INTRODUCTION the brake system. The optimum time

INTRODUCTION

This
report paper analyses a small sensor unit and analogy amplifier which is
positioned at the when of a racing car to monitor the pressure of the tire. The
temperature of the whole system will arise up to 300oC during racing
since the unit will be close to the brake system. The optimum time of operation
should be 180 min for the unit during the race while the total operating period
in a season is a maximum of 500 hours. This extensive cooling unit will not be
possible due to the weight and space reasons. The materials and technologies
that are needed for this unit include pressure sensor, temperature sensor, RF
module, Digital-to-Analog converter, microcontroller, analogue
instrumentation amplifier, display device, timer, and LED indicator.

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LITERATURE REVIEW

The operation of
the sensor unit will majorly deal with the measurement of temperature,
pressure, and timer. This sensor should have detailed features in order for
them to efficiently operate within the required guidelines, these
characteristics include the ability to withstand a temperature of 300oC,
ability to operate for a duration of 180 minutes during the race, and ability
to have a lifespan of more than 500 hours while operating.

Components

The analogue
components and semiconductor technologies that are needed to ensure safe
operation include the pressure sensor, temperature sensor, RF module,
Digital-to-Analog converter, microcontroller, analogue
instrumentation amplifier, the display device, timer, and LED indicator 1. These materials and
technologies of semiconductor that are required for the design of the system of
wheel pressure monitoring are discussed below:

 

Pressure
sensor

This sensor will
be used in determining the pressure of the wheels of the car. From input to the
output, a sensor may possess numerous stages of conversion before it generates
the electric signal. The pressure imposed in the tire will lead to alteration
in strain in the diaphragm which will lead to a deflection. This will lead to
general variations in the strain gauge’s resistance attached to the diaphragm.
The variations in the resistance will lead to unbalance in the circuit of
Strain Gauge Bridge leading to variations in the output voltage in the circuit
of the bridge 2.

The type of
pressure sensor that can be used in this design is a piezoresistive pressure
sensor which is a monolithic, wafer fabricated solid-state sensor by the use of
silicon processing. Since piezoresistive pressure sensors are wafer fabricated,
more than 200 sensors can be produced in a single wafer.

Figure 1: Circuit diagram
of a pressure sensor 3

The pressure
sensor above function by measuring the changes in the resistance which
ultimately represent variations in the pressure of the wheel. Every resistor in
the pressure sensor either stretches or compresses.

Temperature
sensor

This is a gadget which
may be utilized in detecting and measuring hotness and coolness and changes it
into an electrical signal. The temperature sensor that can be used on the
wheels of this racing car is the LM35 series which has a temperature range of
-550C to +1200C. This temperature sensor consists of extensive signal
processing circuitry contained in the similar package as the sensors and for
the sensor IC of temperature the compensation circuit is not needed 4.

Figure 2: Temperature sensor,
LM35 5

The supply of
power of the temperature sensor above needs 5.5V and it has three terminals of
a material which performs its function depending on the temperature to vary
resistance. When there is a rise in voltage, the temperature will also rise.
Temperature sensors connected directly to microprocessor input hence has the
ability to reliably and directly communicate with the microprocessor. The
sensor unit can effectively communicate with processors that are of low cost
without the requirement of analogue to digital converter.  6.

Analog
Instrumentation amplifier (AD8237)

The criteria of
selection for the instrumentation amplifier for this design include low input
offset voltage, low input bias current, and low-frequency noise. There is the necessity
for the noise’s frequency to be as low as possible which is estimated as 10 Hz
to 0.1Hz because the sensor output is similar.  7.

Figure 3: Representation
of analogue instrumentation amplifier 7

Analog
Digital Converter (ADC)

An analogue to
digital converter is a device that is involved in the conversion of analogue
signals such as temperature and pressure signals into the digital signal which
is then fed to the microcontroller. The microcontroller can only interpret a
digital signal, therefore, there is need of converting these analogue signals
of temperature and pressure into digital signals by the ADC before being fed
into the microcontroller.  The other
devices such as the display device, LED indicator, and RF module are devices that
are digital which only interpret the number which as zero and one 8.

Microcontroller

The
microcontroller is involved in accepting data from the analogue to digital
converter, manipulating the data and then produce the required results in this
design of wheel pressure monitoring system. In this case, the input devices
include the timers, pressure sensors, and temperature sensors and then sends
signals to different components which include the display device, RF module,
and LED indicator 9.

RF
Module

RF module is an
abbreviation of radio frequency module and is a minute electronic device which
is used for receiving and transmitting radio signals between two devices. The
RF module received data concerning pressure and temperature from the sensors
through the microcontroller and then transmit these signals to the display
device and LED indicator where necessary steps will be performed.

Figure 4: RF Module 10

This wireless
communication is made possible through radio frequency communication or through
optical communication 10.

Timer

For this design of
the wheel pressure monitoring system, there is need to in-cooperate a timer
which will be involved in the counting of minutes during the period in which
the racing car is in operation. Counting of time for this design is critical
since there is need of informing the driver of the maximum time of operation of
the car during a particular race which has been set to be 180 minutes for any
given race 11.

Display
Device

A typical system
of tire-pressure monitoring integrates numerous functions. Temperature sensors
and pressure sensors in every wheel of the racing car determine pressure and
temperature at intervals that are regular. The information gotten from these
sensors are sent by the signal of radio-frequency to an electric control unit
which is located inside the racing car. This electric control unit is
responsible for analysing the data gotten through the radio-frequency signal
from the temperature and pressure sensors. Initiators interrogate sensors are
required to find out possible warnings rapidly and to make sure the information
that is accurate is transmitted 12.

Figure 5: Display Device 12

The display shows
the data of the quantity of pressure and temperature as determined by the
pressure and temperature sensors. If the temperature of the wheels is above 300oC,
the temperature sensor will detect this rise in temperature and send the data
to the display device which is located inside the racing car where the driver
can observe it. When the pressure of the wheels is below the level that is
allowable, the pressure sensor will convey the information through the RF
module to the electric control unit where the pressure drop value will be showed.
The driver of the car can simply note the drop in pressure value and may make a
decision to increase the stop racing before the wheels could cause an accident 13.

LED
Indicator

The LED indicator
will be used to show a warning in case the information received from the
pressure sensor shows that the wheels’ pressure has dropped beneath a given
level which can be disastrous to the car. The LED indicator is coupled to the
microprocessor such that it will only become active when the temperature goes
above 300oC or pressure of the wheels reduces to 14psi or below. The
LED indicator play a major role in monitoring the pressure and temperature of
the wheel of the racing car by alerting the driver in case critical temperature
and pressure is reached. The remedy can either be to slow down the car and add
pressure in the tyres or stop applying the breaks on the wheels to reduce the temperature 11.

Figure 6: LED Indicator 14

SOLUTION

EVALUATION

The wheel pressure
measuring system is an important unit that plays a critical role in the safety
application of the racing cars. From the components discussed above which
include the microcontroller, the display unit, temperature sensor, RF module,
timer, and instrumentation amplifier are the major components that are needed
for this design of wheel pressure monitoring system 15. The block diagram
of the design after the incorporation of the components discussed above is as
shown in the figure below:

Figure 7: Block diagram
of wheel pressure monitoring system 15

Type
of Materials used in making the Pressure Unit

The operation of
components and made of semi-conductor has been reported at temperatures of
approximately +700oC on a high end and as low as -270oC. The
material used for making the outer section of the pressure sensor was SiC
MOSFET which has an operational temperature of up to +650oC. However,
it has been reported that temperature above +650oC will lead to degradation
of mechanical performance of the pressure sensor. The Si MOSFET high
temperature sensors as developed by the use of piezoresistive and capacitive
sensing technology 14.

Operation
Principle and Architecture of SiC MOSFET

This section deals
with the fabrication process, materials and components used in designing a high
temperature sensor made of SiC MOSFET.

Figure 8: Si MOSFET
pressure sensor

When external
pressure is applied, the SiC MOSFET diaphragm deflects over the dopant
segregated region over the gate on the NiSi. The bending and deflection has a
unique impact since it increases the value of capacitance between the substrate
and diaphragm. Through the modification of the thickness of the diaphragm as
well as the radius, one can attain pressure of touch point and depth which will
result in variations in the value of capacitance 15.  

Sensor
fabrication

The pressure
sensor discussed in this section is based on the piezoresistive pressure sensor
based on silicon on insulator wafers. The first step is to acquire 400 ?m wafer
then designing a pattern layer of approximately 0.34?m on the top layer of the
wafer. The passive layers of SiC are deposited by LPCVD. The MOSFET ohmic
contact is fabricated using self-aligned silicide process. The MOSFET
multilayer films are sputtered and patterned using lift-off to form electrodes
and metal interconnects. The component Ni is introduced in this step to
represent the multilayer electrode 13.

DISCUSSION

Pressure
sensor Design

The wheel pressure
measuring system is an important unit that plays a critical role in the safety
application of the racing cars. The system contains the microcontroller, the
display unit, temperature sensor, RF module, timer, and instrumentation amplifier.
The sensor is a strained gauge and a circular diaphragm type sensor joined on
the opposite diaphragm’s face which was taken as the pressure of reference and
the other section joined to the valve of input pressure. The strain gauge is
based on the principles of piezoresistive such that strain gauge’s resistance
will show a variation. The detailed circuit diagram of the wheel pressure
monitoring system is as shown in the figure below:

Figure 8: Circuit diagram
of the wheel pressure monitoring system 16

Operation
of the Pressure Monitoring System

The sensor unit of
this monitoring will be located at the circular diaphragm of the wheels with
each unit in the four wheels joined together by the microcontroller. The
temperature and pressure sensors are a strain gauge and circular diaphragm
sensor type joined on the opposite diaphragm’s face which was taken as the
pressure of reference and the other section joined to the valve of input
pressure. The pressure sensor is used in determining the pressure of the wheels
of the car. From input to the output, a sensor may possess numerous steps of
conversion before it generates an electric signal. The pressure sensor works
concurrently with the temperature sensor which is a device that is used in
measuring and detecting coolness and hotness of the wheels’ diaphragm and
converts it into an electrical signal 17.

The electrical
signals from the pressure and temperature sensors are then fed to the analogue
instrumentation amplifier whose function is to reduce unwanted noise that might
have been picked have been picked up by the circuit or by the sensors while
converting pressure signals and heat signals into electrical signals. The
noise-free signal from the analogue instrumentation amplifier is then fed into
the analogue to digital converter. An analogue to digital converter is a device
that is involved in the conversion of analogue signals such as temperature and
pressure signals into the digital signal which is then fed to the
microcontroller 18.

This is because
microcontroller can only interpret a digital signal, hence there is need of
converting these analogue signals of pressure and temperature into digital
signals by the analogue to digital converter before being fed into the
microcontroller. The microcontroller is involved in accepting data from the
analogue to digital converter, manipulating the data and then produce the
required results in this design of wheel pressure monitoring system. This
microcontroller takes input from the device it is directing and controls the
device through conveying signals to diverse components of the device 2.

The RF module
received data concerning pressure and temperature from the sensors through the
microcontroller and then transmit these signals to the display device and LED
indicator where necessary steps will be performed. The information gotten from
these sensors are sent by the signal of radio-frequency to an electric control
unit which is located inside the racing car. When the pressure of the wheels is
beneath the level allowed, the pressure sensor will convey the data through the
RF module to the electric control unit where the pressure drop value will be
displayed. The LED indicator play a major role in monitoring the pressure and
temperature of the wheel of the racing car by alerting the driver in case
critical temperature and pressure is reached 6.

ANALYSIS

The components
that have been used in the design of wheel pressure monitoring system have been
analysed in Table 1 below with consideration being taken of the component,
cost, model, and quantity.

Component

Model

Specification

Cost

Use

Pressure
Sensor

Piezoresistive
pressure sensor

0 to 15
psi

$82.00

This
sensor will be used in determining the pressure of the wheels of the car.

Temperature
Sensor

LM35
series

Has a
range of A temperature -550C to +1200C

$75.00

A temperature
sensor is a gadget used for detecting and measuring hotness and coolness and changes
it into an electrical signal 7

RF
Module

ASK RF
transmitter-receiver

Frequency
433MHz or 315MHz

$6.79

The RF
module received data concerning pressure and temperature from the sensors
through the microcontroller and then transmit these signals to the display
device and LED indicator where necessary steps will be performed.

Digital-to-Analog
converter

TLV1572
Analog-to-Digital Converter

12-bit
D/A converter

$169.00

An
analogue to digital converter is a device that is involved in the conversion
of analogue signals such as temperature and pressure signals into the digital
signal which is then fed to the microcontroller.

Microcontroller

PIC16C6x/7x

2048
bytes of EPROM, 128 bytes of RAM, and CPU running at 12 MHz

$21.99

The
microcontroller is involved in accepting data from the analogue to digital
converter, manipulating the data and then produce the required results in
this design of wheel pressure monitoring system.

Analog
instrumentation amplifier

MCP602
Model

The
frequency of about 10 Hz to 0.1 Hz.

$50

This
device reduces
unwanted noise that might have been picked have been picked up by the circuit
or by the sensors while converting pressure signals and heat signals into
electrical signals 13.

Display
device

TFT LCDs

The
appropriate size of the display device is 4 inches with the resolution of
800*600. 

$4.20

The
display shows the data of the quantity of pressure and temperature as
determined by the pressure and temperature sensors

Timer

Digital
clock

Up to
180 minutes

$8.45

The
timer is involved in the calculating of time during the period in which the
racing car is in operation.

LED indicator

HWIP-2FQD

The peak
wavelength variations are up to + or -10nm and operates at a current of  20mA

$17.09

The LED
indicator play a major role in monitoring the pressure and temperature of the
wheel of the racing car by alerting the driver in case critical temperature
and pressure is reached 8.

 

Conclusion

This
report paper analyses a small sensor unit and analogy amplifier which is
positioned at the when of a racing car to monitor the pressure of the tire. The
materials and technologies that are needed for this unit include pressure
sensor, temperature sensor, RF module, Digital-to-Analog converter,
microcontroller, analogue
instrumentation amplifier, display device, timer, and LED indicator. The
pressure sensor will be used in determining the pressure of the wheels of the
car. From input to the output, a sensor may possess numerous steps of
conversion before it generates the electric signal. The temperature sensor is a
used in measuring and detecting coolness and hotness and converts it into an
electrical signal. The analogue instrumentation amplifier assists in reducing
unwanted noise that might have been picked have been picked up by the circuit
or by the sensors while converting pressure signals and heat signals into
electrical signals.

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