Author Topic: Design and Development of Fault Tolerent Control system for an Infant Incubator  (Read 2145 times)

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Author : Suswetha Parisineti, Eswaran.P
International Journal of Scientific & Engineering Research, Volume 2, Issue 5, May-2011
ISSN 2229-5518
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Abstract— This paper proposes the design and implementation of real time monitoring of an infant incubator, based on sensor fault tolerant control system, using a PIC microcontroller. Temperature and humidity are two parameters considered for the design infant incubator. The purpose of a Fault tolerant control systems (FTCS) scheme is to ensure that faults do not result in malfunctioning and system failure and to achieve the of best performance even with minimum number of sensors working. Fault tolerant control systems (FTCS) have ability to detect sensor fault automatically and to isolate faulty sensor which leads to system failure. The fault detection and the isolation (FDI) problem is an inherently complex one and for this reason the immediate goals are to preserve the stability of the process and, if is possible, to control and continue the process in a slightly degraded manner. The role of the FDI algorithms is that the control equipment must automatically isolate the faulted area, to adopt the correct attitude, to generate, to choose and to validate the correct decision. Prototype of infant incubator using FTCS was implemented by using redundant sensor with Build in self test (BIST) facility.

Index Terms— Sensor fault tolerant control, real time based, microcontroller, FTCS.

1   INTRODUCTION                                                                      
THE objective of a fault tolerant control system (FTCS) is to maintain system availability when fault occurs, to improve the reliability of the control system and to minimize the effects on the system performance and safety [1].
Fault is a kind of malfunction in the system, which may lead to system degradation or any unacceptable performance of the system. The output of the Sensor should be constrained between the lower and upper limits, if it crosses these bounds then it is said that the senor is failed.
Fault tolerant control (FTC) has been increasing in the last few years because FTC system has the ability to increase complex systems reliability and performance requirement in the events of faults. The design of a FTC system requires knowledge of advanced control mechanism [3]. Systems mostly are very complicated. Designing a FTC system could also be very challenging. Different types of faults such as actuators, sensors, and system faults can occur. Each type of fault requires different approach to work with. A fault tolerant control system must be able to perform, fault detection, fault isolation, and fault diagnosis [3]. FTC should also have the ability to detect faults and provide correction. Fault tolerant control system results on two approaches: active and passive. The active approach relies on fault detection and isolation (FDI) scheme to detect the occurrence of faults in the system and to identify the source and severity of the faults. Secondly, in passive FTC, potential component faults are known a prior and are all taken into consideration in the control system design stage [5].

Infant incubator provides a controlled environment for newborns needing special care, such as those born prematurely. By placing an infant in an incubator, doctors and nurses can set and monitor different aspects of the child’s environment in order to create ideal conditions for survival and moreover it protect infants from pollutants and infection[2].

This paper proposes the design and development of microcontroller based temperature and humidity controller for an infant incubator monitors and controls these two parameters constantly which are very critical for the normal growth of the new born (premature) babies. Infant incubator is used mainly to keep a baby’s care temperature stable at 37 ̊Celsius and the relative humidity is maintained at  (45 to 55)%RH.This system can automatically control the infant’s temperature at optimum level and to maintain high relative humidity so as to minimize the thermal loss. The developed system must be user friendly, cost effective and accurate.

2   SENSOR FAULT TOLERANT CONTROL SYSTEM
Infant incubators and other advances in medical technology have made it possible for small or premature babies to survive in higher numbers than they did in the middle of the 20th century. An incubator is an infant-stimulating system used for intensive care of the new born, premature or sick baby. It provides a safe and clean environment, which has fresh air, clean and sterile ambient conditions for the babies. In addition to these, the incubator environment provides a homogeneous and stable temperature, a relative humidity (RH) level that are needed especially for intensive care of the premature baby.
The sensor fault tolerant control was implemented for an infant incubator system. The system mainly consists of the microcontroller along with two temperature sensors, two humidity sensors, switches connected on either side of the sensors, a relay board with fan and heater, an LCD and LED’s for display purpose. The block diagram of an infant incubator is shown in the figure 1.
The input of the sensor ambient condition of infant incubator and the output of the sensor is connected to the analog to digital converter (ADC) of the microcontroller. The microcontroller gets the value from the sensors and then displays in LCD display. The control action is taken by the micro controller to detect which sensor is failed or working properly according to the values taken by the sensors. The LED’s, LCD display and the relay board are connected to the I/O ports of the microcontroller. The heater and fan are connected to the relay board.

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