U.S. patent number 3,901,443 [Application Number 05/431,202] was granted by the patent office on 1975-08-26 for ultrasonic wave nebulizer.
This patent grant is currently assigned to TDK Electronics Co., Ltd.. Invention is credited to Sadao Mitsui, Minoru Takahashi.
United States Patent |
3,901,443 |
Mitsui , et al. |
August 26, 1975 |
**Please see images for:
( Certificate of Correction ) ** |
Ultrasonic wave nebulizer
Abstract
An ultrasonic wave nebulizer according to the present invention
comprises a nebulizing chamber containing a liquid to be nebulized
and capable of adjusting the surface level of said liquid to a
predetermined value, a chamber base disposed at the bottom portion
of said nebulizing chamber, a piezo-electric transducer mounted on
said chamber base in such a manner that its vibration surface has
an inclination of 2.degree.-22.degree. with respect to said surface
level of said liquid, a pair of transistors for ultrasonically
oscillating the transducer and directly mounted on said chamber
base, a conical horn having a predetermined reflection surface and
being located on the upper portion of said piezo-electric
transducer which makes contact with the bottom portion of said
liquid, an exhaust cylinder or duct for exhausting fog composed of
minute liquid particles and formed in said nebulizing chamber, and
an air supply inlet for guiding or flowing said fog to the
generating direction of said fog whereby the effective nebulized
amount of said liquid per unit input electric power can be
increased, so that a high nebulizing efficiency can be
provided.
Inventors: |
Mitsui; Sadao (Chiba,
JA), Takahashi; Minoru (Tokyo, JA) |
Assignee: |
TDK Electronics Co., Ltd.
(Tokyo, JA)
|
Family
ID: |
27456387 |
Appl.
No.: |
05/431,202 |
Filed: |
January 7, 1974 |
Foreign Application Priority Data
|
|
|
|
|
Feb 6, 1973 [JA] |
|
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48-15459 |
Feb 12, 1973 [JA] |
|
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48-17601 |
Feb 12, 1973 [JA] |
|
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48-17602 |
Aug 31, 1973 [JA] |
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48-103005 |
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Current U.S.
Class: |
239/102.2;
239/338; 261/DIG.65; 261/DIG.48 |
Current CPC
Class: |
B05B
17/0615 (20130101); Y10S 261/65 (20130101); Y10S
261/48 (20130101) |
Current International
Class: |
B05B
17/04 (20060101); B05B 17/06 (20060101); B05B
003/14 () |
Field of
Search: |
;239/101,102,338 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: King; Lloyd L.
Attorney, Agent or Firm: Burgess, Ryan and Wayne
Claims
What is claimed is:
1. An ultrasonic wave nebulizer comprising a nebulizing chamber
filled with a predetermined amount of liquid, a chamber base formed
at the bottom portion of said nebulizing chamber, a piezo-electric
transducer inserted into and secured to said chamber base so that
the vibration surface of said piezo-electric transducer has an
inclination of 2.degree. - 22.degree. with respect to the surface
of said liquid in said nebulizing chamber, an electric circuit
means for electrically oscillating said transducer with a natural
frequency thereof, an exhaust duct for expelling fog composed of
minute liquid particles and formed above said vibration surface of
said transducer to the exterior, and an air supply inlet for
supplying an air flow to said fog thereby forcibly expelling said
fog through said exhaust cylinder.
2. A nebulizer as claimed in claim 1, further comprising a conical
horn having a predetermined reflection surface provided on the
upper portion of said transducer contacting said liquid to be
nebulized.
3. A nebulizer as claimed in claim 1, further comprising
transistors for ultrasonically driving said transducer directly
attached to said chamber base and cooled by said water used for
producing said fogs via said chamber base.
4. A nebulizer as claimed in claim 1, further comprising a means
for maintaining the surface level of said liquid in said nebulizing
chamber at a constant value.
5. A nebulizer as claimed in claim 4, further comprising a liquid
tank, and means for maintaining the liquid surface level of said
liquid tank equal to the surface level of said liquid in said
nebulizing chamber.
6. A nebulizer as claimed in claim 5, wherein said liquid tank is
disposed in such a manner that said liquid surface level of said
liquid tank is lower than said surface level of said liquid in said
nebulizing chamber, said liquid is supplied from said liquid tank
into said nebulizing chamber by means of a pump and any excess
amount of said supplied liquid is returned back into said liquid
tank via an overflow portion connected to said nebulizing
chamber.
7. A nebulizer as claimed in claim 4, further comprising a pair of
first and second electrodes respectively contained in said
nebulizing chamber and situated with a vertical space within a
range of variations of said surface level of said liquid in said
chamber, said electrodes and the bottom portion of said chamber are
respectively connected to an AC source and an AC voltage is applied
therebetween, a pair of first and second lamps respectively operate
after detecting changes in potentials caused by variations of said
liquid surface level beyond said positions of said electrodes, and
a pair of first and second photoelectric circuits being actuated by
the lights radiated from said lamps, respectively, so that said
liquid surface level in said nebulizing chamber can be
detected.
8. A nebulizer as claimed in claim 1, wherein said air supply inlet
points in the direction of said rising column of fog said fog
assuming the shape of a water column formed on said liquid surface
in said nebulizing chamber, whereby said fog is sent to the
exterior along the direction of said air flow.
Description
The present invention relates to an apparatus for nebulizing
various liquids utilizing an ultrasonic wave in which the effective
nebulized amount of the liquid per unit of input electric power can
be increased.
BACKGROUND OF THE INVENTION
It is well known that in the conventional ultrasonic wave
nebulizer, an ultrasonic wave is injected into a liquid from
beneath the surface thereof toward the vertical upward direction,
whereby a continuously spouting column of liquid is formed in the
injecting direction, and the desired minute liquid particles can be
produced and nebulized at a position adjacent to the top end
portion of the liquid column. However, such an ultrasonic wave
nebulizer as used in the conventional art has objectionable
features as described below.
A. The vibration surface of the transduucer for generating a
supersonic wave is attached to the bottom portion of the nebulizing
chamber in parallel with the surface of the liquid in the
nebulizing chamber so that a continuous stream liquid column is
formed in a direction vertical to the liquid surface, and large
liquid particles and water drops which are not being nebulized are
produced in an area adjacent to the top end portion of said
continuously spouting liquid column, and intermittently fall down
therefrom. As a result of this, the form of the continuously
generating and spouting liquid column is disturbed and nebulization
at the above-mentioned adjacent position is decreased, so that a
fog of minute liquid particles is intermittently produced.
B. Generally, the transducer of the nebulizer is driven by one to
four transistors with an output power of 15 to 50 watts. In this
case, as is well known, it is necessary to disperse the heat
generated in each transistor during its operation so as to operate
the transistor normally. Consequently, in the prior art, a natural
air cooling means is utilized for dispersing the heat generated in
the transistor into the atmosphere, such as a cooling fan
exclusively used for the transistor, or other oscillating frames
having a heat dispersing structure. However, according to this
natural air cooling method, it is necessary to enlarge the
construction of both the heat disperser and entire nebulizer.
c. The relationship between a liquid surface level L (cm), that is
the distance between the supersonic wave source and the liquid
surface, and a nebulized amount of the liquid Q (cc/hr) is as
follows. When the liquid surface level L is in a range of from 0 to
8.0 cm. a sufficient nebulizing capacity can be obtained, and the
more preferable conditions are when the liquid surface level L is
from 5 to 7.5 cm, the frequency is 1.3 MHz and the diameter of the
source is 25.phi.. However, to keep the liquid surface level L
approximately at a constant value, it is necessary to use an
additional liquid supply pump or a liquid surface detector, but in
either case, a driving power source or an additional electron
circuit is needed.
d. Further, in a conventional supersonic wave nebulizer, since the
largest part of an air stream around the spouting liquid formed in
the nebulizing chamber flows vertically upward, parallel to the
forming direction of the spouting liquid and some part of which
flows in the opposite direction, the amount of fog flowing to the
exterior of the chamber, inevitably becomes less than that of the
generated fog.
SUMMARY OF THE INVENTION
The principal object of the present invention is to eliminate the
above-mentioned conventional objectionable features and greatly
increase the nebulized amount of liquid.
The first characteristic feature of the present invention is that a
piezo-electric transducer is mounted on the horizontal bottom
portion of a nebulizing chamber containing a liquid to be nebulized
by said piezo-electric transducer in such a manner than its
vibration surface has a predetermined inclination with respect to
the surface of said liquid, so as to continuously form a liquid
column spouting stream in a direction inclined to said liquid
surface. As a result, large liquid particles and water drops not
being nebulized, produced at a position adjacent to the top end
portion of said liquid column, are prevented from dropping
therethrough.
The second characteristic feature of the present invention is that
a conical horn having a predetermined reflection surface is
provided on the upper portion of said piezo-electric transducer in
contact with the liquid to be nebulized.
The third characteristic feature of the present invention is that
the heat produced by transistors is dispersed by a metallic chamber
base of the nebulizer and by a water cooling means utilizing the
liquid or water to be nebulized as a coolant, so that the
constructions of both the heat disperser and the entire nebulizer
can be miniaturized.
The fourth characteristic feature of the present invention is that
means are provided for maintaining a distance between the
ultrasonic wave source and the liquid surface, that is, the liquid
surface level, is kept approximately at a constant value.
The fifth characteristic feature of the present invention is the
all the produced fog can be expelled from the nebulizing chamber by
arranging the direction of the air flow around the generating
portion of the fog approximately parallel to the direction of the
water spout produced by the transducer is formed the forming
direction of the spouting water.
BRIEF EXPLANATION OF THE DRAWINGS
Further features and advantages of the present invention will be
apparent from the ensuing description with reference to the
accompanying drawings to which, however, the scope of the invention
is in no way limited.
FIG. 1 is a cross-sectional view, along I--I', of FIG. 2, of one
embodiment of a nebulizer according to the present invention,
showing the assembly thereof;
FIG. 2 is a bottom view of the nebulizer shown in FIG. 1;
FIG. 3 is a cross-sectional front view of the piezo-electric
transducer included in FIG. 1, illustrating its mounting portion in
detail;
FIG. 4 is an ultrasonic wave oscillation and amplification circuit
diagram for driving the piezo-electric transducer used in FIG.
1;
FIGS. 5 and 6 are respectively characteristic curves of the
nebulizer shown in FIG. 1;
FIG. 7 is a cross-sectional front view of another embodiment of the
nebulizer according to the present invention;
FIG. 8 is a characteristic curve of the nebulizing apparatus shown
in FIG. 7;
FIGS. 9 and 10 are respectively modified embodiments of the
nebulizer according to the present invention, and;
FIG. 11 is a photoelectric circuit connection diagram used in FIG.
10.
FIRST EMBODIMENT ACCORDING TO THE PRESENT INVENTION
As shown in FIG. 1, an ultrasonic wave nebulizer according to the
present invention comprises a nebulizing chamber 2 containing a
predetermined amount of liquid 1, a piezo-electric transducer 4
inserted into a through hole 3 formed at the bottom portion of said
chamber 2 and tightly secured to the bottom portion of the chamber
2 by means of a pair of thumb screws 20 as shown in FIG. 3. Said
piezo-electric transducer 4 is electrically driven by an ultrasonic
oscillation and amplification circuit shown in FIG. 4 with a
natural frequency. A liquid or water column 5 in the shape of a
spouting stream is formed on the surface of said liquid 1 in a
direction vertical to the transducer surface of said transducer 4,
so that water drops 6 such as large liquid particles and fogs 7,
consisting of minute liquid particles, are produced at a position
adjacent to the top end portion of said water column 5. The fogs 7
so generated are forcibly expelled through an exhaust duct 9
mounted on the upper portion of the nebulizing chamber 2 by
applying an air current from an air supply inlet 8.
FIG. 2 is a bottom view showing the main elements of the nebulizer
shown in FIG. 1. In FIG. 2, there is clearly shown a power
transformer 10, a pair of transistors 11 mounted on the bottom
portion of the nebulizing chamber 2, a printed circuit plate 12 for
mounting or supporting said ultrasonic oscillation and
amplification circuit shown in FIG. 4, a motor 13 for driving a fan
14, a power fuse 15, a power cord 16 and a power cord connector
16a.
FIG. 3 is a diagram showing, in detail, the elements for mounting
or securing the piezo-electric transducer 4 shown in FIG. 1. In
FIG. 3, there is clearly shown a piezo-electric transducer 4
(having a diameter of 20 .phi. and a thickness of 1.66 mm), a
rubber support 17, an aluminum chamber base 18 of the nebulizing
chamber 2, a cap 19 for securing the piezo-electric transducer 4, a
pair of thumb screws 20 for fastening the transducer 4 and the
supporting rubber 17 by securing the cap 19 of the disc 4, and a
pair of through holes 21a formed at the bottom portion of the
liquid tank 21 shown in FIG. 1. Further, a pair of positive and
negative electrodes (not shown) are provided which are sintered on
the top surface of the transducer 4 and turned around from a part
of the top surface to the bottom surface of the transducer 4 and
respectively soldered to lead wires (not shown).
FIG. 4 is an embodiment of an ultrasonic wave oscillation and
amplification circuit diagram for driving the piezo-electric
transducer 4 used in the nebulizer shown in FIG. 1, according to
the present invention. The circuit comprises: an oscillator or
oscillation circuit composed of a transistor Q.sub.1, an inductance
coil L.sub.1, capacitors C.sub.1 - C.sub.3, and resistors R.sub.1 -
R.sub.3 ; a buffer amplifier, composed of a transistor Q.sub.2, a
tuning circuit of C.sub.5 and T.sub.1, capacitors C.sub.6 and
C.sub.7, and resistors R.sub.4 - R.sub.6 ; a power amplifier,
composed of a transistor Q.sub.3, an emitter resistor R.sub.8, and
a tuning circuit of C.sub.8 and T.sub.2. An oscillatory output of
the oscillator is supplied via a coupling condenser C.sub.4 to the
buffer amplifier, via a coupling resistor R.sub.7 to the power
amplifier, and then to the piezo-electric transducer 4 shown in
FIG. 1. Rectifiers D.sub.1 - D.sub.4 and a condenser C.sub.11
compose a rectifier bridge circuit, and a resistor R.sub.9 and
condensers C.sub.9, C.sub.10 compose a smoothing circuit.
The characteristic features of the ultrasonic wave nebulizer having
the above-mentioned construction as shown in FIGS. 1 through 3,
according to the present invention, will hereinafter be illustrated
in detail.
As shown in FIG. 1, the surface of the piezo-electric transducer 4
is not arranged in parallel with the surface of the liquid 1, but
is mounted on a bottom portion of the nebulizing chamber 2 in such
a manner that its vibration surface has a predetermined inclination
.theta..degree. with respect to the surface of the liquid 1.
Consequently, the water column 5 in the shape of the spouting
stream is continuously formed on the surface of the liquid 1 with a
certain inclination to the surface of the liquid 1. In this case,
water drops such as large liquid particles are scattered from the
tip end portion of the water column 5 and drop down onto a position
separated from said tip end portion of the water column 5. As a
result of the above, said water column 5 is steadily formed on the
surface of the liquid 1, and the liquid 1 is continuously nebulized
by the piezo-electric transducer 4. FIG. 5 is an experimental
result showing a change in the amount of the nebulized water when
the inclination angle .theta..degree. of the vibration surface of
the piezo-electric transducer 4 with respect to the surface of the
water 1 was changed from 0.degree. to more than 30.degree., while
maintaining the exciting or driving power of the piezo-electric
transducer 4 at a constant value of 35 W. As is clear from FIG. 5,
the nebulizing capacity can be enhanced about 23% when the
inclination angle .theta..degree. is in a range of from 2.degree.
to 22.degree.. Further, it was found that when the inclination
angle .theta..degree. was increased more than 22.degree., the
reflection of the ultrasonic wave on the liquid or water surface
was increased, while the nebulizing capacity was decreased.
As shown in FIG. 2, since the transistors 11 are directly attached
to the surface of the chamber base 18 of the nebulizing chamber 2,
the transistors 11 are effectively cooled by the water 1 by way of
the chamber base 18.
Generally, the temperature of the water 1 rises to approximately
40.degree. - 50.degree.C, however, if cool water is injected into
the nebulizing chamber 2 during the generation of fog, the cooling
effect on the transistors 11 is further raised.
Further, as shown in FIG. 1, in the ultrasonic nebulizer, the
liquid tank 21 is provided in such a manner that its surface level
becomes equal to the surface level of the water 1 in the nebulizing
chamber 2 so that the nebulization of the liquid 1 can be
continuously carried out for many hours. Generally, the
relationship between the liquid surface level L (cm), that is, the
distance between the ultrasonic wave transducer 4 and the surface
of the liquid 1, and the nebulized amount Q (cc/hr) of the liquid 1
is shown in FIG. 6. As is clear from FIG. 6, when the liquid
surface level L is in a range from 0 to 8.0 cm, a sufficient
nebulizing capacity can be obtained, and the more preferable
conditions are when the liquid surface level L is 5 - 7.5 cm, the
frequency is 1.3 MHz and the diameter of the piezo-electric
transducer is 25 .phi..
In the above-mentioned embodiment, the bottom portion of the
exhausting duct 9 for air and fog 7 is disposed adjacent to the
upper surface of the liquid 1 so as to insert the fog generating
front portion of the water column 5 into the exhaust duct 9. The
air supplied from the air supply inlet 8 flows through a passage
formed between the inside wall of the nebulizing chamber 2 and the
outside wall of the exhaust cylinder 9 and is guided adjacent to
the surface of the liquid 1 in the nebulizing chamber 2. The air
then flows upwardly into the exhaust cylinder 9, while the air
around the fog generating front portion of the water column 5 flows
in the same direction as the water column. Thus, the air, together
with fog 7, are expelled through the exhaust cylinder 9 to the
exterior of its nebulizer. As a result, the generation of fog 7
from the front portion of the water column 5 is not restricted by
the pressure of the air and, also, the air flow in the
above-mentioned passage formed between the inside wall of the
nebulizing chamber 2 and the outside wall of the exhaust cylinder 9
is not disturbed. Consequently, the amount of water drops caused by
the adherence of the fog 7 to the inside wall of the exhaust
cylinder 9 decreases, so that the fog transmitting efficiency is
enhanced. Further, under a condition of absence of air flow, since
the generated fog 7 is floating around the water column 5, the
water column 5 is gradually surrounded by the floating fog 7 and,
therefore, it is difficult to generate a fog 7 of minute liquid
particles, but a fog 7 of large liquid particles is likely to be
produced. However, by flowing the air as mentioned before, a fog 7
of minute liquid particles of a constant small size is easily
produced and this produced fog 7 is effectively expelled. Also,
since the direction of the air flow and the formation direction of
the water column is the same, even if the velocity of the air flow
is increased to some extent, the top portion of the water column 5
is not scattered.
An effect of the nebulizer according to the present invention will
be clearly understood from the following experimental result. This
experiment was carried out at normal temperature and normal
pressure, with a constant ultrasonic wave frequency and a constant
ultrasonic wave intensity, and a constant amount of air was
supplied from the air supply inlet 8. In this experiment, the
measured amount Q (cc/hr) of fog 7 extruded from the exhaust duct
or cylinder 9 was 1,400 cc/hr, while that of the conventional
nebulizer is 600 - 650 cc/hr.
SECOND EMBODIMENT ACCORDING TO THE PRESENT INVENTION
In an ultrasonic wave nebulizer constructed as shown in FIG. 1, an
oscillatory frequency f (Hz) having a wave length of .lambda. (mm)
transmitted through an optional medium at a velocity of V (m/s) is
expressed by the equation: ##EQU1##
A suitable frequency f for nebulizing the liquid is preferably in a
range from 0.8 to 2.0 MHz, and when water is utilized as a medium,
the wave length .lambda. becomes approximately 0.75 - 1.90 mm. In
such a range of the wave length .lambda., to transmit the
oscillation of the oscillator 4 through the medium with a high
efficiency, a conical horn 22 is provided between the bottom of the
nebulizing chamber 2 and the top of the transducer 4 as shown in
FIG. 7. It is possible to obtain a sharp directivity by suitably
selecting the angle of inclination of the conical horn 22. The
relationship between an input power P (W) and a nebulized amount Q
(cc/hr) of the liquid in this second embodiment is graphically
shown in FIG. 8. When the horn 22 is not provided, the curve is as
shown by a broken line in FIG. 8. That is, according to the
nebulizer of the present invention, provided with the horn 22, the
nebulizing efficiency can be increased or improved by approximately
10 - 15%.
SEVERAL MODIFIED EMBODIMENTS ACCORDING TO THE PRESENT INVENTION
In the above-mentioned ultrasonic nebulizer of the first embodiment
shown in FIG. 1, the liquid tank 21 is provided in such a manner
that its surface level becomes equal to that of the nebulizing
chamber 2 so as to maintain the liquid surface level L at a
constant value with respect to the ultrasonic transducer 4. Next,
other modified embodiment for maintaining the liquid surface level
L at a constant value will be explained.
FIG. 9 is a first modified embodiment for maintaining the surface
level L of the liquid 1 contained in the nebulizing chamber 2 at a
constant value. When the transducer 4, mounted on the bottom
portion of the nebulizing chamber 2, is excited by an electric
circuit, the liquid 1 contained in the nebulizing chamber 2 is
nebulized and then expelled through the exhaust duct 9 to the
exterior by the air flow produced by means of the fan 14.
Consequently, the amount of the liquid 1 contained in the
nebulizing chamber 2 decreases. However, the liquid contained in a
liquid tank 27 is pushed upward by means of, for example, a
propeller pump 23 connected to the fan 14, and then the liquid
corresponding to the above-mentioned decreased amount is supplied
from a water supply inlet 24 into said nebulizing chamber 2. In
this case, the amount of the so supplied liquid is somewhat in
excess of the amount of the nebulized and exhausted liquid, and the
extra amount of the supplied liquid is returned to the liquid tank
27 from a vertical over-flow pipe 26 via an overflow portion 25.
Thus, the surface level L of the water 1 contained in the
nebulizing chamber 2 can be maintained at a constant value by the
liquid supply means.
FIG. 10 is a second modified embodiment for maintaining the liquid
surface level L at a constant value. A nebulizer shown in FIG. 10
comprises the nebulizing chamber 2 and the transducer 4 mounted on
the bottom portion of the nebulizing chamber 2. Water is fed into
the nebulizing chamber 2 via a suitable water supply inlet 24.
Further, there is provided a pair of electrodes 28, 29 in the
nebulizing chamber 2. The electrode 28 is situated at a position
where the surface level L of the water 1 in the nebulizing chamber
2 can be maintained at any desired position. The other electrode 29
is disposed at a lower critical position where serious trouble, for
example, damage to the nebulizing chamber 2 is liable to be
produced by some cause when liquid surface level L is lowered
beyond the above-mentioned lower position.
The pair of electrodes 28 and 29 are connected to an electric power
source or circuit 30 via respective condensers C.sub.12 and
C.sub.13, and the nebulizer. An AC voltage suitable for operating
the electric circuit of FIG. 10 is impressed between the pair of
nebulizer and the electrodes 28 and 29. Further, first and second
neon lamps 31 and 32 are provided between the electrodes 28, 29 and
the nebulizer, respectively. A bridge 33 and a smoothing condenser
C.sub.14 respectively contained in the power circuit 30 are used
for supplying DC currents to a pair of first and second
photoelectric circuits 34 and 35.
When the surface level L of the liquid 1 in the nebulizing chamber
2 drops below the lower end of the electrode 28, the electrode 28
is exposed to the air. As a result, the potential difference
between the exposed electrode 28 and the nebulizer increases, so
that the first neon lamp 31 is lighted. Similarly, when the surface
level L drops below the bottom end of the electrode 29, the second
neon lamp 32 is also lighted.
Said first and second photoelectric circuits 34 and 35 are actuated
by receiving light radiated from the first and second neon lamps 31
and 32, respectively. These first and second photoelectric circuits
34 and 35 are respectively constructed as shown in FIG. 11. That
is, each photoelectric circuit 34 or 35 has a photoelectric element
36 (for example, cadmium sulfide cds) placed at a position where
the light radiated from the each neon lamp 31 or 32 can be
received. When the photoelectric element 36 receives luminous flux
beyond a predetermined value, a voltage supplied to a base of a
transistor Q.sub.4 via a resistor R.sub.11 is decreased, so that
the transistor Q.sub.4 is turned off. As a result of this, the
potential of a collector of the transistor Q.sub.4 rises in
accordance with the time constant of a resistor R.sub.12 and a
condenser C.sub.15, and a transistor Q.sub.5 is turned on. Further,
a zener diode ZD inserted between the collector of the transistor
Q.sub.4 and a base of the transistor Q.sub.5 serves to maintain the
impedance of the transistor Q.sub.5, viewed from the transistor
Q.sub.4 side, at a high value during the time the transistor
Q.sub.5 is off, and secure the switching operation of the
transistor Q.sub.5.
When a transistor Q.sub.5 is turned on, a current flows in an
exciting coil of a relay 37, so that the relay 37 is brought into
an operating condition. The relay 37 controls a switch of a supply
mechanism for supplying water into the nebulizing chamber 2 via the
water supply inlet 24 shown in FIG. 9. When the liquid surface
level L in the nebulizing chamber 2 rises to the position of the
electrode 28, the first neon lamp 31 is extinguished due to the
potential drop of the electrode 28. As a result of this, the
transistor Q.sub.4 of the photoelectric circuit 34 is turned on and
energized and the transistor Q.sub.5 is turned off and deenergized,
so that the relay 37 returns to its non-operational condition and
the supply of water into the nebulizing chamber 2 is stopped. By
repeating the above-mentioned operation, the liquid surface level L
can always be maintained within a predetermined range.
Further, when the liquid surface level L is lowered by some
accident beyond the bottom end of the electrode 29, the second neon
lamp 32 lights and this is detected by the second photoelectric
circuit 35, so that the relay 37 is actuated and the operation of
the nebulizer is stopped.
* * * * *