RLAB (john).docx

7/27/2019 RLAB (john).docx

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Objective

Using hot wire as airflow speed sensor

Apparatus

1. Hot wire2. Fan3. Voltmeter and Ampere meter4. Adjustable power supply5. Camcorder6. PC Unit with DAQ and automatic control device

Basic Theory

Single normal probe is a type of hotwire that generally used as sensor to give airflow velocity

information in axial direction only. This probe including a smooth-short-metal wire that

incorporated in the two-wire. Each probe tip is connected to a voltage source. Electrical energy

that flows in the probe will be dissipated by the wire into heat energy. The amount of electrical

energy that dissipated is proportional to the voltage, electric current flowing in the probe, and

duration of electric current flowing.

W = v I t......... (1)

When the probe is blown by air then it will change the value of resistance wire that alter the

amount of electrical current flowing. The faster the airflow, the bigger changes of resistance

value and the electric current that flows also changed. The number of heat transfer that received

by the probe is expressed by overheat ratio, which is defined as:

Rw = wire resistance at operating temperature (blown by air)

Ra = wire resistance at ambient temperature (room)


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Hot wire probe must be calibrated to determine the equation that states the relationship between

voltage wire (wire voltage, E) with a reference velocity (reference velocity, U) after the equation

is obtained, then the information velocity in each experiment can be evaluated using the

equation. Equations derived in the form of linear equations or polynomial equations.

In the experiment about to be done is to measure the voltage wire at ambient temperature and

measure the voltage across the wire when energized air produced by the fan velocity. Airflow

velocity by the fan will be varied through the power supplied to the fan is 70, 110, 150 and 190

of the maximum power of 230 m / s.

Procedure

This rLab experiment can be done by clicking the rLab button at the bottom of this site.


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1. Activate the webcam2. Giving airflow with a speed of 0 m/s, by clicking the drop down option adjust the flow

rate

3. Turning on the fan motor by clicking the radio button on the "turn on the fan powersupply

4. Measure the voltage and electric current in the hotwire by clicking the icon "measure"5. Repeat step 2 until step 4 with the changing speeds of 70, 110, 150, 190 and 230 m/s

Assignment and Evaluation

1. Based on the data obtained, make a graph illustrating the relationship Voltage Hotwirewith time for each air velocity.

2. Based on the data processing above, make a graph illustrating the relationship of hotwirevoltage with wind flow velocity.

3. Make the wind velocity equation as a function of the hotwire voltage.4. Based on the experiments and the data obtained, can we use Hotwire as a wind speed

measure?

5. Give the analysis of the results of this experiment.

Evaluation

1. Graph that illustrating the relationship between Voltage Hotwire and time for each airvelocity.

TimeWind

Speed

V-

HWI-HW

1 0 2.112 54.2

2 0 2.112 54.2

3 0 2.112 54.1

4 0 2.112 54

5 0 2.112 54

6 0 2.112 53.9


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7 0 2.112 53.9

8 0 2.112 53.9

9 0 2.112 53.9

10 0 2.112 53.9

1 70 2.068 55.3

2 70 2.069 55.3

3 70 2.071 55.2

4 70 2.07 55.3

5 70 2.069 55.3

6 70 2.069 55.3

7 70 2.069 55.3

8 70 2.07 55.3

9 70 2.07 55.3

10 70 2.068 55.4

1 110 2.051 55.5

2 110 2.052 55.3

3 110 2.052 55.2

4 110 2.052 55.1

5 110 2.052 55

6 110 2.052 54.9

7 110 2.053 54.8

8 110 2.052 54.8

9 110 2.051 54.8

10 110 2.051 54.8

1 150 2.046 54.5

2 150 2.045 54.5

3 150 2.045 54.6

4 150 2.045 54.6

5 150 2.044 54.7

6 150 2.044 54.8

7 150 2.044 54.9

8 150 2.044 55

9 150 2.043 55.2


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10 150 2.044 55.3

1 190 2.04 54.9

2 190 2.04 54.9

3 190 2.04 54.9

4 190 2.04 54.8

5 190 2.04 54.8

6 190 2.04 54.7

7 190 2.041 54.7

8 190 2.04 54.7

9 190 2.04 54.6

10 190 2.039 54.6

1 230 2.036 55

2 230 2.036 55

3 230 2.036 55

4 230 2.036 55

5 230 2.037 55

6 230 2.037 55.1

7 230 2.037 55.1

8 230 2.037 55.1

9 230 2.038 55.2

10 230 2.037 55.2


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2. The graph which show the relation between voltage and velocity shown below :

V = 0 m/s

V=V= 2.112 volt

V = 70 m/s

V =

V = 2.069 volt

V = 110 m/s

V =

V = 2.051 volt

V = 150 m/s

V =

V = 2.044 volt

V = 190 m/s

2

2.02

2.04

2.06

2.08

2.1

2.12

1 2 3 4 5 6 7 8 9 10

V-HW

v= 0 v= 70 v= 110 v= 150 v= 190 v= 230


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V =

V = 2.04 volt

V = 230 m/s

V =

V = 2.037 volt

3. The wind velocity equation as a function of the hotwire voltage determined by usingLeast Square method

1.98

2

2.02

2.04

2.06

2.08

2.1

2.12

0 70 110 150 190 230

Relation between Voltage and Velocity

Relation between Voltage and Velocity


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N Xi Yi Yi2 Xi2 XiYi

1 0 2.11 4.45 0 0

2 70 2.057 4.23 4900 143.99

3 110 2.039 4.15 12100 224.29

4 150 2.031 4.12 22500 304.65

5 190 2.026 4.10 36100 384.94

6 230 2.023 4.09 52900 465.29

750 12.286 25.16 128500 1523.16

Xi = Wind velocity

Yi = Average voltage

After we make the table we can make the calculation with:

A =

A =

A = 2.092

B =

B =

B = -0.00036

Where B is the gradient value on m, then we add those sum into this equation:

y = mx+a

So, we got this equation where y = - 0.00036x + 2.092


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In this equation y is the voltage hotwire and x is given air flow rate

For instances, based on the equation we have got from the calculation and

equation we can implied it to our test where we can find the voltage of the hotwire by

adding the air flow velocity into the equation given. For example,

V = 110 m/s then we add this value into the equation:

Answer,

y = -0, 00036(110) + 2.092

y = 2.052

Although, it has a slightly different value by a 0.02 we still can conclude that hot

wire can be used as a wind speed measure.

Analysis

ExperimentIn this KR01 experiment that we are using the use of hotwire as speed measure or speed sensor.

Where we place the hotwire in the ambient temperature to be tested. We accomplished thisexperiment to know how the temperature can affected the wire resistance and then will affect the

voltage. We started this experiment using a fan that are use to blow the air through the pipe that

will connect to the hot wire. The varied air velocity is 0 m / s, 70 m / s, 110 m / s, 150 m / s, 190

m / s and 230 m / s. When we started when the value of velocity is 0 m/s the value of the voltageand current values are constant because the hotwire have not been affected by the air. but, when

we turn on the fan with a speed of 70 m/s the air affected the hotwire and come the result where

the voltage of the wire was dropped down because the air blown by the fan affects the

wire resistance and next affecting the voltage and electrical current too.

Result Analysis

as we can see from the result of the table we can simplified that each time the fan increasing

the speed of the air blown for 10 second there are different in the value of the voltage amount.it happen because the electrical current were used to transfer the calor to hotwire, so the the

higher the velocity that fan give to the hotwire the amount of the voltage will be decreased. To

see the decreasing of the voltage we can see it through the table has given. we are going to

compare the analysis through the average voltage counted on the table. So, when the velocity

is 0 m/s the average of the voltage is 2.112 volt when the velocity is 70 m/s the average voltage

is 2.069 and for the 110 m/s is 2.051. Through the data that has been msntion we can see that

the speed is


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The results are shown by the analysis of the average voltage counted in the graph

above. So, for the velocity of 0 m/s we will find the result of average 2.11 volt.

When the velocity is 70 m/s so the result of average velocity will be 2.057 volt. For

the air velocity of 110 m/s it will be 2.039 volt for the average voltage. Differ by

the air velocity of 150 m/s, the average voltage resulted in 2.031 volt. The resultsof average voltage shown 2.026 volt when the fan air velocity reaches 190 m/s.

And lastly, when the velocity of the air reached 230 m/s, it will result in average

voltage of 2.023 volt.

Graphic Analysis

The graph between air velocity and time will differ depends on the experiment

procedure. On this graph, time as the x variable and voltage is defined as Yvariable shows that the air velocity of the fan is constant, so for every time the

fan blows longer, the calor energy will be in a small amount too. So, the value of

the voltage will be smaller by the added time. These less amount of voltage will

be smaller because of the dissipation from hot wire calor effecting to the certain

velocity of the air. On the graph relation between velocity and voltage. The graph

shows if the air velocity are larger, so the electricity voltage will be reduced too.

Conclusion

The graph shows that the voltage will be smaller by the increasing amount of

velocity. It happens because the resistance of the probe will be smaller then

affecting the calor which is dissipated. The hot wire could be used to predict the

wind whether it is big or small but couldnt predict its value. The equation

between air flow and the voltage will be y = -0.000364x + 2.093.

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RLAB (john).docx