RAČUNARSKI SISTEM ZA TERMALNU ANALIZU MATERIJALA COMPUTER CONTROLLED SYSTEM FOR THERMAL ANALYSIS OF MATERIALS

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1 RAČUNARSKI SISTEM ZA TERMALNU ANALIZU MATERIJALA COMPUTER CONTROLLED SYSTEM FOR THERMAL ANALYSIS OF MATERIALS Milan RADIVOJEVIC 1, Mining and metallurgy institute Bor, Bor, Serbia Misa STEVIĆ, Mikroelektronika, Belgrade Zoran STEVIĆ, University of Belgrade, TF Bor, Bor, Serbia U radu je dat kratak pregled računarski kontrolisanog sistema za diferencijalnu termalnu i termogravimetrijsku analizu. Sistem se sastoji od personalnog računara, softvera, akvizicione kartice i interfejsa za obezbeđenje potrebnih uslova za analizu i adaptaciju ulaznih i izlaznih signala. Ceo sistem kontrole, kao i akvizicija, sni-manje i obrada izmerenih podataka rešava se softverski. Aplikacija je zasnovana na programskom paketu LabVIEW Ključne reči: Termogravimetrijska analiza; diferencijalna termalna analiza; hardver; softver; LabVIEW. The paper gives a brief overview of computer controlled thermogravimetric and differential thermal analisys system. The system consists of a personal computer, software, data acquisition card and interface for the provision of the necessary conditions for the analysis and adaptation of input and output signals. The entire control system, as well as the acquisition, recording and processing of measured data is solved by software. Application is based on programming package LabVIEW. Key words: 3D thermogravimetric analysis; differential thermal analisys; hardware; software; LabVIEW. 1 Introduction Thermal Analysis of Materials are techniques where various parameters of substance, in an environment heated or cooled at a controlled rate are recorded as a function of time or temperature [1,2]. Typical Thermal Analysis measurement system consists of a sample holder, thermocouples, sample containers, furnace, temperature programmer and a recording system. In this article, system for diferential thermal analisys (DTA) and thermogravimetric analisys (TGA) is introduced. Diferential therma analisys implies that the difference in temperature between a substance and reference material is recorded in function of temperature, while in thermogravimetric analisys, recorded parameter is mass change of substance, also in function of temperature. In this system PC with data acquisition device, analytical balance and a cheap hardware interface is used for temperature programmer and a recording system purposes. It has several advantages compared to ordinary stand-alone devices: - High-resolution measuring - Compact design - Can be easily adapted and/or modified for any type of measurement - Can be used with any type of thermocouples and furnaces - Much more affordable 2 Hardware For signal generation and data acquisition it was developed a measuring and control system based on personal computer (Fig. 1). Beside PC, hardware consists of AD/DA converter and external 1 Corresponding author, mdradivojevic@gmail.com 5. MKOIEE ICREPS 169

2 interface for analog signals conditioning. AD/DA conversion is performed using commercially available converter NI 6221 from National Instruments. National Instruments high-speed multifunction data acquisition (DAQ) devices are optimized for superior accuracy at fast sampling rates. They have an onboard NI-PGIA2 amplifier designed for fast settling times and high scanning rates, ensuring 16-bit accuracy even when measuring all channels at maximum speeds. All high speed devices have a minimum of 16 analog inputs, 24 digital I/O lines, seven programmable input ranges, analog and digital triggering, and two counter/timers [3,4]. For DTA signal measurement, differential amplifier is used for amplification of temperature difference signal between two thermocouples (TC1 and TC2), while for TGA measurement serial port interface is used for data communication between PC and tha balance. The thermocouples TC3 and TC4 are for temperature measurement of furnaces and low pass filters eliminates any noise from the signals from all of the thermocouples. Power controller regulates the heater intensity and also switches the whole system on and off on demand. Measurement interface designed for the needs of this system is calibrated using high accurate measurement instruments predicted for laboratory instruments adjusting and have the next characteristics: - one analog control voltage input ±10 V for DTA signal, - two analog control voltage input s ±10 V for measuring temperatures of furnaces, with built in cold junction correction, - two analog voltage outputs ±10 V for furnaces control, - one digital control voltage output for system power control - serial port interface for data communication with radwag XA 110 balance, - one differential amplifier with amplification constant A=100, - furnace temperature range C. Fig. 1 Block diagram of TGA hardware 3 Software The software platform for predicted measurement methods was National Instruments LabVIEW package, which is regarded as a high standard in the area of modern virtual instruments. LabVIEW is MKOIEE ICREPS

3 based on the principles of virtual instruments with the graphical user interface [5]. Graphical user interface has two windows: - Control panel for process control and monitoring, - Application diagram which presents used virtual instruments, relations between them, the course of signals and error detection. In LabVIEW, one builds a user interface by using a set of tools and objects. The user interface is known as the front panel. One then add code using graphical representations of functions to control the front panel objects [6]. The block diagram contains this code (Fig. 2 and Fig. 3). DAQ Assistants are used for acquiring the input and generating output signals. Acquired signals from thermocouples are averaged because of eventual noise and measurement errors cancelation and sent to thermocouple linearizer which converts them to an actual temperature. Then PID controller [7] calculates current value of the output signal for the power controller based on desired heating rate. Graphs, text inputs, text controls and switches are also visible on the front panel (Fig. 4) and accessible to user for parameters input and viewing the results. Fig. 2 Application block diagram for DTA Fig. 3 Application block diagram for TGA 5. MKOIEE ICREPS 171

4 Fig. 4 DTA and TGA applications front panels 4 Results The system is tested in detail, which implies big number of tests successfully done with various materials, temperature ranges and working environments and it proved it s reliability and accuracy. Sample result of DTA and TGA done with this system are shown in Fig. 5 and Fig. 6. Fig. 5 Measured DTA diagram sample of land from the mining field Fig. 6 Measured TGA diagram - Calcium oxalate monohydrate sample MKOIEE ICREPS

5 5 Conclusion This system is developed using affordable devices, have a compact design and is equipped with high-resolution measuring interface. The result is the system which have characterisctics similar to most of commercial products of this type, can be used for in all phases of research, quality control, production operations etc. but from financial aspect it is much more affordable. 6 Acknowledgments The authors gratefully acknowledge financial support from the Ministry of Education and Science, Government of the Republic of Serbia through the Projects No References [1] R.F. Speyer, Thermal Analysis of Materials, Marcel Dekker, Inc., New York, 1994, pp [2] M.E. Brown, Introduction to Thermal Analysis: Techniques and Applications, 2nd ed., vol. 1. Kluwer Academic Publishers New York, Boston, Dordrecht, London, Moscow Print, 2004, pp [3] [4] [5] [6] [7] This is an open access article distributed under the CC BY-NC-ND 4.0 terms and conditions. The Proceedings is available at 5. MKOIEE ICREPS 173