260 and V(in2) 262 must be to be
considered equal. Accordingly, R1A, R2A, R1B and R2B are selected
on each side of the amplifiers 268 and 270 to create a desired
margin of equality. This margin of equality is represented by the
factor K in FIG. 15. R3 is selected so as to marginally attenuate
the input signals 260 and 262.
[0170] Because it is possible to independently control parameters
for each side of the amplifiers 268 and 270, sensing may be made
symmetrical or asymmetrical as desired. If sensing is to be
symmetrical, orientation of the sensor on a container is less
critical. In other words, the sensor may be placed upside down on
the side of a container without affecting sensitivity or
reliability. Of course, this may not be necessary if the circuitry
112 hangs from the sensor 114, thus naturally orienting the
sensor.
[0171] A differential detection scheme as explained above could
also be used to compare the electrical loading of the sensor on a
container wall to a pre-defined reference load by using a second
differential amplifier. If the output signals from both sensors are
approximately equal and both sensors indicate a load characteristic
of a detached sensor, an alarm is activated to inform the user that
the sensor has become detached from the container wall, and thus
requires repositioning. Therefore, the advantages of differential
sensing (because of a high CMRR) are realized for the detached
alarm condition as well.
[0172] An alternate differential sensing scheme is possible with
3-port sensors or with two identical 2-port sensors. The output
ports of the coupler or couplers connect directly to the
differential inputs of the amplifier circuitry. Amplifier
components are chosen and arranged to enable operation at the
sensing frequency. The output of the amplifier is then rectified
and integrated to produce a signal which indicates the presence or
absence of fluid. By reversing the order of the differential
amplifier and the R/I circuits, variations in phase and amplitude
of the coupled signals can be detected. The advantages of CMRR are
still realized with this scheme.
[0173] The basic sensor configurations, a few of which were shown
in the examples above in FIGS. 8B to 8Q, can also be adapted to
other situations. For example, two independent amplifiers 268 and
270 (FIG. 15) can be used to detect flow rate and direction of air
in fluid lines, as well as the size of an air bubble. This is
determined by coupling V(out1) and V(out2) (FIG. 15) to the DSP
circuitry.
[0174] The situation being described is illustrated in FIG. 16. A
3-port coupler (sensor) 280 is shown attached to a tube 282 which
has fluid flowing therein. Within the fluid are air bubbles 284.
Now it can be seen that a difference in time between signal events
(expressed as the time 286 it takes for an air bubble 284 to cross
in front of both output sensors) at V(out1) and V(out2) (see FIG.
15) determines the flow velocity of the fluid in the tube 282. The
order of signal events determines flow direction. For the fluid
flow to be in the direction indicated by arrow 288, the first event
will be when an air bubble 284 crosses in front of output sensor
290, and the second event will be when the air bubble 284 crosses
in front of the output sensor 292.
[0175] Finally, the duration of the events is used to determine the
bubble size. In other words, an event in front of a single sensor
will last as long as it takes the air bubble 284 to completely
cross in front of a sensor. This is expressed as the time it takes
the air bubble 284 to travel a distance which is approximately
equal to its diameter 294.
[0176] In addition to being able to make hardware modifications to
the sensor system 110 for adjustment of parameters such as
sensitivity and hysteresis, the DSP 122 (FIG. 5) is configurable
through software. Therefore, many variations of the embodiments
described above are possible without altering the hardware.
[0177] Some examples of possible applications which can be
implemented are the identification of bubble patterns or other
inconsistencies in fluids transported through fluid lines. This
function is most likely to be used when the overall system response
relies on different stimuli. For example, the device can sense flow
rates in a fluid line as determined by detection of small bubbles,
but still be capable of triggering an alarm if larger bubbles are
detected. An alarm can also be triggered if the flow of the fluid
reverses.
[0178] One such use of pattern detection is shown in FIG. 17. A
pump housing 300 is shown with an inlet tube 302 and an outlet tube
304. The sensor system 306 is shown coupled to the pump housing
300. The sensor system 306 is not only capable of identifying the
contents within the pump housing 300, but it can also monitor the
speed of the pump, detect variations in the fluid (caused by air,
contamination, occlusions, etc.) and even detect wear or damage to
the propeller 308.
[0179] The DSP can also be configured so as to save sensor signals
from a known substance, and then make comparisons to received
signals so as to non-invasively detect changes in the properties of
the substance. This ability can be applied to such applications as
analysis of substance purity, leakage detection in soil surrounding
underground storage tanks, or proximity of a substance to a
sensor.
[0180] It is to be understood that the above-described arrangements
are only illustrative of the application of the principles of the
present invention. Numerous modifications and alternative
arrangements may be devised by those skilled in the art without
departing from the spirit and scope of the present invention. The
appended claims are intended to cover such modifications and
arrangements.
* * * * *