Samostojni zapisovalnik temperature s termočleni

ŠTRANCAR, MATJAŽ (author), Jankovec, Marko (mentor)

Cilj magistrskega dela je izdelati samostojno napravo za meritev temperature z osmimi termočleni. Ta naprava nam lahko služi pri analizi segrevanja testnih vezji v delovanju in nam tako poda informacijo ali se analizirani deli vezja oziroma komponente na vezju segrevajo še znotraj dopustnega temperaturnega območja. Izdelana naprava je prenosljiva, saj je baterijsko napajana, lahko se pa tudi napaja prek priključka mikro USB, preko katerega je mogoče tudi polnjenje baterije. Ima osem priključkov za termočlene in režo za pomnilniško kartico mikro SD na kateri lahko uporabnik nastavi želeno konfiguracijo delovanja naprave. Meritve lahko prožimo bodisi s pritiskom na ustrezno tipko ali pa s pravokotnim signalom na priključku BNC naše naprave ter izpisujemo na zaslonu OLED in v datoteko na pomnilniški kartici. Ker so termočleni naprave, katerih izhod je zelo majhen signal je bil največji izziv načrtovanje analognega dela vezja, ki skrbi za ojačenje tega signala. Dodaten izziv pa nam je predstavljala sama postavitev temperaturnega senzorja, ki meri temperaturo hladnega spoja. Želeno merilno območje naše naprave je od –40 °C do 200 °C. Še dopustno je odstopanje meritev v obsegu ±1 °C. Z meritvijo v temperaturni komori smo pridobili rezultate odstopanja izmerjene temperature od dejanske vrednosti, izmerjene z umerjeno napravo za meritev temperature. Meritve čez celo temperaturno območje na dveh izbranih termočlenih naše naprave so podane v grafu. Iz katerega je razvidno, da izmerjena temperatura najmanj odstopa na termočlenu TC3 pri temperaturi 90 °C, kjer je odstopanje 0,01 °C. Najbolj pa odstopa na termočlenu TC5, pri temperaturi –45 °C, kjer je odstopanje od dejanske vrednosti 1,12 °C. K merilni napaki prispeva več izvorov, zato napako delimo na absolutno, ki se nanaša na celotno merilno območje in relativno napako, ki se nanaša na izmerjeno temperaturo. K vsaki napaki se prišteje še napaka zaradi temperaturnega koeficienta, ki je pogojena s temperaturo naše merilne naprave. Z upoštevanjem vseh lahko merilno negotovost podamo v enačbi (8.11). Z izračunom (8.13), kjer vzamemo za primer meritev temperature –40 °C in najslabšo možno temperaturo okolice pa pokažemo, da bi bila merilna negotovost naše naprave v tem primeru ±1,79 °C.

• Language: Slovenian
• Keywords: termočlen, zapisovalnik temperature, mikrokrmilnik
• Work type: Master's thesis/paper
• Organization: FE - Faculty of Electrical Engineering
• Year: 2018
• PID: 20.500.12556/RUL-100912
• Publication date in RUL: 20.04.2018

Secondary language

• Language: English
• Title: Standalone temperature data logger with thermocouples

Abstract

Purpose of this master thesis is to create a standalone device for measuring temperatures by eight thermocouples. This device can be used to analyse thermal properties of electronic circuits to check if any part or component of the circuit is heating outside of the nominal temperature range. Device can be powered directly from the battery or micro USB connector which also charges the internal battery. It has eight connectors for thermocouples and connector for memory card micro SD on which desired configuration of device is stored. There are two ways to trigger measurements. First way is simply by pressing the trigger button, while second trigger can be issued by providing a digital signal to the input connector BNC. All measurements results are displayed on the display OLED and stored in a file on a memory card. Thermocouple is differential device that has a small output signal so a lot of effort was payed to the analog section of a circuit that amplifies this signal and minimizes noise of the measurement. Special attention was payed to place the temperature sensor as close as possible to the cold junction of the thermocouples. Desired temperature measuring range of our device is –40 °C to 200 °C with allowable deviation of ±1 °C. Measurements performed in temperature chamber gave us deviation of measured temperature with our device compared to temperature measured with calibrated device. These measurements were made on two different thermocouples and are presented in graph at the end of this thesis. Minimum deviation was achieved on thermocouple TC3, where temperature differ for 0,01 °C. Maximum deviation was measured on thermocouple TC5 at temperature –45 °C, where deviation was 1,12 °C. We divide total error on absolute error, which relates to whole measuring range and relative error which relates only on temperature measured with our device. In addition, we must consider also temperature coefficient which relates to temperature of our measuring device. In equation (8.11) we pass total uncertainty of our measurements. With equation (8.13) we can take for example temperature measurement at –40 °C in worst case ambient temperature and calculate that total measurement uncertainty would be ±1,79 °C.

• Keywords: thermocouple, temperature data logger, temperature measurement