TEKA. COMMISSION OF MOTORIZATION AND ENERGETICS IN AGRICULTURE – 2013, Vol. 13, No. 1, 15–18 Automatic measurement of time constant for temperature sensors Artur Boguta, Marek Horyński Lublin University of Technology, Faculty of Electrical Engineering and Computer Science, Department of Computer and Electrical Engineering, Nadbystrzycka 38A, 20-618 Lublin, Poland, phone: (+48 81) 53-84-301, fax: (+48 81) 525-46-01, e-mail: a.boguta@pollub.pl, m.horynski@pollub.pl Received February 3.2013; accepted March 14.2013 Summary. The importance of temperature measurements is sigQL¿FDQWLQPDQ\SURFHVVHV7KHDFFXUDF\RIVDLGPHDVXUHPHQWV is essential for the tasks to be performed by a product and for its compliance with requirements of applicable standards. The maintenance of determined temperature regime in individual production process phases is essential for the quality of obtained SURGXFW$SDUWIURPWHPSHUDWXUHPHDVXUHPHQWDFFXUDF\WKHWLPH of sensors response to its change is also extremely important. The response time of temperature regulators and controllers ZKLFKPD\VLJQL¿FDQWO\DIIHFWWKHSDUDPHWHUVRI¿QLVKHGSURGXFW depends on the time of sensor response. The measurements of time constants for temperature sensors are time consuming and proper equipment and knowledge are also required for this purpose. It is rather unproblematic in case of piece production scale but in case of mass production it is necHVVDU\WR¿QGDVROXWLRQHQDEOLQJWKHDXWRPDWLRQRIWLPHFRQVWDQW measuring process and ensuring measurements repeatability. The solution presented in this study will make it possible to automate the process and to reduce the time of measurement. %\PHDQVRISURSHUVRIWZDUHLWZLOOEHSRVVLEOHWRUHDGWKH time constant from measuring system display. Key words: time constant, temperature, temperature sensor. 7+(6758&785(2)$6<67(0)25 $8720$7,&0($685(0(172)7,0( &2167$172)376(16256 The system enabling the measurement of time constant IRU37WHPSHUDWXUHVHQVRUVLVLOOXVWUDWHGLQ)LJ The measurement system consists of a hydraulic assemEO\HQVXULQJWKHÀRZRIÀXLGSUHKHDWLQJWKHVHQVRUEHLQJ WHVWHGDQGFKDQJLQJLWVÀRZUDWHLQLQGLYLGXDOSKDVHVRIV\VWHPRSHUDWLRQ,QWKHLQLWLDOSKDVHWKHÀXLGFLUFXODWHVLQWKH FLUFXLWFRQVLVWLQJRIZDWHUEDWKÀXLGFLUFXODWLQJWXEHVDQG FKHFNYDOYH,QWKLVRSHUDWLRQSKDVHWKHÀXLGÀRZVWKURXJK the system elements and heats the whole circuit. The purpose RIWKHFKHFNYDOYHLVWRHQDEOHWKHÀXLGÀRZZKLOHDQHOHFWUR – valve is closed. The latter opens in the second phase and WKHÀXLGLVVXSSOLHGWRWKHVHQVRUXQGHUWHVWFDXVLQJDVXGGHQ FKDQJHRIVHQVRUWHPSHUDWXUH$QDOJRULWKPUHFRUGLQJWKH sensor temperature change at sudden temperature change is triggered in this operation phase. Temperature changes are UHFRUGHGE\PHDQVRIRQHRIDQDORJXHWRGLJLWDO$'FRQverters of microcontroller. Resistance changes are recorded WLPHVVHFRQGE\PHDQVRIWKHPLFURFRQWUROOHU>@7KH UHFRUGLQJWLPHLVHTXDOWRVDQGLVFRPSOHWHO\VXI¿FLHQW WRHQVXUHWKHVWDELOL]DWLRQRI¿QDOWHPSHUDWXUHRIWKHVHQVRU XQGHUWHVW,QWHUQDOPHPRU\RI$7PHJDPLFURFRQWUROOHU is used to record the values of resistance vs. time. The resistance is recorded as a WORD type variable in the table RIYDULDEOHV>@$QRULJLQDOSURJUDPKDVEHHQFUHDWHG compiled and entered into the microcontroller memory in order to make it possible to determine three time constants 777>@7KHDOJRULWKPFDOFXODWLQJWKH time constants performs the analysis of recorded numerical YDOXHVGLVSOD\HGE\$'FRQYHUWHUDQGGHWHUPLQHVWKUHH YDOXHVLHDQGIRUWKHUHFRUGHGPD[LPXP value. The time elapsed between the system starting and occurrence of determined numerical values is determined on the basis of recorded measurement points (25 times /1s). Corresponding time constants measured by the system are VSHFL¿HGRQWKHEDVLVRIWLPHHODSVHGXQWLOWKHUHFRUGHG PD[LPXPYDOXHDFKLHYHGDQG$IWHU67$57 SXVKEXWWRQLVGHSUHVVHGWKHVLJQDOUHFHLYHGIURP$'FRQverter is continuously analyzed by the microprocessor triggering the measurement procedure when a positive change of sensor temperature is detected. $QRWKHUWDVNRIDSSOLHGPLFURFRQWUROOHUFRQVLVWVLQWKH measurement of water bath temperature and measuring cylLQGHUWHPSHUDWXUH'6%VHPLFRQGXFWRUVHQVRUVKDYH been used for temperatures measurements. The temperatures measurement makes it possible to determine the temperature unit step and to check its conformity with applicable standard [1, 5, 12]. $5785%2*87$0$5(.+25<ē6., Fig. 1. 7KHV\VWHPIRUPHDVXUHPHQWRIWLPHFRQVWDQWIRU37WHPSHUDWXUHVHQVRUV $IWHUFRPSOHWHGPHDVXUHPHQWWKHPHDVXUHGYDOXHVRI time constant are displayed, electro – valve is closed, the ÀXLGLVGLVFKDUJHGIURPPHDVXULQJF\OLQGHULQWRZDWHUEDWK and the fan is turned on in order to cool the system before the next measurement. The system has been equipped with a function protecting against an erroneous measurement (proper temperature difference, sensor not connected or damaged). In case of possibility of an erroneous measurement, the control system will make it impossible to turn on the system. Information DERXWHUURUVZLOOEHVKRZQRQ/&'GLVSOD\DQGLQGLFDWHG E\PHDQVRI/('FRQWUROOLJKWV>@ Figure 2 illustrates the schematic diagram of an electronic system performing the following functions: – temperatures control in course of system operation; – control of electro-valve operation, – control of cooling fan operation, ± PHDVXUHPHQWRI37VHQVRUUHVLVWDQFH – recording of resistance change vs. time, – calculation of time constant value for the sensor under tests. $95$WPHJDPLFURFRQWUROOHUSHUIRUPVWKHIXQFWLRQ of a system monitoring the operation of the whole measuring system. Said microcontroller supports an instrumentation DPSOL¿HUEDVHGXSRQDQLQWHJUDWHG1(RSHUDWLRQDPSOL¿HU>@7KHSXUSRVHRIWKLVDPSOL¿HULVWRPDWFKWKH6LJQDF UHFHLYHGIURP37WHPSHUDWXUHVHQVRUWRDGHTXDWHOHYHO UHTXLUHGE\$'FRQYHUWHU Completed measuring system has been tested in laboratory conditions. The tests were carried out on several PT VHQVRUVDQGGHPRQVWUDWHGWKDWWKHWLPHFRQVWDQWVIRU37 SODWLQXPWHPSHUDWXUHVHQVRUVDUHPHDVXUHGFRUUHFWO\E\ means of designed and completed system. 0($685(0(176 Completed system has been used for testing of temSHUDWXUHVHQVRUVEDVLQJXSRQ37PHDVXULQJHOHPHQW The measurements have been performed for more than ten sensors. The results of measurements for four (4) selected sensors have been presented in Table No 1. Ta b l e 1 . 7LPHFRQVWDQW7IRU37VHQVRUVORFDWHGLQVWHHO MDFNHWVZLWKVLOLFRQH¿OOLQJ Item 1 2 4 5 7 8 $YHUDJH Sensor No 1 Sensor No 2 6HQVRU1R Sensor No 4 T[s] T[s] T[s] T[s] Fig. 2. Schematic diagram of a control and measuring system for determination of temperature sensors time constants CRAMP $8720$7,&0($685(0(172)7,0(&2167$17)257(03(5$785(6(16256 17 18 $5785%2*87$0$5(.+25<ē6., The measurements presented in Table No 1 correspond IRUHYHU\RQH*yUHFNL3$QLQWURGXFWLRQWRPLFURSURto measurements performed manually by means of a stop cessors]. watch and digital multimeter. The results of measurements Górecki P. 2003: (OHNWURQLNDGODZV]\VWNLFK0LNURSURIRULQGLYLGXDOVHQVRUVLQVLJQL¿FDQWO\GLIIHUIURPHDFKRWKHU FHVRURZDRĞODáąF]ND$97QU 7KHGLIIHUHQFHFDQEHFDXVHGE\DQLQVLJQL¿FDQWFKDQJHRI >(OHFWURQLFVIRUHYHU\RQH*yUHFNL3$QLQWURGXFWLRQ VHQVRUUHVLVWDQFHDWWKHWLPHRI¿QDOWHPSHUDWXUHVWDELOL]Dto microprocessors]. WLRQDQGE\OLPLWHGUHVROXWLRQRI$'FRQYHUWHULQDSSOLHG 7. Górecki P. 2004: (OHNWURQLNDGODZV]\VWNLFK0LNURmicrocontroller. SURFHVRURZDRĞODáąF]ND$97QU >(OHFWURQLFVIRUHYHU\RQH*yUHFNL3$QLQWURGXFWLRQ to microprocessors]. &21&/86,216 8. Górecki P. 2005: (OHNWURQLNDGODZV]\VWNLFK0LNURSURFHVRURZDRĞODáąF]ND$97QU>(OHFWURQLFVIRUHYHU\RQH*yUHFNL3$QLQWURGXFWLRQWRPLFURSURFHVVRUV@ The time constants for the transducers under tests are measured correctly by means of presented system designed Hagel A. 1975: 0LHUQLFWZRG\QDPLF]QH:17:DUV]DIRUWKHGHWHUPLQDWLRQRIWLPHFRQVWDQWVIRU37WUDQVwa [Dynamic measurement techniques]. ducers. Obtained results are conforming with the results +RU\ĔVNL0,QGRU&OLPDWH&RQWUROLQ(,%6\VWHP&RPPLVVLRQRI0RWRUL]DWLRQDQG3RZHU,QGXVWU\ REWDLQHGE\PHDQVRIPDQXDOPHWKRG$'FRQYHUWHUZLWK LQ$JULFXOWXUH7(.$;, KLJKHUUHVROXWLRQELWYHUVLRQKDVEHHQXVHGLQWKHV\Vtem) can be used in order to increase the accuracy and re- 11. -DEáRĔVNL70LNURNRQWUROHU\3,&)%7&/HJLRQRZR>3,&)PLFURFRQWUROOHUV@ peatability of measurements. There is a problem in the system being tested due to 12. Kapica J. 2011: $SSOLFDWLRQRI0LFURFRQWUROOHULQ6LPquick cooling of measuring cylinder. The cylinder consists XODWLRQRIWKH3KRWRYROWDLF*HQHUDWRUV&RPPLVVLRQRI 0RWRUL]DWLRQDQG3RZHU,QGXVWU\LQ$JULFXOWXUH7(.$ of a copper tube characterized by good heat conductivity ;, EXWLWVKHDWFDSDFLW\LVKLJK7KLVVLJQL¿FDQWKHDWFDSDFLW\ slows down the measuring cylinder process before the next Michalski L, EckersdorfK. 1980:Pomiary temperatury. PHDVXUHPHQW7KHDSSOLFDWLRQRIPRUHHI¿FLHQWPHDVXULQJ WNT Warszawa [Temperature measurements]. F\OLQGHUSURFHVVE\PHDQVRIDIDQZLWKLQFUHDVHGHI¿FLHQF\ 14. Michalski l., Eckersdorf K. 1971: Pomiary temperatury, RUE\PHDQVRIÀXLGFRXOGVLJQL¿FDQWO\UHGXFHWKHWLPH WNT Warszawa, Wyd. II [Temperature measurements]. 15. Pawluczuk A. 2006: Sztuka programowania mikrokonrequired to complete next measurements. WUROHUyZ$95%7&:DUV]DZD>7KHDUWRI$95PLFURcontrollers programming]. 3ROVND1RUPD(1$ 5()(5(1&(6 17. Tietze U. Schenk CH. 1993: 8NáDG\ SyáSU]HZRGnikowe. WNT Warszawa [Semi-conductor systems]. 1. Baranowski R. 2005: 0LNURNRQWUROHU\$95$7PHJD ZSUDNW\FH%7&/HJLRQRZR>$95$7PHJDPLFURFRQ- 18. :Lą]DQLD03URJUDPRZDQLHPLNURNRQWUROHUyZ ZMĊ]\NX%$6&20%7&:DUV]DZD>0LFURFRQWUROtrollers in practice]. 2. Brzoza-Woch R. 2010: 0LNURSURFHVRU\$7$0 OHU3URJUDPPLQJLQ%$6&20@ :Lą]DQLD0%DVFRP$95ZSU]\NáDGDFK%7& %7&/HJLRQRZR>$7$0PLFURSURFHVVRUV@ /HJLRQRZR>$95LQH[DPSOHV@ 'ROLĔVNL-0LNURNRQWUROHU\$95ZSUDNW\FH Wierzbicki S. 2006: Diagnosing microprocessor-con%7&/HJLRQRZR>$950LFURFRQWUROOHUVLQSUDFWLFH@ 4. 'ROLĔVNL-0LNURNRQWUROHU\$95QLH]EĊGQLN WUROOHGV\VWHPVV7(.$&RPPLVVLRQRI 0RWRUL]DWLRQDQG3RZHU,QGXVWU\LQ$JULFXOWXUH SURJUDPLVW\%7&/HJLRQRZR>$95PLFURFRQWUROOHUV 21. :RáJDMHZ50LNURNRQWUROHU\$95GODSRF]DWprogrammer’s toolbox]. NXMąF\FK%7&/HJLRQRZR>$950LFURFRQWUROOHUVIRU 5. Górecki P. 2002: (OHNWURQLNDGODZV]\VWNLFK0LNURSURbeginners]. FHVRURZDRĞODáąF]ND$97QU>(OHFWURQLFV