超声雾化加湿系统英文文献和中文翻译(4)

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Ultrasonic nebulizer

A block diagram and circuit detail of the ultrasonic nebulizer are shown in figures 3 and 4 respectively. The ultrasonic nebulizer circuit is mainly a power oscillator circuit. The ultrasonic crystal is the main component of the oscillator. The ultrasonic crystal was used for the oscillation at all conditions. Water particles are created by means of ultrasonic vibration. This process is achieved by an ultrasonic crystal that vibrates at 1.73 MHz in some sterilized water in a small water reservoir. In this way, water particles in the range 0.5 – 6 mm, average of 3 mm are produced. A level of 1.73 MHz was sufficient to produce the required particle sizes. If the nebulization frequency is higher, then the particle size is smaller. However, the density of the water droplets depends on the power levels. If the power level of the ultrasonic crystal is increased, the density of the water

Figure 2. Humidity measurement circuit.

Figure 3. Ultrasonic nebulizer.

Figure 4. Circuit of the ultrasonic nebulizer.

droplets increases. A total of 40 VA (Volt-Ampere) power is required for the operation of the ultrasonic nebulizer.

The particle sizes are big enough to humidify the incubator chamber. If required, the density of the water particles can be adjusted using a P3 potentiometer. If the potentiometer P3 is varied, the forward biased base polarity of the power transistor can be increased, so that density of the water particles increases. A DC fan is used to mix the water droplets with the air. The water evaporation is achieved when the water particles are injected in the warm air circulation by using a heater. If it is not, the flow of air from the fan would cause cooling of the baby. The heater and fan are also used to control the temperature of the incubator chamber. Since the water particles are heavier than air, the produced droplets need to be circulating. For this reason, two fans are required. One for circulating the particles out of the nebulizer through the plastic pipe, the other for circulating the heated air into the incubator chamber.

Microcontroller-based control unit

All the control mechanism of the system were performed by a Programmable Interface Controller (PIC) PIC (16C74A, Microchip), because PIC 16C74 A has the RISC architecture so that it is faster than the other microcontrollers. Since it has only 35 instructions, programming is very easy. In addtion, PIC have WDT, POR, PWRT and OST, and BOR timers that provide excellent reliability during the operating of the PIC.

WDT is a free-running on-chip RC oscillator that does not require any external components. During normal operation, a WDT time-out generates a device RESET (Watchdog Timer Reset). This means that if any time- out is occurred in the software of the PIC, the WDT will automatically reset the software. In this way, it is guaranteed that any drawbacks of the software on the PIC will not occur.

The POR pulse is generated on-chip when a Vdd

(supply voltage of the PIC) rise is detected (in the range

1.2 – 1.7 V). When the device starts its normal operation (exists the reset condition), the device operating parameters (voltage, frequency, temperature, etc.) must be met to ensure the operation. If these conditions are not met, the device must be held in rest until the operating conditions are met. Therefore, any error in the software will not happen for the control.