Alabama A&M UniversitySchool of Engineering and TechnologyDepartment of Mechanical Engineering

ME 301L-Analysis /Instrumentation of Physical Systems

Lab #6

Temperature Measurments Using Thermistor

Cameron Alexander

March 19, 2013

Abstract

A thermocouple consists of two dissimilar conductors in contact, which produces

a voltage when heated. The size of the voltage is dependent on the difference of

temperature of the junction to other parts of the circuit. Thermocouples are a widely used

type of temperature sensor for measurement and control and can also be used to convert a

temperature gradient into electricity. Commercial thermocouples are inexpensive,

interchangeable, are supplied with standard connectors, and can measure a wide range of

temperatures. In contrast to most other methods of temperature measurement,

thermocouples are self-powered and require no external form of excitation. The main

limitation with thermocouples is accuracy; system errors of less than one

degree Celsius (°C) can be difficult to achieve.[3]

Introduction

During this lab, we conducted an experiment to demonstrate how thermocouples

can be converted into an electrical signal. We used a program called Lab View. We were

able to analyze the forces using a load cell with temperature generated by our hands.

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Experimental Procedure

1. Use Lab View DAQ system to acquire temperature data from the thermocouple.

2. Turn on the NI-Module and Connect USB to computer.

3. Start: Programs: National Instruments: Lab View 8.5

4. With MAX open, select Data Neighborhood and click Create New.

5.  Select NI-DAQmx Global Virtual Channel and click Next.

6. Select Acquire Signals» Analog Input» Temperature» Thermocouple.

Figure 1. Creating an NI-DAQmx Virtual Channel

7. Creating an NI-DAQmx Virtual Channel

8. Select ai0 or whichever physical channel you intend to connect to your

thermocouple. A physical channel is a terminal or pin at which you can measure

or generate an analog or digital signal. A single physical channel can include

more than one terminal or pin, as in the case of a differential thermocouple input

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channel. In this case, ai0 corresponds to TC0+ and TC0- on the NI USB-9213

pinout diagram.

Figure 2. Device Physical Channels

9. Click Next and enter a name for the global virtual channel or leave the default.

10. Click Finish and you should see the following screen in MAX:

Figure 3. Setting Up a Thermocouple Channel in MAX

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11. On the settings tab, type in the minimum and maximum temperature values you

expect to read from your thermocouple (0 to 100 °C by default).

12. Select your thermocouple type and CJC Source and CJC Value.

13. With NI-DAQmx global virtual channels, you can preview your measurements.

14. With MAX still open, click back on the NI-DAQmx Global Virtual Channel tab and click on the Run button. You see the temperature value of your thermocouple displayed at the top of the screen.

Figure 4. Previewing a Thermocouple Measurement in MAX

15. You can choose to view the signal in tabular form or as a graph by selecting

Graph from the Display Type pull-down menu. You also have the option of

saving your NI-DAQmx Global Virtual Channel should you wish to refer to this

configuration screen again in the future.

16. under Hardware Input and Output» DAQmx» Analog Input» Thermocouple

- SW-Timed Input.vi, and is attached to the end of this article. The front panel of

this example allows the user to:

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a) Select the physical channel(s) of the device from which the thermocouple data

will be taken

b) Set the maximum and minimum temperature range

c) Select the thermocouple type from a list of supported types

d) Choose the physical units to scale the data 

e) Select a source, channel, and value for cold-junction compensation (CJC)

f) Configure the auto zero mode

Figure 8. Thermocouple Example Front Panel

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Results

Lab VIEW MeasurementWriter Version 2Reader Version 2

Separator TabDecimal Separator .

Multi Headings NoX_Columns OneTime Pref AbsoluteOperator Cameron Alexander

Date 3/5/2013Time 15:20.1

Channels 1Samples 10

Date 3/5/2013Time 15:20.9

Y_Unit_Label Deg CX_Dimension Time

X0 0.00E+00Delta_X 0.2

X Value Temperature0 16.41509

0.2 16.415090.4 16.415090.6 16.9589240.8 16.9589241 16.958924

1.2 17.3503441.4 17.3503441.6 17.3503441.8 17.6779992 17.677999

2.2 17.6779992.4 18.0068112.6 18.0068112.8 18.0068113 18.381494

3.2 18.3814943.4 18.3814943.6 18.74614

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3.8 18.746144 18.74614

4.2 19.069854.4 19.069854.6 19.069854.8 19.3554785 19.355478

5.2 19.3554785.4 19.6724765.6 19.6724765.8 19.6724766 20.019479

6.2 20.0194796.4 20.0194796.6 20.3655836.8 20.3655837 20.365583

7.2 20.6526357.4 20.6526357.6 20.6526357.8 20.7768648 20.776864

8.2 20.7768648.4 20.9261528.6 20.9261528.8 20.9261529 21.194152

9.2 21.1941529.4 21.1941529.6 21.4548999.8 21.45489910 21.454899

10.2 21.73843610.4 21.73843610.6 21.73843610.8 22.04830811 22.048308

11.2 22.04830811.4 22.34436411.6 22.34436411.8 22.34436412 22.585821

12.2 22.58582112.4 22.585821

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12.6 22.81686412.8 22.81686413 22.816864

13.2 23.03520813.4 23.03520813.6 23.03520813.8 23.22931514 23.229315

14.2 23.22931514.4 23.40462414.6 23.40462414.8 23.40462415 23.611054

15.2 23.61105415.4 23.61105415.6 23.79529215.8 23.79529216 23.795292

16.2 23.99321916.4 23.99321916.6 23.99321916.8 24.17474417 24.174744

17.2 24.17474417.4 24.35629717.6 24.35629717.8 24.35629718 24.552428

18.2 24.55242818.4 24.55242818.6 24.76504618.8 24.76504619 24.765046

19.2 24.95725119.4 24.95725119.6 24.95725119.8 25.13677620 25.136776

20.2 25.13677620.4 25.33285220.6 25.332852

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Conclusion

This lab was very effective. It thoroughly explains the concepts needed to be

explained. I was able to see a real world application of the given concept so that I can use

it later in my engineering life. However, a more simplistic breakdown during the class

lecture would be greatly appreciate. With that, we will be able to better understand

certain concepts once the lab starts instead on going in blind. Still, this lab was very

effective and should continue to be used.

References Laboratory Notes

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