U.S. patent number RE34,501 [Application Number 07/707,742] was granted by the patent office on 1994-01-11 for sensor and method for ullage level and flow detection.
Invention is credited to Billy V. Clark, Buford R. Jean, Richard W. Newton, Gary L. Warren.
United States Patent |
RE34,501 |
Jean , et al. |
January 11, 1994 |
Sensor and method for ullage level and flow detection
Abstract
A device is provided for detecting the ullage level and flow in
a vessel by detecting the presence of a solid or liquid material in
proximity to a microwave detector. The device may be mounted to the
side of the vessel or suspended inside the vessel so as to bring
the microwave sensor into proximity with the surface of the
contents of the vessel. A microwave bridge circuit may be used to
detect a change in either the amplitude or phase of a signal
reflected by the material within the vessel compared to a reference
signal tuned to either the presence or absence of the anticipated
solid or liquid material. In one embodiment, the reflected material
signal is compared to the signal from a sample chamber containing
the material to be detected. The device can reliably detect the
level of multiple interfaces for various materials having distinct
electric or magnetic properties.
Inventors: |
Jean; Buford R. (Round Rock,
TX), Warren; Gary L. (Round Rock, TX), Newton; Richard
W. (Dallas, TX), Clark; Billy V. (Dallas, TX) |
Family
ID: |
26790685 |
Appl.
No.: |
07/707,742 |
Filed: |
May 30, 1991 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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911157 |
Sep 24, 1986 |
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Reissue of: |
95848 |
Sep 14, 1987 |
04833918 |
May 30, 1989 |
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Current U.S.
Class: |
73/290V;
73/290R |
Current CPC
Class: |
G01F
23/284 (20130101); G01F 23/2845 (20130101); G01S
13/04 (20130101); G01P 13/00 (20130101); G01P
5/00 (20130101) |
Current International
Class: |
G01F
23/284 (20060101); G01P 13/00 (20060101); G01P
5/00 (20060101); G01S 13/00 (20060101); G01S
13/04 (20060101); G01F 023/28 (); G01R
027/06 () |
Field of
Search: |
;73/29R,29B,29V,861,861.18,861.25 ;324/640,644 ;340/612,618-621
;342/124 ;367/908 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0720970 |
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Nov 1965 |
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CA |
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720970 |
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Nov 1965 |
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CA |
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1016784 |
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Jan 1966 |
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GB |
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Primary Examiner: Cuchlinski, Jr.; William A.
Assistant Examiner: Worth; W. Morris
Attorney, Agent or Firm: Payne; Alton
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
The present application is a continuation-in-part application of
the application of Buford R. Jean, Richard W. Newton, Gary L.
Warren and Billy V. Clark, U.S. Ser. No. 911,157, filed Sep. 24,
1986, entitled ULLAGE LEVEL SENSOR AND METHOD now abandoned.
Claims
What is claimed is:
1. A sensor for detecting the movement characteristics of material
in a container or conduit, comprising:
microwave oscillator means for generating a constant propagated
microwave in a frequency range of from 1 to 20 gigahertz;
microwave bridge circuit means for dividing microwave into a
measurement microwave and a reference microwave;
first guide means for injecting the measurement microwave through a
portion of the container substantially transparent to the
propagated microwave frequency and for returning a reflected
measurement microwave to the microwave bridge circuit means
indicative of the reflection coefficient at the boundary layer of
the transparent portion, the coefficient being significantly
altered by one of the presence, the absence and the movement of the
material at the level of the first guide means;
second guide means for transmitting the reference wave from the
microwave bridge circuit means and for returning a reflected
reference wave to the microwave bridge circuit means;
reference wave altering means for altering the reflected reference
wave to correspond in amplitude and phase to the reflected
measurement microwave as altered by the presence, absence or
movement of the material at the level of the first guide means;
the microwave bridge circuit means receiving the reflected
measurement and reference waves and producing a differentiation
signal indicative of a difference in magnitude and phase between
the waves;
detector means for generating an output indicative of the magnitude
of the differentiation signal; and
comparator means for comparing the magnitude of the detector means
output to a preselected signal magnitude and for providing an
actuation signal indicative of the presence, absence or movement of
the material at the level of the first guide means.
2. The sensor as defined in claim 1, wherein the reference wave
altering means comprises:
a sample chamber containing a quantity of the material in the
container and positioned at an end of the second guide means, the
reflected reference microwave being indicative of the reflection
coefficient at the boundary layer of the sample chamber.
3. The sensor as defined in claim 1, wherein the reference wave
altering means comprises:
a resistive tuning means adjustably positionable with respect to
the second guide means for selectively altering the magnitude of
the reflected reference wave to equal the magnitude of the
reflected measurement wave; and
two or more reactive tuning elements adjustably positionable with
respect to the second guide means for selectively altering the
phase of the reflected reference wave to equal the phase of the
reflected measurement wave.
4. The sensor as defined in claim 3, wherein the output of the
detector means is a DC signal whose magnitude is proportional to
the magnitude of the difference in amplitude and phase between the
reflected measurement and reference waves.
5. The sensor as defined in claim 1, wherein the transparent
portion of the container is a dielectric tank wall.
6. The sensor as defined in claim 1, wherein the axis of the first
and second guide means are aligned, and the second guide means
transmits the reference wave to the reference wave altering means
in a direction opposite the transparent portion of the
container.
7. The sensor as defined in claim 1, further comprising:
amplifying means for increasing the magnitude of the output from
the detector means; and
amplifying adjustment means for selectively adjusting the gain of
the amplifying means.
8. The sensor as defined in claim 1, further comprising:
time delay means for receiving the actuation signal and outputting
a control signal when the actuation signal is maintained for at
least a selected time period.
9. The sensor as defined in claim 1, wherein the interior
cross-section of the first guide means is substantially identical
to the interior cross-section of the second guide means.
10. The sensor as defined in claim 1, wherein the microwave bridge
circuit outputs the differential signal in a direction
substantially normal to the axis of the first guide means.
11. A sensor for detecting the movement characteristics of material
in a container, comprising:
microwave oscillator means for generating a constant propagated
microwave in a frequency range of from 1 to 20 gigahertz;
microwave bridge circuit means for dividing the propagated
microwave into a measurement microwave and a reference
microwave;
first guide means for injecting the measurement microwave through a
portion of the container substantially transparent to the
propagated microwave frequency and for returning a reflected
measurement microwave to the microwave bridge circuit means
indicative of the reflection coefficient at the boundary layer of
the transparent portion, the coefficient being significantly
altered by the presence compared to the absence of the material at
the level of the first guide means;
second guide means for transmitting the reference wave from the
microwave bridge circuit means and for returning a reflected
reference wave to the microwave bridge circuit means;
reference wave altering means for altering the reflected reference
wave to correspond to the reflected measurement microwave as
altered by the presence or absence of the material at the level of
the first guide means;
the microwave bridge circuit means receiving the reflected
measurement and reference waves and producing a differentiation
signal indicative of a difference between the waves;
detector means for generating an output indicative of the magnitude
of the differentiation signal; and
comparator means for comparing the magnitude of the detector means
output to a preselected signal magnitude and for providing an
actuation signal indicative of the presence or absence of the
material at the level of the first guide means.
12. The sensor as defined in claim 11, wherein the reference wave
altering means alters the amplitude and phase of the reflected
reference microwave to correspond to the amplitude and phase of the
reflected measurement microwave.
13. The sensor as defined in claim 12, wherein the output of the
detector means is a DC signal whose magnitude is proportional to
the magnitude of the difference in amplitude and phase between the
reflected measurement and reference waves.
14. The sensor as defined in claim 11, wherein the reference wave
altering means comprises:
a resistive tuning means adjustably positionable with respect to
the second guide means for selectively altering the magnitude of
the reflected reference wave to equal the magnitude of the
reflected measurement wave; and
two or more reactive tuning elements adjustably positionable with
respect to the second guide means for selectively altering the
phase of the reflected reference wave to equal the phase of the
reflected reference measurement wave.
15. The sensor as defined in claim 11, further comprising:
amplifying means for increasing the magnitude of the output from
the detector means;
amplifying adjustment means for selectively adjusting the gain of
the amplifying means; and
time delay means for receiving the actuation signal and outputting
a control signal when the actuation signal is maintained for at
least a selected time period.
16. A method for detecting the movement characteristics of material
in a conduit or container, comprising:
generating a constant propagated microwave in a frequency range of
from 1 to 20 gigahertz;
separating the propagating microwave into a measurement microwave
and a reference microwave;
injecting the measurement microwave through a portion of the
container substantially transparent to the propagated microwave
frequency and returning a reflected measurement microwave
indicative of the reflection coefficient at the boundary layer of
the transparent portion, the coefficient being significantly
altered by the presence compared to the absence of the material at
the boundary layer;
transmitting the reference wave and returning a reflected reference
wave;
selectively altering the reflected reference wave to correspond to
the reflected measurement microwave as altered by the presence or
absence of the material at the boundary layer;
receiving the reflected measurement and reference waves and
outputting a differentiation signal indicative of a difference
between the waves;
generating an output indicative of the magnitude of the
differentiation signal; and
comparing the magnitude of the output to a preselected magnitude
and providing an actuation signal indicative of the presence or
absence of the material of the level at the boundary layer.
17. The method as defined in claim 16, wherein the amplitude and
phase of the reflected reference microwave is selectively tuned to
the amplitude and phase of reflected measurement microwave.
18. The method as defined in claim 17, wherein the output
indicative of the magnitude of the differential signal is a DC
output proportional to the difference in amplitude and phase
between the reflected measurement and reference waves.
19. The method as defined in claim 16, wherein the step of
selectively altering the reflected reference wave comprises
subjecting the reference wave to the same material as the material
in the container.
20. The method as defined in claim 16, wherein the step of
selectively altering the reflected reference wave comprises:
adjustably positioning a tuning element to selectively alter the
magnitude of the reflected reference wave to equal the magnitude of
the reflected measurement wave; and
adjustably positioning another tuning element to selectively alter
the phase of the reflected reference wave to equal the phase of the
reflected measurement wave.
21. A method for detecting the movement characteristics of material
in a conduit or container, comprising:
(a) generating a wave having a frequency from 1 to 20
gigahertz;
(b) separating the wave into a measurement wave and a standard
wave;
(c) transmitting and injecting the measurement wave into the
container for impacting the available material and for returning a
reflected measurement wave indicative of the reflection coefficient
at the point of impact, the characteristics of the reflection
coefficient being altered by the movement characteristics of the
material;
(d) transmitting and altering the standard wave for producing a
reflected standard wave having an amplitude and phase corresponding
to an amplitude and phase associated with the measurement wave;
(e) combining the reflected measurement wave with the reflected
standard wave for either constructively enhancing or destructively
reducing the combined waveform for generating a combined wave;
(f) analyzing the combined wave to determine the presence of,
absence of, or motion of the material in the container, and
(g) generating an actuation signal indicative of the presence of,
absence of, or motion of the material in the container.
22. The method as defined in claim 21 wherein the step of
transmitting and altering the standard wave comprises altering the
standard wave with tuning elements for producing a reflected
standard wave having an amplitude and phase equal to the amplitude
and phase of the reflected measurement wave when impacting the
material whose presence or absence is sought to be determined.
23. The method as defined in claim 21 wherein the step of analyzing
the combined wave comprises:
(a) generating a first output by differentiating between the
magnitude of the combined wave and a comparator threshold such that
the comparator output is either low or high indicating the
magnitude of the combined wave is either below or above the
comparator threshold, respectively, and
(a) generating a second output from the first output for activating
a relay which drives lights, alarms, pumps and the like by ramping
down a low first output and by ramping up a high first output
whereby extraneous portions of the first output caused by
splashing, sloshing and the like are selectively purged from the
resultant second output.
24. The method as defined in claim 21 wherein the step of analyzing
the combined wave comprises:
(a) generating a bipolar signal, from the combined wave by taking
the difference between a present instantaneous sample of the
combined wave and a delayed instantaneous sample of the combined
wave whereby no change in the amplitude of the instantaneous
samples creates a zero bipolar signal; and
(b) generating a unipolar signal from the bipolar signal whereby
the magnitude of the unipolar signal is equal to the absolute value
of the bipolar signal.
25. The method as defined in claim 24 further comprising the step
of amplifying the combined wave for enhancing changes caused by the
reflection coefficient.
26. The method as defined in claim 24 wherein the step of
generating a unipolar signal comprises:
(a) generating a dense unipolar signal, and
(b) generating a sparse unipolar signal whereby the dense unipolar
signal indicates a dynamic flow condition, the sparse unipolar
signal indicates intermittent flow conditions, and the absence of
any unipolar signal indicates the absence of flow.
27. A sensor for detecting the movement characteristics of material
in a container or conduit, comprising:
(a) an oscillator for generating a constant propagated microwave in
a frequency range of from 1 to 20 gigahertz;
(b) a bridge for dividing the microwave into a measurement
microwave, a reference microwave and a combined microwave, said
bridge comprising:
(1) a medial waveguide for accepting the microwave from said
oscillator and for egressing the measurement microwave and the
reference microwave,
(2) a measurement waveguide, for accepting the measurement
microwave from said medial waveguide and for impinging the
measurement microwave on, for passage through, a portion of the
container substantially pellucid to the microwave frequency and for
returning a reflected measurement microwave indicative of the
reflection coefficient at the boundary layer of the pellucid
portion, the reflection coefficient being significantly altered by
the presence, the absence and the movement of the material;
(3) a reference waveguide, for accepting the reference microwave
from said medial waveguide and for returning a reflected reference
wave;
(4) an interference waveguide for accepting the reflected
measurement microwave and the reflected reference microwave for
creating a combined reflected microwave characteristic of the
interference caused by the combination of the reflected measurement
microwave and the reflected reference microwave,
(c) a reference wave altering means in operative association with
said reference waveguide for modifying the reference wave to
correspond in amplitude and phase to the reflected measurement
microwave as altered by the presence, absence or movement of the
material at the level of the first guide means;
(d) detector means for receiving said combined reflected microwave
and for generating an output indicative of said combined reflected
microwave; and
(e) comparator means for comparing the magnitude of the detector
means output to a preselected signal magnitude and for providing an
actuation signal indicative of the presence, absence or movement of
the material at the level of the first guide means.
28. A sensor for detecting the movement characteristics of material
in a container or conduit as defined in claim 27 wherein said
measurement waveguide and said reference waveguide are of equal
length. .Iadd.
29. A sensor for detecting movement, and one of presence and
absence, of material comprising:
(a) an oscillator for generating microwaves;
(b) microwave bridge means for dividing the generated microwaves
into measurement microwaves which engage the material and reference
microwaves which engage a tuning means for controlling the
amplitude and phase of the reflected reference microwaves, and for
receiving reflected microwaves after engagement with the material
and tuning means such that the reflected microwaves combine to form
a reflected differential signal, which differential signal is nil
or zero if the impedance at the material and tuning means is
substantially equal,
(c) means for processing the differential signal from said
microwave bridge means for determining movement, and one of
presence and absence, of material as indicated by a change in the
differential signal, said means for processing comprising
(1) means for receiving the differential signal from said microwave
bridge means;
(2) means for comparing the change in the differential signal
amplitude with respect to time for generating a difference
signal,
(3) means for generating an output proportional to variations in
the difference signal,
(4) means for accepting the proportional output and generating a
primary control signal,
(5) means responsive to the differential signal, the difference
signal, a reference voltage and a drive signal for producing an
action signal, and
(d) means for accepting the action signal and the primary control
signal and for generating the drive signal. .Iaddend. .Iadd.
30. A method for detecting movement, and one of presence and
absence, of material comprising the steps of:
(a) generating microwaves;
(b) dividing the generated microwaves into measurement microwaves
and reference microwaves,
(c) reflecting the measurement microwaves from the material and the
reference microwaves from a tuning means for controlling the
amplitude and phase of the reflected reference microwaves,
(d) impressing the reflected measurement microwaves with the
reflected reference microwaves to render a differential signal;
and
(e) processing the differential signal for determining movement,
and one of presence and absence, of material indicated by a change
in the differential signal, said step of processing the
differential signal further comprising the steps of:
(1) receiving the differential signal;
(2) comparing the change in the differential signal amplitude with
respect to time for generating a difference signal,
(3) generating an output proportional to variations in the
difference signal,
(4) generating a primary control signal from the proportional
output,
(5) generating an action signal responsive to the differential
signal, the difference signal, a reference voltage and a drive
signal, and
(f) generating, from the action signal and the primary control
signal, the drive signal representative of movement, and one of
presence and absence, of material for controlling other processing
equipment in response to the flow condition of the material.
.Iaddend.
Description
FIELD OF THE INVENTION
The present invention relates to techniques for detecting when the
contents of a tank or other vessel reach a certain level and, more
particularly, to improved techniques for determining when that
level is obtained utilizing microwave technology having significant
advantages compared to conventional level detection techniques.
Further, the present invention relates to detecting flow or no-flow
through a conduit using the improved techniques.
BACKGROUND OF THE INVENTION
Various mechanical devices have long been used to determine when
the level of material in a tank or other vessel reaches a certain
point. Floats and displacers rely upon the buoyant forces of a
liquid, while other devices use diaphragms or vibrating elements to
sense the presence of a liquid or solid. Such mechanical devices
generally have a high maintenance cost due to deterioration or
binding of various mechanically moving parts.
Sensing devices which rely upon measuring the weight of the tank
contents require precise knowledge of the specific gravity of the
material in order to accurately determine the level of material in
the vessel. Optical sensors generally require an extremely clean
environment for reliable operation, while sonic devices do not
function well in foam or dust environments. Finally, conductivity
sensing devices cannot be reliably used for determining the level
of many solids or liquids in a tank, such as dielectric materials,
and capacitive devices generally are restricted to detecting the
level of nonconductive materials.
Microwave sensors have a significant advantage over the devices
described above in that such devices may be universally employed
for detecting the level of almost any solid or liquid, regardless
of its conductivity or specific gravity. Moreover, microwave
sensors are generally insensitive to dust, vapors, foam layers, or
viscous liquid coatings or thin layers of powder on the sides of
the vessel.
U.S. Pat. No. 4,107,993 discloses microwave techniques for
detecting the level of a liquid in a vessel. An external chamber
constructed of material invisible to microwaves is required, and
the system detects amounts of unabsorbed energy to the receiver.
Microwave devices of this type experience alignment problems since
the transmitter and receiver must be properly positioned with
respect to one another.
U.S. Pat. Nos. 4,218,678, 4,359,902, and 4,044,355 also disclose
microwave sensing devices for determining the level of materials in
a tank. Microwave devices which utilize radar technology generally
seek to determine the travel time of a signal to the detected
material and thence to the receiver. The expense and complexity of
these devices limits their practical use to situations in which the
actual level of the material in the tank must be determined, as
compared to devices which simply determine whether the material has
or has not reached a certain level.
U.S. Pat. Nos. 3,572,119 and 4,458,530 are similarly directed to
devices intended to quantitatively determine the level of liquid in
a vessel. A sensor monitors the alteration of the standing wave
passing through the liquid to determine the liquid level.
The disadvantages of the prior art are overcome by the present
invention, and improved methods and apparatus are hereinafter
described for inexpensively yet reliably determining whether a
solid or liquid material in a container has obtained a certain
level or if such material is flowing or not.
SUMMARY OF THE INVENTION
A propagating wave from a microwave oscillator is divided and
transmitted horizontally through a measurement arm in parallel with
a reference arm. The impedance presented to the propagating
electromagnetic wave in the measurement arm is a function of the
conductivity, permitivity, permeability of the material within the
vessel opposite a dielectric window at the end of the measurement
arm. A change in the presence of or type of the material will thus
produce a change in the amplitude and phase of the reflected wave
due to the impedance change seen by the microwave signal at the
boundary layer. The divided propagating wave in the reference arm
may be altered by resistive and reactive tuning elements, or by
boundary layer impedance when that wave engages a selected material
in a sample chamber.
The reflected measurement and reference waves return to the
microwave bridge circuit and a differential signal indicative of
their difference in magnitude and/or phase is detected by the
microwave detector. The signal output from the bridge circuit may
thus be proportional to the difference between the reflection
coefficient seen by the divided waves in the measurement arm and
the reference arm. The reference arm may be tuned to present to the
bridge circuit an impedance equal to the impedance normally seen by
the measurement arm, thereby increasing the sensitivity of the
sensor. This output is fed to suitable electronics for amplifying
and comparing that output to a trip point, thereby causing the
energization of a suitable relay or other appropriate device for
the actuating of an alarm, pump, or other component.
A significant advantage of the present invention relates to its
high reliability and reduced maintenance costs, since the system
does not utilize moving parts which may wear or bind. If the tank
is made from a metallic material, only a single dielectric window
transparent to microwaves need be provided, and thus there are no
alignment problems between sensors and receivers. If the tank is
manufactured from a dielectric material, e.g., fiberglass, no
openings in the tank are necessary, thereby substantially reducing
installation costs.
The techniques of the present invention achieve a highly reliable
yet inexpensive determination of whether the level of a liquid or
solid in a tank has reached a given point. The same sensor will
work for virtually any material having an impedance different than
the electric and magnetic properties of air. Also, techniques of
the present invention can be easily utilized to detect the level of
an interface between two materials which have different electrical
or magnetic properties, and therefore present different impedence
values to the propagating wave. As an example, the device of the
present invention can easily detect whether the interface between
oil and water has reached the level of the detector. The methods
and apparatus herein described offer increased reliability,
sensitivity, and universal application compared to prior art level
sensing switches, and at a cost substantially less than prior art
microwave ullage sensors which provide an output indicative of the
quantitative level of material in a tank.
An alternative embodiment of the present invention provides a
method and apparatus for detecting whether solid material is
flowing or not flowing through a conduit. The operation of the
flow/no-flow concept of the present invention utilizes the changes
in output from a microwave bridge circuit that are induced by
changes in the reflection coefficient associated with the impact of
the waves on the specific material under investigation. Generally,
the method of the present invention for determining the flow or
no-flow of materials in a conduit or container comprise generating
a wave, separating the wave into a measurement wave and a standard
wave, injecting the measurement wave into the conduit for impacting
the available material and returning the reflected measured wave
indicative of the reflection coefficient at the point of impact,
altering the standard wave for producing a reflected standard wave
having an amplitude and phase corresponding to an amplitude and
phase associated with the measurement wave, combining the reflected
measurement wave with the reflected standard wave for either
constructively enhancing or destructively reducing the combined
waveform for generating a combined wave, generating a bipolar
signal from the combined wave, generating a unipolar signal from
the bipolar signal, and generating a drive signal based upon the
frequency of the unipolar signal for discriminating between
conditions of flow and no-flow as characteristic of the material
being evaluated.
The sensitivity of the present invention for determining the flow
or no-flow of material in a conduit is readily adjustable. The
present invention can be adjusted for discriminating against random
pellets dropping past the detector as well as the movement of
material past the detector and completely engulfing the
conduit.
These and other features and advantages of the present invention
will become apparent from the detail description, wherein reference
is made to the figures in the accompanying drawings.
FIG. 1 is a simplified function block diagram of the microwave
level detector according to the present invention.
FIG. 2 is a simplified pictorial illustration of the detector
according to the present invention mounted on a tank, along with
representative outputs of signal magnitudes depending on whether
the level of material in the tank has reached the level of the
sensor.
FIG. 3 is a pictorial illustration of one embodiment of the present
invention mounted in association with a suitable tank, and also
depicting in block form the decision electronics generally
referenced in FIG. 1.
FIGS. 4A and 4B illustrate a typical signal from the amplifier of
the present invention concerning the detector being near null and
away from null, respectively.
FIGS. 5A and 5B illustrate the resultant signal generally
referenced in FIGS. 4A and 4B, respectively, after
modification.
FIGS. 6A and 6B illustrate the integration of the signals generally
referenced in FIGS. 5A and 5B, respectively.
FIG. 7 is a multisequence illustration of signals generated when
the present invention is used for ullage measurements.
FIG. 8 is a pictorial illustration of another embodiment of the
present invention mounted on a suitable conduit.
FIG. 9 illustrates a block diagram of decision electronics
generally referenced in FIG. 8.
FIGS. 10A and 10B illustrate a typical signal from the input
amplifier associated with the present invention.
FIG. 11 illustrates a typical bipolar signal associated with the
present invention.
FIG. 12 illustrates a typical unipolar signal associated with the
present invention.
FIG. 13 illustrates a typical relay drive output signal associated
with the present invention.
FIG. 14 is a multisequence illustration of signals generated in
association with the present invention when used for determining
flow/no-flow characteristics within a conduit.
The above general description and the following detailed
description are merely illustrative of the generic invention, and
additional modes, advantages and particulars of this invention will
be readily suggested to those skilled in the art by the following
description.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The concept of the present invention is broadly illustrated in
block diagram form in FIG. 1, and includes a microwave oscillator
10 for generating a constant frequency propagating wave, a
microwave bridge circuit 12, a microwave detector 32, decision
electronics 34, and a device controlled by the decision
electronics, such as alarm 35. The microwave bridge circuit 12
serves to (a) functionally divide the propagating wave into two
parallel waves, (b) receive two reflected waves, and (c) output a
reflected differential wave to the detector 32.
One of the divided propagating waves travels down the measurement
arm 16 to the tank, vessel, or container 20 containing a
propagation medium. Depending on the level of the fluid or solid 18
in the tank 20, the propagating medium seen by the wave in the
measurement arm 16 may, in its simplest form, be either air
(perhaps with some tank vapors, dust or foam) or fluid 18. The
measurement arm reflected wave to the microwave bridge circuit 12
will be altered in amplitude or phase by the impedance of the
boundary layer (point of discontinuity) at the end of the
measurement arm, and that impedance will depend on the presence or
absence of material 18 in the tank 20 at the level of the
measurement arm 16.
The other divided propagating wave travels down the reference arm
26 and, in the embodiment shown in FIG. 1, is altered by the
impedance of the boundary layer at the end of the reference arm 26
presented by the sample chamber material 28 housed in the container
30. The container 30 is filled with a selected material, preferably
identical to the material 18 in the tank 20. The reflected
reference arm signal will thus be sufficiently different than the
reflected measurement arm signal unless the level of the material
18 in the tank 20 covers/encompasses the cross-sectional area of
the measurement arm 16 through which the radiation passes.
Accordingly, decision electronics may be provided to either actuate
the alarm 35 is there is a sufficient reflected differential signal
to the detector 32 (when the level of fluid in the tank 20 falls
below the level of the reference arm), or alternatively, when there
is not a sufficient reflected differential signal (when the fluid
level rises to or above the level of the reference arm). In either
case, the technique of the present invention easily, reliably, and
inexpensively enables the detection of whether the material level
in tank 20 is at or below a certain level, i.e., the level of the
reference arm. Moreover, this detection is made without the need
for any sensing element to physically contact the material in the
tank, and can be made almost irrespective of the type of solid or
liquid material in the tank.
The device described above operates on the principle that the
impedance presented to a propagating microwave depends upon the
electric and magnetic properties of the boundary layer material
through which the wave passes. When the wave reaches the boundary
layer, at least some of the wave will be reflected, and the
amplitude and phase of the reflected wave will thus be functionally
related to the boundary layer material, i.e., the material in the
tank. Since some factors affect the impedance seen by a wave due to
any change in the material at the boundary layer, including the
material conductivity, its permitivity, and its permeability, the
device of the present invention is ideally suited to be a universal
level detector without significant regard to the type of material
being detected. A change in the amplitude and phase of the
reflected wave will thus occur in almost every instance with a
change in the material at the boundary layer. In its simplest form,
that change is from air (or vapors, dust, or foam) to a liquid or
solid material. It should be understood, however, that the present
invention is also well suited to determine a change from one liquid
or solid material to another liquid or solid material. The device
of the present invention may thus be used to detect a rising or
falling interface of liquids, such as an oil/water interface.
FIG. 2 depicts a simplified pictorial illustration of the present
invention along with representative outputs of signal magnitudes
depending on whether the level of material has reached the level of
the detector. Microwave oscillator 10 generates and transmits an
incident propagating microwave down the waveguide section 42, which
wave is divided as explained above by the microwave bridge circuit
into two waves travelling down respective waveguide sections or
arms 16 and 26. The reflected differential signal travels down the
waveguide 54, and is detected by the detector 32.
The material in the sample chamber 30 (FIG. 1) may correspond to
the material 18 in the tank. The sample quantity preferably is
sufficiently large so as to appear to be an infinite quantity to
the reference wave, and thus the value of the reflected signal to
the bridge circuit from the sample chamber, SC, will be
substantially constant. The magnitude of the reflected signal to
the microwave bridge circuit from the measurement arm 16 will,
however, depend on the level of fluid in the tank 18. R.sub.1
indicates the magnitude of the reflected reference arm signal when
the material level is above the level of the measurement arm 16,
and R.sub.2 indicates the magnitude of the reflected measurement
arm signal when the material level is below the level of the
reference arm 16.
Accordingly, the difference between the reflected reference arm and
the measurement arm signals, which difference is the magnitude of
the signal transmitted to the detector 32, is represented in FIG. 2
by the designations .DELTA.R.sub.1 and .DELTA.R.sub.2. The
difference may be amplified by standard techniques within the
decision electronics to produce the sizable difference in the
signals KX.DELTA.R.sub.1 and KX.DELTA.R.sub.2. Comparison may thus
easily be made between the respective KX.DELTA.R.sub.1 signal and
the selected trip value, and the output used to either actuate or
not actuate the control device, such as alarm 35.
According to the embodiment as shown in FIGS. 1 and 2, the device
of the present invention may thus be "tuned" or calibrated by
placing in the sample chamber the same material whose presence or
absence is being detected by the reflected reference arm signal.
The embodiment as shown in FIGS. 1 and 2 is thus virtually
insensitive to the effects of temperature and pressure variations
in the material, since the divided propagating waves will be each
identically affected. Moreover, the device as described herein is
substantially insensitive to variations in signal power or
frequency from the oscillator 10, and thus requires no external
tuning.
FIG. 3 depicts an alternate embodiment of the present invention,
wherein the microwave oscillator 10 is a Model GOS 2570 Gunn diode
cavity-type oscillator, commercially sold by Alpha Industries. This
oscillator generates a microwave having a constant frequency of
approximately 10.5 gigahertz. The frequency of the oscillating
microwave according to the present invention is in the range of
from 1 to 20 gigahertz, and preferably from 3 to 15 gigahertz, in
order to maximize the clarity of the reflected measurement arm
signal yet minimize the likelihood that a thin film or powder layer
seen by the measurement arm wave will be improperly interpreted as
a material level higher than the measurement arm.
The propagated microwave 41 from the oscillator 10 is injected by a
waveguide 42 to the bridge circuit. Each of the waveguides 42, 16,
26 and 54 are rectangular in cross-sectional configuration, e.g.,
0.4 inches by 0.9 inches. For the embodiment shown in FIGS. 1 and
2, the measurement arm 16 and the reference arm 26 preferably are
the same length. These wave-guides may be fabricated from WR 90
bronze waveguide commercially available from A. T. Wall.
The microwave 41 is equally divided by a conventional hybrid or
magic Tee within the bridge circuit, which causes propagated waves
to travel horizontally down arms 16 and 26. The waveguides 16 and
26 are axially aligned, while the axis of waveguides 42 and 45 are
perpendicular thereto. At the end of the measurement arm 16 is a
dielectric window 21, which may be fabricated from various plastic
or glass materials, such as Ryton, and is transparent to microwaves
at the frequency level described above. The window 21 is sealingly
positioned within nipple 19, which in turn is affixed to the tank
wall 20 containing fluid or solid material 18. Thus, a maximum of
one window in a vessel will be necessary according to the present
invention. Moreover, if the tank material itself is substantially
transparent to microwaves, e.g. fiberglass, the end of the
waveguide 16 may be positioned against the exterior of the tank
wall, and no special window is necessary in the tank wall.
As previously described, a portion of the propagating wave 46 will
be reflected by the boundary layer at the interior surface of the
window 21. The amplitude and frequency of the reflected wave will
be significantly altered, however, by the impedance of that
material on the microwave. Since air (or vapor, dust or foam)
represent a significantly different impedance value to a microwave
than does a liquid or solid material, the reflected measurement arm
signal 50 will be significantly altered by the presence or absence
of material 18 at the level of the measurement arm.
In the embodiment shown in FIG. 3, the divided microwave 44 travels
down reference arm 26, and is altered by tuning elements 37B, 37A
and 36. These tuning elements may be adjusted so that the reflected
reference arm wave 48 corresponds in amplitude and phase to the
reflected measurement arm wave 50, so that the bridge circuit 12 is
balanced and the reflected differential signal 52 is nil or zero.
Once the bridge circuit is balanced, the differential signal 52
will remain near zero even if the frequency of the propagating wave
from the oscillator 10 drifts slightly in response to uncontrolled
stimuli.
Preferably both resistive and capacitive tuning elements are
provided for altering the reflected signal 48 from the reference
arm to correspond to the reflected signal 50 from the measurement
arm. Resistant tuning element 36 functions to absorb a regulatable
quantity of microwave energy by adjusting its depth with respect to
reference arm 26, and thereby primarily controls the amplitude of
the reflected reference arm signal 48 to correspond to the
amplitude of the reflected measurement arm signal 50. Two
capacitive tuning elements 37A and 37B may also be regulated to
primarily control the phase of the reflected reference arm signal
48. Each of the tuning elements are provided a fixed distance,
e.g., 1/4 wavelength apart, for maximizing their overall control
capability. In the embodiment shown in FIG. 3, the elements 37A,
37B and 36 are placed 1/4 wavelength, 1/2 wavelength, and 3/4
wavelength from the end of the waveguide 26. The placement of the
tuning elements 37A, 37B, and 36 provides the full range of tuning
capability with the fewest number of components. Each of these
tuning elements is commercially available from Johanson
Manufacturing Corp. under Part Nos. 6927-0 and 6952-0,
respectively.
The reflected differential signal 52 travels down waveguide 54 and
is detected by microwave detector 32. A suitable detector 32 is
available from Microwave Associates under Model MA40042. The direct
current output from detector 32 is thus proportional to the
magnitude of the amplitude and phase of the reflected differential
signal, and this output is connected via 56 to the decision
electronics 34.
The decision electronics 34 can be adjusted to establish a detector
output threshold for switching action to controlled apparatus, such
as alarm 35. The signal from the detector 32 is fed to the
amplifier 58, which may be adjusted by an external selectivity
adjustment 60 to alter the multiple constant K. The amplified
output 64 is thus input to comparator 66, and is compared to a
switching threshold value which may either be input manually or fed
by the computer 67 to the comparator 66 via line 68. The output
from the computer 67 thus presents an adjustable threshold which
permits control of the degree of mismatch that must be observed
before a switching action is achieved. If the desired mismatch
value is exceeded, light 72 may be actuated via line 70.
The output from comparator 66 is preferably connected via 74 to
time delay 76, which enables adjustment of the time period
necessary for the necessary mismatch from comparator 66 to be
present before a switching action is obtained. Thus, the output 78
from the time delay 76 presents a switching action signal only if
the desired threshold magnitude if observed for a selected period
of time. This time adjustment feature is particularly useful for
eliminating false switching actions that could otherwise be
generated by the sloshing of agitated liquids within the tank 20.
Finally, conventional failsafe electronic circuit 80 may be
provided so that the relay 84 is responsive not only to the output
from the comparator 80, but also the presence or absence of power
to the circuitry. As previously indicated, the relay 84 may be used
to control various equipment, such as lights, alarms, pumps,
indicators, or other control devices.
It should be understood that the sensitivity of the present
invention is substantially increased by providing a microwave
bridge circuit which produces an output directly indicative of the
difference, in either amplitude or phase, or both, between the
reflected reference arm signal and the reflected measurement arm
signal. Under either of the embodiments described herein, the
reflected reference arm signal may be tuned so as to present an
impedance equal to the impedance normally seen in the reflected
measurement arm signal. While the microwave detector 32
particularly depicted herein has been primarily described as
providing a D.C. output whose amplitude is indicative of both an
amplitude or phase difference in the two reflected signals, it
should be understood that detector circuits are available while
sense only an amplitude imbalance or a phase imbalance in the
microwave bridge signals. Thus, it is within the spirit and scope
of the present invention to provide a microwave detector circuit
which can distinguish between an amplitude and a phase differential
signal, and appropriate modifications would be made to the
decisions electronics described herein, as those skilled in the art
readily appreciate.
FIGS. 4A and 4B illustrate typical signals 64A and 64B from the
amplifier 58. Specifically, the signal 64A illustrates the
differential signal 52 when the detector is near null. Conversely,
signal 64B illustrates the signal from the amplifier 58 when the
detector is away from null and constructive interference
experienced by the differential signal 52. FIGS. 5A and 5B
illustrate the resultant signal after modification of the signals
illustrated in FIGS. 4A and 4B. Signal 74A corresponds to signal
64A after passing through the comparator 66. Similarly, signal 74B
corresponds to signal 64B after passing through the comparator
66.
FIGS. 6A and 6B illustrate the effect of integration on the
comparator output signal as illustrated in FIGS. 5A and 5B. FIG. 6A
illustrates the output from the time delay 76 when the comparator
output is low, e.g., signal 74A. Similarly, FIG. 6B illustrates the
effect on signal 78B when the comparator output is high. FIGS. 6A
and 6B illustrate that a relay trip point can be adjusted at a
specific voltage. When the signals 78A and 78B pass above or below
the specified relay trip voltage, the relay is activated or
deactivated.
FIG. 7 is a multisequence illustration of the signals generated by
the present invention when used for ullage measurement. The
amplifier output 64 is illustrated at the top of FIG. 7. The
amplifier output 64 passes through a sequence of changes as
follows: a null signal 86, a non-null signal 87, a null signal with
a splash 88, a non-null signal 89, a splash signal 90, and a
non-null signal 91. The corresponding output from the comparator is
illustrated in FIG. 7 as signal 92. When the signal from the time
delay 76 is applied to the signal 92, the resultant integrator
output signal 93 is created. The time delay between recognition and
relay tripping is adjustable as illustrated by the spacing 93A. The
activation or deactivation of the relay is illustrated in the
bottom portion of FIG. 7. An open relay is represented by numeral
94 and a closed relay is represented by numeral 95.
FIG. 8 illustrates another embodiment of the present invention
utilized to measure the flow/no-flow characteristics of material in
a conduit. FIG. 8 illustrates granular material 18A passing through
conduit 20A. The oscillator 10 is associated with the conduit 20A
by the window 21. The detector 32 is illustrated associated with
the waveguide 26 and tuning elements 36 and 37. FIG. 8 is similar
to the embodiment illustrated in FIG. 3 for measuring ullage.
FIG. 9 illustrates a block diagram of a preferred form of the
decision electronics as used in conjunction with the apparatus of
the present invention illustrated in FIG. 8. FIG. 9 includes the
input amp 102, the sample/hold circuit 104, the low pass filter
106, the differential amplifier 108, the full wave rectifier 110,
the voltage reference 112, the voltage comparator 114, the
sum/invert circuit 116, the sum/integrate circuit 118 and the
output control/timer 120. The operation of the flow/no-flow
detector of the present invention depends upon observing the
changes in the output signal of the microwave bridge circuit that
are induced by very slight changes in the reflection coefficient
associated with the interface of the material. The signal from the
detector 32 is input to the amplifier 102. The signal 122 passes
from the amplifier 102 into the sample/hold circuit 104. The
sample/hold circuit 104 is used to sample the output pulse and to
hold this voltage constant until the next pulse is observed. If
there are no changes in the pulse-to-pulse signal level, the output
of the sample/hold circuit 104 will not vary.
After the sample/hold circuit 104, it is the objective of the
present invention to detect very slight changes in signal
amplitude. Although there are many circuits available for detecting
a change in the amplitude of a signal, the presently preferred
circuit utilizes the low pass filter 106 and the differential
amplifier 108. The signal received from the sample/hold circuit 104
is divided into two channels, one of which is filtered or
equivalently delayed by the low pass filter 106 and a second
channel which is unfiltered. A differential amplifier 108 operates
on the filtered and unfiltered signals to produce a bipolar output
signal 124 that represents the difference between an instantaneous
value of the output signal and its near term smoothed or delayed
value. The resultant bipolar signal 124 is rectified by the full
wave rectifier 110. The output 126 of the full wave rectifier 110
is input into the voltage comparator 114 in conjunction with the
voltage reference 112. A primary control signal is output from the
voltage comparator 114 and is utilized in conjunction with the
sum/invert circuit 116 and the sum/integrate circuit 118 which acts
generally as an analog threshold computer to create the integrator
output 128. The integrator output 128 is the output from the
sum/integrate circuit 118. The output control/timer 120
.Iadd.responsive to the intergrator output 128 and the primary
control signal .Iaddend.provides the output to drive a relay or the
like.
FIGS. 10A and 10B illustrate a typical signal from the input
amplifier 102 for better describing one aspect of the present
invention. FIG. 10A illustrates the general signal 122 output from
the amplifier 102. As readily indicated on FIG. 10A, the flow of
material is represented by fluctuations in the signal 122. When no
material is flowing, the signal 122 is quiet. FIG. 10B is an
exploded view of a portion of FIG. 10A. As noted on FIG. 10B, there
are instantaneous points 132 through 139. The circuit of the
present invention takes a difference between the present output of
the amplifier 102 and substracts it from a delayed or filtered
version of the output of the amplifier 102. Thus, the circuit of
the present invention substracts a delayed version of the signal
from itself, e.g., in FIG. 10B, point 132 is substracted from point
133, point 134 is substracted from point 135, point 136 is
substracted from point 137, and point 138 is substracted from point
139. It should be noted that it is not the signal level that is
important but rather whether or not the signal changes in amplitude
with respect to time. Thus, any signal that is constant with
respect to time, i.e., flat, will give a zero output regardless of
its magnitude. Any signal 122 that is changing with respect to time
will give a positive or a negative signal depending on whether the
input is going up or down.
FIG. 11 illustrates a typical bipolar signal from the differential
amplifier 108 associated with the present invention. Specifically,
FIG. 11 illustrates the differences as referred to in FIG. 10B. The
flow characteristics associated with the signal are noted on FIG.
11. When the flow of material is present in the conduit 20A, the
signal 124 fluctuates. When there is no flow in the conduit 20A,
the signal 124 is steady.
FIG. 12 illustrates a typical unipolar signal associated with the
present invention. The bipolar signals associated with FIG. 11 are
passed through a full wave rectifier 110 so that the resultant
signal 126 is the absolute value of the signals 124 illustrated in
FIG. 11. FIG. 13 illustrates a typical relay drive output signal
130 which is illustrated in conjunction with the unipolar signals
of FIG. 12.
FIG. 14 illustrates a multisequence illustration of the signals
generated by the present invention when used for flow/no-flow
detection within a conduit. The uppermost portion of FIG. 14
illustrates the output signal 122 from the amplifier 102.
Specifically, numeral 140 illustrates a no-flow/null material
state. The numeral 142 illustrates a flow/null material state. The
numeral 144 illustrates a no-flow/non-null material state. The
numeral 146 represents a state where random pellets are dropping
past the window 121. The amplifier signals 122 are converted by the
differential amplifier 108 to yield the output illustrated in the
middle of FIG. 14. It should be noted that the difference amp
output in FIG. 14 illustrates the same output as illustrated
thereabove as the bipolar signal 124. The lower most portion of
FIG. 14 illustrates the unipolar signal 126 as generated after the
full wave rectifier 110 .[.and operated on by the sum/invert
circuit 116 and sum/integrate circuit 118 to form an integrator
output 128.].. The sequence of pulses represented by numeral 150
illustrate pulses which cause the relay to trip. The sequence of
pulses referenced by numeral 152 can be adjusted to be treated as a
"flow condition" or a "no-flow condition" depending on the
particular system being used.
Although the invention has been described in terms of the specified
embodiments which are set forth in detail, it should be understood
that this is by illustration only and that the invention is not
necessary limited thereto, since alternative embodiments and
operating techniques will become apparent to those skilled in the
art in view of the disclosure. Accordingly, modifications are
contemplated which can be made without departing from the spirit of
the described invention.
* * * * *