IEEE International Workshop on Intelligent Data Acquisition and Advanced Computing Systems: Technology and Applications 21-23 September 2009, Rende (Cosenza), Italy 978-1-4244-4881-4/09/$25.00 ©2009 IEEE 201 The Control System of the Profile of Temperature Field Nadiya Vasylkiv, Orest Kochan, Roman Kochan, Mykhaylo Chyrka Research Institute of Intelligent Computer Systems Ternopil National Economic University nva@tneu.edu.ua, oko@tneu.edu.ua, roman.kochan@gmail.com Abstract - There is proposed method of control which could be implemented for heaters situated across electrodes of the main thermocouple and provides stabilization profile of temperature field. The proposed method has small requirements to memory space and computing power so it could be implemented using 8-bit microcontrollers. Keywords - temperature control, multi zone furnace, profile of the temperature field, microcontroller based system I. INTRODUCTION As it was presented in [1, 2], one of most dangerous and the little investigated (at the present time) component of thermocouple’s errors is error caused by heterogeneity of its thermoelectrodes obtained during exploitation. This error is related with degradation processes in thermoelectrodes caused by the influence of temperature and time of exploitation. There are two characters of display of the heterogeneity error [2]: as a conversion characteristic’s (CC) drift of thermocouples and as dependence of electro motion force (EMF) thermocouple not only from the difference of temperatures of hot and cold junctions but also from the profile of the temperature field between them – considerably bother a fight against influence of this error. In [3, 5] the method influence removal of the acquired heterogeneity is offered by creation it’s own profile of the temperature field, independent of external along the electrodes of main thermocouple of thermocouple with controlled profile of the temperature field (TCPTF). By the set of the heaters and sensors displaced along the axes of thermocouple and which are included in the additional temperature control subsystems. In this case an error caused the purchased heterogeneity of electrodes of thermocouples does not can directly to prove. The however offered method requires complication construction of thermocouple together with additional providing of his capacity due to work of the mentioned temperature control subsystems for all separate areas which create the set the profile of the temperature field along the electrodes of main thermocouple. Basic difficulty for their functionality is dependence of temperature for each zone of the temperature of other zones through the presence of process of transmission of heat along. This dependence creates the danger of excitation of the systems of adjusting (through the considerable delay of process of transmission of thermal influence between areas) and generation of heat-waves along the electrodes of main thermocouple. Therefore control influences of every area must be formed in a complex with other zones [6, 7]. Thus, task of temperature setting in TCPTF is enough difficult. The purpose of this paper is in development control method of profile of the temperature field along the electrodes of main thermocouple, which will allow to provide firmness and necessary exactness of establishment of the set profile without the necessity of difficult theoretical and experimental researches of adjusting object and will have low calculable complication, which will allow him to implement in the systems which are based on microcontrollers. II. BASIC IDEA OF THE PROPOSED METHOD The structure of TCPTF’s heaters is presented on fig.1. There are sections of heaters areas H 1…N…K situated on case of TCPTF. The electrodes of main thermocouple - MTC and thermocouples of temperature control subsystems Ts1…ТС N …ТС K are placed inside a case. All thermocouples are isolated between each other. Their hot junctions are situated in the centers of the proper heaters. Heaters H 1…K are isolated from environment by the layer of heat-insulation. Such construction allows to retain the set profile of the temperature field along the electrodes of MTC, which covers the possible changes of external profile of the temperature field. This profile is formed by the subsystem’s control commands and contained during exploitation and testing of main thermocouple. Thus, heterogeneity of main thermocouple can appear exceptionally as a drift of it CC. However much the same structure creates problems at control (establishment) of areas temperature. Fig. 1 show, that every heater generates four thermal flows: • 1 q oriented to the center of cover. In this case 1 q is useful, just he creates the set profile of the temperature field along electrodes of MTC; • 3 q opposite to 1 q , oriented outside of TBS. 3 q determines thermal losses, that is why his intensity is diminished by heat-insulation; • 2 q oriented to the next area of heater; • 4 q oriented to the previous area of heater. Presence of thermal flows 2 q and 4 q (and also them relatively high intensity, predefined that they go along metallic cover of TCPTF) determines the presence of good thermal connection between areas,