PC-Based Virtual DTA Recording System Design
Contents
1. as leader in virtual instrumentations domain is used to realization our project LabView is a graphical programming development environment based on the G programming language for data acquisition and control data analysis and data presentation LabView gives the flexibility of a powerful programming language without the associated difficulty and complexity because its graphical programming methodology is inherently intuitive to programmers With LabView the user can control own system and present results through interactive graphical front panels On the front panel user places the controls and data displays for own system by choosing objects from the controls palette including numeric displays meters gauges LEDs charts graphs and more To program programmer constructs the block diagram by choosing objects icons from the functions palette and connect them with wires to pass data from one block to the next These blocks range from simple arithmetic functions to advanced acquisition and analysis routines to network and file I O operations Therefore LabView uses a dataflow programming model so called G that frees programmer from the linear architecture of text based languages The realized GUI at on line mode is shown in Fig 4 Two of three real time waveform charts are physical channels while the last temperature difference waveform is arithmetic channel Digital indicators on the charts show instantaneous temperatures values of2. order is used also All measured values show a good agreement with reference values Absolute error was less than 3 C in the temperature range from 20 C to 750 C Described graphical user interface may be modified and upgraded easily by adding new functions for both operating modes in accordance with appropriatelly user requirements by software modifications If some iregulars occur during the on line acquisition like sensors disconnection the software will automaticaly abort the acquisition process Changes of the parameters as port number sample time filter type and cutoff frequency will not be accepted if they made during on line acquisition process Conclusion The described PC based virtual DTA recording system is based on the modern virtual instrumentation concept and recently developed digital temperature sensors The realized system can be used in many applications for temperature monitoring and recording in the wide range but it is primarily intended for metallurgy researches where complex and relatively expensive stand alone DTA system developments are required The total cost of development realization and system maintenance is reduced due to application of digital sensors and LabView programming tools The described system has been verified accros more tests for binary and ternary systems of the metal alloys Acknowledgement This work was supported by the Ministry of Science and Technology of the Republic of Serbia w
3. a dummy sign bit and is always zero Bits D14 D3 contain the converted temperature in the order of MSB to LSB Bit D2 is normally low and goes high when the thermocouple input is open D1 is low to provide a device ID for the MAX6675 and bit DO is three state Initiation a new conversion process starts by forcing CS high IU UUUUUUUUUUUUUUL Fig 2 SPI interface protocol of MAX6675 Table 1 Format of serial data output Bit Dummy 12 Bit Temperature Ther Dev State Sign Bit Reading Input ID Mane State The Xbee PRO RF modules MaxStream are used for wireless connection 9 of the acquisition hardware with other remote PC s GUI It allows the possibility of the real time process monitoring and recording in the isolated room especially for demonstrative student s lessons As can be seen from Fig 1 communication between the PIC MCU and Xbee PRO RF module is established via serial data interface of the module 3 3V CMOS UART S5V tolerant and the configured USART periphery of the PIC MCU The modules operate within the ZigBee protocol 9 and support the unique needs of low cost low power wireless sensor networks The modules require minimal power and provide reliable delivery of data between remote devices within the ISM 2 4 GHz frequency band RF modules have been easily configured by free X CTU configuration software first as Coordinator and second as End device at the point to point topology Bo
4. indicators Described while loop cycle will be repeated in accord with the choosen sampling time Minimal sampling time is 0 25 second exactly and can be adjusted as integer multiple of the minimal sampling time On line acquisition process may be terminated by pressing the STOP button In this way the program leaves while structure sending the stop string to the instrument s hardware and the port closing CLEAR GRAPHS button serves for occasionally graphs cleaning after longer acquisition time File Edit Operate Tools Browse Window Help i a u 18pt Application Font oie e USER S GUIDE Before start the VI application plug in the acquisition hardware in the USB port and then install the CDC_VistaWin7x64 inf driver In the Device Manager configure the virtual COM port and then start the VI application On the front panel adjust the virtual COM port number See Device Manager and sample time on the front panel Minimal sample time amounts 250ms Select the type of digital filtar ex Butterworth and its cut off frequency In the File Path and Name field write the full path and name of the spreadsheet file for logging data For standard better measurement accuracy turn off on the Calibration switch and then click on Run button In the on line mode turn on the Log to File toogle switch for recording process start Before on line process stops turn off the Log to File switch and then click on the Stop button for acquisition s
5. of the proposed system acquisition hardware and PC The MCU has 32Kbytes flash program memory and can store up to 16384 single word instructions The data memory is implemented as static RAM divided into 8 complete banks for a total of 2048 bytes The data EEPROM is a nonvolatile memory array separated from the RAM and program memory that is used for long term storage of program data or constants The MCU PIC18F4550 consists of some standard peripherals as a 10 bit 13 channels analog to digital converter PWM Enhanced USART comparator module and four timers The device has an 31 level deep hardware stack and multiple internal and external interrupt sources with priority levels for interrupts A watchdog timer with its own on chip RC oscillator serves for reliable operation of PRZEGL D ELEKTROTECHNICZNY Electrical Review ISSN 0033 2097 R 87 NR 12a 2011 the device As can be seen in Fig 1 the microcontroller is clocked by 20MHz crystal resonator Precisely sampling time of 250ms is generated including RTC functionality of the 16 bit timer counter TMR1 by adding an external LP watch oscillator An overflow of the TMR1 register causes a TMR1 overflow interrupt if enabled The interrupt service routine can then perform the appropriate task In order to satisfy wide temperature range demand the thermocouples of K type are adopted This thermocouples type is comparatively inexpensive and accessible at the market ANSI type K Iron Con
6. Aleksandar ZORIC ur e PERISIC Slobodan OBRADOVIC Petar SPALEVI Slobomir P University Bosnia and Herzegovina 1 University of PriStina Serbia 2 PC Based Virtual DTA Recording System Design Abstract This article describes a modern design of PC based virtual system for the qualitative differential thermal analysis DTA dedicated to laboratory investigations determining the phase transformation temperatures for binary ternary and other systems of the metal alloys Complete design is devided in two parts acquisition hardware based on the PIC MCU and graphical user interface developed under LabView IDE Obtained experimental results show a very good agreement with the measured reference values and high precision of the proposed system Streszczenie W artykule przedstawiono komputerowy system wirtualny do analizy jako ciowej r nicy termicznej DTA po wi cony badaniom laboratoryjnym okre laniu temperatury przemian fazowych dla binarnych potr jnych i innych system w stop w metali Kompletny projekt jest podzielony na dwie cz ci sprz t w oparciu o mikrokontroler PIC i graficzny interfejs u ytkownika opracowane pod LabView IDE Uzyskane wyniki do wiadczalne wykazuj bardzo dobr zgodno mierzonych warto ci odniesienia i wysok precyzj proponowanego systemu Wirtualny system komputerowy do analizy r nicy termicznej DTA Keywords DTA Microcontroller LabView Thermopair S owa kluczowe r nica
7. all channels The front panel is divided in two parts which may be selected by ON LINE and OFF LINE tab controls 158 PRZEGLAD ELEKTROTECHNICZNY Electrical Review ISSN 0033 2097 R 87 NR 12a 2011 gt DTA_GRAPHO25 vi Front Panel File Edit Operate Tools Browse Help E 776 8 763 7 Temp 2 C s EREGERELEBREEER 1 44 00 11 46 00 11 48 00 11 50 00 11 52 00 11 54 00 iio A 1o d 11 11 57 05 tejoj t6 oaji116 o3j11 16 03 11 16 03 11 6 03 0 11 27 54 11 30 00 11 32 00 11 34 00 11 36 00 11 38 00 11 40 00 11 42 00 1 11 st Mi d 11 16 11 16j u i 1 i 11 1 1 1 6703 1 16 03 16 03 03 03 6 03 6 03 11 16 03 11 16 03 11 16 03 11 TimesDate Fig 4 Instrument front panel view at the on line mode with temperatures waveforms As can be seen from Fig 3 the front panel of the instrument is reviewed intuitive and familiar with other Windows environments ON LINE acquisition default page process starts by pressing the Run arrow button in the upper left corner of the front panel After the virtual serial port opening the instrument s hardware initialization executes by writing appropriate start string to the port After that the program continues within the while loop reading four raw data bytes per sample from the port LP filtering and processing data and showing right values of the temperatures as well as their difference Final results program sends to the waveform charts and digital
8. and comments data into ASCII file During the on line monitoring the user should to has available start and stop options of the recording data operation in the form of file e numeric representations of three channels instant temperatures values during on line monitoring e numeric representation of the surface of a temperature difference curve in the recorded time period e possibility of sampling rate adjustments e zoom tool and cursors for navigation during off line monitoring e portability of the instrument s acquisition hardware and simple connection with PC e simple instrument handshake possibility and electronic user s manual In order to satisfy proposed temperature range the instrument s hardware must uses the thermocouples as sensors This will requires an extra function of open thermocouple detection for both sensors having in mind length of the thermocouples Acquisition hardware arrangement Taking into account the users requirements the acquisition hardware with K type thermocouples is designed to be connected with personal computer The central part of the acquisition hardware is the Microchip microcontroller PIC18F4550 with built in the USB periphery Complete scheme of the system hardware is showed in Fig 1 As shown in Fig 1 communication between the acquisition hardware and PC is established via USB port of the PC or precisely by emulating RS232 serial interface over USB The communication device cl
9. ass CDC specification defines many communication models including serial emulation By using the relevant CDC built in functions integrated in the MCU firmware and appropriate driver virtual COM port has been formed This is necessary because the LabView 7 Express software has not embedded functions for USB control transfer Simultaneously the power lines of the PC s USB port serve as power supply lines of the acquisition hardware due to large current capacity of 5 00mA and stable voltage of 5V In this way the acquisition hardware becomes independent on the external power supply sources Two buttons in the scheme serve for the microcontroller in circuit serial programming ICSP on the base of stand alone USB bootloader program So the engineer can easily upgrade firmware without need of disassembling the hardware and with CCS C compiler software support The PIC18F455 is a high performance enhanced flash USB microcontroller with flexible oscillator structure and many special microcontroller features MAX 6675 kee Od aE t s 330 5V lt ve scx 100n I 5V A es MAX 6675 Pad feno ncf PWR A so ak ql Kee ORL T H 5V lt _ vec sck Reset gt 5 100n I e T ans RB3 D RpoqL sSSSCSCSCC C C CdC Bootload Piragramming j 15p GIRT 15p 20MHz ODO l E PIC18F4550 COM USB cable Vusb j 33p L XT 33p 32K 47 0n 5 f D V Fig 1 The hardware
10. ced Instrumentation Systems Springer Verlag Berlin Heidelberg 2007 728p 9 M Dunbar Plug and Play Sensors in Wireless Networks IEEE Instrumentation and Measurement Magazine 4 1 19 23 2001 Authors prof dr in Aleksandar Zori prof dr in ur e Peri i prof dr in Slobodan Obradovi Faculty of Information Technologies str Pavlovi a put bb 76300 Slobomir Bosnia and Herzegovina E mails aleksandar zoric spu ba dj perisic spu ba slobo obradovic qmail com prof dr inz Petar Spalevic Faculty of Technical Sciences str Knjaza Milosa 7 38220 K Mitrovica Serbia E mail petarspalevic yahoo com 160 PRZEGLAD ELEKTROTECHNICZNY Electrical Review ISSN 0033 2097 R 87 NR 12a 2011
11. es difference is incorporated This parameter program calculates automatically by numeric integration method Simpson s rule As the previously described software part this part of front panel of the instrument is designed to be user friendly The obtained heating curves in Fig 6 represent a result of the thermal testing of an alloy of ternary system Ag Sb Zn recorded by described DTA system under laboratory conditions where Al2O3 is used like reference material For making alloys were used metals of purity of 99 999 The qualitative DTA was executed in the dedicated temperature chamber with constant heating rate controlled by the temperature programmer Both samples in the sample holder assemblies together with the sample containers and thermocouples are subjected to identical heat treatments All of three recorded temperature curves in Fig 6 are showed in one window PRZEGLAD ELEKTROTECHNICZNY Electrical Review ISSN 0033 2097 R 87 NR 12a 2011 159 Using the cursors and legend user can measure the peaks of curves and other characteristic points in the graph Using binary and ternary systems of metal alloys such as Pb Sb Sb Bi Ag Sb Ag Sb Zn In Zn Sb more tests have been performed by the proposed virtual DTA system Additional reference K type thermopairs with cold junctions in ice and a precize digital mV meter have been used in order to evaluate measurement error at more temperature points Polynomial approximation of 9
12. ithin the projects TR47016 and TR35026 REFERENCES 1 A Zori S Obradovi An Inexpensive System for Temperature and Humidity Monitoring Proc of Int Sci Conference UNITECH 06 Gabrovo Bulgaria 2006 Vol I P 104 108 2 M Kosti Data Acquisition and Control Using LabVIEW Virtual Instrument for an Innovative Thermal Conductivity Apparatus Proceedings of Virtual Instrumentation in Education 1997 Conference June 12 1997 MIT 1997 P 131 136 3 K C Yao Single Input Virtual Digital Multi meter Design and Implementation International Journal of Innovative Computing Information and Control 2008 Vol 4 No 12 P 3101 3110 4 Patrick H Garrett Multisensor Instrumentation 6 sigma Design defined accuracy computer integrated measurement systems John Wiley and Sons Inc 2002 209p 5 S Chakravarthy R Sharma and R Kasturi Noncontact Level Sensing Technique Using Computer Vision IEEE Trans on Instrum and Measurement Vol 51 No 2 P 353 361 2002 6 Aleksandar Zori Sini a S Ili PC Based Electrocardiography amp Data Acquisition TELSIKS IEEE 2005 P 619 622 7 C C Ko B M Chen S Y V Ramakrishnan C D Cheng Y Zhuang J Chen A Web Based Virtual Laboratory on a Frequency Modulation Experiment IEEE Transactions on Systems Man and Cybernetics 2001 Vol 31 No 3 P 295 303 8 S Sumathi P Surekha LabVIEW Based Advan
13. o identical thermal treatment during recording temperature difference between tested sample and reference This temperature difference curve is then plotted against time or against temperature DTA curve or thermogram Changes in the sample which lead to the absorption or evolution of heat can be detected relative to the inert reference Namely with increasing temperature a short peak at DTA curve occurs if the tested sample undergoing a phase transformation This occurs because the input heat will raise the temperature of the inert substance but will be incorporated as latent heat in the tested material which undergoing a phase transformation Thus a DTA curve provides data on the transformations that have occurred such as glass transitions crystallization melting and sublimation The area under a DTA peak is the enthalpy change and is not affected by the heat capacity of the sample DTA is widely used in the pharmaceutical and food industries as well as in the environmental studies The virtual DTA system proposed in this paper is based on the IBM compatible PC and the simple microcontroller s acquisition interface with integrated cold junction compensated K thermocouple to digital converters The system is realised in accordance with the user requirements of the laboratory of metallurgy at the Faculty of Technical Sciences in Kosovska Mitrovica It represents an economical high quality replacement of conventional stand alone elect
14. r should selects appropriate recorded file In this mode the program reads data from chosen spreadsheet file and represents the recorded waveforms in the graph field as in Fig 6 Spreadsheet ASCII file containing the measured data may be interpreted by any tabular programs like MS Excel Matlab etc This mode of the user software stops automatically at the end of file after reading data DTA_GRAPH vi Front Panel Bile Edt Operate Tools Growse Window Help Temp 1 Temp 2 amp Difference AnA AA CET a ssis 88 8 fimes Bl1 TE see N TE remp 1 Temp 28 8 I t S mes SURFACE OF TEMP DIFF CURVE CEET iios aa mea 168930 0 Deg centigrade s COMMENT D AgSb2nExp_12 Fig 6 Instrument front panel view at the off line mode with temperatures waveforms obtained by reading appropriate spreadsheet file Fig 6 shows the front panel at off line mode As can be seen there are three cursors with the cursors legend for two temperatures and their difference and for time and date reading graph pallete with zoom tool and scale legend In the recorded time interval the front panel at off line mode automatically calculates and shows min max and average values for all of three quantities From the file program reads and shows the chosen sampling period in seconds and the comment from header of the file Additionally on the base of user demand a numeric display of the surface of the curve of temperatur
15. romechanical recording instrument for DTA A special care is dedicated to the user software designing whose features have the direct influence on the solution quality The user software is realized under LabView IDE Adopted concept enables compact measurements recording and analysis of the obtained graphs as well as easily sensors replacement without the need of calibration Quality and accuracy of the described system is acknowledged by more tests of the binary and ternary systems of the metal alloys User requirements The conventional instrument for DTA is a simple device which consists of two physically coupled thermocouples analogue processing electronics display and thermal 156 PRZEGL D ELEKTROTECHNICZNY Electrical Review ISSN 0033 2097 R 87 NR 12a 2011 recorder The instrument creates the temperatures difference graph versus time of the reference and tested sample By analysing the obtained graph the user can determines most important thermodynamics parameters of the tested sample With regard to the instrument s purpose the user was defines adequate requirements The instrument should to has the following functions e two physical and one arithmetic channel for the real time temperatures measurement of the reference and tested sample and their difference respectively in the range of 0 C 1000 C e on line and off line monitoring possibilities e the storage possibility of the measured and administrative time date
16. stantan and DIN NiCr Ni thermocouples are composed of identical alloys and exhibit similar behavior As can be seen from Fig 1 the MAX6675 cold junction compensated K thermocouple to digital 157 converters Maxim are used for signal processing from a K type thermocouples This converter resolves temperatures to 0 25 C allows readings as high as 1024 C and exhibits thermocouple accuracy of 8 LSBs in temperatures range from 0 C to 700 C Over temperature of 700 C maximum temperature error is about 17 LSBs The thermocouple should be attached as close to the chip as possible so that the cold junction and the chip which is measuring the cold junction temperature internally are isothermal The whole assembly of the cold junction and the chip should be kept away from sources of heat or thermal gradients of any kind perhaps inside an enclosure The cold end temperature of MAX6675 chip can only ranges from 20 C to 85 C The data is output in a 12 bit resolution SPI compatible read only format Fig 2 and Table 1 Maximum conversion time is 0 22 s The MAX6675 includes a thermocouple failure alarm that indicates if one or both thermocouple leads become open This preference is adequate applied in this solution A complete serial interface read requires 16 clock cycles By forcing CS low any conversion process immediately stops Read operation of the 16 output bits occurs on the falling edge of the clock The first bit D15 is
17. t and procedures 6 Virtual instrumentation systems also comprise pure software instruments such as oscilloscopes and spectrum analyzers for processing the collected sensor data and messaging it such that the users can make full use of the data The Internet has enormous potential for distributed virtual instrumentation 7 Various remote devices such as telerobots or remote experimental apparatus can be directly controlled from the Internet There are a great number of research activities that explore how the Internet can be applied to medicine In addition many of virtual instrumentation development tools such as LabView 8 directly support integration of virtual instruments in the Internet environment The Web technologies make possible creation of sophisticated client server applications on various platforms using interoperable technologies such as HTML Java Applets Virtual Reality Modeling Language and multimedia support Qualitative differential thermal analysis DTA is a thermoanalytic technique which can be used as a finger print for identification purposes but usually the applications of this method are the determination of phase diagrams heat change measurements and decomposition in various atmospheres Qualitative DTA is based on monitoring of the temperature difference of two samples when they are heated evenly In DTA the material under study and an inert reference material such as AlzO3 are exposed t
18. termiczna DTA system komputerowy LabView Introduction The concept of virtual instrumentation was born in late 1970s when microprocessor technology enabled a machine s function to be more easily changed by changing its software Virtual instrumentation combines mainstream commercial technologies such as the PC with flexible software and a wide variety of measurement and control hardware so engineers and scientists can create user defined systems that meet their exact application needs Virtual instrumentation refers to the use of general purpose computers and workstations in combination with data collection hardware devices and virtual instrumentation software to construct an integrated instrumentation system 1 2 3 In such a system the data collection hardware devices are used to incorporate sensing elements 4 5 for detecting changes in the conditions of test subjects These hardware devices are intimately coupled to the computer whereby the operations of the sensors are controlled by the computer software and the output of the data collection devices are displayed on the computer screen with the use of displays simulating in appearance of the physical dials meters and other data visualization devices of traditional instruments 4 5 For example increasing number of biomedical applications use virtual instrumentation to improve insights into the underlying nature of complex phenomena and reduce costs of medical equipmen
19. th short 16 bits addresses have been matched as well as the baud rate also The RF module conforms to the 802 15 4 specification and supports both short 16 bit addresses and long 64 bit addresses Every one RF module is equiped with half wave dipole antenna Fig 3 shows simple serial communication betwen the RF module configured as End device and PC s COM port External 5V power supply must be provided for module supply and for MAX232 converter k ee MAX232 RS 232 F Fig 3 RF module connected with PC COM port as END device The microcontroller s firmware is written using CCS C compiler IDE version 4 057 The program includes procedures of the microcontrollers peripherals initialization interrupt service routine one wire and specific two wire protocol for communication with sensors and USB CDC API for virtual COM port creating The system firmware starts or stops program execution after received appropriate string from the PC By comparison the received string with the adopted start and stop string constants within the interrupt service routine the microcontroller resolves appropriate PC request Graphical user interface The user software is realised under Windows operating system which ensure quality graphical environment multitasking and interaction between graphical user interface objects and appropriated subroutines event driven principle The LabView software National Instruments USA 8
20. top Click on the Off Line tab control in order to select the off line mode and then click on the Run button In the opened window select the file and click OK All of the recorded waveforms will appear in the graph field Use the cursors for navigation Technical specifications Sensors K type thermocouple Temperature range 0 to 1024 degree Centigrade Accuracy 8 LSB from 0 to 700 degree Centigrade and 17 LSB over 700 dC Open thermocouple detection sef b Fig 5 On line help subVI During on line acquisition the user can uses on line help which includes electronic user guide and technical specifications of the instrument ON LINE HELP button see Fig 5 The mentioned while loop includes the case structure with ready made file I O functions Write to spreadsheet file starts by turning on the vertical toggle switch LOG TO FILE recording start Header of the file including text control comment on the front panel sampling period and current system date time string first will be saved into the file and then data field which represents three channels The file path and name are specified in the text control on the front panel File writing orocess may be stopped by turning off the vertical toggle switch recording stop during the on line acquisition The user can selects the off line monitoring mode by clicking on OFF LINE tab control After that by clicking on the Run button gt in the new window use
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