and temperature (8C). Measurements  have  been  made at around 2-min intervals and 125 measurements were taken. There was no temperature controller in the incubator. Test results showed that the desired humid- ity level can easily be provided up to 90% RH. Another purpose of the test was to show  that  the  temperature was kept constant. Temperature changes  of  the incubator chamber using three  thermometers  ex- plained above show the constant values. Test results showed that there is a small difference between them (figure 8), since the  sensors  used  have  different response times. Another important parameter is the temperature of the incubator environment. Since any heater is not used for  humidifying,  any  extra  heating does not occur. Therefore, the temperature of the incubator environment is not affected by the humidify- ing processes and it was a constant at 22.88 C during the performance  test  (figure   8).

The second test is on the  low  RH.  In  this  experiment, the desired humidity of the incubator environment was set to 30% RH via a UP  button  on  the  control  panel. The temperature of the incubator environment was measured as 19.48 C and the  humidity  measured was 23% RH initially. Test results showed that there is small difference between them as shown in figure 9, since the used sensors have different response times. Tempera- ture was not affected by the humidifying  processes. Since the ambient  temperature  changed,  there  were small changing in the range 19.4 – 20.18C (figure 9). In addition, the response lines in figure 9 are considerably similar and indicate an offset between the two sensors. The another reason for this is  the  difference  between the  response  time  of  the sensors.

Another test is the middle humidity level test. It can be easily reached at the 50% RH level in the incubator environment (figure 10). Before the humidifying processes, the initial temperature and RH of the incubator environment were measured as 18.88C and 29% RH respectively. The desired humidity level in the incubator environment was set to  50% RH  via  a keyboard on the control  panel  to  humidify  the incubator environment. After the humidifying process was started, the humidity level of the incubator environment   quickly   increased   and   it    reached    50%

RH in 11 min. Since the response time of the IC-type humidity sensor was around 15 s, the humidity level increased further and reached an RH of 53.3%. This overshoot was due to the lag in the system (15 s). The humidifying processes continued with  small  fluctua- tions in these values, and the temperature of the incubator environment was not affected by this process (figure   10).

The last test was the high humidity level test. In this experiment, the desired humidity in the incubator environment was set to 70% via the keyboard on the control unit. Since the temperature of the control environment was in the range 18.9 – 19.18C, it was not possible to provide this RH level in these temperature range any other route. However, using the developed system, the desired humidity level  was easily reached in 22 min (figure 11). The RH levels of the incubator environment were measured in the air at ambient temperatures. However, the system had not been tested with air at a temperature closer to that used normally in an incubator, say about 368C, where  the  absolute humidity levels  would  have  been  required  to  attain the same RH. In addition, it is very difficult  to  cope when a baby is also in  the  incubator,  when  it  is producing heat and moisture, and  when  the  air  is actively  warmed,  i.e.  in  a  dynamic  rather  than  a  stable