1

High Performance Temperature Controller For Infant Incubators

2

What is Infant Incubator ???

It is a Bio- Medical device which provides warmth, Humidity and oxygen all in a controlled environment as required by the new born.

The design basically contains a trolley with a mattress on top covered by a rigid clear plastic cover.

The chamber provides a clean environment and helps to protect the baby from noise, drafts, infection and excess handling.

3

How Temperature plays a role ????

Infants have very low thermal regulation and it is not possible for the feeble body to cope with the thermal loss.

Hence, It requires the body to be kept in a moist condition till the baby is able to cope with the external changes on its own.

Here, the temperature is maintained with minimum variations, which is set by the attending physician, to prevent any harm to the body of infant.

4

FUNCTIONALITY OF SYSTEM-:

BLOCK DIAGRAM

SENSORS

SAFETY

5

BLOCK DIAGRAM OF THE SYSTEM

6

These have an accuracy of ± 0.1C of in the required range of 20C to 40C as the set temperature varies from about 30C to 37C.

Temperature is measured with an accuracy up to a decimal of a degree. Hence, a 10 bit conversion is used which gives us a voltage regulation of 4.88 mv.

The sensor voltage variation over the range of 20c to 40c

is 1.5V to 4.5V.

Here 1 degree Celsius is represented by a minimum of

150mV, therefore a resolution of 4.8mV detects a

minimum variation of 0.0325c.

SENSORS

7

SAFETY

Precautions are taken to isolate the baby from the metal connected as circuit carrying voltage of 230v runs inside the side panel of Incubator.

A Relay of 9v supply is connected in series with line, so that it will cut off the heat supply and sound off the buzzer in case of any malfunction.

Overheating of equipment is watched carefully by microcontroller.

If any of sensor shows temperature more than set pressure, microcontroller will cut off the transistor switch causing the relay to trip.

8

VOLTAGE CONTROL METHOD Power output of Heater is controlled by controlling the voltage given to it. D.C. supply is used in order to extract more than rated output from heater element. It is

advantageous in warm up, where more than 100% more than rated output is required to lessen the warm up time.

A MOSFET is used, driven by a pulse train to switch on/off the current flowing through heater. The duty cycle of the PWM signal generated from microcontroller decides the voltage level of

heater.

The graph here describes about amount of voltage taken to reach a required power level for a heater rated at 230V.

9

WORKING OF CONTROL LOOP

The above illustration is the control loop of the system which in fact is the blueprint of system. In here, initially the chambered temp. is sensed by the temperature sensor and compared with

set temperature by user. After getting the error in digital form, it send to controller which then it adjusts the PWM duty

cycle and then send it to voltage controller which will then control output heat. Further, we will go in details to each sensor shown in block diagram in details.

10

PI Controller-: A PI controller calculates an error value as the difference between a measured process

variable and a desired set point and tries to minimize the error by adjusting the process control inputs.

It’s used over only proportional controller as integrative part is required to reduce the steady state error.

The variation of temperature is rather low as compared to only proportional controller. A PI controller can be represented in Laplace equation-:

… …………..(1)

11

As the controller is digital, it is needed to convert the Laplace domain to Z domain. For that, Bi-Linear transformation is used to take the approx. value by considering the area covered

by time and error.

……………..(2)

By substituting eqn(2) in eqn(1), and applying Z –transform we get output as-:

CONTINUED FROM PI Controller

12

But there is a issue with heating system as once it gets increased, the time taken to dissipate heat is rather very large, as can be seen in the graph.

Hence it is necessary to reduce the overshoot in order to reduce the settling time.

As there is no method of heat absorption, the heater & and the metal parts under mattress is heated more than air and causes the temp. of air to rise even after heater is cut off.

Also level of dissipation varies with set temperature i.e.

Where Q= heat dissipated, K= p –constant, A= area ,θ= temp. of surface & θª= ambient temp.

CONTINUED FROM PI Controller

13

CONTROL ALGORITHM The flow chart shown here is the implementation of

the PI controller in firmware. The user sets the 'set temperature' and the ambient

temperature is obtained as described in above section. The error is obtained from the difference and combining the current error, previous error and previous modified error, the new modified error is obtained using bilinear transform.

According to the modified error, proper amount of power should be given to the heating element of the incubator.

Important factor to keep in mind is that this curve is inverted from the optocoupler , which isolates the high power circuit and the low power circuit.

14

CONCLUSION

After optimising the above methods, it was concluded that controller is set up to operate within a temperature gap of +/- 0.1c.

The Overshoot was minimised in order to reduce the settling time and hence by reducing the time taken for heat dissipation.

The settling time from a cold start was achieved within a few 10 minutes form the start.

15

MORE ADVANCEMENTS-:

SENSOR FAILURE

SKIN MODE

FAST COOLDOWN

MODE

BATTERY BACKUP

RS-482 INTERFACE

16

REFERENCES

UNICEF statistics on Infant Mortality Rates(http://www.childinfo.org/cmr/revis/dbl.htm) BSEN 60601-2-19 1997 (British Standards) Madden, S. The Preemie Parents' Companion, The Harvard Common Press, Boston, 2000. Web-based remote monitoring of infant incubators in the ICU by D.I. Shin, S.J. Huh,, T.S. Lee,

I.Y. Kim – 2003. Datasheet of Exacon temperature probe. Incubator Designs for Space Flight Application Optimization and Automation A. Hoehn, J. B.

Freeman, M. Jacobson and L. S. Stodieck – 1999 Signals and Systems J.I.Nagrath, S.N. Sharan, R.Ranjan, S.Kumar- REFERENCES 2003 pp

426.

17

THANK YOU