MICROCONTROLLER BASED THERMAL CONDUCTIVITYTESTING INSTRUMENT

*Gopalakrishnan D, K.Rafiq** & K.Sundaresan**

*Department of Textile Chemistry, SSM College of Engineering, Komarapalayam – 638 183

**Department of Textile Technology, PSG Polytechnic College, Coimbatore-641004

Abstract

This research deals about design & fabrication of thermal conductivity tester. The

instrument consists of LCD display, heater, brass plate, temperature sensor, microcontroller,

copper vessel. The temperature sensor (1) is connected with the top plate (θ1), temperature

sensor (2) is connected with the bottom plate (θ2).The both sensors (θ1 & θ2) senses the

temperature and transfers the signal to microcontroller. The microcontroller analyzes the signal

and passes the signal to the LCD display. It displays the temperature of heating plate. When

temperature in the heating plate attains a steady state, the micro controller sends signal to a

buzzer through driver unit. Now the user has to taken and the chamber from instrument and

switch off the heater. This instrument was fabricated by using sheet metal.

In existing thermal conductivity testing method (Lee’s Disc method), thermometers &

stop watch are used to measure thermal conductivity. In this method, taking readings

simultaneously from thermometer and stop watch is difficult. Measurement of temperature in the

thermometer, calculation and time consumption are the limitation. So, the main objective of

Microcontroller based thermal conductivity is to provide higher accuracy level, and low cost as

compared with existing instrument and is also less time consumption. The performance of the

developed thermal conductivity tester was compared with existing instrument with more no. of

samples.

The major application of this instrument is in Testing Laboratories and Research &

Education Institutions.

INTRODUCTION

THERMAL CONDUCTIVITY

“The amount of heat per unit time per unit area that can be conducted through a plate of

unit thickness of a given material, the faces of the plate differing by one unit of temperature is

called “Thermal Conductivity”

THERMAL CONDUCTIVITY TESTING

Thermal conductivity testing is a material property measurement associated with the

ease or difficulty with which heat energy is conducted through a specific type of material.

Materials that conduct heat readily with a small imposed temperature gradient have a higher

thermal conductivity than materials that are more resistant (more insulating) to the flow of heat.

Thermal conductivity is a pure material property independent of conduction-area or the material

thickness. ASTM Standard D5470 is intended to standardize the method for thermal

conductivity measurement so that the results will reflect only the material properties without

regard to the specific test equipment utilized. Thermal conductivity is a fundamental material

property that is essential for characterizing conduction heat transfer.

THERMAL CONDUCTIVITY IMPORTANCE

Thermal conductivity is a material property. It will not differ with the dimensions of a

material, but it is dependent on the temperature, the density and the moisture content of the

material. The thermal conductivity of a material depends on its temperature, density and

moisture content. The thermal conductivity normally found in tables is the value valid for normal

room temperature. This value will not differ much between 273 and 343 K

The objective of this work is to use thermal conductivity for temperature measurement.

In order to meet the above requirements, a low cost, versatile, portable data logger is designed.

A microcontroller based thermal conductivity has been developed for measuring temperature at

different input channels.

The device is designed to receive data from temperature sensors and to store the

results on external non-volatile electrically erasable programmable read only memory

(EEPROM) for post process analysis. An integrated Liquid crystal display (LCD) is also used for

real time display of data acquired from various sensors. In the present work, temperatures

indicated by LCD Disply are compared with standard temperature obtained from clinical

thermometer after the intervals of time. Based on these results, the accuracy of the channels is

noted and by comparing them, the most accurate one among these is found.

OBJECTIVES OF THE PROJECT

To design and fabricate the thermal conductivity tester.

The improve accuracy level.

To save the time consumption for the testing.

To reduce cost of testing instrument.

To modification of Lee’s Disc method in thermometers are replaced by using

temperature sensor.

To testing different kinds of fabrics in thermal conductivity.

To reduce man power for testing and calculations.

To store the readings for post process analyses.

METHODOLOGY

The procedure for the thermal conductivity tester is as follows

Sourcing of Materials

To design & Fabrication of sheet metal box

A temperature sensor is designed for the size of lee’s disc hole size

Micro controller and temperature sensor is interface to circuit board

Power IC is connected with circuit board connection

Keypad and LCD Display is interface to microcontroller

Buzzer and Bridge Rectifier is also connected with circuit board

The both sensor (θ1 & θ2) senses the temperature and sends signal to the microcontroller.

The microcontroller analyzes the signal and passes the signal to the LCD display.

Fabric testing

Report preparation

MATERIALS AND METHODS

For the design and development of the system, the methodology used involves

the software and hardware implementation. The actual implementation of the system involves

the following steps:

1. System Definition: Broad definition of system hardware including microcontroller and its

interface with display, memory, keypad etc.

2. Circuit Design: Selection of PIC microcontroller and other interfacing devices, as per

system definition. Design of hardware circuit and its testing on laboratory kits with some

simple microcontroller software routines.

3. PCB Design and Fabrication: Generation of schematic diagrams and the production of

circuit board layout data for the procurement of the circuit board.

4. Hardware Modifications: Making any hardware changes found necessary after the

initial hardware tests, to produce a revised circuit board schematic diagram and layout.

5. Software Design: Developing algorithm for the system, allocating memory blocks as per

functionality, coding and testing.

6. Integration and Final Testing: Integrating the entire hardware and software modules

and its final testing for thermal conductivity operation.

Hardware Implementation

Temperature measurement using microcontroller based thermal conductivity tester

includes the following components:

1. Temperature Sensor.

2. Microcontroller.

3. Keypad Matrix.

4. Liquid Crystal Display.

5. External Memory.

6. IC 7805 (Voltage Regulator IC)

Temperature Sensor PIC Microcontroller 4x3 Matrix Keypad

Liquid Crystal Display EEPROM IC 7805 (Voltage Regulator IC)

Temperature Sensor

The series are precision integrated-circuit temperature sensors, whose output voltage is

linearly proportional to the Celsius (Centigrade) temperature. The sensor thus has an advantage

over linear temperature sensors calibrated in ° Kelvin, as the user is not required to subtract a

large constant voltage from its output to obtain convenient Centigrade scaling. The sensor does

not require any external calibration or trimming to provide typical accuracies of ±L4°C at room

temperature and ±3/4°C over a full -55 to +100°C temperature range. The sensor low output

impedance, linear output, and precise inherent calibration makes interfacing to readout or

control circuitry especially easy. It can be used with single power supplies, or with plus and

minus supplies.

PIC Microcontroller

PIC 16F877A is one of the most advanced microcontroller from Microchip. This controller is

widely used for experimental and modern applications because of its low price, wide range of

applications, high quality, and ease of availability. It is ideal for applications such as machine

control applications, measurement devices, study purpose, and so on. The PIC 16F877A

features all the components which modern microcontrollers normally have.

4x3 Matrix Keypad

At the lowest levels, keyboards are organized in a matrix of rows and columns. The CPU

accesses both the rows and columns through ports, therefore, with two 8-bit ports an 4*3 matrix

of keys can be connected to the microcontroller. When a key is pressed, a row and a column

make a contact, otherwise, there is no connection between rows and columns .The detection of

the key varies from scanning of the key to grounding the rows and columns.

Key no Function of key

1 Mass of lee’s disc value

2 Specific heat capacity value

3 Diameter of lee’s disc

4 Thickness of lee’s disc

5 Thickness of sample

6 Set reading

Liquid Crystal Display

LCD Character Module Display, 4x20 characters, STN yellow/green, amber LED

backlight, Transflective, 6:00, Wide Temperature range, RoHS compliant, Module size 98mm x

60mm, English-European character set. This LCD display uses STN technology, which is much

better quality than the cheaper TN types. It has a better contrast and a wider viewing angle.

EEPROM

EEPROM stands for Electrically Erasable Programmable Read-Only Memory and is a

type of non-volatile memory used in computers and other electronic devices to store small

amounts of data that must be saved when power is removed, e.g., calibration tables or device

configuration

IC 7805 (Voltage Regulator IC)

IC 7805 is a voltage regulator integrated circuit. It is a member of 78xx series of fixed

linear voltage regulator ICs. The voltage source in a circuit may have fluctuations and would not

give the fixed voltage output. The voltage regulator IC maintains the output voltage at a constant

value. The xx in 78xx indicates the fixed output voltage it is designed to provide. 7805 provides

+5V regulated power supply. Capacitors of suitable values can be connected at input and output

pins depending upon the respective voltage levels.

Microcontroller connection diagram Power IC Connection

Temperature Sensor Connection

Thermal Conductivity Setup

In existing thermal conductivity testing method (Lee’s Disc method), thermometers &

stop watch are used to measure thermal conductivity. In this method, taking readings

simultaneously from thermometer and stop watch is difficult. Measurement of temperature in the

thermometer, calculation and time consumption are the limitation. So, the main objective of

Microcontroller based thermal conductivity is to provide higher accuracy level, and low cost as

compared with existing instrument and is also less time consumption.

Design and fabrication method the temperature sensor (1) is connected with the top

plate (θ1), temperature sensor (2) is connected with the bottom plate (θ2).The both sensors (θ1

& θ2) senses the temperature and transfers the signal to microcontroller. The microcontroller

analyzes the signal and passes the signal to the LCD display. It displays the temperature of

heating plate. When temperature in the heating plate attains a steady state, the micro controller

sends signal to a buzzer through driver unit. Now the user has to taken and the chamber from

instrument and switch off the heater. This instrument was fabricated by using sheet metal the

major application of this instrument is in Testing Laboratories and Research & Education

Institutions.

FORMULA USED

The measurement of thermal conductivity and, therefore, paves the way to determine

thermal resistance and thermal conductance. Thermal resistance (R) and thermal conductance

(C) of the materials are reciprocals of one another and can be derived from thermal conductivity

(k) and the thickness of the materials.

Thermal Conductivity

Thermal conductivity is the time rate of steady state heat flow through a unit area of a

homogeneous material induced by a unit temperature gradient in a direction perpendicular to

that unit area, W/m⋅K.

Where,

M - Mass of the brass disc. S - Specific the heat capacity of brass disc. D - Thickness of the bad conductor. A- Area of cross section of Sample. (T1- T2) - temperature difference between the two temperature of bad conductor.

Table 6.12 Comparison between existing method and designed instrument results

0

1

2

3

4

Comparison between Existing method and Designed Instrument

THICKNESS (mm)

Thermal Conductivity (W / mk) Existing Method

Thermal Conductivity (W / mk) Designed Instruments

S.NO SAMPLE THICKNESS (mm)

Thermal Conductivity

(W /m K) Existing method

Thermal Conductivity

(W /m K) Designed Instrument

1 Honey comb Weave (Cotton-woven)

0.72 0.021 0.021

2 Huck-a-Buck Weave (Cotton-woven)

0.69 0.030 0.029

3 Plain Weave (Cotton-woven)

0.19 0.033 0.035

4 Twill Weave (PC Blended woven)

0.51 0.019 0.020

5 100 % Wool (Single Jersey Knitted)

0.61 0.022 0.21

6 100 % Bamboo (Rib Knitted)

0.69 0.023 0.021

7 100 % Cotton (Interlock Knitted)

0.73 0.023 0.023

8 100% Jute (Non-Woven)

2.83 0.018 0.018

9 100% Polyester (Non-Woven)

0.77 0.029 0.030

10 100% Polypropylene (Non-Woven)

1.178 0.040 0.041

CONCLUSION

Through this Research work the following conclusion have been made The micro controller based thermal conductivity tester is a valuable instrument to

analyze thermal conductivity. Thermal conductivity tester are used for measuring the

temperature might have certain limitations in terms of heat, memory and cost. In this work, an

attempt has been done to design a thermal conductivity tester, which is of low cost,

comfortable, very less power consumption, self contained. It is an efficient thermal conductivity

tester, which works in real time mode. A step-by-step approach in designing a microcontroller

based thermal conductivity tester has been followed. According to the study and analysis of

various parts of the system, a design has been carried out. The results obtained from the

measurement have shown that the system perform well under all the conditions. From this

work, it is concluded that in this system among them was successfully carried out and working

properly. We have achieved best physical test results of thermal conductivity. When compare

to existing instrument and designed instrument more or less the thermal conductivity results will

be significant.