The Patient Monitoring System (PMS) Is a Unique System Which Provides The

Introduction

The Patient monitoring system (PMS) is a unique system which provides the user a capability to measure patient’s heart rate (ECG), and body temperature. This new platform will help address some of the most critical issues in healthcare - shortage of nurses and high costs. The patient is strapped with the PMS which consists of different sensors and a microcontroller to keep track of his health conditions which would be known through an LCD display. The microcontroller will then send the data captured to the computer via RF transmitter and receivers, which would help the doctors and nurses keep track of key knowledge required for critical decision making. A speaker would be attached to the final product which would be an indication for emergency.

Freescale’s MC9S12C32 is one of the most essential part and is crucial for all operations of the PMS to function properly. Since all the sensors are connected to the microcontroller, failure of the chip will lead to no data being displayed on the LCD and no information being sent to the computer seen by the doctors and nurses. One of the other critical components of the device would be the sensors, since the temperature and the heart rate is being measured by these sensors. The graphics LCD display is also a key component, since it informs the patient whether or not he is in critical condition. Last but not the least, RF transmitters and Receivers; which are used to send data received by the microcontroller to a computer, are also equally important. Since this product is a socially redeeming device, it is really important that it is safe and reliable. Some of the safety issues to be addressed included, heating of the device leading to patient’s danger. When the device heats up the data is transmitted to the doctor’s computer since the RF connection is lost and may lead to out of control situations. Every component listed above plays a key role in the functioning of the device and since most of them have an operating temperature greater than the room temperature, it was decided to do a reliability and safety check on these components.

Reliability Analysis:

As mentioned earlier the design is an interfacing of many components critical for

the functionality of the device and thus the reliability analysis for these different

components has been done for 106 hours of operation. Much of the necessary information

was derived from the Military Handbook, Reliability Prediction of Electronic Equipment

(MIL-HDBK-217F). The Mean Time to Failure (MTTF) and the number of failures per

106 hours were calculated using this source. The parameters used throughout this

document for the calculation of the MTTF are reiterated below:

λp part failure rate πR power rating factor λb base failure rate πS voltage stress factor C1 die complexity πE environmental constant C2 a constant based on the number of pins πL learning factor πT temperature coefficient πQ quality factor πA application factor

Note : Will be measuring MTTF for temperature sensor and not the heart rate sensor, to accommodate all important devices

I) Microcontroller – MC9S12C32 : The basis to analyze this component was its importance in the overall functioning of the

device. The failure rate for CMOS microcircuit is:

6 λp = (C1πT + C2πE) × πQ × πL Failures/10 Hours Parameter Value Justification Source [1] C1 0.28 16 bit microprocessor (MIL-HDBK-217F, section 5-3)

T 3.1 Operating temperature- (MIL-HDBK-217F, section 5-8) -400C to 1250C C2 0.041 Corresponds to number of (MIL-HDBK-217F, section 5-9) pins for Nonhermitic SMT(as mentioned by the vendor)

E 4 GM is the selected (MIL-HDBK-217F, section 5-10) environment

Q 10 Based on an unknown (MIL-HDBK-217F, section 5-10) screening level

L 1 Has been in production for (MIL-HDBK-217F, section 5-10) more than 2 years. Table 1 : Parameter values for failure detection of the microprocessor Calculations :

λp = (0.28*3.1 + 0.041*4)*10*1

6 λp = 10.32 failures / 10 hours

MTTF = 1 / λp

MTTF = 96899 hours

II) CrystalFontz’s CFAH1602A-YYB-JP graphic LCD display The LCD displays backlight requires current of around 60mA which is the maximum than any other components used for the device. The failure rate for LCD display is

6 p = TQE failures / 10 Hours Parameter Value Justification Source

 0.0065 16 characters possible MIL-HDBK-217F, Section 6.12

 2.1 Tj = 50 C MIL-HDBK-217F, Section 6.12

Q 8.0 Plastic MIL-HDBK-217F, Section 6.12

E 2.0 Ground MIL-HDBK-217F, Section 6.12 Table 3: Parameter values for graphic LCD display Calculations :

λp = 0.0065*2.1*8*2

6 λp = .2184 / 10 Hours

MTTF = 1 / λp

MTTF = 4,578,754 Hours

III) Dallas Semiconductor DS18S20 Temperature sensor This is important to measure the temperature of the body. The failure rate for temperature sensor is

6 λp = (C1πT + C2πE) × πQ × πL Failures/10 Hours Parameter Value Justification

C1 0.040 Assumed 1001 to 3000 gates (MIL-HDBK-217F, Section for a digital MOS device 5.1)

πT 3.1 Digital MOS device Operation should not exceed (MIL-HDBK-217F, Section +125°C (normal operation 5.8) temperature range is -55°C to +125°C), TJ used +125°C

C2 0.0034 8 pin device-Non hemetic (MIL-HDBK-217F, Section 5.9)

πE 2.0 Assumed Ground environment (MIL-HDBK-217F, Section 5.10)

πQ 10 Commercial component (MIL-HDBK-217F, Section 5.10)

πL 1.0 Has been in production for (MIL-HDBK-217F, Section more than 2 years 5.10) Table 4: Parameter values for temperature sensor Calculations :

λp = (0.040*3.1 + 0.0034*2)*10*1

6 λp = 1.308 failures per 10 Hours

MTTF = 1 / λp

MTTF = 764525 hours

IV) Maxim 8860 Linear regulator Since we do not want our device to heat up we have decided to analyze this device.The failure rate for linear regulator is

6 λp = (C1πT + C2πE) × πQ × πL Failures/10 Hours Parameter Value Justification

C1 0.010 <100 transistors for a linear (MIL-HDBK-217F, Section MOS device 5.1)

πT 7 Linear MOS device Operation should not exceed (MIL-HDBK-217F, Section +85°C (normal operation 5.8) temperature range is -55°C to +85°C), TJ used +85°C

C2 0.0034 8 pin device-Non hermetic (MIL-HDBK-217F, Section 5.9)

πE 2.0 Assumed “Ground Fixed” (MIL-HDBK-217F, Section environment 5.10)

πQ 10 Commercial component (MIL-HDBK-217F, Section 5.10)

πL 1.0 Has been in production for (MIL-HDBK-217F, Section more than 2 years 5.10) Table 4: Parameter values for linear regulator Calculations :

λp = (0.020*7+ 0.0034*2)*10*1

6 λp = 0.768 failures per 10 Hours

MTTF = 1 / λp

MTTF = 1302083 hours

Conclusion:

The failure rate for some of the most critical components for the device was calculated. As mentioned earlier the components selected form an integral part of the design and the functioning of which is equally important. The failure rate for the microcontroller, sensors, LCD display and voltage regulator is listed below:

Description P MTTF

Freescale 9S12C32 10.32 105263 LCD display .2184 4,578,754 Hours Dallas DS18S20 1.308 764525 Hours Maxim 8860 linear regulator 0.768 1,302,083 Hours Table 6: Final MTTF values for the components

As seen above, the calculations suggest that the microcontroller is most likely to fail as compared to the other selected components. In most of these calculations the worst case scenario was selected(example: temperature Tj selected to be the highest operating temperature). But since the highest operating temperature of the other devices cannot reach to that level, the microcontroller would not reach to that temperature ever(not taking into fact the surrounding temperature).Based on the above calculation, the MTTF for the PMS is:

λp = 10.32 + 1.308+.768 + .2184

= 12.6144 failures per 106 Hours

MTTF = 79274 hours

Failure modes, Effects and Criticality Analysis(FMECA) Based on the reliability the PMS was divided into five functional blocks each of which are listed below. Two of the criticality levels have also been defined in the following table,

Criticality Failure Effect Maximum Probability -9 High Never happen λp < 10 -5 Low Can happen due to various λp < 10 components Table 6: Criticality Levels

Five Functional Blocks taken into account for FMECA:

A) Power supply(Linear regulator)

B) Microcontroller:

C) Sensors Temp Sensor

Heart rate receiver D) LCD display VCC

R7 1 10k-20k VLED* 2 VSS 3 VCC VDD 4 VO 5 AN01 AO 6 E1 7 E2 8 AN00 DB0 9 PA7 DB1 10 PA6 DB2 11 PA5 DB3 12 PA4 DB4 13 PA3 DB5 14 PA2 DB6 15 PA1 DB7 16 PA0 R/W* CFAG12232D-YYH-N

LCD Connector

E) RF transmitter D E

ANT-315-SPE F

. D D D D D T N N N N N N A G G G G G 1 2 3 4 5 6

VCC LINX TX-LC

1 8 TXD 2 GND GND 7 3 DATAIN VCC 6 4 GND GND 5 IADJ/GND RFOUT R8 430

RF Transmitter Connector FMECA Worksheet

Failure Failure Mode Possible Failure Effects Method of Criticality Remarks No. Causes Detection Linear Failure of No power applied to Observation Low regulator Output = 0V components any of the other A1 such as the critical components linear regulator. Shorted bypass capacitor Output > 5V Failure of Burn up all the Operation High A2 linear components. Would of the regulator. burn up the PMS and device is cause of danger

Micro Uncontrolled Failure of No data displayed on Observation Low Can be detected Controller output of pins 9S12C32 or the LCD by software. No B1 of port A software data display

B2 Uncontrolled Failure of The analog data being Observation Low Can be detected output of ATD 9s12c32 or sent by the sensors by software. pins software would not be Also the data converted into a displayed on digital number and LCD will be thus wrong data some random would be displayed value from the on the LCD memory of the micro which will let the patient know that wrong data is displayed B3 Uncontrolled Failure of The data would not Observation Low Can be detected output of SCI 9S12C32 or be send to the by software. No software computer via RF data will be sent transmitters/Receivers to the doctors or nurses sensors Incorrect Failure of The data displayed on Observation Low Can be detected C1 temperature temperature the LCD of the PMS by software. sensor or for the body Random data 9S12C32 or temperature of the displayed from software patient is not accurate memory of the or completely wrong micro-controller C2 No heart rate Failure of Heart rate not being Observation Low Patient observes (ECG) signal heart rate detected will lead to a Random data receiver or random value on being displayed 9S12C32 or LCD Which is software obtained from memory of micro. LCD No information Failure of LCD does not display Observation Low Patient does not display displayed LCD or data observe any D1 sensors or measurements linear regulator on the display screen D2 Backlight not Failure of Backlight not Observation Low Patient could functioning LCD or linear observed and thus not see data at regulator data not seen at night night

Rf Measured data Failure of RF Computer does not Observation Low No data transmitter not received by transmitters display any data. displayed on the E1 doctors and receivers computer screen References: [1]. Crystalfontz CFAG12232D-YYH-N LCD Screen: http://www.crystalfontz.com/products/character-menubar.gif [2]. Maxim DS18S20 Digital Thermometer: http://pdfserv.maxim-ic.com/en/ds/DS18S20.pdf [3]. Freescale MC9S12C32 Microcontroller: http://www.freescale.com/webapp/sps/site/prod_summary.jsp? code=MC9S12C32&nodeId=0162468636K100 [4]. Polar F-1 Heart Rate Monitor http://www.polar-usa.us/polar-f1.html [5]. Maxim MAX8860 Low dropout Linear regulator: http://pdfserv.maxim-ic.com/en/ds/MAX8860.pdf [6]. Linx technologies 433MHZ Receiver http://www.linxtechnologies.com/images/products_cat/rf_modules/lc_series/lc-s- rxm_manual.pdf [7]. Linx technologies 433MHZ transmitter http://www.linxtechnologies.com/images/products_cat/rf_modules/lc_series/lc-s- txm_manual.pdf