Abstract:
An alarm for indicating a lack of liquid in an ultrasonic nebulizer is disclosed. The alarm is responsive to a level sensing device in the nebulizer used to terminate oscillation in response to a low liquid level situation.

Description:
BACKGROUND AND BRIEF DESCRIPTION OF THE INVENTION 
     The present invention relates to an ultrasonic nebulizer, and more particularly to a device for indicating an abnormal condition in the nebulizer such as by generating an alarm signal when the level of liquid in the nebulizer falls below a predetermined level. 
     It is known to sense liquid level in an ultrasonic nebulizer and to terminate oscillation and consequent nebulizing of the liquid when liquid level falls below a predetermined value (see U.S. Pat. No. 3,989,042). However, there is no means for informing an operator that the liquid is not present in the nebulizing container. Therefore, the operator cannot judge whether the system has been stopped due to an absence of liquid in the container or the system has been shut down due to some other problem. Additionally, there is no signal indicating a need for liquid to be supplied to the system, so that liquid may not be supplied for a long period of time, and the humidity generating function, e.g., of the system will be destroyed. In order to generate an alarm signal showing an absence of liquid, it may be possible to provide an additional float switch and thereby to operate such alarm device as a lamp or buzzer. However, such a prior art system requires an additional float switch, which complicates the entire system and increases the manufacturing cost. 
     It is thus an object of the present invention to provide an ultrasonic nebulizer in which only one float switch is used, and an alarm signal is generated and the oscillating operation in the circuit is terminated when an absence of liquid is determined. 
     The present invention finds application in an ultrasonic nebulizer that includes a container for storing a liquid therein, a transducer located substantially at the bottom part of the container to apply an ultrasonic wave to the liquid and to nebulize the same, an oscillator for energizing the transducer, a float switch for sensing the presence of liquid in the container, means for controlling a biasing voltage in the oscillator dependent upon the output at the float switch and terminating oscillation when liquid falls below a certain level in the container, and an alarm means connected to the float switch. The invention involves use of a two-terminal float switch so that when the liquid level in the container falls below that predetermined level, the float switch is released and a biasing current is no longer applied to the oscillator circuit; at the same time an alarm signal is generated. 
     The invention will be more completely understood by reference to the following detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 shows an ultrasonic nebulizer to which the invention is applicable. 
     FIG. 2 is a circuit diagram of an ultrasonic nebulizer embodying the present invention. 
     FIG. 3 shows voltage curves applicable to the circuit of FIG. 2. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 illustrates a practical example of an ultrasonic nebulizer to which the present invention is applicable. A container 1 stores a liquid such as water. A duct 3 guides a fog generated in the container by an ultrasonic transducer 4 installed substantially at the bottom of the container. A float switch 5 is used to sense the presence of the liquid in the container. For example, the switch 5 may be composed of a permanent magnet that is moved up and down in accordance with the water level, and may include a reed switch (not shown). FIG. 1 of U.S. Pat. No. 3,989,042 shows in more detail such a permanent magnet/reed switch device. An electric circuit 6 is included incorporating therein an oscillator which excites the transducer 4. Under the above described arrangement, when the transducer 4 is oscillated in a range of ultrasonic vibration, the liquid 2 such as water is nebulized, and the generated fog is discharged outside of the duct 3 to perform a humidifying operation, e.g. when the transducer 4 is oscillated and there is no water in the container (that is, non-load condition), both the transducer 4 and the electric circuit 6 may be damaged. To prevent damage, the electric circuit 6 acts to automatically stop oscillation when an absence of water in the container is sensed by the float switch 5. Such an operation is disclosed in U.S. Pat. No. 3,989,042. 
     FIG. 2 illustrates a presently preferred example of an electric circuit in accordance with the present invention. A transistor Tr is self-oscillated, and the transducer 4, such as a piezo-electric vibrator, is excited. Any well-known oscillator circuit may be utilized. In the preferred embodiment of FIG. 2, C 1 , C 2 , and C 3  are capacitors; L 1  and L 2  are inductors; R 1 , R 2 , and R 3  are resistors; D is a diode; REC is a rectifier circuit; A/C is an alternating current power supply. The float switch 5 1 , a two-terminal device, is closed or turned on when liquid is found in the container, and is opened or turned off when no liquid is found in the container. The float switch 5 1  is installed in a base biasing circuit for the transistor Tr and when the float switch is turned off or is opened, the transistor is biased in such a manner as to terminate the oscillation thereof. VR is a variable resistor which is utilized for adjusting the intensity of oscillation, and controls the base biasing of the transistor to provide a desired nebulizing action. 
     The circuit components enclosed by dashed line in FIG. 2 constitute an alarm device in accordance with the present invention. The alarm device is constituted by a resistor r, a zener diode ZD, a capacitor C and an alarm indicated in block form such as a lamp or buzzer. As shown in the drawing, the alarm device is connected between one end or terminal 5a of the float switch 5 1  and the common potential E. The zener diode ZD is mainly used for providing a positive switching operation for the alarm. 
     In the arrangement shown in FIG. 2, the voltage or potential between the points R and E when the float switch 5 1  is off or opened is illustrated by curve (a) in FIG. 3; the voltage between the points R and E when the float switch 5 1  is on or closed is illustrated by the curve (b) in FIG. 3. In FIG. 3, the abscissa is the resistance (KΩ) of the variable resistor VR used to adjust the nebulized volume. The curves result from a power supply voltage A/C of 48 volts; R 1  corresponds to 3900 ohms; R 2  is 5600 ohms; and a maximum value of VR is 5000 ohms. 
     As apparent from FIG. 3, when water is not present in the container (that is, the float switch 5 1  is turned off or is opened), the voltage at the point R is about 9 to 15 volts (curve a). On the other hand, the voltage at the point R (when there is water in the container, i.e., the float switch 5 1  is turned on or is closed) substantially corresponds to 0 volts (curve b), irrespective of the adjustment of resistor VR. 
     Thus, the alarm device connected to the point R is such that it is operated in a range of 10 to 15 volts for the specific values just described. The operation required is positively performed by arranging the zener diode ZD as shown. That is, a zener diode is utilized having a yielding voltage of about 10 volts. When the float switch 5 1  is on or closed, a lower voltage is applied to the alarm device, insufficient to activate the alarm. If the float switch is off or open, and regardless of the setting of the variable resistor VR for adjusting the oscillator output, a higher voltage of about 10 volts is applied to the alarm by the zener diode, and the alarm is accordingly operated. Thus, an absence of liquid in the container is displayed by the lamp or buzzer which may be immediately noted by an operator. At the same time, the transistor oscillator terminates its oscillation, and the transducer terminates its nebulizing operation. When an alarm signal is generated, if the operator supplies water to the container, it is possible to provide uniform control over humidity. 
     As described above, it is possible to add an alarm device to an ultrasonic nebulizer in accordance with the present invention without requiring an additional float switch. It is also possible to provide an easy monitoring of the presence or absence of liquid. 
     The preferred embodiment described above is obviously subject to being modified. Accordingly, the invention should be taken to be defined by the following claims.