U.S. patent application number 14/128258 was filed with the patent office on 2014-07-10 for liquid level sensor.
This patent application is currently assigned to SABAN VENTURES PTY LIMITED. The applicant listed for this patent is Brian Hingley, Michael Potas. Invention is credited to Brian Hingley, Michael Potas.
Application Number | 20140191054 14/128258 |
Document ID | / |
Family ID | 47421925 |
Filed Date | 2014-07-10 |
United States Patent
Application |
20140191054 |
Kind Code |
A1 |
Hingley; Brian ; et
al. |
July 10, 2014 |
LIQUID LEVEL SENSOR
Abstract
A nebuliser cup for maintaining a safe level of liquid during
nebulization, the cup comprising a liquid level sensor comprising:
a first element sensing liquid at or below a position corresponding
to a filled liquid level in the nebuliser cup; a second element
electrically isolated from the first element and located at a
position corresponding to a filled liquid level in the nebuliser
cup; and wherein when the cup is not filled with a liquid to the
filled liquid level, the first element, the liquid and the second
element do not form an electrically coupled circuit; and when the
cup is filled with a liquid to the filled liquid level, the first
element, the liquid and the second element together form an
electrically coupled circuit.
Inventors: |
Hingley; Brian; (Alexandria,
AU) ; Potas; Michael; (Alexandria, AU) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hingley; Brian
Potas; Michael |
Alexandria
Alexandria |
|
AU
AU |
|
|
Assignee: |
SABAN VENTURES PTY LIMITED
Alexandria
AU
|
Family ID: |
47421925 |
Appl. No.: |
14/128258 |
Filed: |
June 25, 2012 |
PCT Filed: |
June 25, 2012 |
PCT NO: |
PCT/AU2012/000735 |
371 Date: |
February 24, 2014 |
Current U.S.
Class: |
239/1 ;
239/74 |
Current CPC
Class: |
B05B 17/0615 20130101;
G01F 23/261 20130101; G01F 23/265 20130101; A61L 2/22 20130101;
B05B 12/081 20130101; A61M 11/005 20130101; G01F 23/241 20130101;
G01F 23/242 20130101; A61M 2202/20 20130101 |
Class at
Publication: |
239/1 ;
239/74 |
International
Class: |
B05B 12/08 20060101
B05B012/08 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 24, 2011 |
AU |
2011902486 |
Claims
1. A nebuliser cup with a liquid level sensor comprising: a first
element sensing liquid at or below a position corresponding to a
filled liquid level in the nebuliser cup; a second element
electrically isolated from the first element and located at a
position corresponding to a filled liquid level in the nebuliser
cup; and wherein when the cup is not filled with a liquid to the
filled liquid level, the first element, the liquid and the second
element do not form an electrically coupled circuit; and when the
cup is filled with a liquid to the filled liquid level, the first
element, the liquid and the second element together form an
electrically coupled circuit.
2. A nebuliser cup according to claim 1 wherein the first and
second sensing elements are independently selected from the group
consisting of electrically resistive and electrically
capacitive.
3. A nebuliser cup according to claim 1 wherein the second element
is a conductive level sensor.
4. A nebuliser cup according to claim 3 wherein the cup has a cup
wall and the sensor passes through an insulated aperture in the cup
wall.
5. A nebuliser cup according to claim 4 wherein the insulated
aperture in the cup wall is an aperture surrounding an insulating
sleeve.
6. A nebuliser cup according to claim 1 wherein the first element
is the nebuliser cup.
7. A nebuliser cup according to claim 6 wherein the nebuliser cup
is an electrically conducting plastic cup or metal cup.
8. A nebuliser cup according to claim 1 in operative contact with
an ultrasonic transducer.
9. A nebuliser cup according to claim 18 in fluid communication
with a sterilizing chamber.
10. (canceled)
11. (canceled)
12. A nebuliser cup according to claim 3 wherein the sensor is
located at a position corresponding to a filled liquid level in the
electrically conducting nebuliser cup.
13. A nebuliser cup according to claim 12 wherein the sensor passes
through an insulated aperture in the cup wall.
14. A nebuliser cup according to claim 13 wherein the insulated
aperture in the cup wall is an aperture surrounding an insulating
sleeve.
15. A nebuliser cup according to claim 14 wherein the insulating
sleeve extends beyond the wall of the cup to a distance such that a
droplet of liquid is unable to complete a circuit with the sensor
and the cup.
16. A nebuliser cup according to claim 15 wherein the insulating
sleeve extends beyond the wall of the cup to a distance of at least
1 mm.
17. A nebuliser cup according to claim 1 in combination with a
feedback loop and a liquid filling reservoir.
18. A nebuliser cup according to claim 8 further comprising an
ultrasonic transducer located at or adjacent to the base of the
nebuliser cup.
19. A nebuliser cup according to claim 18 wherein the ultrasonic
transducer defines at least a portion of the base of the nebuliser
cup.
20. A nebuliser cup according to claim 19 wherein the ultrasonic
transducer acts directly upon the liquid in the cup to apply
ultrasonic energy to the liquid in the cup, thereby resulting in
generation of an aerosol from the surface of the liquid.
21. A method of maintaining a liquid level in a nebuliser cup
during operation, the method comprising: providing a first element
at or below a position corresponding to a filled liquid level in a
nebuliser cup; providing a second element electrically isolated
from the first element to contact a liquid at a position
corresponding to a filled liquid level in the nebuliser cup;
providing sufficient liquid to the nebuliser cup to reach said fill
level thereby to complete an electrically coupled circuit between
the first element, the liquid and the second element; and whereby a
drop in the liquid level to below the fill level triggers a break
in the circuit between the first element, the liquid and the second
element; and whereby the break in the circuit triggers dispensation
of further liquid in the nebuliser cup.
22. A method according to claim 21 wherein the first element is the
nebuliser cup.
23. A method according to claim 21 wherein sufficient further
liquid is dispensed to the conductive nebuliser cup in response to
the break in the circuit to restore the circuit and halt further
dispensation of liquid into the reservoir.
24. A method according to claim 23 wherein the break in the circuit
triggers dispensation of further liquid in the reservoir
immediately.
25. A method according to claim 23 wherein the break in the circuit
triggers dispensation of further liquid in the reservoir after a
predetermined time.
26. (canceled)
27. (canceled)
28. A method according to claim 21 wherein the liquid used for
sterilization is hydrogen peroxide solution or peracetic acid
solution.
29. A method according to claim 21 wherein the sensor at or below
fill level is configured maintain at least 5 mm depth of liquid in
the nebuliser cup.
30. A method according to claim 21 wherein the sensor at or below
fill level is configured to switch off the transducer when the
volume of liquid in the nebuliser cup falls to about at least 1.5
cm.sup.3 of liquid.
Description
FIELD OF THE INVENTION
[0001] The invention relates to methods and apparatus for
sterilisation which employ the use of ultrasonic agitation of
liquids to generate sterilising aerosols.
BACKGROUND OF THE INVENTION
[0002] Any discussion of the prior art throughout the specification
should in no way be considered as an admission that such prior art
is widely known or forms part of the common general knowledge in
the field.
[0003] Sterilisers are used in the medical, food and packaging
industries to kill and thereby prevent the transmission of
transmissible agents such as spores, fungi, and bacteria. A typical
steriliser creates a set of physical conditions in a sterilisation
chamber that effectively kills nearly all of these transmissible
agents.
[0004] Contacting articles in need of sterilisation with sterilant
aerosols is one known method of sterilisation. A typical aerosol
sterilisation apparatus of the prior art has a sterilisation
chamber with inlet and an outlet valves, an aerosol generator
(typically a nebuliser) in fluid communication with the chamber via
the inlet valve and a fan upstream of, and in fluid communication
with, the aerosol generator.
[0005] In use, an article requiring sterilisation is placed in the
chamber, which is then sealed. The aerosol inlet valve is opened
and the outlet valve is closed. The fan is engaged, which creates a
gas stream through or the past the aerosol generator, into the
chamber. A passive vent in the sterilisation chamber allows for
pressure equalization as required, to permit gas flow in and out of
the sterilisation chamber. The aerosol generator, which contains
the desired sterilant, is then activated, putting a large number of
small sterilant droplets into the gas stream. The droplets are
carried by the gas stream to create an aerosol which travels into
the sterilisation chamber. The sterilant then acts upon the
contents of the chamber, killing pathogenic organisms as
required.
[0006] One type of nebuliser which has proved to be well suited for
sterilization applications is an ultrasonic nebuliser.
[0007] In an ultrasonic nebuliser, a sterilization liquid is placed
in a cup which sits above and in contact with an ultrasonic
transducer. Typically, the ultrasonic transducer is a piezoelectric
crystal that changes size or shape in response to electrical
stimulus. The application of alternating current to the crystal at
high frequencies (of the order of several MHz) leads to the
crystals vibrating at a corresponding frequency. This energy is in
turn transferred to the sterilization liquid. The cup and
transducer may typically be configured to focus the distribution of
energy in the sterilization liquid. The energy causes small
microdroplets to be formed from the liquid and become airborne.
Typically, there are many such particles which together form a
nebulant or mist of aerosol particles. This nebulant is then
delivered to the sterilizing chamber.
[0008] One problem with such an arrangement is that if the
sterilizing liquid is fully consumed and the cup becomes empty,
then any continuing operation of the device is likely to result in
damage--the energy is not dissipated by the nebulant, but rather is
retained by the transducer and cup, causing the arrangement to
overheat which can irreversibly damage the transducer unit, for
example, by delamination or depolarisation of the transducer.
[0009] Another problem of such an arrangement is that if the
sterilizing liquid overfills the cup, the transducer experiences an
increase in load and the system efficiency can reduce, potentially
causing an undersupply of sterilizing aerosol and a resulting
failure to sterilize.
[0010] "Sterilization" is generally defined as a process capable of
achieving a log 6 reduction in concentration of spores.
"Disinfection" is a similar process, the difference being that it
results in a lesser degree of biocidal effect. "Sterilization"
includes "disinfection" and "disinfection/sterilization" is an
abbreviation for "disinfection and/or sterilization". In the
present application, "disinfection" and "sterilization" are used
interchangeably.
[0011] Because of the constructional requirements of ultrasonic
sterilizers, it is not a trivial task to in determine when there is
an appropriate level of liquid in the ultrasonic cup. The
sterilizing liquid usually contains hydrogen peroxide, which is
highly toxic and corrosive, requiring the cup and the transducer to
be maintained in a tightly sealed system. Any sensing means needs
to be sufficiently robust to withstand repeated exposure to toxic
and corrosive peroxide liquid and vapour, possibly at high
temperatures. In addition, because of the fluid in the environment
and the possibility of splashing, the sensor need to be highly
accurate in its ability to avoid false positive and false negative
results, which could lead to either destruction of the transducer
element or an undersupply of sterilizing aerosol.
[0012] Thus, there is a need for sensor for determining the level
of liquid in an ultrasonic cup which is robust enough to endure
repeated exposure to sterilization conditions.
SUMMARY OF THE INVENTION
[0013] In a broad first aspect, the invention provides a nebuliser
cup with a liquid level sensor comprising: [0014] a first element
sensing liquid at or below a position corresponding to a filled
liquid level in the nebuliser cup; [0015] a second element
electrically isolated from the first element and located at a
position corresponding to a filled liquid level in the nebuliser
cup; and [0016] wherein [0017] when the cup is not filled with a
liquid to the filled liquid level, the first element, the liquid
and the second element do not form an electrically coupled circuit;
and [0018] when the cup is filled with a liquid to the filled
liquid level, the first element, [0019] the liquid and the second
element together form an electrically coupled circuit.
[0020] The liquid is generally aqueous based, for example aqueous
hydrogen peroxide.
[0021] The first and second elements may be independently selected
from electrically resistive and electrically capacitive
sensors.
[0022] The first and second elements may be resistive; or the first
sensing element is resistive and the second sensing element is
capacitive; or the first sensing element is capacitive and the
second sensing element is resistive; or the first and second
sensing elements are capacitive.
[0023] The element can pass through an insulated aperture in the
cup wall, preferably the insulated aperture in the cup wall is an
aperture surrounding an insulating sleeve.
[0024] In one embodiment, the first element is the nebuliser cup,
such as an electrically conducting plastic cup, metal cup, or a
non-conducting cup incorporating an electrically conductive element
not in direct contact with the liquid.
[0025] According to a second aspect the invention provides a
nebuliser cup with a liquid level sensor comprising: [0026] an
electrically conducting nebuliser cup and a conductive sensor
electrically insulated from the cup and positioned such that when
the cup is filled with a liquid to be nebulised, the cup, liquid
and the conductive sensor together form an electrically coupled
circuit.
[0027] The electrically conducting nebuliser cup may be a metal cup
(for example, aluminium or stainless steel) or an electrically
conducting plastic cup.
[0028] The sensor is a conductive level sensor.
[0029] Preferably, the sensor is located at a position
corresponding to a filled liquid level in the electrically
conducting nebuliser cup.
[0030] In one preferred embodiment, the sensor passes through an
insulated aperture in the cup wall. The insulated aperture in the
cup wall may be an aperture surrounding an insulating sleeve.
[0031] Preferably the insulating sleeve extends beyond the wall of
the cup to a distance such that a droplet of liquid is unable to
complete a circuit with the sensor and the cup.
[0032] In a third aspect, the invention provides a nebuliser cup
with a liquid level sensor according to the preceding aspect in
combination with a feedback loop and a liquid filling
reservoir.
[0033] In a fourth aspect the invention relates to a method of
maintaining a liquid level in a nebuliser cup during operation, the
method comprising: [0034] providing a first element at or below a
position corresponding to a filled liquid level in a nebuliser cup;
[0035] providing a second element electrically isolated from the
first element to contact a liquid at a position corresponding to a
filled liquid level in the nebuliser cup; [0036] providing
sufficient liquid to the nebuliser cup to reach said fill level
thereby to complete an electrically coupled circuit between the
first element, the liquid and the second element; [0037] and
whereby a drop in the liquid level to below the fill level triggers
a break in the circuit between the first element, the liquid and
the second element; and whereby the break in the circuit triggers
dispensation of further liquid in the nebuliser cup.
[0038] According to a fifth aspect the invention provides a method
of maintaining a liquid level in a nebuliser cup during operation
comprising: [0039] positioning a conductive sensor at fill level
relative to a conductive nebuliser cup, said conductive sensor
being electrically insulated from the conductive nebuliser cup;
[0040] providing sufficient liquid to conductive nebuliser cup to
reach said fill level thereby to complete a circuit between the
cup, the liquid and the sensor; [0041] and whereby a drop in the
liquid level to below the fill level triggers a break in the
circuit between the cup, the liquid and the sensor; and [0042]
whereby in turn the break in the circuit triggers dispensation of
further liquid in conductive nebuliser cup.
[0043] Preferably sufficient further liquid is dispensed to the
conductive nebuliser cup in response to the break in the circuit to
restore the circuit and halt further dispensation of liquid into
the reservoir.
[0044] In one embodiment, the break in the circuit triggers
dispensation of further liquid in the reservoir immediately. Such
an embodiment could be used in the case where the liquid was
dispensed to the cup whilst ultrasonic nebulization was in
progress.
[0045] In an alternative embodiment, the break in the circuit
triggers dispensation of further liquid in the reservoir after or
at a predetermined time. That particular embodiment could be used
where the liquid was dispensed to the cup whilst ultrasonic
nebulization was not in progress, i.e. where discrete
non-overlapping nebulization and liquid level sensing periods are
employed. In such a case, sensing of the liquid level may occur
prior to a nebulization period, or may occur after a predetermined
period of nebulization has concluded. In each case, the
determination of the liquid level would either result in a
dispensation of liquid to the nebuliser cup or termination of the
process (if the liquid level was below the sensing threshold) or
would result in the process continuing (if the level was above the
sensing threshold).
[0046] In a sixth aspect, the invention provides a nebuliser cup
according to the first aspect in operative contact with an
ultrasonic transducer.
[0047] In a seventh aspect, the invention provides a nebuliser cup
according to the first or the fifth aspect located in fluid
communication with a sterilizing chamber.
[0048] The liquid used for sterilization is preferably hydrogen
peroxide solution or peracetic acid solution.
[0049] Unless the context clearly requires otherwise, throughout
the description and the claims, the words "comprise", "comprising",
and the like are to be construed in an inclusive sense as opposed
to an exclusive or exhaustive sense; that is to say, in the sense
of "including, but not limited to".
[0050] Unless explicitly stated otherwise, conductive and
conduction is used interchangeably, incorporating both AC and DC
electrical current flow.
[0051] In the present invention, the nebuliser cup has a base, an
upwardly extending wall and an open top whereby nebulised mist can
be generated directly from bulk liquid contained, in use, within
the cup. An ultrasonic transducer is preferably located at or
adjacent to the base of the nebuliser cup or, alternatively, the
ultrasonic transducer defines at least a portion of the base of the
nebuliser cup. In the latter case the ultrasonic transducer acts
directly upon the liquid in the cup, at the base, to apply
ultrasonic energy to the liquid in the cup, thereby resulting in
generation of an aerosol from the surface of the liquid. One face
only of the ultrasonic transducer is in contact with, or
transmissive to the liquid in the cup, and the liquid in the cup
does not pass through the transducer.
DESCRIPTION OF THE DRAWINGS
[0052] FIG. 1 shows a schematic diagram of the nebuliser cup of the
present invention.
[0053] FIGS. 2 and 3 show a preferred nebuliser cup of the present
invention.
[0054] FIG. 4 is an assembly view of a preferred nebuliser cup of
the present invention in its operating environment.
[0055] FIGS. 5a and 5b show alternative embodiments of the
invention
[0056] FIG. 6 shows yet another embodiment of the invention.
DESCRIPTION OF THE INVENTION
[0057] The present invention provides a nebuliser cup which allows
for detection of liquid level in the cup whilst being of
sufficiently simple and robust design to withstand harsh
environments such as may be found within ultrasonic sterilizing
apparatus.
[0058] The general principle of the device is that at least one of
the sensor elements is positioned at an "upper" fill level position
and the other at or below the fill position, which may be called a
"lower" position (although both sensors may be at the fill
position, as long as isolated from each other when liquid is
absent). When the cup is filled with liquid, the upper sensor
element, the lower sensor element and the liquid form a circuit.
When the liquid is consumed, the upper level of the liquid drops
below the upper sensor, breaking the circuit, which in turn
triggers the dispensation of additional liquid to refill the
cup.
[0059] The sensors can either the same or different, and can be
either capacitive or conductive. The options are shown below in
Table 1.
TABLE-US-00001 TABLE 1 Option Sensor 1 (at or below fill level)
Sensor 2 (at fill level) 1 Direct electrical contact with fluid
Direct electrical contact with fluid 2 Capacitive contact with
fluid Direct electrical contact with fluid 3 Direct electrical
contact with fluid Capacitive contact with fluid 4 Capacitive
contact with fluid Capacitive contact with fluid
[0060] The apparatus is described with respect to the drawings, in
which the sensors are both conductive, and in which one of the
sensors, that at or below fill level, is the cup itself.
[0061] Nebuliser cup 1 is in operative engagement with ultrasonic
transducer 2. The transducer is in contact with the base 3 of the
cup, 3. Operation of transducer 2 serves to ultrasonicate liquid,
where present, in cup 1. The liquid in the cup, typically
containing aqueous hydrogen peroxide, is advantageously filled at
least to fill level 4. As transducer 2 operates and the liquid is
ultrasonicated and converted to nebulant, which is dispersed, the
upper level of the liquid drops. As the level of the liquid drops,
the nebulization process can become sub optimal, and on approaching
very low liquid levels, the liquid may be unable to disperse the
ultrasonic energy, and the transducer 2, can begin to heat, with
possibly destructive consequences.
[0062] The present invention includes a sensor 5 which is
positioned at the fill level 4. The fill level can be chosen to
achieve the optimal liquid level height given the other operating
parameters of the device. In this case, the positioning is achieved
by way of an aperture 6 in the cup 1, into which is placed sensor 5
surrounded by an isolating sleeve 7. The isolating sleeve may be of
any suitable material, for example, chemically resistant PVDF
(polyvinylidene fluoride), PEEK, PTFE etc.
[0063] Ideally, the sensor at or below fill level is configured to
switch on the pump or open the valve so as to introduce more liquid
into the nebuliser cup (or switch off the transducer, if the
reservoir is empty) when the level of liquid in the nebuliser cup
falls to a predetermined level. In preferred embodiments, that
predetermined level is at least 5 mm from the base of the cup or
surface of the transducer. That, is, the lower liquid level sensor
is positioned at 5 mm or greater from the base of the cup so that
the cup will always retain a minimum of 5 mm depth in the base of
the cup to ensure that there is sufficient liquid present to absorb
ultrasonic energy and prevent the transducer from destructive
delamination.
[0064] The typical diameter of the nebuliser cup, based upon the
sizing of most ultrasonic transducers, is at least around 20 mm, so
the fill sensors are typically positioned such that the liquid does
not fall below a minimum volume of 1.5 cm.sup.3 of liquid.
[0065] Whilst the main purpose of the present invention is to
protect the nebuliser from running dry, the nebuliser cup of the
present invention also allows the setting of upper and lower sensor
levels to determine optimum performance of the nebuliser. The
ultrasonic transducer focuses energy into the cup, causing a mist
of droplets to arise. In some cases, the mist and droplet profile
can vary depending upon whether the mist is generated from a full
cup or from a cup with a lower liquid level. The upper and lower
sensor levels can be determined, based on the transducer and cup
design, so as to bracket the optimum liquid level. This means that
in use, the nebuliser cup of the present invention can provide a
mist that it consistently around the optimum achievable.
[0066] The sensor is an AC excited coupled liquid level sensor. The
excitation signal may be of any suitable form, for example, a 5
Vp-p 6 kHz square wave and is coupled via a capacitor to the sensor
electrode. This ensures that there is no DC potential on the sensor
electrode; avoiding any problems with electrolysis of the
liquid.
[0067] When the liquid level is at the fill level 4, it contacts
the sensor 5. The sensor has an aluminium, or stainless steel,
sensor pin 5a which contacts the liquid where present. There is a
drop in the electrode signal level that occurs when the
H.sub.2O.sub.2 level in the cup is high enough to contact the
electrode. This shunts some of the signal to earth via the
conductive path formed between the sensor and the earthed metallic
cup.
[0068] When the apparatus is in use, the liquid in the cup is
consumed as a result of the nebulisation process, and the liquid
level falls. At some time, the liquid level will drop to a sub-fill
level 8. At this level, pin 5a will no longer contact the liquid
and sensor 5 will stop sensing it, and that information will be fed
via pathway 9 into controller 10.
[0069] If controller 10 detects a low electrode signal below a
predetermined threshold, then it infers sufficient liquid is
present in the cup. If controller 10 detects a high electrode
signal, above a predetermined threshold, then it infers
insufficient liquid is present in the cup.
[0070] In the case of insufficient liquid level detected by sensor
5, controller 10 triggers the opening of valve 11 which permits
additional liquid to flow from reservoir 12 into cup 1, either
under gravity or by pumping. Alternatively, a peristaltic pump
could be used at 11 to close reservoir 12 when not pumping.
[0071] Controller 10 can be configured to trigger the release of a
liquid either immediately upon detection of a fall in liquid level,
or at a predetermined time after a fall in liquid level is
detected, usually a few seconds, during which time the liquid level
will fall below the sub-fill level 8, but not so much as to reach
the base of the cup. In this way a safe and operationally useful
liquid level is maintained. Importantly, the sensor is sized and
positioned such that liquid droplets such as nebulant particles or
particles of condensate are unable to complete the circuit between
the sensor the conducting cup, thereby generating a false signal
that would result in destruction of the apparatus. Additionally,
the positioning of the sensor and the triggering of additional
liquid can be configured to take into account meniscus formation.
One such example would be an insulating sheath around the sensor to
prevent electrical contact between the cup and the sensor. The
insulating sheath preferably provides around a 1 mm or greater gap
between the sensor and the conducting cup.
[0072] Because the switching is qualitative ("on-off") rather than
quantitative, it is more robust and less prone to error or the need
for recalibration. Also, because of the large difference between on
and off voltages, the system can readily operate over a large range
of sterilization liquids without recalibration or
standardization.
[0073] Additionally, the cup can be used in apparatus where the
nebulization and dispensation of liquid to the cup (refilling)
occur either simultaneously or sequentially. For example, in larger
apparatus, nebulization may take place continuously, and filling
would then take place as needed while nebulization was on going, so
as to maintain the predetermined liquid level. However, in other
embodiments, nebulization takes place on an intermittent basis, and
it may in those cases be advantageous to conduct sensing of the
liquid levels whilst nebulization is off. For example, sensing can
take place before nebulization commences, or between nebulization
intervals. In that case, if insufficient levels are detected, the
nebulizer cup is refilled before nebulization recommences.
[0074] It may be desirable in some cases to overfill the nebulizer
above the fill level. In that case, a further overfill sensor at a
higher level can be used to detect an overfill condition.
Alternatively, the overfill level could be determined by the
refilling liquid volumetric flow rate and a time delay between the
detection of liquid and the cessation of refilling.
[0075] The lower level may also be selected so that it can
accommodate a further predetermined time interval prior to
switching off the transducer or introducing more liquid.
[0076] The cup may be made from any type of conducting material,
for example, a metal such as aluminium or alternatively, the cup
maybe made from a conducting plastic. In an alternative embodiment,
the cup is not made from a conducting material, but instead has an
appropriate conductive portion located inside the cup at fill
level.
[0077] A further embodiment of the device is shown in FIGS. 2 and
3. Cup 1 can be tapered towards the bottom if desired. The
reservoir in this apparatus can be seen to fill via port 13 which
is at the bottom of the reservoir. FIG. 4 is an assembly view.
[0078] FIGS. 5a and 5b show alternative embodiments of the
invention. In this case, the cup 1 is not conductive, but rather
the circuit is completed by way of a sensor element (e.g. an
electrode of some type) which completes the circuit only when the
liquid is at a fill level 4.
[0079] A further embodiment is shown in FIG. 6. In this case the
liquid level sensors 5 are located away from the cup body 1 but are
in fluid communication with the liquid in the cup and are located
at a level corresponding to the fill level 4 of the cup.
[0080] When the apparatus is in use, the liquid in the cup is
consumed as a result of the nebulisation process, and the liquid
level falls. At some time, the liquid level will drop to a sub-fill
level 8. At this level, liquid no longer remains in exit pipe 20,
which has sensors 5 located along it at level corresponding to fill
level 4. The sensors 5 fail to sense the presence of liquid,
leading to an increase in signal, controller 10. The sensors then
sense the presence of liquid in the exit pipe which in turn leads
controller 10 to infer there is insufficient liquid is present in
the cup. Controller 10 then triggers the opening of valve 11 which
permits additional liquid to flow from reservoir 12 into cup 1,
either under gravity or by pumping. Alternatively, a peristaltic
pump could be used at 11 to close reservoir 12 when not
pumping.
[0081] Controller 10 can be configured to trigger the release of a
liquid either immediately upon detection of a fall in liquid level,
or at a predetermined time after a fall in liquid level is
detected, usually a few seconds, during which time the liquid level
will fall below the sub-fill level 8, but not so much as to reach
the base of the cup. In this way a safe and operationally useful
liquid level is maintained.
[0082] Additionally, as mentioned, it is not necessary that either
or both of the sensors are conductive. Either or both of the
sensors may be capacitive. A capacitive sensor has plates which are
not in direct conduct with the liquid, but is physically separated
by way of a barrier layer but is nevertheless electrically coupled
to it. Typically, a capacitive sensor would be present on the
outside of the cup, or placed inside the cup wall material, which
forms a barrier layer. When the liquid comes into contact with the
barrier layer adjacent the capacitive sensor, an AC current is able
to flow if the circuit is otherwise complete (e.g. by way of
another sensor element either directly in contact with the liquid
or in capacitive contact with the fluid).
[0083] In the case of direct sensors, the current can be either AC
or DC, although DC is not preferred as it can lead to electrolysis
of the liquid. In the case of capacitive sensors, or mixed
capacitive/conductive sensors, AC is required.
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