Relative humidity levels of an incubator were measured and controlled. An ultrasonic nebulizer system as an active humidiƒer was used to humidify  the  incubator environment. An integrated circuit-type humidity sensor was used to measure the humidity level of the incubator environment. Measurement and control processes were achieved by a PIC microcontroller. The high-performance and high-speed PIC provided the ƒexibility of the system. The developed system can be used effectively for the intensive care of newborns and/or premature babies. Since the humidiƒer generates an aerosol in ambient conditions, it is possible to provide the high relative humidity level for therapeutic and diagnostic purposes in medicine.70608

Introduction

An incubator is an infant-stimulating system used for intensive care of the newborn, premature or sick baby. It provides a safe and clean environment, which has fresh air, clean and sterile ambient conditions for the babies. In addition to these, the incubator environment provides a homogeneous and stable temperature, a relative humidity (RH) level and oxygen gas concentra- tion that is needed especially for intensive care of the premature  baby  [1 –  3].

Since the incubator is a medical device and has a lot of limitations as other medical equipment, the  most suitable humidity measurement and  humidifying  meth- od have to be used.  For  continuous  recording  and control of the RH level, many kinds of electrical transducers can be employed. Resistive, capacitive, lithium chloride, electrolytic and integrated circuit (IC)-type RH sensors measure the RH level in the air. Owing to the suitable electrical characteristics for the measurement and control process, capacitive and IC- types RH sensors are more suitable than the others [4 – 6].

There are two main methods to humidify the  air, which are known as  the  passive  and  active humidifying method. In the passive method, humidity is produced conventionally by a heater. The humidity content of the air  is  increased  by evaporation  of water by heating it    in

the water container. Since one of the physical control parameters in the incubator chamber is temperature, the passive method is not suitable to humidify the incubator chamber [3]. In addition, because  the humidity level depends on ambient temperature, it is not possible to provide a high humidity level, especially at low temperatures [7]. It is difficult to provide the humidity level 440% RH  at low  temperatures such  as in the range of 23 – 388C. Moreover,  extra heating occurs when the control environment is heated in this way. As a result, the passive method is not suitable to humidify the limited volume of an environment such as an  incubator [3].

In the active method, a heating source is not used to humidify the control environment [8]. Since humidify- ing processes are independent of temperature, it is possible to reach a high humidity level even at a low temperature. As an ultrasonic nebulizer creates an aerosol at ambient conditions and extra heating is not produced in the control environment, it is preferable to humidify the limited volume of the environment such as the incubator system  [3].  The  term  ‘nebulizer’ can be defined as an instrument for converting a liquid into a fine spray, especially for therapeutic purposes in medicine  [8 – 11].

In this work, the humidity measurement circuit which uses an IC-type humidity sensor has been developed to measure the RH of the incubator environment. In addition, a portable ultrasonic nebulizer has been developed for humidifying processes.  Measurement and control circuits are constructed together with the high-performance PIC microcontroller to provide the flexibility of the system. Since a high humidity level is necessary in the incubator environment, an active humidifying method has been used. In this way, a high humidity level can be provided easily even at ambient temperature. In addition to the performance  of  the active humidifying, the effects of the humidifying processes on the temperature have also been investi- gated.