The air in the incubator chamber is continuously replaced by fresh air. For this reason, the water droplets do not condense (or collect as they  are  not saturated) on the baby or another place in the incubator chamber. The incubator can achieve an RH of 100%  at  348C when the humidifier setting is maximum and the ports are closed. When the ambient air of the incubator is saturated, condensation is commonly observed; water starts to run down the side walls, droplets of water may fall on the baby and the mattress even becomes  wet. The use of double-walled incubators (i.e.  incubators with walls of two layers of plexiglas separated by a layer of air 1 – 2 cm thick) is an alternative way of reducing the incidence of condensation somewhat [3]. This is a more reasonable way and very good solution than to leave  the  circulation  fan  ‘ON’  all the time.

Results  and discussion

Because one of the most important stimuluses of the extrauterine world is the humidity level for the  baby, the humidity level of the  incubator environment must be at specified value. As the incubator is analogous and ambient to the mother-holding environment for the baby, it is very important to for them to survive and have intensive care. For this reason, such a system has been developed.

Figure 5. Microcontroller-based  control unit.

Figure 6.   A/D converter circuit.

Figure 7.   Opto-isolator circuit.

To test the developed system, some experiments and measurements have been performed. Since one of the control parameters of the incubator environment is temperature, the effects of humidifying the tempera- ture have been investigated. As the skin of  the  babies may be dried due to their health problems or water lost through  the  skin, it  may  be  necessary  to  reach  the high

humidity level. For this reason, a performance  test of the developed systems has been carried out and the ambient air of the  incubator is  humidified  in  the range

22.2 – 90% RH at 22.88C. To show the stability of the active humidifying method, low, middle and high humidity-level tests have been achieved. In addition to developed system, another RH level meter was used to test the difference between them. This digital RH meter (LUTRON, HT-3004) can measure the RH in the range 10 – 95% RH with an accuracy of + 4% reading,  +1% RH, at 23+ 58C after calibration. The resolution of this device is 0.1% RH. Moreover, using a thermometer, it is possible to determine the effect of the humidifying processes on the temperature of the control environ- ment. For this purpose, the three temperature meters have been used and then their average readings were considered as a temperature of the incubator environ- ment. In this way, more accurate measurements have been achieved. Two of them are the digital temperature meter, which can measure  the  temperature in the range 0 – 608C with a resolution of 0.18C and accuracy of + 0.88C. Another thermometer is a mercury thermo- meter which has high accuracy. The  abbreviation names of these measurement devices are as follows: ‘RH% Ref.’ is the external RH meter. The RH measurement results of the developed system are compared with it. ‘RH% Measured’ is the humidity measurements of the developed system. ‘Temp (De- grees C.)’ is the average temperature of the incubator compartment, which is measured by three thermo- meters explained above.

The first test is on the performance of the developed system. In this experiment, the humidifying  ability  of the developed system was tested. For this reason, the desired humidity level of the incubator  environment was increased step by step by using the UP button  on the control panel. The temperature of the incubator environment was measured as 22.88C and the humidity level was 22.2% RH at the start. According to the measurement results, a graph was sketched (figure 8). In the graph, the horizontal axis shows the number of the measurement, and the vertical axis shows the  RH%