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TEMPERATURE LAB

OBJECTIVES

MATERIALS

NI LabVIEW 8.5.1 or later NI ELVIS II Series Benchtop Workstation NI ELVIS II Series Prototyping Board AC-DC power supply NI ELVISmx 4.0 or later CD High-speed USB 2.0 cable Computer Wires to build circuits Vernier Analog Proto Board Connector (Order Code BTA-ELV) Vernier Surface Temperature Sensor (Order Code STS-BTA)

THEORY

The Surface Temperature Sensor consists of an exposed thermistor. A thermistor is a special kind of resistor whose resistance varies significantly with temperature. Thermistors are manufactured from semiconductor material whose resistivity depends exponentially on ambient temperature. Specifically, this sensor uses the 20 kΩ NTC Thermistor whose resistance decreases nonlinearly with increasing temperature. You can rearrange the voltage divider equation to calculate the thermistor resistance from the input voltage measured by the NI ELVIS II Series. The rearranged voltage divider equation is as follows:

R = R1 *VT/(Vs - VT)

Where R = thermistor resistance, R1 = reference resistance (20 kΩ in this case), VT = measured voltage, and Vs = supply voltage.

This lab uses a LabVIEW program to calculate the thermistor resistance from the above equation and to convert the resistance into temperature using the Steinhart-Hart equation for the 20 kΩ NTC Thermistor:

T = [1.02119-3 +2.2246-4(lnR)+1.33342-7(lnR)3]-1

Where R = thermistor resistance in ohms.

(Summarized from the Surface Temperature Sensor User Guide; http://www.vernier.com)

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BUILDING THE EXPERIMENT ON ELVIS II SERIES

The Vernier sensor attaches to NI ELVIS II Series through the Analog Proto Board Connector. The following steps and Figure 1 below illustrate how to connect the Analog Proto Board Connector to the NI ELVIS II Series Prototyping Board.

Figure 1: Connecting the Analog Proto Board Connector to NI ELVIS II Series

Connect the following pins to wire the connector:

1) AI0+ to SIG1 of the Analog Proto Board Connector2) +5V DC power supply to 5V of the Analog Proto Board Connector3) GROUND power supply to GND of the Analog Proto Board Connector4) AIGND to GND of the Analog Proto Board Connector

RUNNING THE EXPERIMENT

To set up the experiment on NI ELVIS II Series:

1) Connect the USB cable from NI ELVIS II Series to your computer and plug the power supply into a power outlet.

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2) Turn the prototyping board power switch located on the rear panel to the on position (see Figure 2).

3) Turn the prototyping power supply switch located on the benchtop workstation to the on position (see Figure 2).

A green power LED should now be lit, indicating that the full power supply is turned on.

A yellow USB ready LED should also be lit, indicating that the NI ELVIS II Series is properly connected to the USB host.

4) Insert the surface temperature sensor into the Analog Proto Board Connector connected to AI 0+.

Figure 2: NI ELVIS II Series Set-Up

To set up the experiment in LabVIEW:

1) Open the LabVIEW program NI Temperature Lab.vi.2) If the front panel is not already displayed, go to “Window” and select “Show Front Panel”.

The front panel is shown below in Figure 3. The Temperature (C) vs. Time graph displays the temperature recorded by the

surface temperature sensor in Celsius. The Temperature (F) vs. Time graph displays the temperature recorded by the

surface temperature sensor in Fahrenheit. The thermometer indicators to the left of the graphs show the temperature data

from the sensor in a thermometer format. The maximum, minimum, and median temperature indicators display the maximum,

minimum, and median temperatures recorded over the entire length of the experiment, respectively.

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The Physical Channels dropdown menu allows you to choose the device and channel from which to acquire data.

The default experiment length is 30 seconds. The default sampling rate is 1000 samples per second. Switching the “Write to file?” Boolean to ON allows you to save the data as a .lvm file. The “STOP” button will terminate data collection at any point during the

experiment.

Figure 3: Temperature Front Panel

DATA COLLECTION

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Part 1: Skin temperature measurements

The first part of this lab is designed to familiarize you with the surface temperature sensor. Temperature measurements will be taken at various areas of your skin and the trends will later be analyzed. An example front panel from these experiments is shown below in Figure 4.

Fingertip temperature

1) Choose the correct device and channel in the Physical Channels dropdown menu that corresponds to your NI ELVIS II Series.

2) Verify that the length of the experiment has not changed from 30 seconds.3) Press the run arrow button in the upper left-hand corner of the screen to begin collecting

data.4) Place the end of the temperature sensor between your thumb and index finger. Hold the

sensor tightly until the end of the measurement process.5) Record the maximum, minimum, and median temperatures in Table 1.6) Repeat steps 1-5 for each student.

Arm temperature

1) Repeat steps 1-3 from the fingertip temperature steps.2) Place the end of the temperature sensor against an area of your forearm. Hold the sensor

there until the end of the measurement process. 3) Record the maximum, minimum, and median temperatures in Table 2.4) Repeat steps 1-4 for each student.

Cheek temperature

1) Repeat steps 1-3 from the fingertip temperature steps.2) Place the end of the temperature sensor against your cheek. Hold the sensor there until the

end of the measurement process.3) Record the maximum, minimum, and median temperatures in Table 3.4) Repeat steps 1-4 for each student.

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Figure 4: Example Experiment Front Panel

Part 2: Respiration measurements

The second part of this lab will demonstrate how the temperature sensor can be used for respiration studies by displaying the change in temperature from your breaths. An example front panel from this experiment is shown below in Figure 5.

1) Choose the correct device and channel in the Physical Channels dropdown menu that corresponds to your NI ELVIS II Series.

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2) Verify that the length of the experiment has not changed from 30 seconds.3) Press the run arrow button in the upper left-hand corner of the screen to begin collecting

data.4) Place the end of the temperature sensor directly under your nose without actually touching

your nose. Breathe normally, in and out, until the measurement process stops.5) Take a screenshot of the front panel for future reference.6) Repeat steps 1-5 for each student.7) Now repeat the above steps but have each student run in place for 3 minutes before running

the experiment.

Figure 5: Example Front Panel for Respiration Experiment

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DATA ANALYSIS

Part 1: Skin temperature measurements

Table 1: Maximum, Minimum, and Median Fingertip Temperatures for Each Student

Student Name Max. Temp C F

Min. Temp C F

Median Temp C F

Table 2: Maximum, Minimum, and Median Arm Temperatures for Each Student

Student Name Max. Temp C F

Min. Temp C F

Median Temp C F

Table 3: Maximum, Minimum, and Median Cheek Temperatures for Each Student

Student Name Max. Temp C F

Min. Temp C F

Median Temp C F

1) Compare your data with the data of the other members in your group. Does their data follow the same trends as your data?

2) Why would certain areas of the body have a higher surface temperature than other areas?3) Using your answer from the previous question, explain why extremities are the first areas

to succumb to frostbite.

Part 2: Respiration measurements

1) Analyze the screenshot of your personal data from the normal breathing experiment. Count the number of peaks in the temperature graphs and record the number in

Table 4. Multiply the number of peaks by 2 to estimate the number of breaths per minute.

Record this value in Table 4 as your respiratory rate.

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Table 4: Respiratory Rate for Each Student

Student Name Number of Peaks Estimated Respiratory Rate (Breaths per min.)

2) Analyze the screenshot of your personal data from the breathing experiment after physical activity.

Count the number of peaks in the temperature graphs and record the number in Table 5.

Multiply the number of peaks by 2 to estimate the number of breaths per minute. Record this value in Table 5 as your respiratory rate after physical activity.

Table 5: Respiratory Rate for Each Student After Physical Activity

Student Name Number of Peaks Estimated Respiratory Rate (Breaths per min.)

3) What factors could affect respiratory rate?4) Compare the data in Table 4 with the data in Table 5. Do you see a difference?5) Does fitness level appear to make a difference in the data?6) How could respiratory rate measurements be used for diagnosing an illness?

CHALLENGE

This section of the lab will introduce some of the basic concepts about the code used to produce this program. This is meant to give you a chance to explore LabVIEW code and to begin to understand how the program is structured.

The front panel of the VI (see Figure 3) is referred to as the user interface and displays the data acquired by the signal. In this lab, the data is displayed on two waveform charts – one showing Temperature vs. Time in Celsius and the other showing Temperature vs. Time in Fahrenheit. The properties of each chart can easily be altered to change the visual appearance of the plot area (see Figure 6):

1) Select the Temperature ( C) vs. Time chart.2) Right click >> Properties.

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Figure 6: Changing Chart Properties

3) On the properties pop-up menu, look through the tabs to see the different options available. Under the Plots tab, change the color of the plot. Explore the different options to represent the data.

4) Is there a better way to represent the data you have collected? 5) Select the chart again, right click, and move your mouse to show the Visible Items menu.

Select the varying options to explore the different tools you can view that are connected to the chart. Would any of the options be useful in helping you to collect and record more accurate data? How so?

6) Move your mouse over the “Write to file?” Boolean. Booleans are used when you want the user to select between two options. Right click to show the different options. Select “Replace” and move your mouse over the Boolean palette to explore the different options for displaying your Boolean (see Figure 7). The palette displays different graphical options for representing your Boolean.

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Figure 7: Boolean Options

The above options show just a few ways you can modify the front panel to suit your particular application to make a clean, easy-to-follow user interface. Now, switch to the block diagram to display the code (Window>>Show Block Diagram). This code is responsible for taking the user input, acquiring the signal from ELVIS II Series, manipulating the data to display it in the desired output, and displaying the data.

Figure 8: Signal Acquisition, Manipulation, and Display

7) The DAQmx VIs (see Figure 8) automatically acquire the signals read in from the temperature sensor. The DAQmx Read VI (icon with reading glasses) reads in the signal from the sensor and stores it into a channel. This data is output from the DAQmx Read VI in the thick orange wire. Following the data flow through the orange wire, the data flows through two paths: one leading to the subVI that outputs the temperature in Celsius and one leading to the subVI that outputs the temperature in Fahrenheit. HINT: Press Ctrl+H to show the Context Help pop-up box. As you move your mouse over the screen, information and properties about the different icons will appear in the Context Help box. This should help you determine the functions of the different parts on the block diagram.

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8) Using the Context Help tool, explore the properties of a Waveform Chart. What kind of data is accepted for a Waveform Chart? What type of chart results from each type of data?

9) With the Context Help tool still activated, hold your mouse over the wire leading into the Waveform Chart. What type of data is “flowing through” this wire? Was this one of the data types you listed in the previous question? Did the charts from your experiments correspond to the expected resulting chart listed in the Context Help box?

Figure 9: Converting Voltage to Temperature Readings

10) SubVIs are used as functions within LabVIEW to contain a fixed amount of code. They are represented in the block diagram as squares, or icons. Data of one form is passed into the subVI as an input, manipulated within the subVI, and then output. Double-clicking the subVI will open the front panel and block diagram of that VI in two separate windows. Using the Context Help tool, find the subVIs used to convert the voltage readings into temperature readings (Hint: refer to Figure 9). Using the Context Help window, what types of inputs and outputs are there?

11) Click on the dropdown menu that says “Celsius” that is being input to the subVI (Refer to Figure 9). Notice that you can choose Celsius, Fahrenheit, Kelvin, or Rankine if you want to change the temperature unit that is being displayed on each chart.

12) This program takes the outputs from the subVIs and displays them in three forms – in a chart , in numerical format, and in thermometer format. Which icon represents the chart? Which icon represents the numerical format? Which icon represents the thermometer format? (To double-check your answer, double-click on the icons to select and show the corresponding element on the front panel.)

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REFERENCES

Surface Temperature Sensor User Guide. Vernier Software & Technology. Rev. 2/17/10. Accessed 7/29/11. www.vernier.com.

NI Educational Laboratory Virtual Instrumentation Suite II Series (NI ELVIS II Series) User Manual. National Instruments. Austin, TX: National Instruments Corporation. 1/09. www.ni.com.