Thermocouple find voltage vs. temperature

Array=csvread('ambient.csv');

x1=Array(:,1);

y1=Array(:,2);

nexttile

plot(x1,y1)

title('Voltage vs. Time of Ambient');

xlabel('Time');

ylabel('Voltage');

%Find mean

time=Array(:,1);

meanta=mean(time)

voltage=Array(:,2);

meanva=mean(voltage)

hold on

%icewater

Array2=csvread('icewater.csv');

x2=Array2(:,1);

y2=Array2(:,2);

nexttile

plot(x2,y2)

title('Voltage vs. Time of Ice Water');

xlabel('Time');

ylabel('Voltage');

hold on

%Find mean

time1=Array2(:,1);

meanti=mean(time1)

voltage1=Array2(:,2);

meanvi=mean(voltage1)

Answer 1

[Clayton Gotberg]

You're trying to make a calibration curve for your thermocouple, so you should know the temperature at two calibration points. Did your lab test the voltage at two known temperatures? Often, students measure the voltage of a thermocouple when it is inserted into boiling water and melting water (mixed water and ice).

If you know the voltage and temperature for two points, you can figure out how much the voltage changes when the temperature changes (the sensitivity). For example, if I read 10.5 volts when the thermocouple is in the freezing water and 0.5 volts when the thermocouple is in the hot water, I know that the voltage decreases 10 V over 100°C, meaning that the voltage changes by -0.1V/°C. Now, if I measure 5.5 V from the thermocouple, I can relate that to 50°C.

[Joy]

They want us to find a voltage vs time

[Clayton Gotberg]

This is my interpretation of the data you've attached:

icewater contains the voltage measurement of the thermocouple when it is immersed in ice, for a few seconds.

ambient contains the same measurement but of ambient air.

In order to get the sensitivity for your thermocouple, you need to know the voltages of the thermocouple and the temperatures of ice water and ambient air.

We have many measurements of the voltage of the thermocouple, so for simplicity's sake we take the average of all of those measurements to get and . This is the mean that your TA was referring to; the time data is unrelated to anything for this step.

Next, we need to know the temperature of ice water and of ambient air ( and ). Ice water is simple; for this lab, you can probably treat it as 0°C. Ambient air will depend on where the measurement is being taken. If it's outside, you'd need to look at the weather; inside, it will be close to whatever is on the thermostat. If you have no idea, you can probably use the accepted value for "room temperature" (around 20°C).

What you need is the sensitivity, a measure of how much the voltage changes for a given change in temperature. This will let you determine what the temperature is based on the measured voltage. Take a look at the sample calculation at the end of my answer if this operation is what's confusing you.

[Joy]

If I find the sensitivity, I'm able to find the voltage vs. temperature and create a graph from that ?

[Clayton Gotberg]

Precisely! If you find the change in temperature per unit voltage, Temp-Low_Temp= Sensitivity*Voltage

[Joy]

Oh I see, so I did my coding and it worked, I'm struggling to create a text to insert on the graph, but I'll figure it out eventually.

Why would I need the body temperature graph if I already found a voltage vs temp graph?

[Clayton Gotberg]

My best guess is that your lab requirements include both the calibration curve and the results curves, but I'm not in your course so I really can't be sure about why it's being requested.

For text, check out both the text function built in to MATLAB and the labelpoints package on the File Exchange!

[Joy]

Thank you so much for your help!