SENSORS FOR TEMPERATURE MEASUREMENT: ERROR MEASUREMENT OF TYPE K THERMOCOUPLE MAULANA BIN HANAPI

SENSORS FOR TEMPERATURE

MEASUREMENT:

ERROR MEASUREMENT

OF TYPE K THERMOCOUPLE

MAULANA BIN HANAPI

LA _Y,

N ý M Pº

(ý) QC 271 M447 2002

Universiti

Malaysia

Sarawak

2002

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SENSORS FOR TEMPERATURE MEASUREMENT: ERROR

MEASUREMENT OF TYPE K THERMOCOUPLE

MAULANA BIN HANAPI

This report submitted in partial fulfilment of the requirement for the degree of Bachelor of Engineering (Hons. ) Mechanical Engineering and Manufacturing

System from the faculty of Engineering

Universiti Malaysia Sarawak

2002

It

BORANG PENYERAHAN TESIS

Judul: SENSORS FOR TEMPERATURE MEASUREMENT : ERROR MEASUREMENT OF TYPE K THERMOCOUPLE

SESI PENGAJIAN: 1999 / 2002

Saya MAULANA BIN HANAPI

mengaku membenarkan tesis ini disimpan di Pusat Khidmat Maklumat Akademik, Universiti Malaysia Sarawak dengan syarat-syarat kegunaan seperti berikut:

1. Hakmilik kertas projek adalah di bawah nama penulis melainkan penulisan sebagai projek bersama dan dibiayai oleh UNIMAS, hakmiliknya adalah kepunyaan UNIMAS.

2. _{Naskhah salinan di dalam bentuk kertas atau mikro hanya boleh dibuat dengan kebenaran} hertulis daripada penulis.

3. Pusat Khidmat Maklumat Akademik, UNIMAS dibenarkan membuat salinan untuk pengajian mereka.

4. _{Kertas projek hanya boleh diterbitkan dengan kebenaran penulis. Bayaran royalti adalah} mengikut kadar yang dipersetujui kelak.

5. * Saya membenarkan/tidak membenarkan Perpustakaan membuat salinan kertas projek ini sehagai bahan pertukaran di antara institusi pengajian tinggi.

6. _{*'" Sila tandakan ( ti/ )}

F7

i

a

SULIT (Mengandungi maklumat yang berdarjah keselamatan _atau kepentingan Malaysia seperti yang termaktub di dalam AKTA RAHSIA RASMI 1972).

TERHAD _{(Mengandungi maklumat TERHAD yang telah ditentukan oleh} organisasi/ badan di mana penyelidikan dijalankan).

TIDAK TERHAD

Disahkan oleh

rvvshl

4

(TANDATANGAN PENULIS) (TANDATAN(IANPENYELIA)

Alamat tetap: l. o 570. Lrg Sentosa Timur 3A t Nama Penyelia: Rubi .

vah Hi Baini Kpg. Usaha Jaya Baru

96000. Sibu Sarawak

Tarikh: ý Lo 4 34 4 L Tarikh: T)bf 1^7 QÜ7.

CATATAN * _{Potong yang tidak berkenaan.}

** _{Jika Kertas Projek itd SULIT atau TERHAD, sila lampirkan surat} daripada _{pibak berkuasa/ organisasi} berkenaan _{dengan menyertakan} sekali tempoh kertas projek. Ini perlu dikelaskan sebagai SULIT atau TERHAD.

This project report entitled " SENSORS FOR TEMPERATURE MEASUREMENT:

ERROR MEASUREMENT OF TYPE K THERMOCOUPLE " was prepared by

Maulana b. Hanapi _{as a partial fulfillment of the requirements} for the Bachelor of Engineering (Hons. ) in Mechanical Engineering & Manufacturing System, is hereby read and approved by,

8'oý2:

_{e z.}

Rubiyah Hj. Baini

Date

(Supervisor)

To APAK & MAK and

to

_all

_{say colleagues}

_and

_staffs

of

Engineering

Faculty.

ACKNOWLEDGEMENT

The author would like to express his sincere thanks and deep appreciation to Mrs. Rubiyah Hj. Baini for her guidance and encouragement throughout the duration of this project. Indeed, her support played a vital role in the completion of this project.

Extended thanks to Mr. John Button (Senior Customer Support Engineer of Armfield) for

most valuable information and friendship.

The author would also like to acknowledge all those who have contributed their help in

ABSTRAK

Thermocouple adalah sejenis sensor yang digunakan untuk mengira suhu berdasarkan prinsipalnya yang mana apabila dua logam yang berbeza dicantumkan, perubahan arus elektrik akan berlaku jika terdapat perubahan suhu diantara dua bahagian cantuman iaitu cantuman rujukan dan cantuman pengesan. Projek ini adalah tentang thermocouple jenis K yang digunakan dalam alat Penentu Suhu yang terdapat di dalam lab mekanikal di UNIMAS. Alat Penentu Suhu ini juga dikenali sebagai THI. Objektif utama projek ini adalah untuk mengira ralat yang berlaku di dalam thermocouple jenis K untuk alat THI. Terdapat dua ralat yang akan dibuat iaitu ralat untuk bacaan yang diperoleh melalui eksperimen dan ralat untuk bacaan yang telah dilinearkan. Ralat-ralat ini akan dibandingkan dengan ralat yang telah dispesifikasikan pembuat model TH I.

ABSTRACT

Thermocouple _{is a type of sensors to measure temperature. It is based on the principle} that when two dissimilar metals are joined, a predictable voltage will be generated in accordance to the difference in temperature between the measuring junction and the reference junction. This project is about the type K thermocouple used in Temperature Measurement _{equipment that is available at UNIMAS'} Mechanical Engineering laboratory. The equipment is named THI. The main objective of this project is to determine the error range occurs in type K thermocouple used in THI. The error range will consist of error range based on experimental and linearized results. These errors will then to be compared to the manufacturer's specification.

a.

CONTENTS

APPROVAL

DEDICATION

ACKNOWLEDGEMENTS

ABSTRAK

ABSTRACT

CONTENTS

LIST OF FIGURES

LIST OF TABLES

LIST OF GRAPHS

CHAPTER 1: INTRODUCTION

1.1 GENERAL OVERVIEW

1.2 SENSORS

1.2.1 Definition

1.2.2 Forms of Sensor Outputs

(I)

(II)

(III)

Analog Signal

Digital Signal

Carrier Signal

1.3 MEASUREMENT SYSTEMS 1.3.1 Overview

1.3.2 Basic Electronic Measuring System

1.3.3 Signal Conditioning

(I)

Data Sampling

PUSat KPljCjn at MßK1Unt*t AK2ae i UNIVERSITI MALAYSIA SARAV AK

94300 Kota Sa: rarohan

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ii itl IV V vi ix X X

3

3

4

4

5

6

7

ß IQ VI

(II)

Data Conversion

1.4 EFFICIENT DATA ACQUISITION

1.5 OBJECTIVES

CHAPTER 2: LITERATURE REVIEW

2.1 TEMPERATURE MEASUREMENT

2.1.1 Review

(I) _{Definition of Temperature} (II) Temperature Sensors 2.2 THERMOCOUPLES 2.2.1 General Review 2.2.2 Thermometric Laws 2.2.3 Thermocouples Materials 2.2.4 Thermocouple Selection 2.3 EQUIPMENT DESCRIPTION 2.3.1 General Review

2.3.2 Type K Thermocouple

CHAPTER 3: METHODOLOGY

3.1 CONSIDERATION 3.1.1 Safety

3.1.2 Apparatus Accuracy

3.1.3 Apparatus Maintenance

3.2 EXPERIMENTATION

3.2.1 Objective

3.2.2 Experiment Consideration

lI 13 16

17

17

18

19

21

21

23

25

26

28

28

29

30

30

31

31

32

32

33

vii

(I) Equipment Set Up 34 (II) Procedure 35 (III) Results 35

CHAPTER 4: RESULTS

4.1 REFERENCE TABLE 38 4.2 EXPERIMENTAL RESULT 39

4.3 GRAPH Vactuai vs. T,,, AND Ve vs. T. 41

4.4 OFFSET LINEAR APPROXIMATION 43

CHAPTER 5: DISCUSSION

5.1 ERROR DURING DATA ACQUISITION

45

5.2 APPROXIMATION EQUATION

45

5.2.1 Linear Approximation Equation

45

5.2.2 Offset Approximation Equation

46

5.3 ERROR IN TYPE K THERMOCOUPLE

49

CHAPTER 6: CONCLUSION AND RECOMMENDATIONS

6.1 CONCLUSION

6.2 RECOMMENDATIONS

52

53

BIBLIOGRAPHY

54

YlYi

LIST OF FIGURES

Figure 1.1:

An analog signal of the outside air temperature.

Figure 1.2: Figure 1.3: Figure 1.4: Figure 1.5: Figure 2.1: Figure 2.2: Figure 2.3: Figure 2.4: Figure 2.5:

A digital signal of the outside air temperature

Basic electronic measuring system

" Measuring Transmitter

Frequency spectrum an analog signal

Simple thermocouple circuit

Seebeck Effect

5

9

II

22

23

Circuits illustrating the law of intermediate temperatures 24

Basic thermocouple properties 25

Temperature Measurement (THI) Equipment 28

Figure 2.6:

TH 1: Schematic diagram of hypsori terfieated water bath

29

LIST OF TABLES

Table 4. I : Type-K Thermocouple Reference Data 38

Table 4.2: Type-K Thermocouple Experimental Data of 39

Emf Value at Every 5°C Increments from 0 to 50°C

Table 4.3: Comparison Between Actual and Experimental Data 40

Table 4.4: Type K Reference Data 40

Table 4.5: _{Experimental Data For One-Sixth and Five-Sixth of 50°C} 43 Table 5. 1: _{Comparison of calculated, actual and experimental results} 49 Table 5.2: _{Differences of Error between experimental and linearized} 50

data with actual data.

Table 5.3: _{Range of Error} 51

LIST OF GRAPHS

Graph 4.1: Type K Thermocouple Characteristic Vartua, vs. T,,, and 41 Linear Approximation

Graph 4.2: _{V, vs. T,,,}

42

Graph 4.3:

_{Solid - Line Linear Approximation That Reduced by}

44/47

The Added of Offset Value

CHAPTER 1

INTRODUCTION

1.1

GENERAL OVERVIEW

Electronic _{measurements have become a part of everyday life. Sensors and} transducer are the eyes and ears of modern measurement instrumentation and control systems. Many types of machines depend on sensors to provide input data about environment. Carr (1993) claimed that sensors represent both one of the oldest segments of the electronic industry and one of the most modern.

Sensors of all types provide the computer with the information it needs to perform monitoring and control tasks. Development in the use of laser and microelectronics sensors make possible the rapid measurement of physical properties that were previously difficult to measure.

A digital computer requires an input of signals in digital form. However, the plant

being controlled has signals that vary continuously with time, i. e. are analogues

signal. The analog and continuous time signals measured by the sensor and

modified by the signal conditioning circuitry must converted into the form a

computer can understand. This is what

is referred to here as data acquisition.

CHAPTER I INTRODUCTION

Data acquisition is the process of taking analog signals from the real world, processing them, converting them into digital data and finally bringing the resulting digital data into the computer memory. Data acquisition system (DAS) is a system that conditions a number of analog signals and converts them into digital form for processing by a computer. Data from latter are collected automatically

by a data acquisition system (DAS), which can report, for example the number of

parts being produced per unit time, their dimensional accuracy, their surface

finish, their weight, and so on, at specified rates of sampling.

The components of DAS include microprocessors, transducers, and analog-to-

digital converters (ADCs). Data acquisition systems are also capable of analyzing

the data and transferring them to other computers for purposes such as statistical

analysis, data presentation, and the forecasting of product demand.

This project is basically focuses on sensors. As mentioned above, transducer is

one of the important parts of DAS. And transducer is a combination of

several

sensors.

CHAPTER I INTRODUCTION

1.2

SENSORS

1.2.1 Definition

People who work with sensors and transducers everyday tend to use these two words somewhat interchangeably in their speech. This is no hard and fast rule as to what distinguishes an electrical from an electrical sensor. Ask any number of engineers or scientists for their definitions of these two terms and you will probably get that many different answers.

As according to Carstens (1993), sensor is a device that converts a quantity or an energy form into an electrical output signal. The form of that output signal, whether it is an ac or a dc signal, whether the signal is digital or analog, to name just a few, is determined by the sensor's electromechanical and/or chemical makeup. He again claimed that the transducer is a device comprised of a sensor whose output signal is modified or conditioned to suit a particular application or needs by its user.

In other study about sensor, Christiansen (1998) claimed that a sensor is basically

equivalent to the word of transducer.

According to him, a sensor, or transducer is

a device that converts energy derived

from a physical phenomenon into an

electrical current or voltage, for purposes of measurement, control, or

information.

CHAPTER I INTRODUCTION

Hordeski (1985) stated that a sensor is a device that converts information about the environment or internal state of a system from one form into another. It converts a measurand (signal to be measured) into a signal in a different form. The measurand is the input to the sensor and the signal produced by the sensor is the output. In data acquisition system, sensor is an element that converts changes in a physical parameter into electrical signals.

1.2.2 Forms of Sensor Outputs

(I) Analog Signal

Very simply stated, an analog signal is a continuous (not interrupted) data signal comprised of a flow of current or a voltage level whose amplitude, frequency, or phase relationship with some reference signal contains data information. This information _represents a proportional relationship or analog of the input ineasurand that is controlling the signal [0' Higgins, 1996].

The Measurand is the quantity, or condition that is measured (then sensed and

converted into a useable electrical output) by a transducer

[Norton, I989].

Bateson (1999) stated that an analog signal varies in a continuous manner and

CHAPTERI INTRODUCTION

continuous recording of the outside air temperature as shown by Figure 1.1. The

recording is a continuous line (a characteristic of all analog signals).

Figure 1.1 : An analog signal of the outside air temperature. [Bateson, 1999]

(II) Digital Signal

According to Carstens (1993), a digital signal is comprised of a series of

interrupted flow, or pulses, of current or voltage levels. Each pulses or series of

pulses contains the encoded information corresponding to the

input data. A

decoding process must then be used to decipher the desired information.

The same study on digital signal, Bateson (1999) claimed that a digital signal

varies in a discrete manner and may take only certain discrete values between its

limits. Figure 1. 2 shows an example of a digital signal is an outdoor sign that

CHAPTER 1 INTRODUCTION

displays the outside air temperature to the nearest degree once each minute. A graph of the signal produced by the sign does not change during an interval, but it

may jump to a new value for the next interval.

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Figure 1. 2: A digital signal of the outside air temperature. [Bateson, 1999]

(III) Carrier Signal

A carrier signal is an electromagnetic wave of constant amplitude that acts as an electromagnetic vehicle for transporting data. Data being transmitted by a carrier may be either analog or digital, depending on the methods used to modulate the carrier [Carstens, 1993].

CHAPTERI INTRODUCTION

1.3

MEASUREMENT SYSTEMS

1.3.1 Overview

The simplest measuring system would be a sensing device that also displays the measured value, such as a mercury-in-glass thermometer or pressure gage. If the measured value needs to be recorded at certain times, a human observer with a clipboard, pencil, and wristwatch can be employed for this purpose. In this example, the operator, clipboard, pencil, and wristwatch, become a part of the system.

When a measured value is to be displayed some distance away from the point of

measurement, a link between the two points becomes necessary. This link can be

mechanical (e. g., an automobile speedomotor cable), pneumatic (a pipe filled with

air whose pressure is varied by the sensing device, with a pressure indicator used

for display), or electrical (an electrical cable). Electrical wiring is used in

electronic measuring systems, in which the sensing device (sensor) has an,

electrical output and the display device accepts an electrical signal [Nachtigal,

CHAPTER 1 INTRODUCTION

1.3.2 Basic Electronic Measuring System

A basic electronic measurement system is shown by Figure 1. 3. It consists of

i. The transducer, which converts the measurand into a usable electrical

output.

ii. The signal conditioner, which converts the transducer output into the

type of electrical signal that the display device will accept.

iii. The display device (or readout device), which displays the required information about the measurand.

iv. The power supply, which feeds the required voltages to the signal

conditioner.

! r

CHAPTER I

1.3.3 Signal Conditioning

INTRODUCTION

A study regarding to measuring system, Bateson (1999) stated that a signal conditioner is required to convert the sensor output into an electrical (or pneumatic) signal suitable for use by a controller or display device. The sensor and its signal conditioner comprise the two parts of a measuring transmitter which

is as shown by Figure 1. 4 [Bateson, 1999].

External energy ý---,. ---_ --- Sensor uWpui disptacemeni _Signal 10-1 _-4 Nieaaurcd Serra« vc+l4ge, conditioner variable, C nesisawsre, etc. Messuri transmitter o1ltput r cm

Figure 1. 4: Measuring Transmitter [Bateson, 19991

Signal conditioning is one of the most important components of any data

acquisition system. It is the interface

between real-world analog signals and the

rest of the system. If the signal conditioner

is not specified properly, the data

acquisition system most likely will output meaningless information. Data

acquisition involves two very important concepts that are data sampling and data conversion.

CHAPTER 1 INTRODUCTION

(1) Data Sampling

The rate at which need to sample an analogue signal, to get a good digital representation, depends on how fast the signal is changing. It is all about how accuracy the data sampling process to be. Data sampling is a process in which a switch connects momentarily to an analog signal in a sequence of pulses separated by evenly spaced increments of time called the sampling interval [Bolton, 1992].

For frequency components the Nyquist criterion demands that the signal be sampled at least twice in each cycle, otherwise the amplitude of this frequency component will distort the signal at lower frequencies.

The Nyquist criterion may be stated as follows: All the information in the original signal can be recovered if it is sampled at least twice during each. cycle of the highest frequency component [Kilian, 19961.

If f,, is the highest frequency that occurs in the original signal, then the minimum

sampling rate is given by the following equations.

Minimum sampling rate = fg (min) = 2f

CHAPTER 1 INTRODUCTION

. frtqucwý

a) Frequency

spectrum

of original

signal

h

ý

fs

b) Frcquency

_spectrum

of sampled

signal with

f, > 2fh

ý

0 Frequency

Frequency

A

A

? is

c) Frequency

spe4trurm

of sampled signal with f, c

2fh

Figure 1. 5 : Frequency spectrum an analog signal [Bateson, 1999].

Figure 1.5a shows how typical frequency spectrum of an analog signal. A frequency spectrum is simply a plot of the maximum voltage of each possible component of a signal versus the frequency of the component. The main point in Figure _{1.5a is that there are no components of the original signal with a}