Electronics of the system

The system mainly consists of four units: the incubator chamber, the RH measurement circuit, the ultrasonic nebulizer and the microcontroller-based control circuit. The walls of the incubator are of plexiglas and do not have   any   air   flow.   Plexiglas   contains   the   air   in  the

incubator. Although any material would do this, the physical characteristics of plexiglas are  different  from the others, such as thermal conductivity. Therefore, it is very suitable for insulating the heat passing in or out of the incubator chamber [1]. In addition, some  babies may receive phototherapy. Since the plexiglas is a transparent material, it is suitable for use in  a phototherapy environment. On the other hand, since glass is very fragile, it has never been used  for this purpose. The block diagram of  the  microcontroller- based humidity measurement and control system are shown  in  figure  1.

The system works as the following: predetermined RH is entered via the UP button according to patients’ (premature, sick or newborn babies) requirements. Determined values are shown on the three-digit display unit at RH% level. When the system is activated by pressing the START button on the keyboard, deter- mined values and the RH of the incubator environment measured by humidity sensor are compared in the control unit. If the determined values are higher than the measured values, the ultrasonic nebulizer is energized through the opto-isolator unit and it converts some fresh, distilled and sterilized water in the small container into fine water particles. Since the water particles are heavier than air, they should be circulated. Air circulation is provided by a 12 V DC fan driven through the opto-isolator by a microcontroller. In this way, water particles are moved into the incubator environment. Therefore, the RH of the control environment is gradually increased. Measured RH  of the incubator environment is continuously compared with the determined RH  by  the  microcontroller. If these values are equal or greater than the determined RH, the ultrasonic humidifier and circulation fan are stopped. If the humidity is higher than the required level, the air needs to be replaced. Since the incubator chamber is a non-hermetic  environment, there are small holes on the walls. After the ultrasonic nebulizer was stopped, the humidity level starts to decrease and even access ports are closed.

Patient isolation and safety requirements are the most important situations in the developed incubator. Electronic components of the measurement system, humidifier and driver circuit were selected with respect to the patient isolation and safety standards (IEC 60601- 2-19)  in   the   circuit  design   [12].  In   addition, materials

Figure 1. Microcontroller-based humidity measurement and control system.

used for the mechanical construction of the  system were selected according to safety requirements. Since the developed systems are programmable, software was developed according to IEC 60601-1-4 Programmable Electrical Medical System [13]. For example, Watchdog timer (WDT), Power-on Reset (POR), Power-up Timer (PWRT), Oscillator Start-up Timer (OST) and Brown- out Reset (BOR) were used in the software for the reliability and security of the  system.  Humidifier and RH measurement circuits have also been designed by considering IEC 60601-1-1 standards [14]. Power delivery of the measurement system is obtained by mains on a DC/DC converter that provided 6 kV DC isolation, so there is not any direct connection between the patient and the RH sensor. The nebulizer has a modular construction. Produced water particles are moved into the incubator chamber by a  plastic  pipe. The  length  and  diameter  of  the  pipe   are   1  m  and 22 mm respectively. As a result, the nebulizer and incubator chamber is electrically well insulated for the patient safety according to IEC 60601  standards.