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DEVELOPMENT OF VERSATILE CONTROL SYSTEM FOR CONTROL OF
CRYSTAL GROWTH FURNACE AND ANCILLARY SYSTEMS USING
NATIONAL INSTRUMENTS® DEVICES AND LabVIEW
® PROGRAM
By
CHANDRASEKAR MINNAL
A thesis submitted in the partial fulfillment of
the requirements for the degree of
MASTER OF SCIENCE IN MECHANICAL ENGINEERING
WASHINGTON STATE UNIVERSITY
School of Mechanical and Materials Engineering
DECEMBER 2010
ii
To the Faculty of Washington State University
The members of the Committee appointed to examine the thesis of
CHANDRASEKAR MINNAL find it satisfactory and recommend that it be accepted
Kelvin G. Lynn, Ph.D., Chair
Uma Jayaram, Ph.D.
Jow – Lian Ding, Ph.D.
iii
ACKNOWLEDGEMENT
I sincerely thank Dr. Kelvin Lynn for believing in me and providing me this opportunity
to work in a challenging yet exciting project that has allowed me to study in a world class
institution, enhance my knowledge, skills and gained an experience for my professional and
personal development. It was his constant motivation and encouragement that inspired me to
successfully complete my master‟s education. I would like to make a special thanks to Dr. Kelly
Jones and Dr. Romit Dhar who mentored, guided and taught me valuable lessons for my career
and for life. I thank my CMR colleagues Raji Soundararajan, Santosh Swain, Amlan Datta for
their help and support. I would like to thank the CMR staff Roger Saunders, Becky Griswold,
Yulia Bunakov for their help. A special thanks to Abe Jones, CMR‟s IT coordinator for helping
me in setting up the control system. I thank my friends Raghu, Harish, Senthil, Muthu, Vijay,
Arun, Dilip, Thanigai and Archana who provided emotional support and made me feel at home
during my stay in Pullman.
I would like to thank Avinash Harjani and Clarke Atkinson from National Instruments for
their guidance and support in selecting the control system components and developing the
control program. This work was funded by US Department of Energy‟s National Nuclear
Security Administration under contract no DE-FG52-08NA28769.
iv
DEVELOPMENT OF VERSATILE CONTROL SYSTEM FOR CONTROL OF
CRYSTAL GROWTH FURNACE AND ANCILLARY SYSTEMS USING
NATIONAL INSTRUMENTS® DEVICES AND LabVIEW
® PROGRAM
Abstract
by Chandrasekar Minnal, M.S.
Washington State University
December 2010
Chair: Kelvin G. Lynn
A versatile control system is developed to control a multi zone furnace and its ancillary
systems which are used in the study of a semiconductor crystal growth process. Semiconductor
crystals are grown in a furnace to study its growth process, identify the factors influencing its
growth, understand their effects and develop growth method(s) (by controlling the factors
directly or indirectly) to produce a high quality (uniform, homogeneous, defect free) crystal. A
control system aids in implementing the crystal growth profile on the furnace by providing an
interface between the researcher and the furnace. Since the objective is to understand the growth
process and factors affecting it, the control system should implement the growth profile as
accurately as possible.
The study uses a commercial control system for the crystal growth process but due to
limitations in its performance and accuracy the objective of the study couldn‟t be achieved. A
new versatile, stand alone, real time control system is developed using National Instruments
devices and its Labview graphical programming language to overcome the limitations of the
commercial system and achieve the objective. This thesis discusses about (1) the development of
v
National Instruments control system with functions and attributes similar to the commercial
system and the crystal growth process made with it, (2) compares the crystal growth processes
performed with the National Instruments system and commercial system in order to evaluate the
performance of the National Instruments system and finally (3) development of a versatile
system by enhancing its functions i.e. monitoring and controlling of additional
devices/instruments in addition to the furnace, to observe and/or to control directly or indirectly
the factors affecting the growth process.
vi
TABLE OF CONTENTS
Page
ACKNOWLEDGEMENTS .................................................................................................iii
ABSTRACT ......................................................................................................................... iv
LIST OF TABLES ............................................................................................................... vi
LISTOF FIGURES ............................................................................................................. vii
CHAPTER
1. INTRODUCTION ................................................................................................. 1
2. CRYSTAL GROWTH SETUP ............................................................................... 7
3. FURNACE CONTROL SYSTEM ........................................................................ 12
4. MELLEN CONTROL SYSTEM ........................................................................... 16
5. NI CONTROL SYSTEM ....................................................................................... 22
6. COMPARISON: MELLEN SYSTEM VS NI SYSTEM ...................................... 33
7. DEVELOPMENT OF VERSATILE SYSTEM .................................................... 36
8. CONCLUSION ...................................................................................................... 40
9. FUTURE WORK ................................................................................................... 41
REFERENCES ................................................................................................................... 43
APPENDIX
A. MANUAL FOR NI LABVIEW CONTROL PROGRAM .................................. 45
vii
LIST OF TABLES
Table
1.1 CZT Growth Methods ..................................................................................................... 4
6.1 Mellen vs. NI system .................................................................................................... 33
6.2 Mellen vs. NI system – Performance Comparison ....................................................... 35
viii
LIST OF FIGURES
Figure
1.1 Fully grown CZT ingot ................................................................................................... 5
2.1 Crystal growth setup ....................................................................................................... 7
2.2 User defined growth profile with five segments ............................................................. 8
2.3 Mellen EDG Furnaces..................................................................................................... 9
3.1 Furnace control system flow diagram ........................................................................... 12
3.2 Feedback control logic .................................................................................................. 14
3.3 PID function block diagram .......................................................................................... 15
4.1 Actual process value plot .............................................................................................. 17
4.2 % Power Plot................................................................................................................. 17
4.3 CG82 PV Plot ............................................................................................................... 19
4.4 CG82 %Power Plot ....................................................................................................... 19
4.5 CG82 Deviation Plot ..................................................................................................... 20
4.6 CG82 Fully Grown Ingot .............................................................................................. 20
5.1 NI Control System with Host Machine on a Rack ........................................................ 22
5.2 NI PXI controller with data acquisition and control devices on a chassis .................... 23
5.3 NI Program Front Panel ................................................................................................ 25
5.2 Flow diagram of NI control system control program ................................................... 28
5.3 CG92 PV Plot ............................................................................................................... 31
5.4 CG92 % Power Plot ...................................................................................................... 31
5.5 CG92 Deviation Plot ..................................................................................................... 32
5.6 CG92 Grown Ingot ....................................................................................................... 32
ix
6.1 CG82 Deviation Plot during growth ............................................................................. 34
6.2 CG92 Deviation Plot ..................................................................................................... 34
6.3 CG82 % Power Plot during Soak.................................................................................. 34
6.4 CG92 % Power Plot during Soak.................................................................................. 34
7.1 CG93 Ingot with growth profile ................................................................................... 37
7.2 CG93 with estimated profile ......................................................................................... 37
7.3 Forced Nucleation Auxiliary Temperature ................................................................... 38
7.4 Slice of force nucleated crystal ..................................................................................... 38
7.5 ACRT Motor attached to Furnace................................................................................. 39
9.1 CG93 PV Plot ............................................................................................................... 41
9.2 CG93 % Power Plot ...................................................................................................... 41
9.3 CG93 Deviation Plot ..................................................................................................... 42
9.4 CG93 Crystal Slice ....................................................................................................... 42
x
DEDICATION
This thesis is dedicated to my mother and father
1
CHAPTER ONE
Introduction
1.1 Introduction to Control System
Control of a process involves measuring the controlled parameter and generating a
control signal to regulate it to the desired value. A Control system is a device developed to
control the processes automatically (with minimal or no human intervention) thereby reducing
human hardship and error. The history of control systems can be dated back to ancient times;
however they began to gain prominence during 18th
century industrial revolution. Advancement
in engineering and mathematics evolved numerous control theories and methods to implement
them. Classical control theory is the earliest theory to be formulated and it is still widely used.
Proportional Integral Derivative function (PID) based feedback control logic is the most popular
classical control theory based principle for automatic control. Control systems employing this
principle are called closed loop feedback control systems. Advent of computers and related
electronic technologies in the mid 20th
century created a whole new dimension for automatic
process control systems.
Computer based closed loop control systems were developed enabling complex processes
to be controlled straight forward. This computer operated and controlled control systems consist
of data acquisition & control devices to perform the feedback logic and a control program which
perform the proportional integral derivative logic. Characteristics of the control system are
determined by the accuracy and performance of the devices. This thesis discusses about the
development of a closed loop feedback control system to control a furnace used in the study of a
crystal growth process.
2
1.2 Motivation and Introduction to the Crystal Growth Study
The Center for Materials Research (CMR) at Washington State University is involved in
the study of crystal growth of Cadmium Zinc Telluride (CZT) radiation detection material by
modified vertical Bridgman method. The study involves growing of CZT crystals to understand
its growth process to produce large bulks (75mm – 100mm in diameter and 50mm – 75 mm in
length) of high quality (uniform, homogeneous, defect free) crystals.
Cadmium Zinc Telluride (CZT)
CZT crystals are semiconducting materials having a wide band gap energy, high
resistivity and excellent charge transport properties making them a highly promising device for
room temperature radiation detection. They have the potential to be used in wide range of
applications such as medical imaging, security inspection, solar cells etc [1-2]. For a CZT crystal
to be a good detector it should have qualities such as homogeneous single crystal with high
resistivity, less inclusions and low defects. The growth process and the properties of Cadmium,
Zinc and Tellurium during the growth affect the quality of CZT crystal.
Crystal Growth of CZT
CZT crystal growth is a challenging task. CZT growth is a user defined and controlled
process. The crystal is grown by melting the solid chunks of Cadmium (Cd), Zinc (Zn) and
Tellurium (Te) and cooling the molten CZT by imposing a temperature gradient inside a furnace.
High Pressure Bridgman (HPB) [3] method and Travelling Heater Method (THM) [4] are the
most extensively used methods to grow detector grade CZT crystals.
Crystals grown under high pressure in the HPB method; temperature gradient for the
growth of crystal from the melt is induced by moving the ampoule across the furnace length
(50mm – 75mm). Crystals with low defects and inclusions are grown quickly (0.5-4mm/hr) by
3
the HPB but the yield of large single crystals is less. Low crystal yield and high cost of the
equipment and its maintenance make this method less desirable for CZT growth.
In the THM, crystals are grown at atmospheric room pressure conditions at temperatures
700°C to 900°C. Temperature gradient to grow the crystal out of the molten charge is obtained
by moving either the furnace or the ampoule. THM is able to produce bulks of large single
crystals but takes longer growth period (<1mm/day). The crystals grown by THM have high
defects and inclusions rendering the crystal a poor quality detector. Post processing has to be
done to improve the quality which increases the cost and time.
Growth methods alternate to the HPB and THM are explored, growth method that can
overcome their limitations but retain the advantages is desired.
Vertical Gradient Freeze (VGF) Method
In the VGF method the crystal is grown by melting of solidifying solid chunks of
crystal‟s raw materials (Cd, Zn, Te) at atmospheric room pressure [5-6]. The raw materials are
placed and sealed inside a vacuum ampoule/crucible and loaded vertically into the furnace.
Furnace is heated uniformly to melt the solid charge. Crystal is grown out of the melt by cooling
the molten charge from bottom to top. Cooling is done by imposing a temperature gradient
(temperature just below the melting point of CZT) across a specific length at the bottom of the
ampoule. This creates a solid-liquid interface inside the ampoule. Interface is moved across to
top of the ampoule by moving the temperature gradient at a specific rate called growth rate. Once
all the molten charge has solidified the furnace is cooled back to room temperature at a specific
rate called cool down rate. Once growth is completed, the crystal is removed from the furnace.
Samples are cut from crystal to test its characteristics. Infrared imaging/mapping is done on the
4
samples to check for inclusions and defects. The sample is then tested to determine its resistivity,
charge mobility and its response and resolution to radiation detection.
The difference between VGF and LPB is the method of imparting the temperature
gradient, in VGF temperature gradient is imposed electronically through a computer control
system without moving the ampoule as in the LPB. Hence VGF can also be called as computer-
controlled Modified Vertical Bridgman (MVB) method [7].
High Pressure Bridgman
Method Travelling Heater Method
Vertical Gradient Freeze
Method
Crystal growth under high
pressure
Crystal growth at atmospheric
pressure
Crystal growth at atmospheric
pressure
Temperature gradient by
moving the ampoule
Temperature gradient by
moving the furnace and/or
ampoule
Temperature gradient by
electronically controlling the
furnace heating elements
Advantages: Quick growth
time, low defects and
inclusions
Advantages: Large
homogeneous single crystals
(high yield)
Advantages: Short growth
time, lower equipment and its
maintenance cost, no moving
parts
Limitations: Smaller crystals
(low yield), high equipment
and its maintenance cost,
Limitations: Longer growth
time, high defects and
impurities increases the cost
Limitations: Low yield,
impurities and inclusions
Table 1.1 CZT Growth Methods
1.3 Objective of the Study
Develop growth method(s) capable of growing large bulks of detector quality CZT
crystal by the VGF method. Growth methods are developed on trial and error basis by changing
the controllable growth parameters such as temperature gradient, growth rate, cool down rate
method which are known to directly influence the crystal‟s qualities and properties. CZT crystals
are grown by the VGF method to understand the effects of the controllable growth parameters on
the growth process, identify factors influencing its growth, understand their effects and develop
growth method(s) (by controlling the factors directly or indirectly). To make a detailed
5
understanding of the growth process, the grown CZT crystal (fig 1.1) is analyzed and tested to
observe their characteristics, properties and working as a good detector. The VGF method uses a
multi zone (43 independent zones) Electro Dynamic Gradient (EDG) freeze furnace which is
operated and controlled via a control system. Growth methods/profile is developed by the crystal
grower (user) and implemented on the furnace through the control system. A control system that
can implement the user developed growth profile as accurately as possible on the furnace is
desired in order to make a successful study
Fig 1.1 Fully Grown CZT Crystal
1.4 Objective of the Thesis
Furnace control system forms the back bone of the growth process as it implements the
growth process by interacting between the user and furnace. The system aims to help in
understanding the control parameters on the full growth process. The accuracy with which the
growth profile is implemented depends on the accuracy of the control system; since studies are
being made to identify the parameters influencing the growth process it is necessary for the
control system to strictly implement the user defined growth process. Also, a multitude of known
and/or unknown parameters influence the process, hence it is necessary for the control system to
HEEL
MID
SHOULDER
TIP
6
have capabilities to observe and/or control these parameters either directly or indirectly through
additional devices/instruments. This thesis is focused on developing such a control system
capable of controlling the crystal growth process and its ancillary systems in order to grow large
bulks of detector quality CZT crystals.
7
CHAPTER 2
Crystal Growth Setup
The crystal growth setup comprises of (1) user defined crystal growth profile, (2) multi
zone crystal growth furnace system and (3) furnace control system as shown in fig 2.1.
Fig 2.1 Crystal Growth Setup
2.1 Crystal Growth Profile
Growth profile is a series of set points of temperature vs. time developed by the user. It
defines the different temperatures at which the furnace needed to be maintained over time in
order to melt and grow CZT from the solid charge. The profile is designed based on controllable
parameters such as temperature gradient, growth rate and cool down rate. The growth profile can
be divided into five segments (1) charge melting, (2) mixing, (3) quick freeze, (4) growth and (5)
cool down as in fig 2.1.1.
8
Fig 2.2 User defined growth profile with five segments
(1) Ramp segment – Charge melting, (2) Mixing/Soak segment, (3) Quick freeze, (4)
Growth and (5) Cool down
First segment is the charge melting segment where the furnace is ramped up from room
temperature to a temperature above the melting point of the solid charge. Next is the mixing
segment; furnace is maintained at a constant temperature for a certain time to allow a thorough
mixing of molten charge. In third segment, furnace is cooled rapidly to quickly freeze the molten
charge to maintain the homogeneity of the CZT. Fourth is growth segment, the furnace is heated
back to temperature slightly above the melting point and the crystal is grown by applying a
gradient and moving it across each growth zones of the furnace, at a constant rate called growth
9
rate, to grow the CZT crystal from the melt. Finally, once the entire crystal is solidified the
furnace is cooled to room temperature at a specified rate.
2.2 Crystal Growth Furnace System
The CZT crystal is grown using Mellen Company‟s multi zone Electro Dynamic Gradient
freeze furnace. The system comprises of furnace, sensors and actuators.
Furnace
Fig 2.3 Mellen EDG Furnaces
The crystal growth furnace (fig 2.2.1) has 43 control zones, arranged vertically.
The control zones are divided into growth and non growth zones. Each zone has a thermocouple
10
and power controller to measure and control respective zone‟s temperature. In addition it has
eight auxiliary thermocouples which just help in monitor the growth process.
Electro Dynamic Gradient (EDG)
EDG [8] refers to the method applying the temperature gradient across the furnace
growth zones for the growth of crystal out of the melt. This is the characteristic feature of the
VGF method where the temperature gradient is imposed by controlling the temperature of the
growth zones rather than moving the furnace or the ampoule. Temperature of growth zones are
controlled electronically through the control system.
Thermocouple
Thermocouples are used to measure temperatures. They work on the principle of
thermoelectric effect, when a junction of two dissimilar metals experiences heat an electromotive
force (emf) is induced across the junction and any change in the heat will change the induced
emf. Measuring this emf will give the temperature.
The furnace uses Type S thermocouple which is made of Platinum-10%Rhodium and
Platinum. It can measure temperature within -50°C to 1768.3°C range.
Signal Conditioning Device (SC)
Emf generated by thermocouples is very low in the order of magnitude of few milli volts
(mV). At such low values noise and disturbance from other electronic devices or due to improper
grounding can be added to the signal there by corrupting it. Signal conditioning device are used
to amplify and filter these signals to eliminate the noise and ensure and improve the accuracy of
the measurement.
11
Furnace Power Controller
Furnace power controller controls the power to the heating coils which heats the furnace.
The power controller consists of a triac and a transformer. The triac [9-10] is a bidirectional
current regulator; it receives a control signal from control system based on which it regulates the
current to the transformer thereby controlling the power to the heating coils.
Heating Elements
The furnace uses an electrically high conducting low resistance material as heating
element. It works on the principle of electric heating which converts electrical energy to heat.
2.3 Furnace Control System:
Control system is a device which controls a process automatically as defined by the user.
Control systems in crystal growth are used to control the growth process by controlling the
crystal growth furnace and its ancillary systems. The NI control system is primarily developed to
control the growth of CZT crystals by the EDG method though it can also be used to grow other
semiconductor crystals. Furnace control system is discussed more in detail in chapter 3.
12
CHAPTER 3
Furnace Control System
Personal Computer (PC) based feedback control system is used to implement, control,
monitor and record the crystal growth process on the furnace.
3.1 Components of Furnace Control System
The components of furnace control system are (1) Controller, (2) Data acquisition device, (3)
control software program and (4) control device fig 3.1 shows control system and its
components.
Fig 3.1 Furnace control system flow diagram
Controller
It is a hardware platform for which houses the devices and control program. . It runs the
devices and control program and enables the user to access them through its operating software.
Control System
3. Control
Program
User
interface
2. Data
acquisition
device
4. Control
device
1. Controller
from
sensors/signal
conditioning
devices
to actuators/
power
controllers
13
An example of controller is Microsoft Windows OS based Personal computer which uses a
Central Processing Unit (CPU). The CPU process the user commands on to several software
through the microprocessor, chips, devices and operating software.
Data acquisition (DAQ)
It is a device interacts with the furnace thermocouples/signal conditioning devices to
measure the actual furnace value. DAQ devices are nothing but Analog to Digital Converters
(ADC) which convert the amplified thermocouple analog voltage signal to a digital value.
Samples and buffer size determines how many are sample points are obtained and converted to
read into the ADC. The digital values are then used in the control program to generate control
action.
Control program
It has two main functionalities, one to generate control action to control the furnace and
other to display and save the control data for user‟s reference. The control program is written in a
computer language. Program uses Proportional Integral Derivative (PID) function to generate
control actions. PID function is a mathematical function which generates control action based on
the difference between the actual value and the desired value (error). The program interacts with
the devices to acquire the digital value of furnace temperature from the DAQ device, uses the
PID algorithm to generate the appropriate digital value of the control signal and sends it to the
control device. Control program is the main interface through which the user monitors and
controls the process. The control program has a user interface which displays the actual furnace
temperature, desired temperature, error, control signal value and the PID constants to the user.
The user can alter the growth profile, control signal value and PID constants. These data‟s are
also saved for future references.
14
Control device
It is a Digital to Analog Converter (DAC) which converts the digital value of the control
action to analog value. The analog value is send to the actuators (furnace power controller)
which can directly controls the power to the furnace heating coils thereby controlling the furnace
temperature.
3.2 Operation of Furnace Control System
Feedback Control Logic
Control system employs the feedback control logic [11] (fig 3.2) to automatically control
the furnace as defined by the user. The state of the system is feedback to the controller to
generate the control signal. User inputs the temperature profile or set points (SP) into the
program. DAQ device acquires the amplified digital value of actual furnace temperature or
process variables (PV). Program converts the amplified value to actual value, compares with SP
and generates digital control action using the PID function. Digital control value is sent to the
control device by the program which converts it back to analog signal. Analog control signal are
sent to actuator/power controller thereby controlling the temperature of furnace to its specified
value.
Control action
Control program
Fig 3.2 Feedback control logic
Set points PID
Log`
Actuator System
SC/Sensor
15
Proportional Integral Derivative (PID) Function
PID is a mathematical function which generated the value for the control signal. In the
control program the actual value is compared against the required set point value to obtain an
error (e) value (difference between the two). The PID function uses this error value to generate
the control signal value. The standard PID function [12] in shown in fig 3.3
Error (e)
Fig 3.3 Standard PID function
The Integral function is
I = 1/Ti*(∑n
i=0 e) where, Ti = Integral time in minutes
Derivative function is
D = Td*(en-en-1) where Td = Derivative time in minutes
Integral
Function
Derivative
Function
∑ Proportional
Gain, Kc
16
CHAPTER 4
Mellen Control System
The study initially used a commercial Mellen control system to control the Mellen EDG
furnace. Several CZT crystal growths were performed using Mellen system. This chapter
discusses about the specifics of Mellen control system and crystal growth performed using it
4.1 Details of Mellen Control System
4.1.1 Controller
Mellen uses Microsoft Windows OD based Personal Computer (PC) as a controller. The
devices are plugged into the PC ports and the control software program is installed in it.
Properties
Processor: Intel Pentium IV 2.4GHz
Communication platform: PCI
RAM: 512MB of RAM
Hard Disk: 40GB
OS: Windows XP
4.1.2 Signal Conditioning & Thermocouple
Initially the Mellen system didn‟t use any signal conditioning module. Crystal growths
performed showed high fluctuations (noise) in the process variables and in the power (fig 4.1 &
fig 4.2 respectively). Mathematical analysis showed that the fluctuation were around 1-2°C for
the process values from the setpoint and the power fluctuated between 2-3%. 5B-37 S Type
thermocouple non linear amplification module was then used to amplify and filter
17
thermocouple‟s millivolt value to increase the accuracy. The 5B modules are mounted on 16
channels ISO Rack, each having its own cold junction compensation sensor. The amplified
signals are then sent to the DAQ device through the multiplexer.
Fig 4.1 Actual temperature plot Fig 4.2 % Power Plot
4.1.3 Data Acquisition device
Mellen system uses „Measurement Computing‟ CIO-DAS1402 16 channel data
acquisition device to convert the analog temperature value to a digital value. The ADC scans and
reads each channel in a sequence.
Properties of CIO-DAS1402
16 Analog Input Channels
16 bit ADC
5 – 25 samples
Burst mode timing
Since the ADC can read only 16 channel at once; in order to all the 51 thermocouples a
multiplexer is uses which sends signals in a sequence to the ADC.
18
4.1.4 Control Program
The Mellen control system uses „ADAPT‟ control program to interact between the user
and furnace. The details of the control program is not known
Control Logic:
The mathematical function of PID control logic used by the ADAPT system is
Control output p = Kc e + 1/Ti*(∑n
i=0 e) + Td*(en-en-1)
Error, e = Process Variable values – Setpoints values
Where Gain, Kc = 100/PB, PB = Proportional band, Integral Time, Ti, Derivative time, Td
4.1.5 Control Device
The Mellen system has developed its own control device to convert the digital value to
analog signal. The details of the device are unknown.
4.2 Crystal Growth (CG) with Mellen System
Several crystal growths were performed with the Mellen system and CZT crystals with
good detector grade properties were successfully grown. One of the crystal growths by the
Mellen system is studied to observe its performance and characteristics.
4.2.1 Crystal Growth #82
Design of Experiment;
Growth Rate: 0.55mm/hr and time 441.91 hrs
Temperature Gradient 50°/inch
Cool down time 23.73hrs
19
The design of experiment describes about the controllable growth parameters used to
develop the crystal growth profile. Fig 4.1 shows the CG82 PV values and fig 4.2 shows CG82
% power values in all the zones.
Fig 4.3 CG82: Actual temperature plot during growth
Fig 4.4 CG82 % Power Plot
20
Fig 4.3 shows the deviation of PV‟s from SP‟s and fig 4.4 shows the fully grown CG82
ingot
Fig 4.5 CG82 Deviation (difference between actual temperature and setpoint value) plot
Fig 4.6 CG82 Fully Grown Crystal
21
CZT crystals with detector quality matching to present industry level standards have been
successfully grown using the Mellen system, however the yield is poor making VGF method of
CZT growth similar to HPB and THM. Objective of the study is to develop growth methods
capable of growing bulks of detector grade CZT crystals using the VGF method. To make further
progress in the study new growth methods have to be developed, which might need to use
additional devices and/or instruments. Low channel count, low accuracy of the Mellen‟s DAQ
device along with the use of multiplexer reduces the accuracy of measurement, increases the
system response. Also, lack of technical and working details of control device and lack of
programming access to the control program further adds to the disadvantage of Mellen system.
These reasons propel the need to develop a new control system with high accuracy, speed and
high channel count which can control the furnace to implement the crystal growth process and
also control additional devices to reach the objective of the study. National Instruments (NI)
devices and its LabVIEW programming language seems to satisfy our requirements and facilitate
the design of the new control system.
22
CHAPTER 5
NI Control System
A real time stand alone control system using National Instruments data acquisition and
control device and LabVIEW programming language is developed to control the furnace. Unlike
the Mellen control system the NI system uses a specifically designated controller platform to
operate the devices and control program. A stand alone controller offers fast responding system
capable of implementing real time control. Real time control means generating and
implementing control action in timely and reliable manner.
Fig 5.1 NI Control System with Host Machine on a Rack
23
5.1 Details of NI Control System
Controller
A stand alone controller is used specifically for the control system unlike the Mellen
system which uses a PC. The controller has its own processor, hard disk and memory. User can
interact with this controller using a PC; thereby this controller act as a remote satellite system
and PC act as HOST system.
Fig 5.2 NI PXI controller with data acquisition and control devices on a chassis
Properties:
Processor: 2.4GHz dual core processor
Communication Platform: PXI
Hard disc capacity: 60GB
RAM : 2GB of RAM
OS: LabVIEW Real Time Version 8.4
24
Signal Conditioning
5B-37 S Type thermocouple non linear amplification module is used to amplify and filter
the thermocouple millivolt analog signal. The modules are mounted on a backplane which is
connected to data acquisition device.
Data Acquisition device
NI control system uses PXI-6289 32 channel data acquisition device. It has one ADC
which scans and converts the analog temperature value to digital value in a user specified
sequence.
Properties
32 Channel Analog input
18 bit ADC
625,000 samples per second
Software and/or hardware timed
The 18 bits of ADC resolution gives an accuracy of only 40µV over 0-5V range. From
the NIST ITR-90 millivolt to temperature conversion table difference in millivolt value between
two successive temperatures values is approximately 5-8µV (varies as temperature increases). So
this gives the accuracy of the DAQ device as ±5-8°C.
Control Program
The control program is developed using LabVIEW graphical programming language.
LabVIEW structures, arrays, functions and programming loops are used to develop the control
program. The control program is developed similar to the Mellen „ADAPT‟ program.
25
LabVIEW program has a front panel which the user can use to interact with the furnace, a block
diagram where the program code is written.
Control Program Setup
Fig 5.3 NI Program Front Panel
User uses control program front panel to interact with the furnace. The front panel has
controls and indicators with which the use can command and monitor the furnace. The program
front panel has three tabs, (1) Program SETUP tan, (2) Program MONITOR tab and (3) Full PID
Table tab.
Program SETUP tab – In this tab the user sets the growth profile (setpoints SP) and PID
file path for the program to read from. The user also selects the control mode (auto/manual),
thermocouple (TC) type and data record option. This tab has two tables (1) Setpoints Table –
user can read and change the growth profile through this table. (2) Program Parameter table –
26
user can read and change each zones control mode, % power output value, deviation limit and
TC type through this table. This tab also has an alarm LED display and a program stop button.
Program MONITOR tab – this tab has a table in which the user can see the furnace
conditions. The table displays conditions such as actual furnace temperature (process variables
PV), SP, deviation, % power, P, I, D values, high and low deviation limit, TC type. It also
displays the RUN start, elapsed, end time, segments start, remaining and end time
Full PID table tab – this tab has a table in which the loaded PID file can be read and
changed. There is a P, I, D column for each zone and each segment.
Control Program Working
Program Setup
A text file of the growth profile segments (Setpoints SP) and PID file has to be loaded
into the controller‟s hard disk. The control program will read these files first and load them into
the program. PID file consists of P, I, D values for every control zone and for every growth
profile segments. After saving these files to disk, the user opens the labview control program.
Under program setup tab in the front panel the user sets the file SP and PID file, selects the
control mode, TC type, data record interval time. Once every thins is set the user runs the
program
Program Control and Monitor
The program executes three loops. The first loop is the read and initialize loop. In this
loop the program reads the SP, PID file from memory and loads it to the program (Setpoints
table in front panel). The TC type, control mode type, deviation limit will also be read and
displayed in the program parameter table. This loop executes only once and the program stops
27
The user re-starts the program, the second loop begins to execute. The second loop is
the control loop, once the files are read the program acquires first set of temperature data from
the thermocouples. This is a continuous execution loop which will keep on going until the user
press the „STOP‟ button in the front panel. The program uses labview setpoint generation
function which generates a setpoint value of the loop corresponding to the growth profile. The
program acquires data from DAQ device at regular intervals. The acquired data is an amplified
mV value of the temperature; this value is converted to °C. The program converts the millivolt
value to temperature value to °C using NIST ITR-90 Type S thermocouples mV to °C
conversion equations.
Once the furnace temperature data in °C is obtained it is sent to the PID control function
along with the generated setpoints and P, I, D values from the PID file. The PID function uses
PID logic to generate a control signal value in 0-100% range called % power. This is the % of
power sent to the furnace heating coils to maintain it at the desired temperature
Control output p = Kc e + 1/Ti*(∑n
i=0 e) + Td*(en-en-1)
Error, e = Process Variable values – Setpoints values
Proportional Gain, (Kc) Integral Time, (Ti), Derivative time (Td)
The % power control signal value is sent to the control device which converts the digital
data to an analog signal. Furnace power controller can accept control signals only in 0-5 VDC
range. Since the control signal is in 0-100% range the program converts it 0-5VDC range.
The final loop in the program is the record and display loop which saves and records
parameters such as PV, SP, deviation, % power, P, I, D values, high deviation, low deviation
limit and TC type for the user. The execution is described in the flow diagram fig 5.4
28
Fig 5.4 Flow diagram of NI control system control program
Accuracy Tests
We know the 18bit ADC can give an accuracy of ±5-8°C. The accuracy can be further
increase using statistics. By employing running double averaging method i.e. the ADC obtains
and converts 1000 sample data from each channel in one loop. Taking average of these 1000
values we get 1 value; collecting 500 such values (from 1000 X 500 points) and taking average
again in these 500 points we get a double averaged single value. This value is then sent to mV to
29
°C conversion function. Double averaging gives us an accuracy of 1µ°C which is approximately
±0.2 to 0.13°C.
Control Program Functions
Alarm
Control program has an alarm system to notify the user if the furnace temperature shoots
above or below a certain limit from its setpoint value. The deviation limits are set in the program
and they can be read and changed from the program parameter table. The alarm uses digital TTL
logic to send signals to a pager dialer. Phone and/or pager numbers are programmed into the
dialer and if the alarm goes ON the dialer calls the user. Digital signals are nothing but ON and
OFF signals, when the furnace is working fine the alarm is in OFF state which sends a constant
+5 VDC signal to the dialer, when the furnace temperature exceeds the limit the alarm goes ON
it shuts the +5 VDC signal to 0 VDC which triggers the pager dialer to call the user.
Pause Program
The program has a PAUSE switch which when pressed on will pause the program i.e.
keep furnace at that setpoint value until it is switched off. The program will send signals to
maintain the furnace at that setpoint value
Forward/Reverse Segment
The user can jump to any segments in the growth profile using this function, he skip
segments.
Control Device
The system uses PXI-6704 32 channel device to convert the digital control signal value
into an analog signal.
30
Properties
32 Channel Analog Output (16 Voltage outputs and 16 Current outputs)
16 bit DAC
8 Digital 5VDC TTL I/O
Scan interval between each channel is 50µS and the same channel gets scanned in
a interval of 1.8mS
Furnace power controller can accept control signals only in 0-5VDC range. Since there
are 43 control zones it is necessary to use the 16 current outputs. The current output is
converted to voltage output by using a 250Ω resistor across the output terminals.
5.2 Crystal Growth (CG) with NI Control System
Total of 4 crystal growth have been successfully made using the NI control system.
Grown crystal have been tested and found to have properties at par with those grown with the
Mellen system. One of the crystal growths is studied to understand the performance and
characteristics of the NI system
5.2.1 NI Control System – Crystal Growth #92
Design of experiment
Growth rate 0.55mm/hr and growth time 483.89hrs
Gradient 50C/inch
Cool down time 70.71hrs
Fig 5.5and fig 5.6 shows CG92 PV and % power profile in all the growth zones during
the growth segment.
31
Fig 5.5 CG92 PV Plot
Fig 5.6 CG92 % Power Plot
Fig 5.7 shows the deviation of PV from SP in the CG92 growth and fig 5.8 shows the
fully grown CG92 ingot
32
Fig 5.7 CG92 Deviation Plot
Fig 5.8 CG92 Fully Grown Ingot
33
CHAPTER 6
Comparison: Mellen System vs. NI System
Component Mellen System NI System
Controller
Intel Pentium IV 2.4GHz for
Windows
Intel Pentium IV 2.4GHz
Operation Software Windows XP LabVIEW Real Time 8.6
Data Acquisition Device
1 - 16bit, 16 channel
(multiplexed)
2 - 18bit, 32channel
Control Device N/A 2 - 16bit, 32channel
Control Program N/A LabVIEW 8.6
Samples and Buffers 5-25 each channel 1000 & 10000 each channel
Table 6.1 Mellen System vs. NI System
A comparison of crystal growths made with Mellen and NI system is made to evaluate
the working and performance of the NI system. Systems characteristics such as RMS noise of
thermocouple signal, deviation between of PV from SP, RMS noise of control signal (% power
to furnace controller) are studied and compared from the crystal growths performed using them.
Commercial system‟s characteristics are studied based on CG 82 and NI system‟s are studied
based on CG 92. Fig 6.1 & 6.2 shows the deviation (PV-SP) in the furnace growth zones during
the growth period. Fig 6.3 & 6.4 shows the % power values in control zones during soak period.
Comparison in Growth Zone deviation between Mellen‟s CG82 and NI CG92
34
Fig 6.1 CG82 Deviation Plot Fig 6.2 CG92 Deviation Plot
Fig 6.3 CG82 % Power Plot during Soak Fig 6.4 CG92 % Power Plot during Soak
The RMS noise of thermocouple signal and RMS noise of % power (table 6.2) is calculated
based on these data.
35
System Name Growth Name Deviation RMS Noise % Power RMS Noise
Commercial System CG 82.Pt 03 0.15 °C – 0.20°C 0.8 – 0.9
NI System CG 92. Pt 0.06 °C – 0.09 °C 0.3 – 0.4
Table 6.2 Commercial vs. NI system – Performance Comparison
Comparison shows that the NI control system with its high channel count and high accuracy
device performs better than the commercial system which was the desired outcome. With
successful development of a fully functional control system steps are taken to transform it into a
versatile system.
36
CHAPTER 7
Development of Versatile System
Flexibility of LabVIEW programming language and the capability of the control system
devices allow us to develop a versatile system. As our objective is to identify the parameters that
influence the successful growth of bulk single crystals of detector grade CZT‟s. Several
parameters affect this; hence we must have ability to directly and/or indirectly measure and/or
control them.
7.1 Multiple furnace control
Two different Mellen EDG furnaces are used in the study. The flexibility of NI
LabVIEW program has enabled to develop a control program to control these two different
furnaces. Control system can be used as a plug and play device by switching furnaces
thermocouple and power controller connections
7.2 Estimation of Growth Profile and Interface location
Interface location and shape influences the growth of single crystals; it is
controlled by growth rate and temperature gradient defined in the growth profile [13].
Inconsistent growth rate may affect the interface shape thereby introducing grain boundaries and
defects. Attempt is made to estimate the actual growth rate and to indentify the location of
interface. A growth rate estimation module is added to the LabVIEW control program. The
module is sub program developed using LabVIEW mathematical function. From literature we
know that the melting point of CZT varies across the length i.e. varies with zinc and tellurium
37
concentration. Analysis of CZT crystal shows that there is uneven distribution in the zinc and
tellurium across the crystal length. Zinc segregates at the bottom or tip of the crystal and
tellurium segregates at the top or heel. Hence the melting point of CZT varies with its tip having
a high melting point value and its heel having a low melting point.
We know a rough estimate in variation of the melting point of CZT across the length, so
an approximate melting point values anticipated for each growth zones. The module is
programmed to record the time and date when each zone temperature falls within that anticipated
temperature range. Calculating the time interval in recording value between successive growth
zones we can roughly estimate the actual growth rate and interface location. Fig 7.1 & 7.2 shows
the growth profile, modeled growth rate estimation and the CZT crystal.
Fig 7.1: Grown Ingot vs. growth profile Fig 7.2 Ingot slice vs. growth rate estimate
The test has revealed that the designed growth rate is 0.5mm/hr while estimated growth rate
based on (1) interface location is 0.47mm/hr. This function was developed as a trial just to see if
numerical studies can be performed simultaneously in the program. Steps are being taken to
improvise this module
38
7.3 Control of Gas Flow Controller (GFC)
The CZT crystal is grown under an inert gas (Argon) environment inside the furnace to
prevent ampoule failure due to devitrification. The Argon gas is flowed from the bottom of the
furnace, it flows directly to the tip of the ampoule. The amount of Argon gas flowed into the
furnace is varied during the growth and this process is manually controlled by the user. Also
there is no alarm/indicator to notify the user when the gas is empty. Control systems versatility
allow using a gas flow controller (GFC) to automatically control, monitor and record the argon
flow through the control program. GFC has 0-5 VDC analog input and output channels. Argon
flow is measured and controlled through the control program by connecting these channels to the
systems DAQ & control devices. A current output with the 250Ω metal film resistor is used to
control the argon flow rate. Fig 7.3 show the auxiliary temperatures at the tip (bottom) of the
ingot, fig 7.4 shows grain structure of vertical slice of the force nucleated CZT ingot
Fig 7.3 Forced Nucleation Auxiliary Temperature Fig 7.4 Slice of force nucleated crystal
39
7.4 Accelerated Crucible Rotating Technique (ACRT)
Homogeneous crystal is another requirement for detector quality CZT crystal. Literature
[14-15] has showed that rotating the ampoule by accelerating and decelerating in clockwise and
counter clockwise directions produces a uniform mixture. A variable speed motor capable of
switching directions is used and controlled via the NI control system to implement ACRT. The
motor has a controller which controls the speed and rotation direction. The controller has 0-5
VDC analog input/output channel and ON/OFF (normally open NO/ normally close NC)
channels which enables to measure, control the speed of motor and switch the direction using the
control system. Motor speed is controlled through a current output channel of the control device.
Two 0/5 VDC TTL switches connected two digital lines of the control devices are used to make
the NO/NC connections with the controller thereby switching the motor direction. Fig 7.5 shows
the ACRT motor setup attached to the crystal growth furnace.
Fig 7.5 ACRT Motor attached to Furnace
ACRT
Motor
ACRT
Ampoule
Support
40
CHAPTER 8
Summary and Conclusion
The objective of this thesis was to develop a control system that would help us in
understanding the effects of the controllable growth parameters in crystal growth of CZT crystals
by the Vertical Gradient Freeze Method. A high speed, high accuracy control system which can
impart real time, stand alone control was developed using National Instruments devices and
programming language and CZT crystals were successfully grown. To evaluate the performance
the crystal growth process performed with the NI system was compared against those made with
the Mellen system. Comparison showed that NI system was able to grow CZT crystals similar to
the ones grown using the Mellen system while performing better than the Mellen.
Development of a successful control system motivated to transform it into a versatile
system that might help us in achieving our objective. A versatile system which can control the
furnace and additional devices was developed by enhancing the control system‟s control program
and hardware capabilities. This system can also be used to grow other semiconductor crystals
other than CZT demonstrating its versatility. New program/modules were added to the control
program to make new numerical studies and to control additional devices. Initial results have
shown that the new versatile system is capable of producing uniform, homogenous CZT crystals.
The new NI control system is certainly the right tool to help us in realizing the objective of the
study.
41
CHAPTER 9
Future Work
In the near future more software and hardware additions to the NI control system have
been planned
9.1 % Power based Control
Occasional disturbances/spikes can be observed in the PV profile which in turn affects
the % power control signal (fig 9.1 & 9.2); these disturbances may be due to unwanted noise
picked by the thermocouples and/or the devices or also due to improper grounding (9.3 & 9.4). It
is believed that these disturbances may cause unwanted grains in the crystal thereby reducing the
yield. Since it is proved that NI system‟s % power control output is smooth and uniform a
control program is developed to grow crystal based on a % power profile instead of the
temperature profile.
Fig 9.1 CG93 PV Plot Fig 9.2 CG93 % Power Plot
42
Fig 9.3 CG93 Deviation Plot Fig 9.4 CG93 Crystal Slice
9.2 Infrared Imaging Camera
To further enhance the estimation of interface location and growth rate it is planned to
use an infrared camera. CZT‟s are transparent to infrared rays, hence using the camera we can
monitor the growth process, locate the interface shape which will offer more insights to the
actual material properties of CZT in its liquid and solid phase.
43
REFERENCES
[1] R.B. James, B. Brunett, J. Heffelfinger, J. Van Scyoc, J. Lund, F.P. Doty, C.L. Lingren, R.
Olsen, E. Cross, H. Hermon, H. yoon, N. Hilton, M.Schieber, E.Y. Lee, J. Toney, T.T.
Schlesinger, M. Goorsky, W. Yao, H. Chen, and A. burger - Journal of Electronic Materials,
Vol. 27, No. 6, 1998
[2] P. Fougeres, P. Si!ert, M. Hageali, J.M. Koebel, R. Regal - Nuclear Instruments and Methods
in Physics Research A 428 (1999) 3844
[3] V. Komar, A. Gektin, D. Nalivaiko, I. Klimenko, V. Migal, O. Panchuk, A. Rybka - Nuclear
Instruments and Methods in Physics Research A 458 (2001) 113122
[4] S.A. Awadalla, J.Mackenzie, H.Chen, B.Redden, G.Bindley, M.C.Duff, A.Burger, M.Groza,
V. Buliga, J.P.Bradley, Z.R.Dai, N.Teslich, D.R.Black - Journal of Crystal Growth 312 (2010)
507–513
[5] Csaba Szeles, Scott E. Cameron, Jean-Olivier Ndap, and William C. Chalmers - IEEE
Transactions on Nuclear Science, vol. 49, no. 5, october 2002
[6] T. Asahi, O. Oda, Y. Taniguchi, A. Koyama – Journal of Crystal Growth 161 (1996) 20-27
[7] S. Sen, W.H. Konkel, S.J. Tighe, L.G. Bland, S.R. Sharma and R.E. Taylor – Journal of
Crystal Growth 86 (1988) 111-117
[8] S. Rajendran and R,H, Mellen Sr. – Journal of Crystal Growth 85 (1987) 130- 135
[9] www.allaboutcircuits.com/vol_3/chpt_7/5.html
[10] www.athenacontrols.com/downloads/power_controllers/scr900m019u00b.pdf
[11] C.L. Phillips, R.D. Harbor – Feedback Control Systems, 3rd
edition
[12] Process Control and Optimazation Vol. II – Instrument Engineers Handbook (IV Edition)
44
[13] Y. Okano, H. Kondo, S. Dost – Journal of Crystal Growth 237-239 (2002) 1769-1772
[14] P. Capper, J.E. Harris, E. O‟Keefe, C.L. Jones, C.K. Ard, P. Mackett, D. Dutton – Material
Science and Engineering B16 (1993) 29-39
[15] P. Sonda, A. Yeckel, J.J. Derby, P. Daoutidis - Computers and Chemical Engineering 29
(2005) 887–896
45
APPENDIX
46
APPENDIX A: MANUAL – LabVIEW Control Program
This manual explains about using the LabVIEW control program to run the Mellen EDG
furnace
PART 1: IN ANY PC THAT HAS MS EXCEL
1. Creating Set Points (SP) file from excel file.
a. OPEN the SP growth profile excel file located in T:\Semicon\CMR CdZnTe Crystal
Growth\”CG #”\Doc Data.
b. COPY the entire data.
c. OPEN the excel template located in T:\Semicon\CMR CdZnTe Crystal
Growth\DOCS\CG SP Template for NI PXI
d. PASTE the data starting on the first row and first column
e. The SP growth profile in additive seconds and extended quadrant zones will be
created from COLUMN Z till COLUMN BQ
f. NOTE: You will see on COLUMN Z that Segment 1 starts at time 0.00 seconds. This
is a necessary criterion for the LabVIEW program. The Segment 1 of SP profile
should always start from 0.00 seconds. For example if there are only 67 segments
then in the modified SP table you will see 68 segments where Segment 1 always
starts from 0.00s
g. COPY the data from COLUMN Z till ZOLUMN BQ and ROWS of all segments
h. OPEN „NOTEPAD‟ PASTE the copied data. SAVE the data as “SPCG#” inside
T:\Semicon\CMR CdZnTe Crystal Growth\”CG#”\Doc Data folder. The file will
automatically be saved with a”.txt” extension.
47
i. SAVE the modified „CG SP Template for NI PXI.xls‟ excel file as „CG SP NI PXI
CG#.xls‟ under the T:\Semicon\CMR CdZnTe Crystal Growth\”CG#”\Doc Data
folder.
j. Do not save or modify the ORIGINAL „CG SP Template for NI PXI‟ excel file.
k. If you had modified the original excel template then there is a backup under
T:\Semicon\Chandra\CMR\MS OFFICE Files\„CG SP Template for NI PXI.xls‟
2. CREATING multiple PID Data file
a. Need to create a PID table for each segments and zones. Each segment and each
individual zone will have a P, I, D value
b. So if there are 68 segments then the PID table will have 43 ROWS (for each zone)
and 68X3(=204) COLUMNS (for each segment).
c. Ideal PID values:
For Zone 1: Ramp – P=4, I=8, D=0 and Soak – P=1.5, I=1, D=0.
For Zone 3,5,6&43: Ramp – P=4, I=8, D=0 and Soak – P=0.8, I=2, D=0.
For all other Zones: Ramp – P=6, I=10, D=0 and Soak – P=0.8, I=2, D=0. OR
d. Previous PID file „EXCEL‟ or „NOTEPAD‟ files were created for CG 87, CG90,
CG92, CG93, CG95, and CG99. Use these files instead
e. Create this PID table in MS Excel. COPY the 43 ROWS 204 COLUMNS values and
PASTE in „NOTEPAD‟
f. Save the notepad file as “CG#PID” inside the T:\Semicon\CMR CdZnTe Crystal
Growth\”CG#”\Doc Data folder.
48
PART 2: IN THE NI PC SYSTEM
3. COPYING ‘SP’ and ‘PID’ file onto Remote (satellite) PXI Hard Disk
a. OPEN/ACCESS the PXI system by opening either MY DOCUMENTS or
WINDOWS EXPLORER
b. In the address bar type „ftp: //192.168.0.2‟. This is the current IP address of the PXI
system
c. If you don‟t know the IP address of the PXI system OPEN „Measurement and
Automation Explorer (MAX)‟ located in the desktop. Then click to expand on the
„Remote Target – NIPXIRT8106-2F11 (192.168.0.2). you can see the IP address on
right window
d. Once you have accessed and opened the PXI hard disk PASTE the „SP‟ and „PID‟
notepad file inside the „CG Read‟ folder.
e. CLOSE the window.
4. Restart Host Desktop And PXI Satellite
a. Restart the HOST desktop WINDOWS XP system.
b. Restart the NI PXI satellite system by switching OFF. Switch ON the NI PXI satellite
system once the HOST desktop is fully functional after the restart.
c. DO NOT RUN LabVIEW with the NI PXI satellite system OFF
5. OPENING LabVIEW Mellen Furnace Control Program
a. On the HOST „DESKTOP‟ click on START Programs National Instruments
LabVIEW 8.6
49
b. A LabVIEW MAIN window will open GOTO FileOpen ProjectMy
Documents LabVIEW Data Mellen Furnace Control Program „Mellen Furnace
Control ProgramV3.lvproj‟ file.
c. LabVIEW will load the „PROJECT EXPLORER‟ window of the „Mellen Furnace
Control ProgramV3.lvproj‟ program
d. Inside the project explorer window you will see two tabs
e. My Computer – This is the HOST machine.
f. OPEN „Mellen Host Plot DataV3.vi‟. This program is used to display and plot data.
g. DO NOT START/RUN this program now.
h. Open the „REMOTE TARGET NI- PXI8106-2F11705F (192.168.0.2)‟ tab in the
Project Explorer window below the MY COMPUTER tab
i. REMOTE TARGET – RT PXI 8106 – 2F1107FS (192.168.0.2) – This is the PXI
satellite system
j. EXPAND this tab by clicking on the „+‟ sign located left to it
k. You will see a „Mellen Furnace ProgramV3.vi‟. RIGHT CLICK on this and SELECT
„DEPLOY‟
l. This deploys the „Mellen Furnace Program.vi‟ from the host to the PXI satellite
machine along with the associated sub VI‟s and other necessary functions.
m. Once deploying is completed the FRONT PANEL of the „Mellen Program.vi‟ will
open.
50
6. LOADING CG SP File and PID File and STARTING RUN
a. The FRONT PANEL of the „Mellen Furnace Program.vi‟ has a 3 tab WINDOW
(i) Program SETUP (ii) Monitor Table (iii) Full PID table and (iv) timing tab
1. Program Setup TAB:
a. Enter/Write the Set Point file name – „SPCG#‟ – CASE SENSITIVE
b. Enter/Write the PID file name – „PIDCG#‟ – CASE SENSITIVE
c. Enter/Write the RUN NAME „CG#‟
d. Select the Furnace – FURNACE SELECTOR
51
e. Select the Power Control Mode – „A‟ for Automatic and/or „M‟ for Manual
f. SELECT the thermocouple type – „TC S‟ – CASE SENSITIVE
g. PLACE Check MARK on „DATA RECORD‟
h. Set the RECORD TIME in seconds
i. Enter the Total no of segments
j. DO NOT CHECK MARK on FW/RW Segments? Unless you want to skip to
another segment – See HOW TO SKIP SEGEMNTS below
k. PLACE Check MARK on the „CONTROL ON/OFF‟ – to begin CONTROL
l. PLACE check MARK on Aux ALARM ON/OFF
m. Argon Flow Rate SETUP – SEE BELOW in „#8a‟
n. NOTE: TWO STEP OPERATION TO RUN THE PROGRAM
o. STEP ONE : Slide the READ PROFILE switch to ON (UP)
p. CLICK on „RUN‟ arrow on the LEFT TOP CORNER of the FRONT PANEL
window.
q. This will read and load the SP and PID file into the program
r. The PROGRAM WILL STOP RUNNING AFTER LOADING THE SP and
PID Files
s. Once the FILES are READ the entire SP profile will be displayed in the „Set
Point Table‟ under this TAB. SCROLL OVER THE SP Table and FULL PID
table to make sure SP and PID values are correctly READ.
t. Also the program parameter‟s – such as the power output mode (A/M),
manual % power output value, high deviation value, low deviation value, TC
type will be displayed in the „Program Parameter Table‟ under this TAB.
52
u. STEP TWO – SWITCH OFF i.e. Slide down the READ PROFILE SWITCH
to OFF position
v. CLICK on „RUN‟ arrow on the LEFT TOP CORNER of the FRONT PANEL
window AGAIN TO START the RUN
w. Then START – CLICK RUN on the „Mellen Host Plot Data.vi‟ opened
previously to plot the data.
7. CHECK PROGRAM
a. PROGRAM SETUP TAB
1. Entire SP profile will be displayed in the „Set Point Table‟ under this TAB.
2. Also the program parameter‟s – such as the power output mode (A/M), manual %
power output value, high deviation value, low deviation value, TC type will be
displayed in the „Program Parameter Table‟ under this TAB.
3. Current PID setting will also be displayed in the „Current PID Table‟ under this
TAB
b. Monitor Program TAB:
1. Check if all the zones TC are reading properly
2. Check if the Set Points are generated properly for all the control Zones.
3. Check if % Power values are generated
c. Full PID Table TAB
1. The entire PID table will be listed in this TAB
53
8. MAKING Changes to the PORGRAM/RUN
a. Argon Flow Rate Setup – This is similar to the SP Profile table where the COLUMN
1 is time and COLUMN 2 is Argon flow rate Set Point
1. Argon PV and time elapsed (iGFC) is DISPLAYED on RIGHT to the TABLE
2. Programming Argon Flow SP Table – Program the table just like the SP table –
Ar flow time in seconds & Ar flow SP in LPM
Ar Segment Time (s) Ar Flow SP LPM
1 0 5
2 60 5
3 120 10
4 360 10
5 480 5
3. The above table roughly explains the RAMP UP. SOAK and RAMP DOWN in
Ar Flow Rate SP value.
4. SEGMENT1 is DEFAULT – DO NOT CHANGE THIS
5. NOTE - Time must always be in seconds and additive of the previous segment
time
6. EXPLANATION – At 0 second the Flow is set to 5LPM and it will remain at
5LPM up to next 1min (60s), Then it will RAMP UP to 10 LPM in the next 1 min
(since additive, hence 60+60=120) it SOAK at 10LPM for the next 4min
(120+240=360). Then it will RAMP DOWN to 5 LPM in the next 2mins
(360+120=480). The Ar will CONTINUE to flow at 5 LPM even after completion
of segment 5(i.e after end of 480s) i.e until a new segment is added
7. If you want to program Ar flow rate after some time then succeeding segments
should like this
54
Ar Segment Time (s) Ar Flow SP
6 18000 5
7 18060 10
8 18180 10
9 18240 5
8. EXPLANATION – Say you program TABLE 1 at the start of run in DAY 1 and
then you leave, Ar will follow the profile and Continue to flow 5LPM after the
end of 480s.
9. Now you want to change Ar flow in DAY2 where 17800s has elapsed (you can
see the elapsed Ar time for „iGFC‟ display next to the table – use table 2 as an
example to program further Ar flow rates.
10. NOTE – Ar flow SP value must be same in the succeeding segments before you
make a new profile i.e. note Segment 5 and 6
11. A default value of 5LPM is given at the start of the run
12. To RAMP and SOAK CHANGE Ar flow in between the run – use the „iGFC‟
which displays elapsed time in seconds
b. Forward/Reverse Segment:
1. In Program SETUP TAB - PLACE CHECK MARK „FW/RW Segments?‟Enter
the segment # to go to. NOTE: Enter one value lesser than the segment you want
to go to i.e. If you want to forward to Segment 9 then you have to enter 8 in the
„Enter Segment #‟ because remember that always the first segment should start
from 0s. So when you enter 8 Segment 8 will start from 0s and the program will
skip and start to execute from Segment 9 onwards.
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c. Adding/Changing Segment:
1. Place the cursor on the „Set Point Table‟ and RIGHT CLICK. Select „Insert
ROW‟ to add a new segment and/or „DELETE ROW‟ to remove a segment.
2. If you want to change SP of particular segment or particular zone – make those
necessary changes in this table
d. Changing Program Parameters – Program Parameter Table
1. To Change Power output mode – Automatic/Manual Mode
2. Initially we select the output power mode to be automatic by selecting „A‟
3. To change to manual enter „M‟ for that particular zone in the „Program Parameter
Table‟. To change back to automatic mode enter „A‟
4. To change the % power output value during the manual mode operation enter the
% power value under the % MPO (% Manual power output) COLUMN for the
corresponding zone in this table.
5. To change high and low deviation for particular zone – make changes under the
High Dev and Low Dev columns of the appropriate zones.
6. To Change TC Type Enter „TC R‟ (CASE SENSITIVE) under the TC type
COLUMN of this table
7. If you want to make changes to the PID settings – note the current segment #.
8. Open the FULL PID Table TAB – go to the corresponding – „P#‟ „I#‟ „D#‟ to
change the current PID settings values.
e. PAUSE PROGRAM:
1. Pause the program – there is a „PAUSE PROGRAM‟ switch in bottom of the
FRONT PANEL.
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2. Switch it to ON position – the program pauses and maintains at the Set Point
value at that time until the user switches OFF the PAUSE.
f. CHANGE ENTIRE RUN PROFILE
1. To change the entire run profiles or make entirely a new run without
STOP/Interrupting the RUN (to eliminate disturbance).
2. Prepare the SP and PID text file and COPY it to the „CG Read‟ folder of the PXI
hard disk by the before mentioned processes.
3. Then under the Program SETUP TAB – write the new „SP Profile File Name‟ and
„PID File Name‟ (done similarly at the START of the run).
4. SWITCH PROFILE switch is located in the bottom of the FRONT PANEL above
the PAUSE PROGRAM switch.
5. Switch it to ON state – the program starts to read the new SP and PID profiles.
The switch will automatically go to OFF state once the new SP Profile has been
loaded.
6. It is also necessary to give a NEW RUN NAME in order to save data of the
NEW/Modified Profile.
g. When ALARM goes ON
1. There is an LED ALARM INDICATOR in the bottom of the FRONT PANEL.
Next to the LED ALARM INDICATOR there are two small LED indicator‟s to
represent the control zone‟s condition and auxiliary TC‟s condition.
2. If the program is running without any problem the big ALARM LED will be
invisible and the two small LED‟s will be turned ON and glow „GREEN‟
indicating normal operations.
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3. If there is any problem (if the alarm goes on) the big ALARM LED will start to
BLINK and either or both the small LED‟s will be turned off depending on the
occurrence of the problem.
4. The only case alarm goes on is if the thermocouples deviate above or below the
set deviation limit.
5. Look which thermocouple/zone is deviating in the Monitor Program Table under
the Monitor Program TAB.
6. To make changes to the deviation limit go to Program Parameter Table under the
Program SETUP TAB and change the deviation limit for the corresponding zone.
9. END OF RUN
a. Once the run has ended CLICK on the STOP button on the bottom of the program
FRONT PANEL to stop the Program.
b. Once the STOP button is HIT the 5 Power Output Values are reset to „0V‟ i.e. the
power cabinet transformers are turned OFF. The ALARM is also reset.
c. To stop the „Mellen Host Plot Data.vi‟ hit the STOP SIGN button on the TOP LEFT
corner next to the RUN ARROW SIGN.
