temperature technical

8/9/2019 Temperature Technical

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Proceedings of the 2ndMAE paper writingMAE241

Spring 2011, Coral Gables, Florida, SA

!"!2011#241

!EMPE$A!$E MEAS$EME%! S&%G A $ES&S!A%CE !EMPE$A!$E'E!EC!($ A%' !)E$M(C(P*E

!hien "an !ranMAE 241

Coral Gables, Florida, SA

A+S!$AC!A resistance temperature detector and thermocouple

were used to measure the time constant as a result ofstep changes in temperature. The RTD produced 3.12!" 1.#1!s for the step up in temperature$ and 4.1##! "3.!#s for the step down. The thermocouple produced%.!#2% " %.1&''s for the step up and %.422' " 2.1'!&sfor the step down. (or the RTD$ time of rise from 1%) to%) was #.2! " 1.!! seconds$ while the fall time was.1!4# " &.'%2 seconds. (or the thermocouple$ the risetime was 1.23! " %.33 seconds while the fall time was%.2 " 4.'%2 seconds. All calculations were associatedwith a !) confidence inter*al.

&%!$('C!&(%Resistance Temperature Detectors +RTDs, and

Thermocouples are -oth first order instruments formeasuring temperature. The RTD measures the changein temperature - detecting changes in resistance as asmall current is passed through the resistor element. Thista/es ad*antage of the accurate direct relationship-etween temperature and resistance. The RTD consistsof a length of fine coiled wire wrapped around a core ofglass or ceramic. The RTD is made of a single metal$whose resistance at temperatures is documented andstandardi0ed.

The thermocouple measures *oltage changes

due to temperature changes 1. t is made up of twodissimilar metals$ oined together at a single end. Theappear in the form of a wire. The RTD is used foraccurate readings o*er narrow temperature spans$ whilethe thermocouple is used for reading e5treme ranges 2.Therefore the RTD will ha*e a much longer responsethan the thermocouple. 6sing sudden e5tremetemperature differences$ the time constant +, for rise andfall of temperature was determined for each sensor.

%(ME%C*A!$ET Temperature

Temperature reached at infinit

nitial temperatures 7econdst Time

6ncertaint associated with precision

7tudent8s t9distri-ution *alue: 1 ; confidence inter*al

7tandard de*iation<


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until the reading stopped decreasing$ at which point thetime was started and the pro-e was transferred to the-oiling water. The *alues displaed - the RTD wererecorded. This was repeated for a second set of data.This process was then re*ersed$ so that the pro-e wasinitiall placed in the -oiling water and then transferred tothe ice water solution. This was repeated to o-tain twosets of *alues. The results for the RTD measurementscan -e seen in figure1$ and the *alues for thethermocouple can -e seen in figure 2.

(igure 1. @lot showing measurements from RTD sensor for step up intemperature

(igure 2. Measurements from RTD for step down in temperature

(igure 3. =raph showing the lineari0ation of RTD step up in temperaturee5ponential$ trial 1

2 Copyright 2009 by ASME


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(igure 4. =raph showing the lineari0ation of RTD step up in temperaturee5ponential$ trial 2

(igure !. =raph showing the lineari0ation of RTD step down in temperaturee5ponential$ trial 1

(igure #. =raph showing the lineari0ation of RTD step down in temperaturee5ponential$ trial 2

(igure &. Thermocouple step up measurements in temperature

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(igure '. Thermocouple measurements for step down temperature

There were onl three *alues that appearedconsecuti*el with enough room in -etween to anal0eand fit to the model of e>uation +1,. owe*er$ since there

were less data points to fit$ the lineari0ation was muchmore accurate$ as illustrated in figures and 1% with r9s>uared *alues close to one.

Figure 9. Linearization of thermocouplestep up in teperature

(igure 1%. Bineari0ation of thermocouple step down in temperature

$ES*!SThe a*erage time response constant was

calculated to -e 3.12! " 1.#1!s for the RTD rise$ and

4.1##! " 3.!#s for the fall. (or the thermocouple$ wascalculated to -e %.!#2% " %.1&''s for the rise and %.422'" 2.1'!&s for the fall. The rise time to go from 1%) to%) of the step was calculated using the followinge>uation?

+2,

The rise time for the RTD was #.2! " 1.!! secondswhile the fall time was .1!4# " &.'%2 seconds. (or thethermocouple$ the rise time was determined to me 1.23!" %.33 seconds while the fall time was %.2 " 4.'%2seconds. All error -ands are presented with a !)

confidence inter*al.

A%A*-S&SThe e>uation +1, was lineari0ed to ma/e analsis

possi-le in MATBAC. The cur*es were plotted$ and E5ce

was used to create lines of -est fit. C adusting the

*alues manuall$ the r9s>uared *alue$ or the coefficient oflinear correlation$ changed to approach the num-er oneThe results of this lineari0ation are illustrated in figures 3and 4 for the rise in RTD$ and figures ! and # for the RTD

down. The closest -ecame the num-er used in the

actual Tau calculations. The instruments were nopro*ided with an -ias error$ and therefore the onl error

resulted from precision -ias$ which was calculated usingthe following e>uation?

+3,

The -ias was calculated using a confidence inter*al of!). The error was relati*el high$ since onl twoseparate samples were used for the e*aluation of the

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time constant. owe*er$ since there was relati*el littlehuman interaction in ac>uiring data points$ these errorsdid not propagate into larger *alues during calculations.7ources of error were associated with the placing of thetemperature pro-es$ for -oth sensors. (or the RTD$ theposition of the pro-e in the ice water solution affected thetemperature measured. 7ince the ice floated to thesurface$ placing the pro-e at *aring depths wouldproduce inaccurate temperature readings. n the case ofthe thermocouple$ the temperature reading umped o*er

1%%elsius at se*eral points. This ma ha*e -een dueto the contact end touching the sides or -ottom of the-ea/er$ since li>uid water is una-le to reach atemperature of o*er 1%%. Also$ the color of the water wasslightl purple$ and ma ha*e contained dissol*edchemicals from the temperature pro-e that caused the-oiling point to rise.

The thermocouple had a rise time of 1.23! "%.1&''s$ which was appro5imatel si5 times less thanthat of the RTD. Thus$ ac>uiring points that werescattered -etween the temperature e5tremes wasdifficult$ as seen in figures & and '.

C(%C*S&(%The time constant of the resistance

temperature detector was e*aluated to -e 3.12! "1.#1!s for the step up in temperature$ and 4.1##! "3.!#s for the step down. (or the thermocouple$ the timeconstant was calculated to -e %.!#2% " %.1&''s for thestep up and %.422' " 2.1'!&s for the step down. Thetime to rise and fall -etween 1%) and %) of thetemperatures was also determined. (or the RTD$ time of

rise was #.2! " 1.!! seconds$ while the fall time was.1!4# " &.'%2 seconds. (or the thermocouple$ the risetime was determined to -e 1.23! " %.33 seconds whilethe fall time was %.2 " 4.'%2 seconds. These error-ands were all calculated for a !) confidence inter*alThe time constant did not seem to depend on the si0e ofthe temperature step$ -ut it did seem to -e affected -direction. The tau for stepping up was smaller than that ofstepping down.

The rise time for the thermocouple was indeed

much smaller than that of the RTD$ which supports thefact that each instrument was -uilt for differing purposesThe RTD is more useful in measuring temperatures in anarrow range$ ma/ing its response time less critical. Thethermocouple is more functional in measuring e5treme

temperature ranges$ appro5imatel -etween 92#& and

231# 4.

$EFE$E%CES"1# $urns Engineering% &n'. ()* or )hero'oup+e,http-///.burnsengineering.'oo'uentpapersrtsthero'oup+e.pf

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