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
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of sensors response to its change is also extremely important.
The response time of temperature regulators and controllers
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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.
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time constant from measuring system display.
Key words: time constant, temperature, temperature sensor.
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The system enabling the measurement of time constant
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The measurement system consists of a hydraulic assemEO\HQVXULQJWKHÀRZRIÀXLGSUHKHDWLQJWKHVHQVRUEHLQJ
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the system elements and heats the whole circuit. The purpose
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– valve is closed. The latter opens in the second phase and
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sensor temperature change at sudden temperature change is
triggered in this operation phase. Temperature changes are
UHFRUGHGE\PHDQVRIRQHRIDQDORJXHWRGLJLWDO$'FRQverters of microcontroller. Resistance changes are recorded
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is used to record the values of resistance vs. time. The resistance is recorded as a WORD type variable in the table
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compiled and entered into the microcontroller memory in
order to make it possible to determine three time constants
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time constants performs the analysis of recorded numerical
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value. The time elapsed between the system starting and
occurrence of determined numerical values is determined
on the basis of recorded measurement points (25 times /1s).
Corresponding time constants measured by the system are
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PD[LPXPYDOXHDFKLHYHGDQG$IWHU67$57
SXVKEXWWRQLVGHSUHVVHGWKHVLJQDOUHFHLYHGIURP$'FRQverter is continuously analyzed by the microprocessor triggering the measurement procedure when a positive change
of sensor temperature is detected.
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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].
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time constant are displayed, electro – valve is closed, the
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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
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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,
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– recording of resistance change vs. time,
– calculation of time constant value for the sensor under tests.
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of a system monitoring the operation of the whole measuring
system. Said microcontroller supports an instrumentation
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Completed measuring system has been tested in laboratory conditions. The tests were carried out on several PT
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means of designed and completed system.
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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.
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Sensor No 1 Sensor No 2 6HQVRU1R Sensor No 4
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Fig. 2. Schematic diagram of a control and measuring system for determination of temperature sensors time constants
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The measurements presented in Table No 1 correspond
IRUHYHU\RQH*yUHFNL3$QLQWURGXFWLRQWRPLFURSURto measurements performed manually by means of a stop
cessors].
watch and digital multimeter. The results of measurements Górecki P. 2003: (OHNWURQLNDGODZV]\VWNLFK0LNURSURIRULQGLYLGXDOVHQVRUVLQVLJQL¿FDQWO\GLIIHUIURPHDFKRWKHU
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WLRQDQGE\OLPLWHGUHVROXWLRQRI$'FRQYHUWHULQDSSOLHG 7. Górecki P. 2004: (OHNWURQLNDGODZV]\VWNLFK0LNURmicrocontroller.
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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\
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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
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of a copper tube characterized by good heat conductivity
;,
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slows down the measuring cylinder process before the next Michalski L, EckersdorfK. 1980:Pomiary temperatury.
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WNT Warszawa [Temperature measurements].
F\OLQGHUSURFHVVE\PHDQVRIDIDQZLWKLQFUHDVHGHI¿FLHQF\ 14. Michalski l., Eckersdorf K. 1971: Pomiary temperatury,
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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].
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17. Tietze U. Schenk CH. 1993: 8NáDG\ SyáSU]HZRGnikowe. WNT Warszawa [Semi-conductor systems].
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