1. Incubators
Compiled and Presented by:
Dr. Judith Justin M.Tech., Ph.D.,
Prof. & Head,
Department of Biomedical Instrumentation Engineering
Faculty of Engineering
Avinashilingam University
Coimbatore - 641 108
3. Introduction
• Premature newborns require their body temperature to be
elevated & controlled within a specific range
• When kept in a temperature controlled chamber, the oxygen
requirements are minimized
• Premature newborns are more susceptible for developing
respiratory problems, because their lungs are unable to
supply enough oxygen
• By minimizing oxygen demands for maintaining temperature,
more oxygen is available for growth
• Such controlled temperature environments are maintained in
infant incubators.
4. Infant Incubator
• Temperature controlled air is passed through a chamber in which baby
is located to maintain it at a set temperature
• Temperature is maintained by use of a proportional control system.
• Temperature in a air-supply line varies a thermistor resistance that is
compared with a fixed resistance which corresponds to the set
temperature
• If the temperature of air entering the infants chamber is lower than the
set temperature, power is applied to the heater (to switch ‘ON’ and) to
correct the difference
• In the proportional controller system, the amount of power applied to
the heater is proportional to the difference between actual air
temperature and the set point.
• This means that the amount of power decreases as temperature
approaches the set point, an important feature in effecting more
precise control and minimizing overshoot of the set point
5. Comparator
Gate pulse
generator
Thermistor
Bridge
Set-point
resistor 1-Hz sawtooth
generator
Silicon-
controlled
switch
Heater
Amplifier ν1
ν2
ν3 ν4
ν5
Power
line
Block Diagram
• The control system shown in fig. uses thermistor in a bridge
circuit, with the set point resistance as another arm of the
bridge.
• The bridge output is amplified, giving the voltage V1 at the
output, which is proportional to the difference in temperature
between thermistor and the set point
6. • Some incubators measure skin temperature of infant over the
liver, instead of air temperature in the chamber.
• In such cases, the thermistor is strapped to the body of the
infant
• Incubators have an alarm to alert clinical staff when there is
overheating
• Buzzer is connected in series with a switch which is activated
by a bimetallic strip
• In some cases when infants skin surface has to be exposed to
carry special procedures/attach diagnostic or therapeutic
devices then we use heated air and convection
• In such cases radiant warmers are used
7. Radiant warmer
• Infant is placed on a mattress under a radiant heating element.
• Low walls surround the mattress so that the infant does not fall off.
• In other incubators, the infant must be accessed through arm ports
• The radiant warmer consists of a heating element such as a coil of
high-resistivity wire
• A heat reflector above this wire helps to focus the heat energy on the
mattress.
• The current through the heater element is controlled and overheating
is avoided. Proportional control is used to achieve this.
• A thermistor is placed on the exposed skin or abdomen of the infant
to measure the skin surface temperature.
• This thermistor could get heated by the radiant source giving
erroneous reading.
• It is attached to the infant through a special pad that consists of a
foam pad with a shiny metallized surface that reflects thermal
radiation.
8. Apnea monitor
• Sometimes infants develop respiratory distress or anomalies.
They can stop breathing
• An alarm is sounded when respiratory activity ceases for
periods greater than 15 to 30 seconds.
